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''Near Earth Asteroid Rendezvous – Shoemaker'' (''NEAR Shoemaker''), renamed after its 1996 launch in honor of planetary scientist Eugene Shoemaker, was a robotic
space probe A space probe is an artificial satellite that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; o ...
designed by the
Johns Hopkins University Johns Hopkins University (Johns Hopkins, Hopkins, or JHU) is a private research university in Baltimore, Maryland. Founded in 1876, Johns Hopkins is the oldest research university in the United States and in the western hemisphere. It consi ...
Applied Physics Laboratory for
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, succeedin ...
to study the
near-Earth asteroid A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun ( perihelion) is less than 1.3 astronomical units (AU) ...
Eros from close orbit over a period of a year. It was the first spacecraft to successfully orbit an asteroid and also land on an asteroid. In February 2000, the mission succeeded in closing in with the asteroid and afterwards orbited it several times. On February 12, 2001, the mission succeeded in touching down on the asteroid. It was terminated just over two weeks later. The primary scientific objective of ''NEAR'' was to return data on the bulk properties, composition,
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
ogy, morphology, internal
mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different ele ...
distribution and
magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
of Eros. Secondary objectives include studies of regolith properties, interactions with the solar wind, possible current activity as indicated by dust or gas, and the asteroid spin state. This data will be used to help understand the characteristics of
asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
s in general, their relationship to meteoroids and
comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
s, and the conditions in the early Solar System. To accomplish these goals, the spacecraft was equipped with an
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
/ gamma-ray spectrometer, a near-infrared imaging spectrograph, a multi-spectral camera fitted with a CCD imaging detector, a
laser rangefinder A laser rangefinder, also known as a laser telemeter, is a rangefinder that uses a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in ...
, and a
magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...
. A radio science experiment was also performed using the ''NEAR'' tracking system to estimate the
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 ...
field of the asteroid. The total mass of the instruments was , requiring 80 watts of power.


Development

NEAR was the first robotic
space probe A space probe is an artificial satellite that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; o ...
built by
Johns Hopkins University Johns Hopkins University (Johns Hopkins, Hopkins, or JHU) is a private research university in Baltimore, Maryland. Founded in 1876, Johns Hopkins is the oldest research university in the United States and in the western hemisphere. It consi ...
's Applied Physics Laboratory (APL). A previous plan for the mission was for it to go to 4660 Nereus and do a flyby of 2019 van Albada en route. In January 2000 it would rendezvous with Nereus but instead of staying it would visit multiple asteroids and comets. Some of the choices that were discussed were 2P/Encke,
433 Eros Eros (minor planet designation: (433) Eros), provisional designation is a stony asteroid of the Amor group and the first discovered and second-largest near-Earth object with an elongated shape and a mean diameter of approximately . Vis ...
(which became the mission's primary target), 1036 Ganymed,
4 Vesta Vesta ( minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of . It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, t ...
, and
4015 Wilson–Harrington 4015 Wilson–Harrington is an active asteroid known both as comet 107P/Wilson–Harrington and as asteroid 4015 Wilson–Harrington. It will pass from Earth on 20 July 2022 and then pass perihelion (closest approach to the Sun) on 24 August 20 ...
. The Small-Body Grand Tour was a plan for visiting two asteroids and two comets over a span of a decade with the spacecraft.Extended-mission opportunities for a Discovery-class asteroid rendezvous mission
/ref>


