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Non-ballistic atmospheric entry is a class of
atmospheric entry Atmospheric entry (sometimes listed as Vimpact or Ventry) is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. Atmospheric entry may be ''uncontrolled entr ...
trajectories that follow a non-
ballistic trajectory In physics, projectile motion describes the motion of an object that is launched into the air and moves under the influence of gravity alone, with air resistance neglected. In this idealized model, the object follows a parabolic path determin ...
by employing
aerodynamic lift When a fluid flows around an object, the fluid exerts a force on the object. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the force paral ...
in the high upper atmosphere. It includes trajectories such as skip and glide. Skip is a flight trajectory where the spacecraft goes in and out the atmosphere. Glide is a flight trajectory where the spacecraft stays in the atmosphere for a sustained flight period of time. In most examples, a skip reentry roughly doubles the range of suborbital spaceplanes and
reentry vehicle Atmospheric entry (sometimes listed as Vimpact or Ventry) is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. Atmospheric entry may be ''uncontrolled entr ...
s over the purely ballistic trajectory. In others, a series of ''skips'' allows the range to be further extended. Non-ballistic atmospheric entry was first seriously studied as a way to extend the range of
ballistic missile A ballistic missile is a type of missile that uses projectile motion to deliver warheads on a target. These weapons are powered only during relatively brief periods—most of the flight is unpowered. Short-range ballistic missiles (SRBM) typic ...
s, but was not used operationally in this form as conventional missiles with extended range were introduced. The underlying aerodynamic concepts have been used to produce
maneuverable reentry vehicle The maneuverable reentry vehicle (abbreviated MARV or MaRV) is a type of warhead for ballistic missile, ballistic missiles that is capable of maneuvering and changing its trajectory. There are two general reasons to use MARV. One is to make it ...
s (MARV), to increase the accuracy of some missiles like the Pershing II. More recently, the concepts have been used to produce hypersonic glide vehicles (HGV) to avoid interception as in the case of the Avangard. The range-extension is used as a way to allow flights at lower altitudes, helping avoid
radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...
detection for a longer time compared to a higher ballistic path. The concept has also been used to extend the reentry time for vehicles returning to Earth from the Moon, which would otherwise have to shed a large amount of velocity in a short time and thereby suffer very high heating rates. The
Apollo Command Module The Apollo command and service module (CSM) was one of two principal components of the United States Apollo (spacecraft), Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functi ...
also used what is essentially a skip re-entry, as did the Soviet Zond and Chinese
Chang'e 5-T1 Chang'e 5-T1 () was an experimental robotic spacecraft that was launched to the Moon on 23 October 2014, by the China National Space Administration (CNSA) to conduct atmospheric re-entry tests on the capsule design planned to be used in the Ch ...
.


