![Entry](https://upload.wikimedia.org/wikipedia/commons/4/4e/Entry.jpg)
Atmospheric entry is the movement of an object from
outer space
Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, pred ...
into and through the gases of an
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
of a
planet
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
,
dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to p ...
, or
natural satellite
A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''moons'' ...
. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the entry of
astronomical object
An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
s,
space debris
Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) are defunct human-made objects in space—principally in Earth orbit—which no longer serve a useful function. These include derelict spacecr ...
, or
bolide
A bolide is normally taken to mean an exceptionally bright meteor, but the term is subject to more than one definition, according to context. It may refer to any large crater-forming body, or to one that explodes in the atmosphere. It can be a ...
s; and ''controlled entry'' (or ''reentry'') of a spacecraft capable of being navigated or following a predetermined course. Technologies and procedures allowing the controlled atmospheric ''entry, descent, and landing'' of spacecraft are collectively termed as ''EDL''.
![Meteoroid meteor meteorite](https://upload.wikimedia.org/wikipedia/commons/6/63/Meteoroid_meteor_meteorite.gif)
Objects entering an atmosphere experience
atmospheric drag
In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding flu ...
, which puts mechanical stress on the object, and
aerodynamic heating
Aerodynamic heating is the heating of a solid body produced by its high-speed passage through air. In science and engineering, an understanding of aerodynamic heating is necessary for predicting the behaviour of meteoroids which enter the earth's ...
—caused mostly by compression of the air in front of the object, but also by drag. These forces can cause loss of mass (
ablation
Ablation ( la, ablatio – removal) is removal or destruction of something from an object by vaporization, chipping, erosion, erosive processes or by other means. Examples of ablative materials are described below, and include spacecraft materi ...
) or even complete disintegration of smaller objects, and objects with lower
compressive strength
In mechanics, compressive strength or compression strength is the capacity of a material or structure to withstand loads tending to reduce size (as opposed to tensile strength which withstands loads tending to elongate). In other words, compre ...
can explode.
Crewed space vehicles must be slowed to subsonic speeds before parachutes or air brakes may be deployed. Such vehicles have kinetic energies typically between 50 and 1,800 megajoules per kilogram, and atmospheric dissipation is the only way of expending the kinetic energy. The amount of rocket fuel required to slow the vehicle would be nearly equal to the amount used to accelerate it initially, and it is thus highly impractical to use
retro rockets for the entire Earth reentry procedure. While the high temperature generated at the surface of the
heat shield
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
is due to
adiabatic compression
In thermodynamics, an adiabatic process (Greek: ''adiábatos'', "impassable") is a type of thermodynamic process that occurs without transferring heat or mass between the thermodynamic system and its environment. Unlike an isothermal process, an ...
, the vehicle's kinetic energy is ultimately lost to gas friction (viscosity) after the vehicle has passed by. Other smaller energy losses include
black-body radiation
Black-body radiation is the thermal electromagnetic radiation within, or surrounding, a body in thermodynamic equilibrium with its environment, emitted by a black body (an idealized opaque, non-reflective body). It has a specific, continuous spect ...
directly from the hot gases and chemical reactions between ionized gases.
Ballistic warheads and expendable vehicles do not require slowing at reentry, and in fact, are made streamlined so as to maintain their speed. Furthermore, slow-speed returns to Earth from near-space such as
parachute jumps from balloons do not require heat shielding because the gravitational acceleration of an object starting at relative rest from within the atmosphere itself (or not far above it) cannot create enough velocity to cause significant atmospheric heating.
For Earth, atmospheric entry occurs by convention at the
Kármán line
The Kármán line (or von Kármán line ) is an attempt to define a boundary between Earth's atmosphere and outer space, and offers a specific definition set by the Fédération aéronautique internationale (FAI), an international record-keeping ...
at an altitude of above the surface, while at
Venus atmospheric entry occurs at and at
Mars atmospheric entry
Mars atmospheric entry is the entry into the atmosphere of Mars. High velocity entry into Martian air creates a CO2-N2 plasma, as opposed to O2-N2 for Earth air. at about . Uncontrolled objects reach high velocities while accelerating through space toward the Earth under the influence of Earth's
gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
, and are slowed by friction upon encountering Earth's atmosphere. Meteors are also often travelling quite fast relative to the Earth simply because their own orbital path is different from that of the Earth before they encounter Earth's
gravity well
The Hill sphere of an astronomical body is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere. That moon would, in turn, have a Hill sp ...
. Most objects enter at
hypersonic speeds due to their
sub-orbital
A sub-orbital spaceflight is a spaceflight in which the spacecraft reaches outer space, but its trajectory intersects the atmosphere or surface of the gravitating body from which it was launched, so that it will not complete one orbital re ...
(e.g.,
intercontinental ballistic missile
An intercontinental ballistic missile (ICBM) is a ballistic missile with a range greater than , primarily designed for nuclear weapons delivery (delivering one or more thermonuclear warheads). Conventional, chemical, and biological weapons c ...
reentry vehicles),
orbital (e.g., the
Soyuz Soyuz is a transliteration of the Cyrillic text Союз (Russian and Ukrainian, 'Union'). It can refer to any union, such as a trade union (''profsoyuz'') or the Union of Soviet Socialist Republics (Сою́з Сове́тских Социалис ...
), or
unbounded (e.g.,
meteor
A meteoroid () is a small rocky or metallic body in outer space.
Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as micr ...
s) trajectories. Various advanced technologies have been developed to enable atmospheric reentry and flight at extreme velocities. An alternative method of controlled atmospheric entry is
buoyancy
Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the p ...
which is suitable for planetary entry where thick atmospheres, strong gravity, or both factors complicate high-velocity hyperbolic entry, such as the atmospheres of
Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
,
Titan
Titan most often refers to:
* Titan (moon), the largest moon of Saturn
* Titans, a race of deities in Greek mythology
Titan or Titans may also refer to:
Arts and entertainment
Fictional entities
Fictional locations
* Titan in fiction, fictiona ...
and the
gas giant
A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...
s.
History
![Blunt body reentry shapes](https://upload.wikimedia.org/wikipedia/commons/2/23/Blunt_body_reentry_shapes.png)
The concept of the ablative
heat shield
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
was described as early as 1920 by
Robert Goddard
Robert Hutchings Goddard (October 5, 1882 – August 10, 1945) was an American engineer, professor, physicist, and inventor who is credited with creating and building the world's first Liquid-propellant rocket, liquid-fueled rocket. ...
: "In the case of meteors, which enter the atmosphere with speeds as high as per second, the interior of the meteors remains cold, and the erosion is due, to a large extent, to chipping or cracking of the suddenly heated surface. For this reason, if the outer surface of the apparatus were to consist of layers of a very infusible hard substance with layers of a poor heat conductor between, the surface would not be eroded to any considerable extent, especially as the velocity of the apparatus would not be nearly so great as that of the average meteor."
Practical development of reentry systems began as the range, and reentry velocity of
ballistic missiles
A ballistic missile is a type of missile that uses projectile motion to deliver warheads on a target. These weapons are guided only during relatively brief periods—most of the flight is unpowered. Short-range ballistic missiles stay within the ...
increased. For early short-range missiles, like the
V-2
The V-2 (german: Vergeltungswaffe 2, lit=Retaliation Weapon 2), with the technical name ''Aggregat 4'' (A-4), was the world’s first long-range guided ballistic missile. The missile, powered by a liquid-propellant rocket engine, was developed ...
, stabilization and aerodynamic stress were important issues (many V-2s broke apart during reentry), but heating was not a serious problem. Medium-range missiles like the Soviet
R-5, with a range, required ceramic composite heat shielding on separable reentry vehicles (it was no longer possible for the entire rocket structure to survive reentry). The first
ICBM
An intercontinental ballistic missile (ICBM) is a ballistic missile with a range greater than , primarily designed for nuclear weapons delivery (delivering one or more thermonuclear warheads). Conventional, chemical, and biological weapons c ...
s, with ranges of , were only possible with the development of modern ablative heat shields and blunt-shaped vehicles.
In the United States, this technology was pioneered by
H. Julian Allen
Harry Julian Allen (April 1, 1910 – January 29, 1977), also known as Harvey Allen, was an aeronautical engineer and a Director of the NASA Ames Research Center, most noted for his "Blunt Body Theory" of atmospheric entry which permitted successf ...
and
A. J. Eggers Jr. of the
National Advisory Committee for Aeronautics
The National Advisory Committee for Aeronautics (NACA) was a United States federal agency founded on March 3, 1915, to undertake, promote, and institutionalize aeronautical research. On October 1, 1958, the agency was dissolved and its assets ...
(NACA) at
Ames Research Center
The Ames Research Center (ARC), also known as NASA Ames, is a major NASA research center at Moffett Federal Airfield in California's Silicon Valley. It was founded in 1939 as the second National Advisory Committee for Aeronautics (NACA) laborat ...
. In 1951, they made the counterintuitive discovery that a blunt shape (high drag) made the most effective heat shield. From simple engineering principles, Allen and Eggers showed that the heat load experienced by an entry vehicle was inversely proportional to the
drag coefficient
In fluid dynamics, the drag coefficient (commonly denoted as: c_\mathrm, c_x or c_) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water. It is used in the drag equ ...
; i.e., the greater the drag, the less the heat load. If the reentry vehicle is made blunt, air cannot "get out of the way" quickly enough, and acts as an air cushion to push the shock wave and heated shock layer forward (away from the vehicle). Since most of the hot gases are no longer in direct contact with the vehicle, the heat energy would stay in the shocked gas and simply move around the vehicle to later dissipate into the atmosphere.
The Allen and Eggers discovery, though initially treated as a military secret, was eventually published in 1958.
Terminology, definitions and jargon
When atmospheric entry is part of a spacecraft landing or recovery, particularly on a planetary body other than Earth, entry is part of a phase referred to as ''entry, descent, and landing'', or EDL. When the atmospheric entry returns to the same body that the vehicle had launched from, the event is referred to as reentry (almost always referring to Earth entry).
The fundamental design objective in atmospheric entry of a spacecraft is to
dissipate
In thermodynamics, dissipation is the result of an irreversible process that takes place in homogeneous thermodynamic systems. In a dissipative process, energy (internal, bulk flow kinetic, or system potential) transforms from an initial form to a ...
the
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
of a spacecraft that is traveling at
hypersonic speed
In aerodynamics, a hypersonic speed is one that exceeds 5 times the speed of sound, often stated as starting at speeds of Mach 5 and above.
The precise Mach number at which a craft can be said to be flying at hypersonic speed varies, since i ...
as it enters an
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
such that equipment, cargo, and any passengers are slowed and land near a specific destination on the surface at zero velocity while keeping stresses on the spacecraft and any passengers within acceptable limits.
This may be accomplished by
propulsive or
aerodynamic
Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dyn ...
(vehicle characteristics or
parachute
A parachute is a device used to slow the motion of an object through an atmosphere by creating drag or, in a ram-air parachute, aerodynamic lift. A major application is to support people, for recreation or as a safety device for aviators, who ...
) means, or by some combination.
Entry vehicle shapes
There are several basic shapes used in designing entry vehicles:
Sphere or spherical section
![Apollo cm](https://upload.wikimedia.org/wikipedia/commons/8/87/Apollo_cm.jpg)
The simplest axisymmetric shape is the sphere or spherical section. This can either be a complete sphere or a spherical section forebody with a converging conical afterbody. The aerodynamics of a sphere or spherical section are easy to model analytically using Newtonian impact theory. Likewise, the spherical section's heat flux can be accurately modeled with the Fay–Riddell equation.
The static stability of a spherical section is assured if the vehicle's center of mass is upstream from the center of curvature (dynamic stability is more problematic). Pure spheres have no lift. However, by flying at an
angle of attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...