Mission profile


Summary

The primary goal of the mission was to study the near-Earth asteroid
433 Eros Eros (minor planet designation: (433) Eros), provisional designation is a stony asteroid of the Amor group and the first discovered and second-largest near-Earth object with an elongated shape and a mean diameter of approximately . Vis ...
from orbit for approximately one year. Eros is an
S-type asteroid S-type asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are of this type, making it the secon ...
approximately 13 × 13 × 33 km in size, the second largest near-Earth asteroid. Initially the orbit was circular with a radius of 200 km. The radius of the orbit was brought down in stages to a 50 × 50 km orbit on April 30, 2000, and decreased to 35 × 35 km on July 14, 2000. The orbit was raised over succeeding months to a 200 × 200 km orbit and then slowly decreased and altered to a 35 × 35 km retrograde orbit on December 13, 2000. The mission ended with a touchdown in the "saddle" region of Eros on February 12, 2001. Some scientists claim that the ultimate goal of the mission was to link Eros, an asteroidal body, to meteorites recovered on Earth. With sufficient data on chemical composition, a causal link could be established between Eros and other S-type asteroids, and those meteorites believed to be pieces of S-type asteroids (perhaps Eros itself). Once this connection is established, meteorite material can be studied with large, complex, and evolving equipment, and the results extrapolated to bodies in space. ''NEAR'' did not prove or disprove this link to the satisfaction of scientists. Between December 1999 and February 2001, ''NEAR'' used its gamma-ray spectrometer to detect
gamma-ray bursts In gamma-ray astronomy, gamma-ray bursts (GRBs) are immensely energetic explosions that have been observed in distant galaxies. They are the most energetic and luminous electromagnetic events since the Big Bang. Bursts can last from ten millis ...
as part of the
InterPlanetary Network The InterPlanetary Network (IPN) is a group of spacecraft equipped with gamma ray burst (GRB) detectors. By timing the arrival of a burst at several spacecraft, its precise location can be found. The precision for determining the direction of a ...
.


The journey to Mathilde

After launch on a Delta 7925-8 (a
Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas. Delta II was part of the Delta rocket family and entered service in 1989. Delta II vehicles included the Delta 6000, and the two later Delta 7000 va ...
launch vehicle with nine strap-on solid-rocket boosters and a Star 48 (PAM-D) third stage) on February 17, 1996, and exit from Earth orbit, ''NEAR'' entered the first part of its cruise phase. ''NEAR'' spent most of the cruise phase in a minimal activity "hibernation" state, which ended a few days before the flyby of the 61 km diameter asteroid
253 Mathilde Mathilde ( minor planet designation: 253 Mathilde) is an asteroid in the intermediate asteroid belt, approximately 50 kilometers in diameter, that was discovered by Austrian astronomer Johann Palisa at Vienna Observatory on 12 November 1885. It ...
. On June 27, 1997, ''NEAR'' flew by Mathilde within 1200 km at 12:56 UT at 9.93 km/s, returning imaging and other instrument data. The flyby produced over 500 images, covering 60% of Mathilde's surface, as well as gravitational data allowing calculations of Mathilde's dimensions and mass.


The journey to Eros

On July 3, 1997, ''NEAR'' executed the first major deep space maneuver, a two-part burn of the main 450 N thruster. This decreased the velocity by 279 m/s and lowered perihelion from 0.99  AU to 0.95 AU. The Earth gravity assist swingby occurred on January 23, 1998, at 7:23 UT. The closest approach was 540 km, altering the orbital
inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Ea ...
from 0.5 to 10.2 degrees, and the
aphelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ell ...
distance from 2.17 to 1.77 AU, nearly matching those of Eros. Instrumentation was active at this time.


Failure of first attempt at orbital insertion

The first of four scheduled rendezvous burns was attempted on December 20, 1998, at 22:00 UT. The burn sequence was initiated but immediately aborted. The spacecraft subsequently entered safe mode and began tumbling. The spacecraft's thrusters fired thousands of times during the anomaly, which expended 29 kg of propellant reducing the program's propellant margin to zero. This anomaly almost resulted in the loss of the spacecraft due to lack of solar orientation and subsequent battery drain. Contact between the spacecraft and mission control could not be established for over 24 hours. The root cause of this incident has not been determined, but software and operational errors contributed to the severity of the anomaly. The original mission plan called for the four burns to be followed by an orbit insertion burn on January 10, 1999, but the abort of the first burn and loss of communication made this impossible. A new plan was put into effect in which ''NEAR'' flew by Eros on December 23, 1998, at 18:41:23 UT at a speed of 965 m/s and a distance of 3827 km from the center of mass of Eros. Images of Eros were taken by the camera, data were collected by the near IR spectrograph, and radio tracking was performed during the flyby. A rendezvous maneuver was performed on January 3, 1999, involving a thruster burn to match ''NEAR'' orbital speed to that of Eros. A
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 ...
thruster burn took place on January 20 to fine-tune the trajectory. On August 12 a two-minute thruster burn slowed the spacecraft velocity relative to Eros to 300 km/h.