History


Early concepts

The conceptual basis was first noticed by German artillery officers, who found that their ''Peenemünder Pfeilgeschosse'' arrow shells traveled much further when fired from higher altitudes. This was not entirely unexpected due to geometry and thinner air, but when these factors were accounted for, they still could not explain the much greater ranges being seen. Investigations at
Peenemünde Peenemünde (, ) is a municipality on the Baltic Sea island of Usedom in the Vorpommern-Greifswald district in Mecklenburg-Vorpommern in north-eastern Germany. It is part of the ''Amt (country subdivision), Amt'' (collective municipality) of Used ...
led them to discover that the longer trajectories in the thinner high-altitude air resulted in the shell having an
angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a Airfoil#Airfoil terminology, reference line on a body (often the chord (aircraft), chord line of an airfoil) and the vector (geometry), vector representing the relat ...
that produced
aerodynamic lift When a fluid flows around an object, the fluid exerts a force on the object. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the force paral ...
at supersonic speeds. At the time this was considered highly undesirable because it made the trajectory very difficult to calculate, but its possible application for extending range was not lost on the observers. In June 1939, Kurt Patt of
Klaus Riedel Klaus Riedel (2 August 1907 – 4 August 1944) was a German rocket pioneer. He was involved in many early liquid-fuelled rocket experiments, and eventually worked on the V-2 missile programme at Peenemünde Army Research Center. A Lunar crat ...
's design office at Peenemünde proposed wings for converting rocket speed and altitude into aerodynamic lift and range. He calculated that this would roughly double range of the A-4 rockets from to about . Early development was considered under the A-9 name, although little work other than
wind tunnel A wind tunnel is "an apparatus for producing a controlled stream of air for conducting aerodynamic experiments". The experiment is conducted in the test section of the wind tunnel and a complete tunnel configuration includes air ducting to and f ...
studies at the Zeppelin-Staaken company would be carried out during the next few years. Low-level research continued until 1942 when it was cancelled. The earliest known proposal for the boost-glide concept for truly long-range use dates to the 1941 '' Silbervogel'', a proposal by
Eugen Sänger Eugen Sänger (22 September 1905 – 10 February 1964) was an Austrian aerospace engineer best known for his contributions to lifting body and ramjet technology. Early career Sänger was born in the former mining town of Preßnitz (Příse� ...
for a rocket powered
bomber A bomber is a military combat aircraft that utilizes air-to-ground weaponry to drop bombs, launch aerial torpedo, torpedoes, or deploy air-launched cruise missiles. There are two major classifications of bomber: strategic and tactical. Strateg ...
able to attack
New York City New York, often called New York City (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...
from bases in
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
then fly on for landing somewhere in the
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...
held by the
Empire of Japan The Empire of Japan, also known as the Japanese Empire or Imperial Japan, was the Japanese nation state that existed from the Meiji Restoration on January 3, 1868, until the Constitution of Japan took effect on May 3, 1947. From Japan–Kor ...
. The idea would be to use the vehicle's wings to generate lift and pull up into a new ballistic trajectory, exiting the atmosphere again and giving the vehicle time to cool off between the skips. It was later demonstrated that the heating load during the skips was much higher than initially calculated, and would have melted the spacecraft. In 1943, the A-9 work was dusted off again, this time under the name A-4b. It has been suggested this was either because it was now based on an otherwise unmodified A-4, or because the A-4 program had "national priority" by this time, and placing the development under the A-4 name guaranteed funding. A-4b used
swept wing A swept wing is a wing angled either backward or occasionally forward from its root rather than perpendicular to the fuselage. Swept wings have been flown since the pioneer days of aviation. Wing sweep at high speeds was first investigated in Ge ...
s in order to extend the range of the V2 enough to allow attacks on UK cities in
the Midlands The Midlands is the central region of England, to the south of Northern England, to the north of southern England, to the east of Wales, and to the west of the North Sea. The Midlands comprises the ceremonial counties of Derbyshire, Herefords ...
or to reach
London London is the Capital city, capital and List of urban areas in the United Kingdom, largest city of both England and the United Kingdom, with a population of in . London metropolitan area, Its wider metropolitan area is the largest in Wester ...
from areas deeper within Germany. The A-9 was originally similar, but later featured long ogival delta shaped wings instead of the more conventional swept ones. This design was adapted as a crewed upper stage for the A-9/A-10 intercontinental missile, which would glide from a point over the Atlantic with just enough range to bomb New York before the pilot bailed out.