, a spherical section has modest aerodynamic lift thus providing some cross-range capability and widening its entry corridor. In the late 1950s and early 1960s, high-speed computers were not yet available and
computational fluid dynamics
Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate th ...
was still embryonic. Because the spherical section was amenable to closed-form analysis, that geometry became the default for conservative design. Consequently, crewed capsules of that era were based upon the spherical section.
Pure spherical entry vehicles were used in the early Soviet
Vostok Vostok refers to east in Russian but may also refer to:
Spaceflight
* Vostok programme, Soviet human spaceflight project
* Vostok (spacecraft), a type of spacecraft built by the Soviet Union
* Vostok (rocket family), family of rockets derived from ...
and
Voskhod capsules and in Soviet Mars and
Venera
The Venera (, , which means "Venus" in Russian) program was the name given to a series of space probes developed by the Soviet Union between 1961 and 1984 to gather information about the planet Venus. Ten probes successfully landed on the s ...
descent vehicles. The
Apollo command module
The Apollo command and service module (CSM) was one of two principal components of the United States Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functioned as a mother ship ...
used a spherical section forebody heat shield with a converging conical afterbody. It flew a lifting entry with a hypersonic trim angle of attack of −27° (0° is blunt-end first) to yield an average L/D (lift-to-drag ratio) of 0.368. The resultant lift achieved a measure of cross-range control by offsetting the vehicle's center of mass from its axis of symmetry, allowing the lift force to be directed left or right by rolling the capsule on its
longitudinal axis. Other examples of the spherical section geometry in crewed capsules are
Soyuz Soyuz is a transliteration of the Cyrillic text Союз (Russian and Ukrainian, 'Union'). It can refer to any union, such as a trade union (''profsoyuz'') or the Union of Soviet Socialist Republics (Сою́з Сове́тских Социалис ...
/
Zond,
Gemini
Gemini may refer to:
Space
* Gemini (constellation), one of the constellations of the zodiac
** Gemini in Chinese astronomy
* Project Gemini, the second U.S. crewed spaceflight program
* Gemini Observatory, consisting of telescopes in the Northern ...
, and
Mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
. Even these small amounts of lift allow trajectories that have very significant effects on peak
g-force
The gravitational force equivalent, or, more commonly, g-force, is a measurement of the type of force per unit mass – typically acceleration – that causes a perception of weight, with a g-force of 1 g (not gram in mass measure ...
, reducing it from 8–9 g for a purely ballistic (slowed only by drag) trajectory to 4–5 g, as well as greatly reducing the peak reentry heat.
Sphere-cone
The sphere-cone is a spherical section with a
frustum
In geometry, a (from the Latin for "morsel"; plural: ''frusta'' or ''frustums'') is the portion of a solid (normally a pyramid or a cone) that lies between two parallel planes cutting this solid. In the case of a pyramid, the base faces are p ...
or blunted cone attached. The sphere-cone's dynamic stability is typically better than that of a spherical section. The vehicle enters sphere-first. With a sufficiently small half-angle and properly placed center of mass, a sphere-cone can provide aerodynamic stability from Keplerian entry to surface impact. (The ''half-angle'' is the angle between the cone's axis of rotational symmetry and its outer surface, and thus half the angle made by the cone's surface edges.)
![Mk 2](https://upload.wikimedia.org/wikipedia/commons/f/f6/Mk_2.jpg)
The original American sphere-cone aeroshell was the Mk-2 RV (reentry vehicle), which was developed in 1955 by the
General Electric
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
Corp. The Mk-2's design was derived from blunt-body theory and used a radiatively cooled thermal protection system (TPS) based upon a metallic heat shield (the different TPS types are later described in this article). The Mk-2 had significant defects as a weapon delivery system, i.e., it loitered too long in the upper atmosphere due to its lower
ballistic coefficient
In ballistics, the ballistic coefficient (BC, ''C'') of a body is a measure of its ability to overcome air resistance in flight. It is inversely proportional to the negative acceleration: a high number indicates a low negative acceleration—the d ...
and also trailed a stream of vaporized metal making it very visible to
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
. These defects made the Mk-2 overly susceptible to anti-ballistic missile (ABM) systems. Consequently, an alternative sphere-cone RV to the Mk-2 was developed by General Electric.
![Mk 6 reentry vehicle on display at National Atomic Museum](https://upload.wikimedia.org/wikipedia/commons/d/da/Mk_6_reentry_vehicle_on_display_at_National_Atomic_Museum.jpg)
This new RV was the Mk-6 which used a non-metallic ablative TPS, a nylon phenolic. This new TPS was so effective as a reentry heat shield that significantly reduced bluntness was possible. However, the Mk-6 was a huge RV with an entry mass of 3,360 kg, a length of 3.1 m and a half-angle of 12.5°. Subsequent advances in nuclear weapon and ablative TPS design allowed RVs to become significantly smaller with a further reduced bluntness ratio compared to the Mk-6. Since the 1960s, the sphere-cone has become the preferred geometry for modern ICBM RVs with typical half-angles being between 10° to 11°.
Reconnaissance satellite
A reconnaissance satellite or intelligence satellite (commonly, although unofficially, referred to as a spy satellite) is an Earth observation satellite or communications satellite deployed for military or intelligence applications.
The ...
RVs (recovery vehicles) also used a sphere-cone shape and were the first American example of a non-munition entry vehicle (
Discoverer-I, launched on 28 February 1959). The sphere-cone was later used for space exploration missions to other celestial bodies or for return from open space; e.g.,
''Stardust'' probe. Unlike with military RVs, the advantage of the blunt body's lower TPS mass remained with space exploration entry vehicles like the
Galileo Probe
''Galileo'' was an American robotic space probe that studied the planet Jupiter and its moons, as well as the asteroids Gaspra and Ida. Named after the Italian astronomer Galileo Galilei, it consisted of an orbiter and an entry probe. It was ...
with a half-angle of 45° or the
Viking aeroshell with a half-angle of 70°. Space exploration sphere-cone entry vehicles have landed on the surface or entered the atmospheres of
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
,
Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
,
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
, and
Titan
Titan most often refers to:
* Titan (moon), the largest moon of Saturn
* Titans, a race of deities in Greek mythology
Titan or Titans may also refer to:
Arts and entertainment
Fictional entities
Fictional locations
* Titan in fiction, fictiona ...
.
Biconic
![Delta Clipper DC-X first flight](https://upload.wikimedia.org/wikipedia/commons/8/88/Delta_Clipper_DC-X_first_flight.jpg)
The
biconic
Many shapes have metaphorical names, i.e., their names are metaphors: these shapes are named after a most common object that has it. For example, "U-shape" is a shape that resembles the letter U, a bell-shaped curve has the shape of the vertical ...
is a sphere-cone with an additional frustum attached. The biconic offers a significantly improved L/D ratio. A biconic designed for Mars aerocapture typically has an L/D of approximately 1.0 compared to an L/D of 0.368 for the Apollo-CM. The higher L/D makes a biconic shape better suited for transporting people to Mars due to the lower peak deceleration. Arguably, the most significant biconic ever flown was the ''Advanced
Maneuverable Reentry Vehicle
The maneuverable reentry vehicle (abbreviated MARV or MaRV) is a type of warhead for ballistic missiles that is capable of maneuvring and changing its trajectory.
MaRV can be capable of autonomously tracking ground targets to make sure the mis ...
'' (AMaRV). Four AMaRVs were made by the
McDonnell Douglas
McDonnell Douglas was a major American aerospace manufacturing corporation and defense contractor, formed by the merger of McDonnell Aircraft and the Douglas Aircraft Company in 1967. Between then and its own merger with Boeing in 1997, it produ ...
Corp. and represented a significant leap in RV sophistication. Three AMaRVs were launched by
Minuteman-1 ICBMs on 20 December 1979, 8 October 1980 and 4 October 1981. AMaRV had an entry mass of approximately 470 kg, a nose radius of 2.34 cm, a forward-frustum half-angle of 10.4°, an inter-frustum radius of 14.6 cm, aft-frustum half-angle of 6°, and an axial length of 2.079 meters. No accurate diagram or picture of AMaRV has ever appeared in the open literature. However, a schematic sketch of an AMaRV-like vehicle along with trajectory plots showing hairpin turns has been published.
AMaRV's attitude was controlled through a split body flap (also called a ''split-windward flap'') along with two yaw flaps mounted on the vehicle's sides.
Hydraulic actuation was used for controlling the flaps. AMaRV was guided by a fully autonomous navigation system designed for evading
anti-ballistic missile
An anti-ballistic missile (ABM) is a surface-to-air missile designed to counter ballistic missiles (missile defense). Ballistic missiles are used to deliver nuclear weapon, nuclear, Chemical weapon, chemical, Bioagent, biological, or conventiona ...
(ABM) interception. The
McDonnell Douglas DC-X
The DC-X, short for Delta Clipper or Delta Clipper Experimental, was an uncrewed prototype of a reusable single-stage-to-orbit launch vehicle built by McDonnell Douglas in conjunction with the United States Department of Defense's Strategic ...
(also a biconic) was essentially a scaled-up version of AMaRV. AMaRV and the DC-X also served as the basis for an unsuccessful proposal for what eventually became the
Lockheed Martin X-33
The Lockheed Martin X-33 was a proposed uncrewed, sub-scale technology demonstrator suborbital spaceplane that was developed for a period in the 1990s. The X-33 was a technology demonstrator for the VentureStar orbital spaceplane, which was pla ...
.
Non-axisymmetric shapes
Non-
axisymmetric
Rotational symmetry, also known as radial symmetry in geometry, is the property a shape has when it looks the same after some rotation by a partial turn. An object's degree of rotational symmetry is the number of distinct orientations in which i ...
shapes have been used for crewed entry vehicles. One example is the winged orbit vehicle that uses a
delta wing
A delta wing is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (Δ).
Although long studied, it did not find significant applications until the Jet Age, when it proved suitabl ...
for maneuvering during descent much like a conventional glider. This approach has been used by the American
Space Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...
and the Soviet
Buran. The
lifting body
A lifting body is a fixed-wing aircraft or spacecraft configuration in which the body itself produces lift. In contrast to a flying wing, which is a wing with minimal or no conventional fuselage, a lifting body can be thought of as a fuselage wi ...
is another entry vehicle geometry and was used with the
X-23 PRIME
The Martin X-23A PRIME (Precision Reentry Including Maneuvering reEntry) (SV-5D) was a small lifting-body re-entry vehicle tested by the United States Air Force in the mid-1960s. Unlike ASSET, primarily used for structural and heating research, ...
(Precision Recovery Including Maneuvering Entry) vehicle.
Entry heating
![Gemini2reentry](https://upload.wikimedia.org/wikipedia/commons/a/ae/Gemini2reentry.jpg)
Objects entering an atmosphere from
space
Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually consider ...
at high velocities relative to the atmosphere will cause very high levels of
heating
A central heating system provides warmth to a number of spaces within a building from one main source of heat. It is a component of heating, ventilation, and air conditioning (short: HVAC) systems, which can both cool and warm interior spaces.
...
. Atmospheric entry heating comes principally from two sources:
*
convection
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
of hot gas flow past the surface of the body and
catalytic
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
chemical recombination reaction
A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...
s between the surface and atmospheric gases; and
*
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
from the energetic
shock layer that forms in the front and sides of the body
[
As velocity increases, both convective and radiative heating increase, but at different rates. At very high speeds, radiative heating will dominate the convective heat fluxes, as radiative heating is proportional to the eighth power of velocity, while convective heating is proportional to the third power of velocity. Radiative heating thus predominates early in atmospheric entry, while convection predominates in the later phases.]
During certain intensity of ionization, a ''radio-blackout'' with the spacecraft is produced.
While Earth entry interface is considered to take place at the Kármán line
The Kármán line (or von Kármán line ) is an attempt to define a boundary between Earth's atmosphere and outer space, and offers a specific definition set by the Fédération aéronautique internationale (FAI), an international record-keeping ...
, the main heating during controlled entry takes place at altitudes of , peaking at .