Orbital insertion

Orbital insertion Orbit insertion is the spaceflight operation of adjusting a spacecraft’s momentum, in particular to allow for entry into a stable orbit around a planet, moon, or other celestial body. This maneuver involves either deceleration from a speed in ex ...
around Eros occurred on February 14, 2000, at 15:33 UT (10:33 EST) after ''NEAR'' completed a 13-month heliocentric orbit which closely matched the orbit of Eros. A rendezvous maneuver was completed on February 3 at 17:00 UT, slowing the spacecraft from 19.3 to 8.1 m/s relative to Eros. Another maneuver took place on February 8 increasing the relative velocity slightly to 9.9 m/s. Searches for satellites of Eros took place on January 28 and February 4 and 9; none were found. The scans were for scientific purposes and to mitigate any chances of collision with a satellite. ''NEAR'' went into a 321×366 km elliptical orbit around Eros on February 14. The orbit was slowly decreased to a 35 km circular polar orbit by July 14. ''NEAR'' remained in this orbit for 10 days and then was backed out in stages to a 100 km circular orbit by September 5, 2000. Maneuvers in mid-October led to a flyby of Eros within 5.3 km of the surface at 07:00 UT on October 26. File:NEARtrajectory.jpg, Trajectory graphic depicting the voyage of the ''NEAR'' spacecraft File:Animation of NEAR Shoemaker trajectory.gif, Animation of ''NEAR Shoemaker'' trajectory from February 19, 1996, to February 12, 2001 File:Animation of NEAR Shoemaker trajectory around 433 Eros.gif, Animation of ''NEAR Shoemaker'' trajectory around Eros from April 1, 2000, to February 12, 2001


Orbits and landing

Following the flyby, ''NEAR'' moved to a 200 km circular orbit and shifted the orbit from prograde near-polar to a retrograde near-equatorial orbit. By December 13, 2000, the orbit was shifted back to a circular 35 km low orbit. Starting on January 24, 2001, the spacecraft began a series of close passes (5 to 6 km) to the surface and on January 28 passed 2 to 3 km from the asteroid. The spacecraft then made a slow controlled descent to the surface of Eros ending with a touchdown just to the south of the saddle-shaped feature Himeros on February 12, 2001, at approximately 20:01 UT (3:01 p.m. EST). To the surprise of the controllers, the spacecraft was undamaged and operational after the landing at an estimated speed of 1.5 to 1.8 meters per second (thus becoming the first spacecraft to soft-land on an asteroid). After receiving an extension of antenna time on the Deep Space Network, the spacecraft's gamma-ray spectrometer was reprogrammed to collect data on Eros's composition from a vantage point about from the surface where it was ten times more sensitive than when it was used in orbit. This increase in sensitivity was in part due to the increased ratio of the signal from Eros compared to noise generated by the probe itself. The impact of cosmic rays on the sensor was also reduced by about 50%. At 7 p.m. EST on February 28, 2001, the last data signals were received from ''NEAR'' Shoemaker before it was shut down. A final attempt to communicate with the spacecraft on December 10, 2002, was unsuccessful. This was likely due to the extreme −279 °F (−173 °C, 100 K) conditions the probe experienced while on Eros.