Post-war development

In the immediate post-war era, Soviet rocket engineer
Aleksei Isaev Aleksei Mikhailovich Isaev (also Isayev; Russian: Алексе́й Миха́йлович Иса́ев; October 24, 1908, in Saint Petersburg – June 10, 1971, in Moscow) was a Soviet engineer in the Soviet space program, working on rocket comb ...
found a copy of an updated August 1944 report on the ''Silbervogel'' concept. He had the paper translated to Russian, and it eventually came to the attention of
Joseph Stalin Joseph Vissarionovich Stalin (born Dzhugashvili; 5 March 1953) was a Soviet politician and revolutionary who led the Soviet Union from 1924 until Death and state funeral of Joseph Stalin, his death in 1953. He held power as General Secret ...
who was intensely interested in the concept of an antipodal bomber. In 1946, he sent his son Vasily Stalin and scientist Grigori Tokaty, who had also worked on winged rockets before the war, to visit Sänger and Irene Bredt in Paris and attempt to convince them to join a new effort in the
Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
. Sänger and Bredt turned down the invitation. In November 1946, the Soviets formed the NII-1
design bureau OKB () is a transliteration of the Russian initials for "" (), which translates to "Experimental Design Bureau." It could also mean or "Special Design Bureau" in english. During the Soviet era, OKBs were closed institutions working on design and ...
under
Mstislav Keldysh Mstislav Vsevolodovich Keldysh (; – 24 June 1978) was a Soviet mathematician who worked as an engineer in the Soviet space program. He was the academician of the Academy of Sciences of the Soviet Union (1946), President of the Academy of Sc ...
to develop their own version without Sänger and Bredt. Their early work convinced them to convert from a rocket powered hypersonic skip-glide concept to a
ramjet A ramjet is a form of airbreathing jet engine that requires forward motion of the engine to provide air for combustion. Ramjets work most efficiently at supersonic speeds around and can operate up to . Ramjets can be particularly appropriat ...
powered supersonic
cruise missile A cruise missile is an unmanned self-propelled guided missile that sustains flight through aerodynamic lift for most of its flight path. Cruise missiles are designed to deliver a large payload over long distances with high precision. Modern cru ...
, not unlike the Navaho being developed in the United States during the same period. Development continued for a time as the Keldysh bomber, but improvements in conventional ballistic missiles ultimately rendered the project unnecessary. In the United States, the skip-glide concept was advocated by many of the German scientists who moved there, primarily
Walter Dornberger Major-General Dr. Walter Robert Dornberger (6 September 1895 – 26 June 1980) was a German Army artillery officer whose career spanned World War I and World War II. He was a leader of Nazi Germany's V-2 rocket programme and other projects a ...
and Krafft Ehricke at
Bell Aircraft The Bell Aircraft Corporation was an American aircraft manufacturer, a builder of several types of fighter aircraft for World War II but most famous for the Bell X-1, the first supersonic aircraft, and for the development and production of many i ...
. In 1952, Bell proposed a bomber concept that was essentially a vertical launch version of ''Silbervogel'' known as Bomi. This led to a number of follow-on concepts during the 1950s, including Robo, Hywards, Brass Bell, and ultimately the Boeing X-20 Dyna-Soar. Earlier designs were generally bombers, while later models were aimed at reconnaissance or other roles. Dornberger and Ehricke also collaborated on a 1955 ''Popular Science'' article pitching the idea for airliner use. The introduction of successful
intercontinental ballistic missile An intercontinental ballistic missile (ICBM) is a ballistic missile with a range (aeronautics), range greater than , primarily designed for nuclear weapons delivery (delivering one or more Thermonuclear weapon, thermonuclear warheads). Conven ...
s (ICBMs) in the offensive role ended any interest in the skip-glide bomber concepts, as did the
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 ...
for the spyplane roles. The X-20 space fighter saw continued interest through the 1960s, but was ultimately the victim of budget cuts; after another review in March 1963,
Robert McNamara Robert Strange McNamara (; June 9, 1916 – July 6, 2009) was an American businessman and government official who served as the eighth United States secretary of defense from 1961 to 1968 under presidents John F. Kennedy and Lyndon B. Johnson ...
canceled the program in December, noting that after $400 million had been spent they still had no mission for it to fulfill.