Shock layer gas physics
At typical reentry temperatures, the air in the shock layer is both ionized
Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule ...
and dissociated
Dissociation in chemistry is a general process in which molecules (or ionic compounds such as salts, or complexes) separate or split into other things such as atoms, ions, or radicals, usually in a reversible manner. For instance, when an acid ...
. This chemical dissociation necessitates various physical models to describe the shock layer's thermal and chemical properties. There are four basic physical models of a gas that are important to aeronautical engineers who design heat shields:
Perfect gas model
Almost all aeronautical engineers are taught the perfect (ideal) gas model during their undergraduate education. Most of the important perfect gas equations along with their corresponding tables and graphs are shown in NACA Report 1135. Excerpts from NACA Report 1135 often appear in the appendices of thermodynamics textbooks and are familiar to most aeronautical engineers who design supersonic aircraft.
The perfect gas theory is elegant and extremely useful for designing aircraft but assumes that the gas is chemically inert. From the standpoint of aircraft design, air can be assumed to be inert for temperatures less than 550 K at one atmosphere pressure. The perfect gas theory begins to break down at 550 K and is not usable at temperatures greater than 2,000 K. For temperatures greater than 2,000 K, a heat shield designer must use a ''real gas model''.
Real (equilibrium) gas model
An entry vehicle's pitching moment can be significantly influenced by real-gas effects. Both the Apollo command module and the Space Shuttle were designed using incorrect pitching moments determined through inaccurate real-gas modelling. The Apollo-CM's trim-angle angle of attack was higher than originally estimated, resulting in a narrower lunar return entry corridor. The actual aerodynamic center of the ''Columbia'' was upstream from the calculated value due to real-gas effects. On ''Columbia''s maiden flight ( STS-1), astronauts John Young John Young may refer to:
Academics
* John Young (professor of Greek) (died 1820), Scottish professor of Greek at the University of Glasgow
* John C. Young (college president) (1803–1857), American educator, pastor, and president of Centre Coll ...
and Robert Crippen
Robert Laurel Crippen (born September 11, 1937) is an American retired naval officer and aviator, test pilot
A test pilot is an aircraft pilot with additional training to fly and evaluate experimental, newly produced and modified aircra ...
had some anxious moments during reentry when there was concern about losing control of the vehicle.
An equilibrium real-gas model assumes that a gas is chemically reactive, but also assumes all chemical reactions have had time to complete and all components of the gas have the same temperature (this is called ''thermodynamic equilibrium
Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In thermod ...
''). When air is processed by a shock wave, it is superheated by compression and chemically dissociates through many different reactions. Direct friction upon the reentry object is not the main cause of shock-layer heating. It is caused mainly from isentropic
In thermodynamics, an isentropic process is an idealized thermodynamic process that is both adiabatic and reversible. The work transfers of the system are frictionless, and there is no net transfer of heat or matter. Such an idealized process ...
heating of the air molecules within the compression wave. Friction based entropy increases of the molecules within the wave also account for some heating. The distance from the shock wave to the stagnation point
In fluid dynamics, a stagnation point is a point in a flow field where the local velocity of the fluid is zero.Clancy, L.J. (1975), ''Aerodynamics'', Pitman Publishing Limited, London. A plentiful, albeit surprising, example of such points seem ...
on the entry vehicle's leading edge is called ''shock wave stand off''. An approximate rule of thumb for shock wave standoff distance is 0.14 times the nose radius. One can estimate the time of travel for a gas molecule from the shock wave to the stagnation point by assuming a free stream velocity of 7.8 km/s and a nose radius of 1 meter, i.e., time of travel is about 18 microseconds. This is roughly the time required for shock-wave-initiated chemical dissociation to approach chemical equilibrium
In a chemical reaction, chemical equilibrium is the state in which both the reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the sy ...
in a shock layer for a 7.8 km/s entry into air during peak heat flux. Consequently, as air approaches the entry vehicle's stagnation point, the air effectively reaches chemical equilibrium thus enabling an equilibrium model to be usable. For this case, most of the shock layer between the shock wave and leading edge of an entry vehicle is chemically reacting and ''not'' in a state of equilibrium. The Fay–Riddell equation, which is of extreme importance towards modeling heat flux, owes its validity to the stagnation point being in chemical equilibrium. The time required for the shock layer gas to reach equilibrium is strongly dependent upon the shock layer's pressure. For example, in the case of the ''Galileo'' probe's entry into Jupiter's atmosphere, the shock layer was mostly in equilibrium during peak heat flux due to the very high pressures experienced (this is counterintuitive given the free stream velocity was 39 km/s during peak heat flux).
Determining the thermodynamic state of the stagnation point is more difficult under an equilibrium gas model than a perfect gas model. Under a perfect gas model, the ''ratio of specific heats'' (also called ''isentropic exponent'', adiabatic index
In thermal physics and thermodynamics, the heat capacity ratio, also known as the adiabatic index, the ratio of specific heats, or Laplace's coefficient, is the ratio of the heat capacity at constant pressure () to heat capacity at constant volu ...
, ''gamma'', or ''kappa'') is assumed to be constant along with the gas constant
The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol or . It is the molar equivalent to the Boltzmann constant, expressed in units of energy per temperature increment per ...
. For a real gas, the ratio of specific heats can wildly oscillate as a function of temperature. Under a perfect gas model there is an elegant set of equations for determining thermodynamic state along a constant entropy stream line called the ''isentropic chain''. For a real gas, the isentropic chain is unusable and a ''Mollier diagram'' would be used instead for manual calculation. However, graphical solution with a Mollier diagram is now considered obsolete with modern heat shield designers using computer programs based upon a digital lookup table (another form of Mollier diagram) or a chemistry based thermodynamics program. The chemical composition of a gas in equilibrium with fixed pressure and temperature can be determined through the ''Gibbs free energy method''. Gibbs free energy
In thermodynamics, the Gibbs free energy (or Gibbs energy; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work that may be performed by a thermodynamically closed system at constant temperature and pr ...
is simply the total enthalpy
Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant ...
of the gas minus its total entropy
Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...
times temperature. A chemical equilibrium program normally does not require chemical formulas or reaction-rate equations. The program works by preserving the original elemental abundances specified for the gas and varying the different molecular combinations of the elements through numerical iteration until the lowest possible Gibbs free energy is calculated (a Newton–Raphson method
In numerical analysis, Newton's method, also known as the Newton–Raphson method, named after Isaac Newton and Joseph Raphson, is a root-finding algorithm which produces successively better approximations to the roots (or zeroes) of a real-valu ...
is the usual numerical scheme). The data base for a Gibbs free energy program comes from spectroscopic data used in defining partition functions
Partition may refer to:
Computing Hardware
* Disk partitioning, the division of a hard disk drive
* Memory partition, a subdivision of a computer's memory, usually for use by a single job
Software
* Partition (database), the division of a ...
. Among the best equilibrium codes in existence is the program ''Chemical Equilibrium with Applications'' (CEA) which was written by Bonnie J. McBride and Sanford Gordon at NASA Lewis (now renamed "NASA Glenn Research Center"). Other names for CEA are the "Gordon and McBride Code" and the "Lewis Code". CEA is quite accurate up to 10,000 K for planetary atmospheric gases, but unusable beyond 20,000 K (double ionization Double ionization is a process of formation of doubly charged ions when laser radiation is exerted on neutral atoms or molecules. Double ionization is usually less probable than single-electron ionization. Two types of double ionization are disting ...
is not modelled)
CEA can be downloaded from the Internet
along with full documentation and will compile on Linux under the G77 Fortran compiler.
Real (non-equilibrium) gas model
A non-equilibrium real gas model is the most accurate model of a shock layer's gas physics, but is more difficult to solve than an equilibrium model. The simplest non-equilibrium model is the ''Lighthill-Freeman model'' developed in 1958. The Lighthill-Freeman model initially assumes a gas made up of a single diatomic species susceptible to only one chemical formula and its reverse; e.g., N2 ? N + N and N + N ? N2 (dissociation and recombination). Because of its simplicity, the Lighthill-Freeman model is a useful pedagogical tool, but is unfortunately too simple for modelling non-equilibrium air. Air is typically assumed to have a mole fraction composition of 0.7812 molecular nitrogen, 0.2095 molecular oxygen and 0.0093 argon. The simplest real gas model for air is the ''five species model'', which is based upon N2, O2, NO, N, and O. The five species model assumes no ionization and ignores trace species like carbon dioxide.
When running a Gibbs free energy equilibrium program, the iterative process from the originally specified molecular composition to the final calculated equilibrium composition is essentially random and not time accurate. With a non-equilibrium program, the computation process is time accurate and follows a solution path dictated by chemical and reaction rate formulas. The five species model has 17 chemical formulas (34 when counting reverse formulas). The Lighthill-Freeman model is based upon a single ordinary differential equation and one algebraic equation. The five species model is based upon 5 ordinary differential equations and 17 algebraic equations. Because the 5 ordinary differential equations are tightly coupled, the system is numerically "stiff" and difficult to solve. The five species model is only usable for entry from low Earth orbit
A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...
where entry velocity is approximately . For lunar return entry of 11 km/s, the shock layer contains a significant amount of ionized nitrogen and oxygen. The five-species model is no longer accurate and a twelve-species model must be used instead.
Atmospheric entry interface velocities on a Mars–Earth trajectory
A trajectory or flight path is the path that an object with mass in motion follows through space as a function of time. In classical mechanics, a trajectory is defined by Hamiltonian mechanics via canonical coordinates; hence, a complete traj ...
are on the order of .
Modeling high-speed Mars atmospheric entry—which involves a carbon dioxide, nitrogen and argon atmosphere—is even more complex requiring a 19-species model.
An important aspect of modelling non-equilibrium real gas effects is radiative heat flux. If a vehicle is entering an atmosphere at very high speed (hyperbolic trajectory, lunar return) and has a large nose radius then radiative heat flux can dominate TPS heating. Radiative heat flux during entry into an air or carbon dioxide atmosphere typically comes from asymmetric diatomic molecules; e.g., cyanogen
Cyanogen is the chemical compound with the formula ( C N)2. It is a colorless and highly toxic gas with a pungent odor. The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups – analogous to diatomic halogen molecule ...
(CN), carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
, nitric oxide
Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...
(NO), single ionized molecular nitrogen etc. These molecules are formed by the shock wave dissociating ambient atmospheric gas followed by recombination within the shock layer into new molecular species. The newly formed diatomic
Diatomic molecules () are molecules composed of only two atoms, of the same or different chemical elements. If a diatomic molecule consists of two atoms of the same element, such as hydrogen () or oxygen (), then it is said to be homonuclear. Ot ...
molecules initially have a very high vibrational temperature that efficiently transforms the vibrational energy
In physics, sound energy is a form of energy that can be heard by living things. Only those waves that have a frequency of 16 Hz to 20 kHz are audible to humans. However, this range is an average and will slightly change from individ ...
into radiant energy
Radiant may refer to:
Computers, software, and video games
* Radiant (software), a content management system
* GtkRadiant, a level editor created by id Software for their games
* Radiant AI, a technology developed by Bethesda Softworks for ''The ...
; i.e., radiative heat flux. The whole process takes place in less than a millisecond which makes modelling a challenge. The experimental measurement of radiative heat flux (typically done with shock tubes) along with theoretical calculation through the unsteady Schrödinger equation
The Schrödinger equation is a linear partial differential equation that governs the wave function of a quantum-mechanical system. It is a key result in quantum mechanics, and its discovery was a significant landmark in the development of the ...
are among the more esoteric aspects of aerospace engineering. Most of the aerospace research work related to understanding radiative heat flux was done in the 1960s, but largely discontinued after conclusion of the Apollo Program. Radiative heat flux in air was just sufficiently understood to ensure Apollo's success. However, radiative heat flux in carbon dioxide (Mars entry) is still barely understood and will require major research.