Spacecraft and subsystems


Spacecraft

The spacecraft has the shape of an octagonal prism, approximately 1.7 m on a side, with four fixed
gallium arsenide Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a zinc blende crystal structure. Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated c ...
solar panel A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
s in a windmill arrangement, a fixed 1.5 m X-band high-gain radio antenna with a
magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...
mounted on the antenna feed, and an X-ray solar monitor on one end (the forward deck), with the other instruments fixed on the opposite end (the aft deck). Most electronics were mounted on the inside of the decks. The propulsion module was contained in the interior. The decision to mount instruments on the body of the spacecraft rather than using booms resulted in the gamma-ray spectrometer needing to be shielded from noise generated by the craft. A
bismuth germanate Bismuth germanium oxide or bismuth germanate is an inorganic chemical compound of bismuth, germanium and oxygen. Most commonly the term refers to the compound with chemical formula (BGO), with the cubic evlitine crystal structure, used as a sci ...
shield was used although this proved only moderately effective. The craft was three-axis stabilized and used a single bipropellant (
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 ...
/ nitrogen tetroxide) 450 newton (N) main thruster, and four 21 N and seven 3.5 N hydrazine thrusters for propulsion, for a total
delta-V Delta-''v'' (more known as " change in velocity"), symbolized as ∆''v'' and pronounced ''delta-vee'', as used in spacecraft flight dynamics, is a measure of the impulse per unit of spacecraft mass that is needed to perform a maneuver such a ...
potential of 1450 m/s. Attitude control was achieved using the hydrazine thrusters and four reaction wheels. The propulsion system carried 209 kg of hydrazine and 109 kg of NTO oxidizer in two oxidizer and three fuel tanks. Power was provided by four 1.8 by 1.2 meter
gallium arsenide Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a zinc blende crystal structure. Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated c ...
solar panels which could produce 400 
watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James ...
s at 2.2  AU (329,000,000 km), ''NEAR'' maximum distance from the Sun, and 1800 watts at one AU (150,000,000 km). Power was stored in a nine-ampere-hour, 22-cell rechargeable super nickel-cadmium battery. Spacecraft guidance was achieved through the use of a sensor suite of five digital solar attitude detectors, an inertial measurement unit (IMU), and a star tracker camera pointed opposite the instrument pointing direction. The IMU contained hemispherical resonator
gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rot ...
s and accelerometers. Four
reaction wheel A reaction wheel (RW) is used primarily by spacecraft for three-axis attitude control, and does not require rockets or external applicators of torque. They provide a high pointing accuracy, and are particularly useful when the spacecraft must be ...
s (arranged so that any three can provide complete three-axis control) were used for normal attitude control. The thrusters were used to dump
angular momentum In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity—the total angular momentum of a closed syst ...
from the reaction wheels, as well as for rapid slew and propulsive maneuvers. Attitude control was to 0.1 degree, line-of-sight pointing stability is within 50 microradians over one second, and post-processing attitude knowledge is to 50 microradians. The command and data handling subsystem was composed of two redundant command and telemetry processors and solid state recorders, a power switching unit, and an interface to two redundant 1553 standard data buses for communications with other subsystems. ''NEAR'' was the first APL spacecraft to use significant numbers of plastic encapsulated microcircuits (PEMs), and the first to use solid-state data recorders for mass storage—previous APL spacecraft used magnetic tape recorders or magnetic cores. The solid state recorders are constructed from 16 Mbit IBM Luna-C
DRAM Dynamic random-access memory (dynamic RAM or DRAM) is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal-oxid ...
s. One recorder has 1.1
gigabit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented ...
s of storage, the other has 0.67 gigabits. The ''NEAR'' mission was the first launch of NASA's Discovery Program, a series of small-scale spacecraft designed to proceed from development to flight in under three years for a cost of less than $150 million. The construction, launch, and 30-day cost for this mission is estimated at $122 million. The final total mission cost was $224 million which consisted of $124.9 million for spacecraft development, $44.6 million for launch support and tracking, and $54.6 million for mission operations and data analysis.


Scientific payload and experiments

The science payload includes: * The Multi-Spectral Imager (MSI) designed and built by the
Johns Hopkins University Johns Hopkins University (Johns Hopkins, Hopkins, or JHU) is a private research university in Baltimore, Maryland. Founded in 1876, Johns Hopkins is the oldest research university in the United States and in the western hemisphere. It consi ...
Applied Physics Laboratory, provided visible images of the asteroid surface. * The NEAR IR Spectrograph (NIS) covers a 0.8 to 2.6 micrometer spectral range in 62 bins. * A three-axis fluxgate magnetometer supplied by NASA's
Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...
, can measure the asteroid's magnetic field from DC to 10 Hz. * The X-ray/Gamma-Ray Spectrometer (XGRS) is really two instruments. The x-ray spectrometer measures x-ray fluorescence on the asteroid excited by solar flare x-rays. The gamma-ray spectrometer is a NaI scintillator with an active BGO shield. * The laser rangefinder (NLR) is a direct-detection single-pulse rangefinder.


References

* Text adapted from public domain NAS
webpage
* * *


External links


''NEAR'' Shoemaker Profile
b
NASA's Solar System Exploration

NSSDC Master Catalog: Spacecraft – ''NEAR'' Shoemaker


* ttp://near.jhuapl.edu Official ''NEAR'' Mission Site (Johns Hopkins Applied Physics Laboratory)
Near Earth Asteroid Rendezvous

''NEAR Mission Archive''
at the NASA Planetary Data System, Small Bodies Node {{Authority control NASA space probes Derelict landers (spacecraft) Derelict space probes Discovery Program Missions to near-Earth asteroids Orbiters (space probe) Planetary defense Spacecraft launched by Delta II rockets Spacecraft launched in 1996