Missile use

Through the 1960s, the skip-glide concept saw interest not as a way to extend range, which was no longer a concern with modern missiles, but as the basis for maneuverable reentry vehicles for ICBMs. The primary goal was to have the RV change its path during reentry so that
anti-ballistic missile An anti-ballistic missile (ABM) is a surface-to-air missile designed to Missile defense, destroy in-flight ballistic missiles. They achieve this explosively (chemical or nuclear), or via hit-to-kill Kinetic projectile, kinetic vehicles, which ma ...
s (ABMs) would not be able to track their movements rapidly enough for a successful interception. The first known example was the Alpha Draco tests of 1959, followed by the Boost Glide Reentry Vehicle (BGRV) test series,
ASSET In financial accounting, an asset is any resource owned or controlled by a business or an economic entity. It is anything (tangible or intangible) that can be used to produce positive economic value. Assets represent value of ownership that can b ...
and
PRIME A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways ...
. This research was eventually put to use in the Pershing II's MARV reentry vehicle. In this case, there is no extended gliding phase; the warhead uses lift only for short periods to adjust its trajectory. This is used late in the reentry process, combining data from a Singer Kearfott
inertial navigation system An inertial navigation system (INS; also inertial guidance system, inertial instrument) is a navigation device that uses motion sensors (accelerometers), rotation sensors (gyroscopes) and a computer to continuously calculate by dead reckoning th ...
with a Goodyear Aerospace active
radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...
. Similar concepts have been developed for most nuclear-armed nations'
theatre ballistic missile A theatre ballistic missile (TBM) is any ballistic missile used against targets "Theater (warfare), in-theatre". Examples of this type of in-theatre missile are the Soviet Union, Soviet RT-15, TR-1 Temp and United States, American PGM-19 Jupiter ...
s. The
Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
had also invested some effort in the development of MARV to avoid US ABMs, but the closure of the US defenses in the 1970s meant there was no reason to continue this program. Things changed in the 2000s with the introduction of the US's
Ground-Based Midcourse Defense Ground-Based Midcourse Defense (GMD), previously National Missile Defense (NMD), is an anti-ballistic missile system implemented by the United States of America for defense against ballistic missiles, during the midcourse phase of ballistic t ...
, which led
Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
to reanimate this work. The vehicle, referred to as ''Object 4202'' in the Soviet era, was reported in October 2016 to have had a successful test. The system was revealed publicly on 1 March 2018 as the hypersonic glide vehicle (HGV) Avangard (; ), which officially entered active service as an ICBM payload on 27 December 2019.
Vladimir Putin Vladimir Vladimirovich Putin (born 7 October 1952) is a Russian politician and former intelligence officer who has served as President of Russia since 2012, having previously served from 2000 to 2008. Putin also served as Prime Minister of Ru ...
announced that Avangard had entered serial production, claiming that its maneuverability makes it invulnerable to all current missile defences.
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
has also developed a boost-glide warhead, the DF-ZF (known to US intelligence as "WU-14"). In contrast to the US and Russian MARV designs, the DF-ZF's primary goal is to use boost-glide to extend range while flying at lower altitudes than would be used to reach the same target using a purely ballistic path. This is intended to keep it out of the sight of the
US Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...
's Aegis Combat System radars as long as possible, and thereby decrease the time that system has to respond to an attack. DF-ZF was officially unveiled on 1 October 2019. Similar efforts by Russia led to the Kholod and GLL-8 Igla hypersonic test projects, and more recently the Yu-71 hypersonic glide vehicle which can be carried by
RS-28 Sarmat The RS-28 Sarmat (, named after the Sarmatians; NATO reporting name: SS-X-29 or SS-X-30), often colloquially referred to as Satan II by media outlets, is a three-stage Russian silo-based, liquid-fueled, HGV-capable and FOBS-capable super-h ...
. Boost-glide became the topic of some interest as a possible solution to the US
Prompt Global Strike Conventional Prompt Strike (CPS), formerly called Prompt Global Strike (PGS), is a United States Armed Forces, United States military effort to develop a system that can deliver a precision-guided munition, precision-guided conventional weapon ...
(PGS) requirement, which seeks a weapon that can hit a target anywhere on the Earth within one hour of launch from the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
. PGS does not define the mode of operation, and current studies include Advanced Hypersonic Weapon boost-glide
warhead A warhead is the section of a device that contains the explosive agent or toxic (biological, chemical, or nuclear) material that is delivered by a missile, rocket (weapon), rocket, torpedo, or bomb. Classification Types of warheads include: *E ...
, Falcon HTV-2
hypersonic aircraft Hypersonic flight is flight through the atmosphere below altitudes of about at Hypersonic speed, speeds greater than Mach 5, a speed where Dissociation (chemistry), dissociation of air begins to become significant and high heat loads exist. Spe ...
, and submarine-launched missiles.
Lockheed Martin The Lockheed Martin Corporation is an American Arms industry, defense and aerospace manufacturer with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta on March 15, 1995. It is headquartered in North ...
is developing this concept as the hypersonic AGM-183A ARRW.