Frozen gas model
The frozen gas model describes a special case of a gas that is not in equilibrium. The name "frozen gas" can be misleading. A frozen gas is not "frozen" like ice is frozen water. Rather a frozen gas is "frozen" in time (all chemical reactions are assumed to have stopped). Chemical reactions are normally driven by collisions between molecules. If gas pressure is slowly reduced such that chemical reactions can continue then the gas can remain in equilibrium. However, it is possible for gas pressure to be so suddenly reduced that almost all chemical reactions stop. For that situation the gas is considered frozen.
The distinction between equilibrium and frozen is important because it is possible for a gas such as air to have significantly different properties (speed-of-sound, viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the inte ...
etc.) for the same thermodynamic state; e.g., pressure and temperature. Frozen gas can be a significant issue in the wake behind an entry vehicle. During reentry, free stream air is compressed to high temperature and pressure by the entry vehicle's shock wave. Non-equilibrium air in the shock layer is then transported past the entry vehicle's leading side into a region of rapidly expanding flow that causes freezing. The frozen air can then be entrained into a trailing vortex behind the entry vehicle. Correctly modelling the flow in the wake of an entry vehicle is very difficult. Thermal protection shield (TPS) heating in the vehicle's afterbody is usually not very high, but the geometry and unsteadiness of the vehicle's wake can significantly influence aerodynamics (pitching moment) and particularly dynamic stability.
Thermal protection systems
A thermal protection system, or TPS, is the barrier that protects a spacecraft
A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
during the searing heat of atmospheric reentry. A secondary goal may be to protect the spacecraft from the heat
In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...
and
or AND may refer to:
Logic, grammar, and computing
* Conjunction (grammar), connecting two words, phrases, or clauses
* Logical conjunction in mathematical logic, notated as "∧", "⋅", "&", or simple juxtaposition
* Bitwise AND, a boole ...
cold
Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjective perception. A lower bound to temperature is absolute zero, defined as 0.00K on the Kelvin scale, an absolute thermodynamic ...
of space while in orbit. Multiple approaches for the thermal protection of spacecraft are in use, among them ablative heat shields, passive cooling, and active cooling of spacecraft surfaces.
Ablative
The ablative
In grammar, the ablative case (pronounced ; sometimes abbreviated ) is a grammatical case for nouns, pronouns, and adjectives in the grammars of various languages; it is sometimes used to express motion away from something, among other uses. T ...
heat shield functions by lifting the hot shock layer gas away from the heat shield's outer wall (creating a cooler boundary layer
In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces a no-slip boundary condi ...
). The boundary layer comes from ''blowing'' of gaseous reaction products from the heat shield material and provides protection against all forms of heat flux. The overall process of reducing the heat flux experienced by the heat shield's outer wall by way of a boundary layer is called ''blockage''. Ablation occurs at two levels in an ablative TPS: the outer surface of the TPS material chars, melts, and sublimes
Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. Sublimation is an endothermic process that occurs at temperatures and pressures below a substance's triple point i ...
, while the bulk of the TPS material undergoes pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
and expels product gases. The gas produced by pyrolysis is what drives blowing and causes blockage of convective and catalytic heat flux. Pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
can be measured in real time using thermogravimetric analysis
Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal analysis in which the mass of a sample is measured over time as the temperature changes. This measurement provides information about physical phenomena, such ...
, so that the ablative performance can be evaluated. Ablation can also provide blockage against radiative heat flux by introducing carbon into the shock layer thus making it optically opaque. Radiative heat flux blockage was the primary thermal protection mechanism of the Galileo Probe TPS material (carbon phenolic). Carbon phenolic was originally developed as a rocket nozzle throat material (used in the Space Shuttle Solid Rocket Booster
The Space Shuttle Solid Rocket Booster (SRB) was the first solid-propellant rocket to be used for primary propulsion on a vehicle used for human spaceflight. A pair of these provided 85% of the Space Shuttle's thrust at liftoff and for the first ...
) and for reentry-vehicle nose tips.
Early research on ablation technology in the USA was centered at NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
's Ames Research Center
The Ames Research Center (ARC), also known as NASA Ames, is a major NASA research center at Moffett Federal Airfield in California's Silicon Valley. It was founded in 1939 as the second National Advisory Committee for Aeronautics (NACA) laborat ...
located at Moffett Field
Moffett Federal Airfield , also known as Moffett Field, is a joint civil-military airport located in an Local government in California#Counties, unincorporated part of Santa Clara County, California, Santa Clara County, California, United States, ...
, California. Ames Research Center
The Ames Research Center (ARC), also known as NASA Ames, is a major NASA research center at Moffett Federal Airfield in California's Silicon Valley. It was founded in 1939 as the second National Advisory Committee for Aeronautics (NACA) laborat ...
was ideal, since it had numerous wind tunnels
Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...
capable of generating varying wind velocities. Initial experiments typically mounted a mock-up of the ablative material to be analyzed within a hypersonic
In aerodynamics, a hypersonic speed is one that exceeds 5 times the speed of sound, often stated as starting at speeds of Mach 5 and above.
The precise Mach number at which a craft can be said to be flying at hypersonic speed varies, since in ...
wind tunnel. Testing of ablative materials occurs at the Ames Arc Jet Complex. Many spacecraft thermal protection systems have been tested in this facility, including the Apollo, space shuttle, and Orion heat shield materials.
The thermal conductivity
The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa.
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
of a particular TPS material is usually proportional to the material's density. Carbon phenolic is a very effective ablative material, but also has high density which is undesirable. If the heat flux experienced by an entry vehicle is insufficient to cause pyrolysis then the TPS material's conductivity could allow heat flux conduction into the TPS bondline material thus leading to TPS failure. Consequently, for entry trajectories causing lower heat flux, carbon phenolic is sometimes inappropriate and lower-density TPS materials such as the following examples can be better design choices:
Super light-weight ablator
''SLA'' in ''SLA-561V'' stands for ''super light-weight ablator''. SLA-561V is a proprietary ablative made by Lockheed Martin
The Lockheed Martin Corporation is an American aerospace, arms, defense, information security, and technology corporation with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It ...
that has been used as the primary TPS material on all of the 70° sphere-cone entry vehicles sent by NASA to Mars other than the Mars Science Laboratory
Mars Science Laboratory (MSL) is a robotic spacecraft, robotic space probe mission to Mars launched by NASA on November 26, 2011, which successfully landed ''Curiosity (rover), Curiosity'', a Mars rover, in Gale (crater), Gale Crater on August ...
(MSL). SLA-561V begins significant ablation at a heat flux of approximately 110 W/cm2, but will fail for heat fluxes greater than 300 W/cm2. The MSL aeroshell TPS is currently designed to withstand a peak heat flux of 234 W/cm2. The peak heat flux experienced by the ''Viking 1
''Viking 1'' was the first of two spacecraft, along with ''Viking 2'', each consisting of an orbiter and a lander, sent to Mars as part of NASA's Viking program. The lander touched down on Mars on July 20, 1976, the first successful Mars land ...
'' aeroshell which landed on Mars was 21 W/cm2. For ''Viking 1'', the TPS acted as a charred thermal insulator and never experienced significant ablation. ''Viking 1'' was the first Mars lander and based upon a very conservative design. The Viking aeroshell had a base diameter of 3.54 meters (the largest used on Mars until Mars Science Laboratory). SLA-561V is applied by packing the ablative material into a honeycomb core that is pre-bonded to the aeroshell's structure thus enabling construction of a large heat shield.
Phenolic-impregnated carbon ablator
''Phenolic-impregnated carbon ablator'' (PICA), a carbon fiber
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
preform impregnated in phenolic resin
Phenol formaldehyde resins (PF) or phenolic resins (also infrequently called phenoplasts) are synthetic polymers obtained by the reaction of phenol or substituted phenol with formaldehyde. Used as the basis for Bakelite, PFs were the first commerc ...
, is a modern TPS material and has the advantages of low density (much lighter than carbon phenolic) coupled with efficient ablative ability at high heat flux. It is a good choice for ablative applications such as high-peak-heating conditions found on sample-return missions or lunar-return missions. PICA's thermal conductivity is lower than other high-heat-flux-ablative materials, such as conventional carbon phenolics.
PICA was patented by NASA Ames Research Center
The Ames Research Center (ARC), also known as NASA Ames, is a major NASA research center at Moffett Federal Airfield in California's Silicon Valley. It was founded in 1939 as the second National Advisory Committee for Aeronautics (NACA) laborat ...
in the 1990s and was the primary TPS material for the Stardust aeroshell. The Stardust sample-return capsule was the fastest man-made object ever to reenter Earth's atmosphere ( at 135 km altitude). This was faster than the Apollo mission capsules and 70% faster than the Shuttle. PICA was critical for the viability of the Stardust mission, which returned to Earth in 2006. Stardust's heat shield (0.81 m base diameter) was made of one monolithic piece sized to withstand a nominal peak heating rate of 1.2 kW/cm2. A PICA heat shield was also used for the Mars Science Laboratory
Mars Science Laboratory (MSL) is a robotic spacecraft, robotic space probe mission to Mars launched by NASA on November 26, 2011, which successfully landed ''Curiosity (rover), Curiosity'', a Mars rover, in Gale (crater), Gale Crater on August ...
entry into the Martian atmosphere
The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.8%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and no ...
.
=PICA-X
=
An improved and easier to produce version called PICA-X was developed by SpaceX
Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal of ...
in 2006–2010 for the Dragon
A dragon is a reptilian legendary creature that appears in the folklore of many cultures worldwide. Beliefs about dragons vary considerably through regions, but dragons in western cultures since the High Middle Ages have often been depicted as ...
space capsule
A space capsule is an often-crewed spacecraft that uses a blunt-body reentry capsule to reenter the Earth's atmosphere without wings. Capsules are distinguished from other satellites primarily by the ability to survive reentry and return a payl ...
. The first reentry test of a PICA-X heat shield was on the Dragon C1
SpaceX COTS Demo Flight 1 was the first orbital spaceflight of the Dragon cargo spacecraft, and the second overall flight of the Falcon 9 rocket manufactured by SpaceX. It was also the first demonstration flight for NASA's Commercial Orbital Tra ...
mission on 8 December 2010.[Dragon could visit space station next]
''msnbc.com
MSNBC (originally the Microsoft National Broadcasting Company) is an American news-based pay television cable channel. It is owned by NBCUniversala subsidiary of Comcast. Headquartered in New York City, it provides news coverage and political ...
'', 2010-12-08, accessed 2010-12-09. The PICA-X heat shield was designed, developed and fully qualified by a small team of a dozen engineers and technicians in less than four years.[
]
PICA-X is ten times less expensive to manufacture than the NASA PICA heat shield material.
=PICA-3
=
A second enhanced version of PICA—called PICA-3—was developed by SpaceX during the mid-2010s. It was first flight tested on the Crew Dragon
Dragon 2 is a class of partially reusable spacecraft developed and manufactured by American aerospace manufacturer SpaceX, primarily for flights to the International Space Station (ISS). SpaceX has also launched private missions such as Insp ...
spacecraft in 2019 during the flight demonstration mission, in April 2019, and put into regular service on that spacecraft in 2020.
SIRCA
Silicone-impregnated reusable ceramic ablator (SIRCA) was also developed at NASA Ames Research Center and was used on the Backshell Interface Plate (BIP) of the ''Mars Pathfinder
''Mars Pathfinder'' (''MESUR Pathfinder'') is an American robotic spacecraft that landed a base station with a roving probe on Mars in 1997. It consisted of a lander, renamed the Carl Sagan Memorial Station, and a lightweight, wheeled robot ...
'' and Mars Exploration Rover
NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, ''Spirit (rover), Spirit'' and ''Opportunity (rover), Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rover ...
(MER) aeroshells. The BIP was at the attachment points between the aeroshell's backshell (also called the afterbody or aft cover) and the cruise ring (also called the cruise stage). SIRCA was also the primary TPS material for the unsuccessful Deep Space 2
Deep Space 2 was a NASA space probe, part of the New Millennium Program. It included two highly advanced miniature space probes that were sent to Mars aboard the Mars Polar Lander in January 1999. The probes were named "Scott" and "Amundsen", in h ...
(DS/2) Mars impactor probes with their aeroshells. SIRCA is a monolithic, insulating material that can provide thermal protection through ablation. It is the only TPS material that can be machined to custom shapes and then applied directly to the spacecraft. There is no post-processing, heat treating, or additional coatings required (unlike Space Shuttle tiles). Since SIRCA can be machined to precise shapes, it can be applied as tiles, leading edge sections, full nose caps, or in any number of custom shapes or sizes. , SIRCA had been demonstrated in backshell interface applications, but not yet as a forebody TPS material.
AVCOAT
AVCOAT
AVCOAT 5026-39 is a NASA code for a specific ablative heat shield material created by Avco (acquired by Textron in 1984).
It is an epoxy novolac resin with special additives in a fiberglass honeycomb matrix. In fabrication, the empty honeycomb i ...
is a NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
-specified ablative heat shield, a glass-filled epoxy
Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...
–novolac
Novolaks (sometimes: novolacs) are low molecular weight polymers derived from phenols and formaldehyde. They are related to Bakelite, which is more highly crosslinked. The term comes from Swedish "lack" for lacquer and Latin "novo" for new, sinc ...
system.[Flight-Test Analysis Of Apollo Heat-Shield Material Using The Pacemaker Vehicle System]
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
Technical Note D-4713, pp. 8, 1968–08, accessed 2010-12-26. ''"Avcoat 5026-39/HC-G is an epoxy novolac resin with special additives in a fiberglass honeycomb matrix. In fabrication, the empty honeycomb is bonded to the primary structure and the resin is gunned into each cell individually. ... The overall density of the material is 32 lb/ft3 (512 kg/m3). The char of the material is composed mainly of silica and carbon. It is necessary to know the amounts of each in the char because in the ablation analysis the silica is considered to be inert, but the carbon is considered to enter into exothermic reactions with oxygen. ... At 2160O R (12000 K), 54 percent by weight of the virgin material has volatilized and 46 percent has remained as char. ... In the virgin material, 25 percent by weight is silica, and since the silica is considered to be inert the char-layer composition becomes 6.7 lb/ft3 (107.4 kg/m3) of carbon and 8 lb/ft3 (128.1 kg/m3) of silica."''
NASA originally used it for the Apollo command module
The Apollo command and service module (CSM) was one of two principal components of the United States Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functioned as a mother ship ...
in the 1960s, and then utilized the material for its next-generation beyond low-Earth-orbit Orion crew module, which first flew in a December 2014 test and then operationally in November 2022.[NASA.gov NASA Selects Material for Orion Spacecraft Heat Shield]
, 2009-04-07, accessed 2011-01-02. The Avcoat to be used on Orion has been reformulated to meet environmental legislation that has been passed since the end of Apollo.
Thermal soak
Thermal soak is a part of almost all TPS schemes. For example, an ablative heat shield loses most of its thermal protection effectiveness when the outer wall temperature drops below the minimum necessary for pyrolysis. From that time to the end of the heat pulse, heat from the shock layer convects into the heat shield's outer wall and would eventually conduct to the payload. This outcome can be prevented by ejecting the heat shield (with its heat soak) prior to the heat conducting to the inner wall.
Refractory insulation
Refractory insulation keeps the heat in the outermost layer of the spacecraft surface, where it is conducted away by the air. The temperature of the surface rises to incandescent levels, so the material must have a very high melting point, and the material must also exhibit very low thermal conductivity. Materials with these properties tend to be brittle, delicate, and difficult to fabricate in large sizes, so they are generally fabricated as relatively small tiles that are then attached to the structural skin of the spacecraft. There is a tradeoff between toughness and thermal conductivity: less conductive materials are generally more brittle. The space shuttle used multiple types of tiles. Tiles are also used on the Boeing X-37
The Boeing X-37, also known as the Orbital Test Vehicle (OTV), is a reusable robotic spacecraft. It is boosted into space by a launch vehicle, then re-enters Earth's atmosphere and lands as a spaceplane. The X-37 is operated by the United Stat ...
and in the Dream Chaser
Dream Chaser is an American reusable lifting-body spaceplane being developed by Sierra Nevada Corporation (SNC) Space Systems. Originally intended as a crewed vehicle, the Dream Chaser Space System is set to be produced after the cargo varian ...
and SpaceX Starship
Starship is a Fully-reusable orbital launch vehicle, fully reusable, super heavy-lift launch vehicle under development by SpaceX, an American aerospace company. With more than twice the thrust of the Saturn V, it is designed to be the most powe ...
designs.
Because insulation cannot be perfect, some heat energy is stored in the insulation and in the underlying material ("thermal soaking") and must be dissipated after the spacecraft exits the high-temperature flight regime. Some of this heat will re-radiate through the surface or will be carried off the surface by convection, but some will heat the spacecraft structure and interior, which may require active cooling after landing.[
Typical Space Shuttle TPS tiles (]LI-900
LI-900 is a type of reusable surface insulation tile developed and manufactured by Lockheed Missiles and Space Company in Sunnyvale, California. It was designed for use on the Space Shuttle orbiter as part of its thermal protection system to mi ...
) have remarkable thermal protection properties. An LI-900 tile exposed to a temperature of 1,000 K on one side will remain merely warm to the touch on the other side. However, they are relatively brittle and break easily, and cannot survive in-flight rain.
Passively cooled
In some early ballistic missile RVs (e.g., the Mk-2 and the sub-orbital
A sub-orbital spaceflight is a spaceflight in which the spacecraft reaches outer space, but its trajectory intersects the atmosphere or surface of the gravitating body from which it was launched, so that it will not complete one orbital re ...
Mercury spacecraft
Project Mercury was the first human spaceflight program of the United States, running from 1958 through 1963. An early highlight of the Space Race, its goal was to put a man into Earth orbital spaceflight, orbit and return him safely, ideally ...
), ''radiatively cooled TPS'' were used to initially absorb heat flux during the heat pulse, and, then, after the heat pulse, radiate and convect the stored heat back into the atmosphere. However, the earlier version of this technique required a considerable quantity of metal TPS (e.g., titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
, beryllium
Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form mi ...
, copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
, etc.). Modern designers prefer to avoid this added mass by using ablative and thermal-soak TPS instead.
Thermal protection systems relying on emissivity
The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation that most commonly includes both visible radiation (light) and infrared radiation, which is n ...
use high emissivity coatings (HECs) to facilitate radiative cooling
In the study of heat transfer, radiative cooling is the process by which a body loses heat by thermal radiation. As Planck's law describes, every physical body spontaneously and continuously emits electromagnetic radiation.
Radiative cooling ha ...
, while an underlying porous ceramic layer serves to protect the structure from high surface temperatures. High thermally stable emissivity values coupled with low thermal conductivity are key to the functionality of such systems.
Radiatively cooled TPS can be found on modern entry vehicles, but reinforced carbon–carbon
Carbon fibre reinforced carbon (CFRC),
carbon–carbon (C/C),
or reinforced carbon–carbon (RCC)
is a composite material consisting of carbon fiber reinforcement in a matrix of graphite. It was developed for the reentry vehicles of intercontin ...
(RCC) (also called ''carbon–carbon'') is normally used instead of metal. RCC was the TPS material on the Space Shuttle's nose cone and wing leading edges, and was also proposed as the leading-edge material for the X-33
The Lockheed Martin X-33 was a proposed uncrewed, sub-scale technology demonstrator suborbital spaceplane that was developed for a period in the 1990s. The X-33 was a technology demonstrator for the VentureStar orbital spaceplane, which was pla ...
. Carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
is the most refractory material known, with a one-atmosphere sublimation temperature of for graphite. This high temperature made carbon an obvious choice as a radiatively cooled TPS material. Disadvantages of RCC are that it is currently expensive to manufacture, is heavy, and lacks robust impact resistance.
Some high-velocity aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
, such as the SR-71 Blackbird
The Lockheed SR-71 "Blackbird" is a long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft developed and manufactured by the American aerospace company Lockheed Corporation. It was operated by the United States Air Force ...
and Concorde
The Aérospatiale/BAC Concorde () is a retired Franco-British supersonic airliner jointly developed and manufactured by Sud Aviation (later Aérospatiale) and the British Aircraft Corporation (BAC).
Studies started in 1954, and France an ...
, deal with heating similar to that experienced by spacecraft, but at much lower intensity, and for hours at a time. Studies of the SR-71's titanium skin revealed that the metal structure was restored to its original strength through annealing due to aerodynamic heating. In the case of the Concorde, the aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
nose was permitted to reach a maximum operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
of (approximately warmer than the normally sub-zero, ambient air); the metallurgical implications (loss of temper
Temper, tempered or tempering may refer to:
Heat treatment
* Tempering (metallurgy), a heat treatment technique to increase the toughness of iron-based alloys
**Temper mill, a steel processing line
* Tempering (spices), a cooking technique where ...
) that would be associated with a higher peak temperature were the most significant factors determining the top speed of the aircraft.
A radiatively cooled TPS for an entry vehicle is often called a ''hot-metal TPS''. Early TPS designs for the Space Shuttle called for a hot-metal TPS based upon a nickel superalloy
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, g ...
(dubbed René 41 René 41 is a nickel-based high temperature alloy developed by General Electric
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The comp ...
) and titanium shingles. This Shuttle TPS concept was rejected, because it was believed a silica tile-based TPS would involve lower development and manufacturing costs. A nickel superalloy
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, g ...
-shingle TPS was again proposed for the unsuccessful X-33
The Lockheed Martin X-33 was a proposed uncrewed, sub-scale technology demonstrator suborbital spaceplane that was developed for a period in the 1990s. The X-33 was a technology demonstrator for the VentureStar orbital spaceplane, which was pla ...
single-stage-to-orbit
A single-stage-to-orbit (SSTO) vehicle reaches orbit from the surface of a body using only propellants and fluids and without expending tanks, engines, or other major hardware. The term usually, but not exclusively, refers to reusable vehicles ...
(SSTO) prototype.
Recently, newer radiatively cooled TPS materials have been developed that could be superior to RCC. Known as Ultra-High Temperature Ceramics, they were developed for the prototype vehicle Slender Hypervelocity Aerothermodynamic Research Probe (SHARP). These TPS materials are based on zirconium diboride
Zirconium diboride (ZrB2) is a highly covalent refractory ceramic material with a hexagonal crystal structure. ZrB2 is an ultra high temperature ceramic (UHTC) with a melting point of 3246 °C. This along with its relatively low density of ...
and hafnium diboride
Hafnium diboride belongs to the class of ultra-high-temperature ceramics, a type of ceramic composed of hafnium and boron. It has a melting temperature of about 3250 °C. It is an unusual ceramic, having relatively high thermal and electrical c ...
. SHARP TPS have suggested performance improvements allowing for sustained Mach 7 flight at sea level, Mach 11 flight at altitudes, and significant improvements for vehicles designed for continuous hypersonic flight. SHARP TPS materials enable sharp leading edges and nose cones to greatly reduce drag for airbreathing combined-cycle-propelled spaceplanes and lifting bodies. SHARP materials have exhibited effective TPS characteristics from zero to more than , with melting points over . They are structurally stronger than RCC, and, thus, do not require structural reinforcement with materials such as Inconel. SHARP materials are extremely efficient at reradiating absorbed heat, thus eliminating the need for additional TPS behind and between the SHARP materials and conventional vehicle structure. NASA initially funded (and discontinued) a multi-phase R&D program through the University of Montana
The University of Montana (UM) is a public research university in Missoula, Montana. UM is a flagship institution of the Montana University System and its second largest campus. UM reported 10,962 undergraduate and graduate students in the fal ...
in 2001 to test SHARP materials on test vehicles.
Actively cooled
Various advanced reusable spacecraft and hypersonic aircraft designs have been proposed to employ heat shields made from temperature-resistant metal alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...
s that incorporate a refrigerant or cryogenic fuel circulating through them.