Reentry vehicle use

The technique was used by the Soviet Zond series of circumlunar spacecraft, which used one skip before landing. In this case a true skip was required in order to allow the spacecraft to reach the higher-latitude landing areas.
Zond 6 Zond 6 was a formal member of the Soviet Zond program, and an unpiloted version of the Soyuz 7K-L1 crewed Moon-flyby spacecraft. It was launched on a lunar flyby mission on November 10, 1968, from a parent satellite (68-101B) in Earth parking o ...
,
Zond 7 The Zond 7 spacecraft, part of the Soviet Zond program, was launched towards the Moon on a Proton-K D rocket on August 7, 1969. Its mission was to support studies of the Moon and circumlunar space, to obtain color photography of Earth and the ...
and
Zond 8 Zond 8, also known as L-1 No.14, was the last in the series of circumlunar spacecraft, a member of the Soviet Zond program, designed to rehearse a piloted circumlunar flight, an uncrewed version of Soyuz 7K-L1 crewed circumlunar flight spacec ...
made successful skip entries, although
Zond 5 Zond 5 () was a spacecraft of the Soviet Zond program. In September 1968 it became the first spaceship to travel to and circle the Moon in a circumlunar trajectory, the first Moon mission to include animals, and the first to return safely to Ea ...
did not. The
Chang'e 5-T1 Chang'e 5-T1 () was an experimental robotic spacecraft that was launched to the Moon on 23 October 2014, by the China National Space Administration (CNSA) to conduct atmospheric re-entry tests on the capsule design planned to be used in the Ch ...
, which flew mission profiles similar to Zond, also used this technique. The
Apollo Command Module The Apollo command and service module (CSM) was one of two principal components of the United States Apollo (spacecraft), Apollo spacecraft, used for the Apollo program, which landed astronauts on the Moon between 1969 and 1972. The CSM functi ...
used a skip-like concept to lower the heating loads on the vehicle by extending the re-entry time, but the spacecraft did not leave the atmosphere again and there has been considerable debate whether this makes it a true skip profile.
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
referred to it simply as "lifting entry". A true multi-skip profile was considered as part of the Apollo Skip Guidance concept, but this was not used on any crewed flights. The concept continues to appear on more modern vehicles like the
Orion spacecraft Orion (Orion Multi-Purpose Crew Vehicle or Orion MPCV) is a partially reusable crewed spacecraft used in NASA's Artemis program. The spacecraft consists of a Crew Module (CM) space capsule designed by Lockheed Martin that is paired with a Eu ...
, which made the first American skip entry in the
Artemis 1 Artemis I, formerly Exploration Mission-1 (EM-1), was an uncrewed Moon-orbiting mission that was launched in November 2022. As the first major spaceflight of NASA's Artemis program, Artemis I marked the agency's return to lunar exploration a ...
mission, using onboard computers.


Flight mechanics

Using simplified equations of motion and assuming that during the atmospheric flight both drag and lift forces will be much larger than the gravity force acting on the vehicle, the following analytical relations for a skip reentry flight can be derived: \gamma_\mathrm = -\gamma_\mathrm, where \gamma is the flightpath angle relative to the local horizontal, the subscript E indicates the conditions at the start of the entry and the subscript F indicates the conditions at the end of the entry flight. The velocity V before and after the entry can be derived to relate as follows: \frac = \exp, where L/D is the
lift-to-drag ratio In aerodynamics, the lift-to-drag ratio (or L/D ratio) is the Lift (force), lift generated by an aerodynamic body such as an aerofoil or aircraft, divided by the aerodynamic drag caused by moving through air. It describes the aerodynamic efficie ...
of the vehicle.


See also

* High Speed Strike Weapon (HSSW) (USA) * DF-ZX (China) * DF-17 (China) *
Prompt Global Strike Conventional Prompt Strike (CPS), formerly called Prompt Global Strike (PGS), is a United States Armed Forces, United States military effort to develop a system that can deliver a precision-guided munition, precision-guided conventional weapon ...
(PGS) (USA) * Alpha Draco (USA) * ArcLight (missile) (USA) * DARPA Falcon Project (USA) * Boeing X-51 Waverider (USA) *
North American X-15 The North American X-15 is a Hypersonic speed, hypersonic rocket-powered aircraft which was operated by the United States Air Force and the National Aeronautics and Space Administration (NASA) as part of the List of X-planes, X-plane series of ...
(USA) * Tupolev Tu-130 (Russia) *
BrahMos-II BrahMos-II or BrahMos-2 or BrahMos Mark II is a hypersonic scramjet-propelled missile currently under joint development by India's Defence Research and Development Organisation and Russia's NPO Mashinostroyenia, which have together formed Brah ...
(India / Russia) * Hypersonic Technology Demonstrator Vehicle (India) *
Multiple independently targetable reentry vehicle A multiple independently targetable reentry vehicle (MIRV) is an exoatmospheric ballistic missile payload containing several warheads, each capable of being aimed to hit a different target. The concept is almost invariably associated with i ...
* Planar reentry equations


Notes


References


Citations


Bibliography

* * {{Missile types Cancelled military aircraft projects of the United States Atmospheric entry Apollo program Spaceplanes Space weapons Hypersonic aircraft