Such a TPS concept was proposed for the X-30 National Aerospace Plane (NASP) in the mid-80s. The NASP was supposed to have been a scramjet
A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to compress the incoming air forcefully ...
powered hypersonic aircraft, but failed in development.
In 2005 and 2012, two unmanned lifting body
A lifting body is a fixed-wing aircraft or spacecraft configuration in which the body itself produces lift. In contrast to a flying wing, which is a wing with minimal or no conventional fuselage, a lifting body can be thought of as a fuselage wi ...
craft with actively cooled hulls were launched as a part of the German Sharp Edge Flight Experiment
SHEFEX (Sharp Edge Flight Experiment), is an experiment conducted by the German Aerospace Center (DLR), for the development of some new, cheaper and safer design principles for space capsules, hypersonic vehicles and space planes with re-entry c ...
(SHEFEX).
In early 2019, SpaceX
Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal of ...
was developing an actively cooled heat shield for its Starship
A starship, starcraft, or interstellar spacecraft is a theoretical spacecraft designed for interstellar travel, traveling between planetary systems.
The term is mostly found in science fiction. Reference to a "star-ship" appears as early as 188 ...
spacecraft where a part of the thermal protection system will be a transpirationally cooled outer-skin design for the reentering spaceship.[Why Elon Musk Turned to Stainless Steel for SpaceX's Starship Mars Rocket]
, Mike Wall, space.com, 23 January 2019, accessed 23 March 2019.[SpaceX CEO Elon Musk explains Starship's "transpiring" steel heat shield in Q&A]
, Eric Ralph, ''Teslarati News'', 23 January 2019, accessed 23 March 2019 However, SpaceX abandoned this approach in favor of a modern version of heat shield tiles later in 2019.
In the early 1960s various TPS systems were proposed to use water or other cooling liquid sprayed into the shock layer, or passed through channels in the heat shield. Advantages included the possibility of more all-metal designs which would be cheaper to develop, be more rugged, and eliminate the need for classified and unknown technology. The disadvantages are increased weight and complexity, and lower reliability. The concept has never been flown, but a similar technology (the plug nozzle) did undergo extensive ground testing.
Propulsive entry
Fuel permitting, nothing prevents a vehicle from entering the atmosphere with a retrograde engine burn, which has the double effect of slowing the vehicle down much faster than atmospheric drag alone would, and forcing the compressed hot air away from the vehicle's body. During reentry, the first stage of the SpaceX Falcon 9
Falcon 9 is a partially reusable medium lift launch vehicle that can carry cargo and crew into Earth orbit, produced by American aerospace company SpaceX.
The rocket has two stages. The first (booster) stage carries the second stage and payl ...
performs an entry burn to rapidly decelerate from its initial hypersonic speed.
Feathered entry
In 2004, aircraft designer Burt Rutan
Elbert Leander "Burt" Rutan (; born June 17, 1943) is a retired American aerospace engineer and entrepreneur noted for his originality in designing light, strong, unusual-looking, and energy-efficient air and space craft. He designed the record- ...
demonstrated the feasibility of a shape-changing airfoil for reentry with the sub-orbital SpaceShipOne
SpaceShipOne is an experimental air-launched rocket-powered aircraft with sub-orbital spaceflight capability at speeds of up to 3,000 ft/s (900 m/s, 3240 km/h), using a hybrid rocket motor. The design features a unique "feathering" a ...
. The wings on this craft rotate upward into the ''feathered configuration'' that provides a shuttlecock
A shuttlecock (also called a birdie or shuttle) is a high-drag projectile used in the sport of badminton. It has an open conical shape formed by feathers or plastic (or a synthetic alternative) embedded into a rounded cork (or rubber) base. T ...
effect. Thus SpaceShipOne achieves much more aerodynamic drag on reentry while not experiencing significant thermal loads.
The configuration increases drag, as the craft is now less streamlined and results in more atmospheric gas particles hitting the spacecraft at higher altitudes than otherwise. The aircraft thus slows down more in higher atmospheric layers which is the key to efficient reentry. Secondly, the aircraft will ''automatically'' orient itself in this state to a high drag attitude.
However, the velocity attained by SpaceShipOne prior to reentry is much lower than that of an orbital spacecraft, and engineers, including Rutan, recognize that a feathered reentry technique is not suitable for return from orbit.
On 4 May 2011, the first test on the SpaceShipTwo
The Scaled Composites Model 339 SpaceShipTwo (SS2) is an air-launched suborbital spaceplane type designed for space tourism. It is manufactured by The Spaceship Company, a California-based company owned by Virgin Galactic.
SpaceShipTwo is car ...
of the feathering mechanism was made during a glideflight after release
from the White Knight Two. Premature deployment of the feathering system was responsible for the 2014 VSS ''Enterprise'' crash, in which the aircraft disintegrated, killing the co-pilot.
The feathered reentry was first described by Dean Chapman of NACA
The National Advisory Committee for Aeronautics (NACA) was a United States federal agency founded on March 3, 1915, to undertake, promote, and institutionalize aeronautical research. On October 1, 1958, the agency was dissolved and its assets ...
in 1958. In the section of his report on ''Composite Entry'', Chapman described a solution to the problem using a high-drag device:
Inflatable heat shield entry
Deceleration for atmospheric reentry, especially for higher-speed Mars-return missions, benefits from maximizing "the drag area of the entry system. The larger the diameter of the aeroshell, the bigger the payload can be."[ An inflatable aeroshell provides one alternative for enlarging the drag area with a low-mass design.
]
Russia
Such an inflatable shield/aerobrake was designed for the penetrators of Mars 96
Mars 96 (sometimes called Mars-8) was a failed Mars mission launched in 1996 to investigate Mars by the Russian Space Forces and not directly related to the Soviet Mars probe program of the same name. After failure of the second fourth-stage bu ...
mission. Since the mission failed due to the launcher malfunction, the NPO Lavochkin and DASA/ESA have designed a mission for Earth orbit. The Inflatable Reentry and Descent Technology (IRDT) demonstrator was launched on Soyuz-Fregat on 8 February 2000. The inflatable shield was designed as a cone with two stages of inflation. Although the second stage of the shield failed to inflate, the demonstrator survived the orbital reentry and was recovered. The subsequent missions flown on the Volna
Space launch vehicle Volna (russian: Волна "wave"), is a converted Submarine-launched ballistic missile used for launching satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except ...
rocket failed due to launcher failure.
NASA IRVE
NASA launched an inflatable heat shield experimental spacecraft on 17 August 2009 with the successful first test flight of the Inflatable Re-entry Vehicle Experiment (IRVE). The heat shield had been vacuum-packed into a payload shroud and launched on a Black Brant 9 sounding rocket
A sounding rocket or rocketsonde, sometimes called a research rocket or a suborbital rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The rockets are used to ...
from NASA's Wallops Flight Facility on Wallops Island, Virginia. "Nitrogen inflated the heat shield, made of several layers of silicone
A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cooking ...
-coated Kevlar">/nowiki>Kevlar">Kevlar.html" ;"title="/nowiki>Kevlar">/nowiki>Kevlar/nowiki> fabric, to a mushroom shape in space several minutes after liftoff."[ The rocket apogee was at an altitude of where it began its descent to supersonic speed. Less than a minute later the shield was released from its cover to inflate at an altitude of . The inflation of the shield took less than 90 seconds.][NASA Launches New Technology: An Inflatable Heat Shield]
, NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
Mission News, 2009-08-17, accessed 2011-01-02.
NASA HIAD
Following the success of the initial IRVE experiments, NASA developed the concept into the more ambitious Hypersonic Inflatable Aerodynamic Decelerator (HIAD). The current design is shaped like a shallow cone, with the structure built up as a stack of circular inflated tubes of gradually increasing major diameter. The forward (convex) face of the cone is covered with a flexible thermal protection system robust enough to withstand the stresses of atmospheric entry (or reentry).
In 2012, a HIAD was tested as Inflatable Reentry Vehicle Experiment 3 (IRVE-3) using a sub-orbital sounding rocket, and worked.
See also Low-Density Supersonic Decelerator, a NASA project with tests in 2014 & 2015 of a 6m diameter SIAD-R.
LOFTID
A inflatable reentry vehicle, ''Low-Earth Orbit Flight Test of an Inflatable Decelerator'' (LOFTID), was launched in Nov 2022, inflated in orbit, reentered faster than Mach 25, and was successfully recovered on November 10.
Entry vehicle design considerations
There are four critical parameters considered when designing a vehicle for atmospheric entry:
# Peak heat flux
# Heat load
# Peak deceleration
# Peak dynamic pressure
Peak heat flux and dynamic pressure
In fluid dynamics, dynamic pressure (denoted by or and sometimes called velocity pressure) is the quantity defined by:Clancy, L.J., ''Aerodynamics'', Section 3.5
:q = \frac\rho\, u^2
where (in SI units):
* is the dynamic pressure in pascals ( ...
selects the TPS material. Heat load selects the thickness of the TPS material stack. Peak deceleration is of major importance for crewed missions. The upper limit for crewed return to Earth from low Earth orbit (LEO) or lunar return is 10''g''. For Martian atmospheric entry after long exposure to zero gravity, the upper limit is 4''g''.[ Peak dynamic pressure can also influence the selection of the outermost TPS material if ]spallation
Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection of material from a target during impact by a projectile. In planetary p ...
is an issue.
Starting from the principle of ''conservative design'', the engineer typically considers two worst-case
In computer science, best, worst, and average cases of a given algorithm express what the resource usage is ''at least'', ''at most'' and ''on average'', respectively. Usually the resource being considered is running time, i.e. time complexity, b ...
trajectories, the undershoot and overshoot trajectories. The overshoot trajectory is typically defined as the shallowest-allowable entry velocity angle prior to atmospheric skip-off. The overshoot trajectory has the highest heat load and sets the TPS thickness. The undershoot trajectory is defined by the steepest allowable trajectory. For crewed missions the steepest entry angle is limited by the peak deceleration. The undershoot trajectory also has the highest peak heat flux and dynamic pressure. Consequently, the undershoot trajectory is the basis for selecting the TPS material. There is no "one size fits all" TPS material. A TPS material that is ideal for high heat flux may be too conductive (too dense) for a long duration heat load. A low-density TPS material might lack the tensile strength to resist spallation if the dynamic pressure is too high. A TPS material can perform well for a specific peak heat flux, but fail catastrophically for the same peak heat flux if the wall pressure is significantly increased (this happened with NASA's R-4 test spacecraft).[ Older TPS materials tend to be more labor-intensive and expensive to manufacture compared to modern materials. However, modern TPS materials often lack the flight history of the older materials (an important consideration for a risk-averse designer).
Based upon Allen and Eggers discovery, maximum aeroshell bluntness (maximum drag) yields minimum TPS mass. Maximum bluntness (minimum ballistic coefficient) also yields a minimal ]terminal velocity
Terminal velocity is the maximum velocity (speed) attainable by an object as it falls through a fluid (air is the most common example). It occurs when the sum of the drag force (''Fd'') and the buoyancy is equal to the downward force of gravit ...
at maximum altitude (very important for Mars EDL, but detrimental for military RVs). However, there is an upper limit to bluntness imposed by aerodynamic stability considerations based upon ''shock wave detachment''. A shock wave will remain attached to the tip of a sharp cone if the cone's half-angle is below a critical value. This critical half-angle can be estimated using perfect gas theory (this specific aerodynamic instability occurs below hypersonic speeds). For a nitrogen atmosphere (Earth or Titan), the maximum allowed half-angle is approximately 60°. For a carbon dioxide atmosphere (Mars or Venus), the maximum-allowed half-angle is approximately 70°. After shock wave detachment, an entry vehicle must carry significantly more shocklayer gas around the leading edge stagnation point (the subsonic cap). Consequently, the aerodynamic center moves upstream thus causing aerodynamic instability. It is incorrect to reapply an aeroshell design intended for Titan entry ( ''Huygens'' probe in a nitrogen atmosphere) for Mars entry (''Beagle 2
The ''Beagle 2'' is an inoperative British Mars lander that was transported by the European Space Agency's 2003 ''Mars Express'' mission. It was intended to conduct an astrobiology mission that would have looked for evidence of past life on Mar ...
'' in a carbon dioxide atmosphere). Prior to being abandoned, the Soviet Mars lander program achieved one successful landing (Mars 3
Mars 3 was a robotic space probe of the Soviet Mars program, launched May 28, 1971, nine days after its twin spacecraft Mars 2. The probes were identical robotic spacecraft launched by Proton-K rockets with a Blok D upper stage, each consisting ...
), on the second of three entry attempts (the others were Mars 2
The Mars 2 was an uncrewed space probe of the Mars program, a series of uncrewed Mars landers and orbiters launched by the Soviet Union beginning 19 May 1971. The Mars 2 and Mars 3 missions consisted of identical spacecraft, each with an orbit ...
and Mars 6
Mars 6 (), also known as 3MP No.50P was a Soviet spacecraft launched to explore Mars. A 3MP bus spacecraft launched as part of the Mars program, it consisted of a lander, and a coast stage with instruments to study Mars as it flew past.
Spacecr ...
). The Soviet Mars landers were based upon a 60° half-angle aeroshell design.
A 45° half-angle sphere-cone is typically used for atmospheric probes (surface landing not intended) even though TPS mass is not minimized. The rationale for a 45° half-angle is to have either aerodynamic stability from entry-to-impact (the heat shield is not jettisoned) or a short-and-sharp heat pulse followed by prompt heat shield jettison. A 45° sphere-cone design was used with the DS/2 Mars impactor and Pioneer Venus
The Pioneer Venus project was part of the Pioneer program consisting of two spacecraft, the Pioneer Venus Orbiter and the Pioneer Venus Multiprobe, launched to Venus in 1978. The program was managed by NASA's Ames Research Center.
The Pione ...
probes.
Notable atmospheric entry accidents
Not all atmospheric reentries have been completely successful:
*Voskhod 2
Voskhod 2 (russian: Восход-2, , ''Sunrise-2'') was a Soviet crewed space mission in March 1965. The Vostok-based Voskhod 3KD spacecraft with two crew members on board, Pavel Belyayev and Alexei Leonov, was equipped with an inflatable air ...
– The service module failed to detach for some time, but the crew survived.
*Soyuz 5
Soyuz 5 (russian: Союз 5, ''Union 5'') was a Soyuz mission using the Soyuz 7K-OK spacecraft launched by the Soviet Union on 15 January 1969, which docked with Soyuz 4 in orbit. It was the first docking of two crewed spacecraft of any natio ...
– The service module failed to detach, but the crew survived.
*Apollo 15
Apollo 15 (July 26August 7, 1971) was the ninth crewed mission in the United States' Apollo program and the fourth to Moon landing, land on the Moon. It was the first List of Apollo missions#Alphabetical mission types, J mission, with a ...
- One of the three ringsail parachutes failed during the ocean landing, likely damaged as the spacecraft vented excess control fuel. The spacecraft was designed to land safely with only two parachutes, and the crew were uninjured.
*Mars Polar Lander
The Mars Polar Lander, also known as the Mars Surveyor '98 Lander, was a 290-kilogram robotic spacecraft lander launched by NASA on January 3, 1999, to study the soil and climate of Planum Australe, a region near the south pole on Mars. It for ...
– Failed during EDL. The failure was believed to be the consequence of a software error. The precise cause is unknown for lack of real-time telemetry
Telemetry is the in situ data collection, collection of measurements or other data at remote points and their automatic data transmission, transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Gr ...
.
* Space Shuttle ''Columbia'' STS-1 – a combination of launch damage, protruding gap filler, and tile installation error resulted in serious damage to the orbiter, only some of which the crew was aware. Had the crew known the true extent of the damage before attempting reentry, they would have flown the shuttle to a safe altitude and then bailed out. Nevertheless, reentry was successful, and the orbiter proceeded to a normal landing.
* Space Shuttle ''Atlantis'' STS-27
STS-27 was the 27th NASA Space Shuttle mission, and the third flight of Space Shuttle ''Atlantis''. Launching on December 2, 1988, on a four-day mission, it was the second shuttle flight after the Space Shuttle ''Challenger'' disaster of Janu ...
– Insulation from the starboard solid rocket booster
A solid rocket booster (SRB) is a large solid propellant motor used to provide thrust in spacecraft launches from initial launch through the first ascent. Many launch vehicles, including the Atlas V, SLS and space shuttle, have used SRBs to give ...
nose cap struck the orbiter during launch, causing significant tile damage. This dislodged one tile completely, over an aluminum mounting plate for a TACAN antenna. The antenna sustained extreme heat damage, but prevented the hot gas from penetrating the vehicle body.
* ''Genesis'' – The parachute failed to deploy due to a G-switch having been installed backwards (a similar error delayed parachute deployment for the ''Galileo'' Probe). Consequently, the Genesis entry vehicle crashed into the desert floor. The payload was damaged, but most scientific data were recoverable.
*Soyuz TMA-11
Soyuz TMA-11 was a human spaceflight mission using a Soyuz-TMA spacecraft to transport personnel to and from the International Space Station (ISS). The mission began at 13:22 UTC on October 10, 2007, when the spacecraft was launched from the ...
– The Soyuz propulsion module failed to separate properly; fallback ballistic reentry was executed that subjected the crew to accelerations of about . The crew survived.
Some reentries have resulted in significant disasters:
*Soyuz 1
Soyuz 1 (russian: Союз 1, ''Union 1'') was a crewed spaceflight of the Soviet space program. Launched into orbit on 23 April 1967 carrying cosmonaut colonel Vladimir Komarov, Soyuz 1 was the first crewed flight of the Soyuz spacecraft. The ...
– The attitude control
Attitude control is the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc.
Controlling vehicle ...
system failed while still in orbit and later parachutes got entangled during the emergency landing sequence (entry, descent, and landing (EDL) failure). Lone cosmonaut Vladimir Mikhailovich Komarov
Vladimir Mikhaylovich Komarov ( rus, Влади́мир Миха́йлович Комаро́в, p=vlɐˈdʲimʲɪr mʲɪˈxajləvʲɪtɕ kəmɐˈrof; 16 March 1927 – 24 April 1967) was a Soviet test pilot, aerospace engineer, and cosmonaut. ...
died.
*Soyuz 11
Soyuz 11 (russian: link=no, Союз 11, lit=Union 11) was the only crewed mission to board the world's first space station, Salyut 1 (Soyuz 10 had soft-docked, but had not been able to enter due to latching problems). The crew, Georgy Dobrov ...
– During tri-module separation, a valve seal was opened by the shock, depressurizing the descent module, the crew of three asphyxiated in space minutes before reentry.
*STS-107
STS-107 was the 113th flight of the Space Shuttle program, and the 28th and final flight of Space Shuttle ''Columbia''. The mission launched from Kennedy Space Center in Florida on January 16, 2003, and during its 15 days, 22 hours, 20 minutes ...
– The failure of a reinforced carbon–carbon
Carbon fibre reinforced carbon (CFRC),
carbon–carbon (C/C),
or reinforced carbon–carbon (RCC)
is a composite material consisting of carbon fiber reinforcement in a matrix of graphite. It was developed for the reentry vehicles of intercontin ...
panel on a wing leading edge caused by debris impact at launch led to breakup of the orbiter on reentry resulting in the deaths of all seven crew members.
Uncontrolled and unprotected entries
Of satellites that reenter, approximately 10–40% of the mass of the object is likely to reach the surface of the Earth. On average, about one catalogued object reenters per day.
Due to the Earth's surface being primarily water, most objects that survive reentry land in one of the world's oceans. The estimated chances that a given person will get hit and injured during their lifetime is around 1 in a trillion.
On January 24, 1978, the Soviet
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
Kosmos 954
Kosmos 954 (russian: Космос 954) was a reconnaissance satellite launched by the Soviet Union in 1977. A malfunction prevented safe separation of its onboard nuclear reactor; when the satellite reentered the Earth's atmosphere the follow ...
() reentered and crashed near Great Slave Lake
Great Slave Lake (french: Grand lac des Esclaves), known traditionally as Tıdeè in Tłı̨chǫ Yatıì (Dogrib), Tinde’e in Wıìlıìdeh Yatii / Tetsǫ́t’ıné Yatıé (Dogrib / Chipewyan), Tu Nedhé in Dëne Sųłıné Yatıé (Chi ...
in the Northwest Territories
The Northwest Territories (abbreviated ''NT'' or ''NWT''; french: Territoires du Nord-Ouest, formerly ''North-Western Territory'' and ''North-West Territories'' and namely shortened as ''Northwest Territory'') is a federal territory of Canada. ...
of Canada. The satellite was nuclear-powered and left radioactive debris near its impact site.
On July 11, 1979, the US Skylab
Skylab was the first United States space station, launched by NASA, occupied for about 24 weeks between May 1973 and February 1974. It was operated by three separate three-astronaut crews: Skylab 2, Skylab 3, and Skylab 4. Major operations in ...
space station () reentered and spread debris across the Australian Outback
The Outback is a remote, vast, sparsely populated area of Australia. The Outback is more remote than the bush. While often envisaged as being arid, the Outback regions extend from the northern to southern Australian coastlines and encompass a n ...
. The reentry was a major media event largely due to the Cosmos 954 incident, but not viewed as much as a potential disaster since it did not carry toxic nuclear or hydrazine
Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
fuel. NASA had originally hoped to use a Space Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...
mission to either extend its life or enable a controlled reentry, but delays in the Shuttle program, plus unexpectedly high solar activity, made this impossible.
On February 7, 1991, the Soviet Salyut 7
Salyut 7 (russian: Салют-7; en, Salute 7) (a.k.a. DOS-6, short for Durable Orbital Station) was a space station in low Earth orbit from April 1982 to February 1991. It was first crewed in May 1982 with two crew via Soyuz T-5, and last vi ...
space station (), with the Kosmos 1686
Kosmos 1686 (russian: Космос 1686 meaning ''Cosmos 1686''), also known as TKS-4, was a heavily modified TKS spacecraft which docked unmanned to the Soviet space station Salyut 7 as part of tests to attach scientific expansion modules to sta ...
module () attached, reentered and scattered debris over the town of Capitán Bermúdez
Capitán Bermúdez is a city in the provinces of Argentina, province of Santa Fe Province, Santa Fe, Argentina, located within the metropolitan area of Greater Rosario, (north of Rosario, Santa Fe, Rosario, immediately north of Granadero Baigorria) ...
, Argentina. The station had been boosted to a higher orbit in August 1986 in an attempt to keep it up until 1994, but in a scenario similar to Skylab, the planned Buran shuttle
''Buran'' (russian: Буран, , meaning "Snowstorm" or "Blizzard"; GRAU index serial number: 11F35 1K, construction number: 1.01) was the first spaceplane to be produced as part of the Soviet/Russian Buran program. Besides describing the fir ...
was cancelled and high solar activity caused it to come down sooner than expected.
On September 7, 2011, NASA announced the impending uncontrolled reentry of the Upper Atmosphere Research Satellite
The Upper Atmosphere Research Satellite (UARS) was a NASA-operated orbital observatory whose mission was to study the Earth's atmosphere, particularly the protective ozone layer. The satellite was deployed from Space Shuttle ''Discovery'' durin ...
() and noted that there was a small risk to the public. The decommissioned satellite reentered the atmosphere on September 24, 2011, and some pieces are presumed to have crashed into the South Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
over a debris field long.
On April 1, 2018, the Chinese Tiangong-1
Tiangong-1 () was China's first prototype space station. It orbited Earth from September 2011 to April 2018, serving as both a crewed laboratory and an experimental testbed to demonstrate orbital rendezvous and docking capabilities during it ...
space station () reentered over the Pacific Ocean, halfway between Australia and South America. The China Manned Space Engineering Office
China Manned Space Agency or CMSA () is an agency of the People's Republic of China responsible for the administration of China Manned Space Program, the Chinese human spaceflight program.
Name
The native name of the organization (') was i ...
had intended to control the reentry, but lost telemetry
Telemetry is the in situ data collection, collection of measurements or other data at remote points and their automatic data transmission, transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Gr ...
and control in March 2017.
On May 11, 2020, the core stage of Chinese Long March 5B
Long March 5 (LM-5; zh, s=长征五号 , p=Chángzhēng wǔ hào), or Changzheng 5 (CZ-5), and also by its nickname "''Pang-Wu''" (胖五, "''Fat-Five''"), is a Chinese heavy-lift launch vehicle developed by the China Academy of Launch Vehicle ...
(COSPAR ID
The International Designator, also known as COSPAR ID, is an international identifier assigned to artificial objects in space. It consists of the launch year, a three-digit incrementing launch number of that year and up to a three-letter code repr ...
2020-027C) weighing roughly ) made an uncontrolled reentry over the Atlantic Ocean, near West African coast. Few pieces of rocket debris reportedly survived reentry and fell over at least two villages in Ivory Coast
Ivory Coast, also known as Côte d'Ivoire, officially the Republic of Côte d'Ivoire, is a country on the southern coast of West Africa. Its capital is Yamoussoukro, in the centre of the country, while its largest city and economic centre is ...
.
On May 8, 2021, the core stage of Chinese Long March 5B
Long March 5 (LM-5; zh, s=长征五号 , p=Chángzhēng wǔ hào), or Changzheng 5 (CZ-5), and also by its nickname "''Pang-Wu''" (胖五, "''Fat-Five''"), is a Chinese heavy-lift launch vehicle developed by the China Academy of Launch Vehicle ...
(COSPAR ID
The International Designator, also known as COSPAR ID, is an international identifier assigned to artificial objects in space. It consists of the launch year, a three-digit incrementing launch number of that year and up to a three-letter code repr ...
2021-0035B) weighing ) made an uncontrolled reentry, just west of the Maldives in the Indian Ocean (approximately 72.47°E longitude and 2.65°N latitude). Witnesses reported rocket debris as far away as the Arabian peninsula.
It is expected that the Cruise Mass Balance Devices (CMBDs) from the Mars 2020
Mars 2020 is a Mars rover mission forming part of NASA's Mars Exploration Program that includes the rover ''Perseverance'', the small robotic, coaxial helicopter '' Ingenuity'', and associated delivery vehicles. Mars 2020 was launched from Ear ...
mission, which are ejected prior to the spacecraft entering the atmosphere, will survive re-entry and impact the surface on Thursday 18 February 2021. The CMBDs are 77 kg tungsten blocks used to adjust the spacecraft's trajectory prior to entry. The Science Team of another NASA mission, InSight
Insight is the understanding of a specific cause and effect within a particular context. The term insight can have several related meanings:
*a piece of information
*the act or result of understanding the inner nature of things or of seeing intu ...
, announced in early 2021 that they would attempt to detect the seismic waves from this impact event.
In 2022 it was confirmed that space debris that had landed in New South Wales
)
, nickname =
, image_map = New South Wales in Australia.svg
, map_caption = Location of New South Wales in AustraliaCoordinates:
, subdivision_type = Country
, subdivision_name = Australia
, established_title = Before federation
, es ...
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
were from a SpaceX
Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal of ...
craft that had launched in 2020.
Deorbit disposal
Salyut 1
Salyut 1 (DOS-1) (russian: Салют-1) was the world's first space station launched into low Earth orbit by the Soviet Union on April 19, 1971. The Salyut program followed this with five more successful launches of seven more stations. The fi ...
, the world's first space station, was deliberately de-orbited into the Pacific Ocean in 1971 following the Soyuz 11
Soyuz 11 (russian: link=no, Союз 11, lit=Union 11) was the only crewed mission to board the world's first space station, Salyut 1 (Soyuz 10 had soft-docked, but had not been able to enter due to latching problems). The crew, Georgy Dobrov ...
accident. Its successor, Salyut 6
Salyut 6 (russian: Салют-6; lit. Salute 6), DOS-5, was a Soviet orbital space station, the eighth station of the Salyut programme. It was launched on 29 September 1977 by a Proton rocket. Salyut 6 was the first space station to receiv ...
, was de-orbited in a controlled manner as well.
On June 4, 2000 the Compton Gamma Ray Observatory
The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting photons with energies from 20 k eV to 30 GeV, in Earth orbit from 1991 to 2000. The observatory featured four main telescopes in one spacecraft, covering X-ra ...
was deliberately de-orbited after one of its gyroscopes failed. The debris that did not burn up fell harmlessly into the Pacific Ocean. The observatory was still operational, but the failure of another gyroscope would have made de-orbiting much more difficult and dangerous. With some controversy, NASA decided in the interest of public safety that a controlled crash was preferable to letting the craft come down at random.
In 2001, the Russian ''Mir
''Mir'' (russian: Мир, ; ) was a space station that operated in low Earth orbit from 1986 to 2001, operated by the Soviet Union and later by Russia. ''Mir'' was the first modular space station and was assembled in orbit from 1986 to&n ...
'' space station was deliberately de-orbited, and broke apart in the fashion expected by the command center during atmospheric reentry. Mir entered the Earth's atmosphere on March 23, 2001, near Nadi
Nadi (pronounced ) is the third-largest conurbation in Fiji. It is located on the western side of the main island of Viti Levu, and had a population of 42,284 at the most recent census, in 2007. A 2012 estimate showed that the population had ...
, Fiji
Fiji ( , ,; fj, Viti, ; Fiji Hindi: फ़िजी, ''Fijī''), officially the Republic of Fiji, is an island country in Melanesia, part of Oceania in the South Pacific Ocean. It lies about north-northeast of New Zealand. Fiji consists ...
, and fell into the South Pacific Ocean.
On February 21, 2008, a disabled U.S. spy satellite
A reconnaissance satellite or intelligence satellite (commonly, although unofficially, referred to as a spy satellite) is an Earth observation satellite or communications satellite deployed for military or intelligence applications.
The ...
, USA-193
USA-193, also known as NRO Launch 21 (NROL-21 or simply L-21), was a United States military reconnaissance satellite (radar imaging) launched on 14 December 2006. It was the first launch conducted by the United Launch Alliance (ULA). Owned by ...
, was hit at an altitude of approximately with an SM-3
The RIM-161 Standard Missile 3 (SM-3) is a ship-based surface-to-air missile system used by the United States Navy to intercept short- and intermediate-range ballistic missiles as a part of Aegis Ballistic Missile Defense System. Although primari ...
missile fired from the U.S. Navy cruiser
A cruiser is a type of warship. Modern cruisers are generally the largest ships in a fleet after aircraft carriers and amphibious assault ships, and can usually perform several roles.
The term "cruiser", which has been in use for several hu ...
off the coast of Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...
. The satellite was inoperative, having failed to reach its intended orbit when it was launched in 2006. Due to its rapidly deteriorating orbit it was destined for uncontrolled reentry within a month. U.S. Department of Defense
The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national secur ...
expressed concern that the fuel tank containing highly toxic hydrazine
Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
might survive reentry to reach the Earth's surface intact. Several governments including those of Russia, China, and Belarus
Belarus,, , ; alternatively and formerly known as Byelorussia (from Russian ). officially the Republic of Belarus,; rus, Республика Беларусь, Respublika Belarus. is a landlocked country in Eastern Europe. It is bordered by R ...
protested the action as a thinly-veiled demonstration of US anti-satellite capabilities. China had previously caused an international incident when it tested an anti-satellite missile in 2007.
File:Closeup of Gemini 2 heatshield.jpg, Closeup of Gemini 2
Gemini 2 (Gemini-Titan 2; GT-2) was the second spaceflight of the American human spaceflight program Project Gemini, and was launched and recovered on January 19, 1965. Gemini 2, like Gemini 1, was an uncrewed mission intended as a test fligh ...
heat shield
File:Cross section of Gemini 2 heatshield.jpg, Cross section of Gemini 2 heat shield
Successful atmospheric entries from orbital velocities
Crewed orbital reentry, by country/governmental entity
* – Shenzhou
* / – Vostok Vostok refers to east in Russian but may also refer to:
Spaceflight
* Vostok programme, Soviet human spaceflight project
* Vostok (spacecraft), a type of spacecraft built by the Soviet Union
* Vostok (rocket family), family of rockets derived from ...
, Voskhod, Soyuz Soyuz is a transliteration of the Cyrillic text Союз (Russian and Ukrainian, 'Union'). It can refer to any union, such as a trade union (''profsoyuz'') or the Union of Soviet Socialist Republics (Сою́з Сове́тских Социалис ...
* – Mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
, Gemini
Gemini may refer to:
Space
* Gemini (constellation), one of the constellations of the zodiac
** Gemini in Chinese astronomy
* Project Gemini, the second U.S. crewed spaceflight program
* Gemini Observatory, consisting of telescopes in the Northern ...
, Apollo
Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label=Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label= ...
, Space Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...
Crewed orbital reentry, by commercial entity
* SpaceX
Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal of ...
– Dragon 2
Dragon 2 is a class of partially reusable spacecraft developed and manufactured by American aerospace manufacturer SpaceX, primarily for flights to the International Space Station (ISS). SpaceX has also launched Private spaceflight, private m ...
Uncrewed orbital reentry, by country/governmental entity
*
* European Space Agency
, owners =
, headquarters = Paris, Île-de-France, France
, coordinates =
, spaceport = Guiana Space Centre
, seal = File:ESA emblem seal.png
, seal_size = 130px
, image = Views in the Main Control Room (1205 ...
* / Indian Space Research Organisation
The Indian Space Research Organisation (ISRO; ) is the national space agency of India, headquartered in Bengaluru. It operates under the Department of Space (DOS) which is directly overseen by the Prime Minister of India, while the Chairman ...
*
* /
*
Uncrewed orbital reentry, by commercial entity
* SpaceX
Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal of ...
– Dragon
A dragon is a reptilian legendary creature that appears in the folklore of many cultures worldwide. Beliefs about dragons vary considerably through regions, but dragons in western cultures since the High Middle Ages have often been depicted as ...
* Boeing
The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and product ...
- Starliner
Selected atmospheric entries
This list includes some notable atmospheric entries in which the spacecraft was not intended to be recovered, but was destroyed in the atmosphere.
Gallery
Soyuz TMA-05M spacecraft reentry.jpg, Close up of reentry trail (Soyuz)
Soyuz TMA-05M capsule reentry.jpg, Early reentry plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
trail (Soyuz)
File:Re-entry of Progress Spacecraft 42P - NASA Earth Observatory.jpg, Progress
Progress is the movement towards a refined, improved, or otherwise desired state. In the context of progressivism, it refers to the proposition that advancements in technology, science, and social organization have resulted, and by extension wi ...
during atmospheric entry over Earth
STS-135 Space Shuttle Atlantis reentry seen from the ISS.jpg, Space Shuttle reentry
ISS-46 Soyuz TMA-17M reentry.jpg, Plume remains after reentry of a Soyuz
See also
*
*
*
*
*
*
*
*
*
*
*
*
*
References
Further reading
*
*
*
*
*
*
* A revised version of this classic text has been reissued as an inexpensive paperback: reissued in 2004
*
External links
Aerocapture Mission Analysis Tool (AMAT)
provides preliminary mission analysis and simulation capability for atmospheric entry vehicles at various Solar System destinations.
Center for Orbital and Reentry Debris Studies (The Aerospace Corporation)
Apollo Atmospheric Entry Phase
1968, NASA Mission Planning and Analysis Division, Project Apollo. video (25:14).
Buran's heat shield
on the history of space rescue crafts, including some reentry craft designs.
{{DEFAULTSORT:Atmospheric entry
Aerospace engineering
Flight phases