NEAR Shoemaker

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NEAR Shoemaker
NEAR Shoemaker spacecraft model.png
Model of the NEAR Shoemaker spacecraft
Mission typeOrbiter (433 Eros)
Operator NASA  · APL
COSPAR ID 1996-008A
SATCAT no. 23784 Blue pencil.svg
Mission duration5 years, 21days
Spacecraft properties
Launch mass~800 kilograms (1,800 lb)
Dry mass487 kilograms (1,074 lb)
Power1,800 W
Start of mission
Launch dateFebruary 17, 1996 (1996-02-17) 20:43:27 UTC
(23 years, 1 month and 12 days ago)
Rocket Delta II 7925-8
Launch site Cape Canaveral LC-17B
End of mission
Last contactFebruary 28, 2001 (2001-02-28) ~00:00 UTC
(18 years, 1 month and 1 day ago)
Landing dateFebruary 12, 2001 (2001-02-12) 20:01 UTC
(18 years, 1 month and 17 days ago)
Landing siteSouth of Himeros crater, 433 Eros
Flyby of 253 Mathilde
Closest approachJune 27, 1997 (1997-06-27) 12:56 UTC
(21 years, 9 months and 2 days ago)
Distance1,212 kilometers (753 mi)
433 Eros orbiter
Orbital insertionFebruary 14, 2000 (2000-02-14) 15:33 UTC
(19 years, 1 month and 15 days ago)
Orbits230 orbits [1]
NEAR Shoemaker insignia.png
Official insignia of the NEAR Shoemaker mission  

The Near Earth Asteroid Rendezvous – Shoemaker (NEAR Shoemaker), renamed after its 1996 launch in honor of planetary scientist Eugene Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a period of a year. The mission succeeded in closing in with the asteroid and orbited it several times, finally terminating by touching down on the asteroid on 12 February 2001.

Eugene Merle Shoemaker American geologist and astronomer

Eugene Merle Shoemaker, also known as Gene Shoemaker, was an American geologist and one of the founders of the field of planetary science. He is best known for co-discovering the Comet Shoemaker–Levy 9 with his wife Carolyn S. Shoemaker and David H. Levy. This comet hit Jupiter in July 1994: the impact was televised around the world.

Robotic spacecraft uncrewed spacecraft, usually under telerobotic control

A robotic spacecraft is an uncrewed spacecraft, usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to lower cost and lower risk factors. In addition, some planetary destinations such as Venus or the vicinity of Jupiter are too hostile for human survival, given current technology. Outer planets such as Saturn, Uranus, and Neptune are too distant to reach with current crewed spacecraft technology, so telerobotic probes are the only way to explore them.

Space probe unmanned robotic spacecraft that does not orbit the Earth, but, instead, explores further into outer space

A space probe is a robotic spacecraft that does not orbit Earth, but instead, explores further into outer space. A space probe may approach the Moon; travel through interplanetary space; flyby, orbit, or land on other planetary bodies; or enter interstellar space.


The primary scientific objective of NEAR was to return data on the bulk properties, composition, mineralogy, morphology, internal mass distribution and magnetic field 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 asteroids in general, their relationship to meteoroids and comets, and the conditions in the early Solar System. To accomplish these goals, the spacecraft was equipped with an X-ray/gamma-ray spectrometer, a near-infrared imaging spectrograph, a multi-spectral camera fitted with a CCD imaging detector, a laser rangefinder, and a magnetometer. A radio science experiment was also performed using the NEAR tracking system to estimate the gravity field of the asteroid. The total mass of the instruments was 56 kg, and they required 80 W power.

Mineral Element or chemical compound that is normally crystalline and that has been formed as a result of geological processes

A mineral is, broadly speaking, a solid chemical compound that occurs naturally in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are usually excluded, but some minerals are often biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings often synthesize inorganic minerals that also occur in rocks.

Mass Quantity of matter

Mass is both a property of a physical body and a measure of its resistance to acceleration when a net force is applied. The object's mass also determines the strength of its gravitational attraction to other bodies.

Magnetic field spatial distribution of vectors allowing the calculation of the magnetic force on a test particle

A magnetic field is a vector field that describes the magnetic influence of electric charges in relative motion and magnetized materials. Magnetic fields are observed in a wide range of size scales, from subatomic particles to galaxies. In everyday life, the effects of magnetic fields are often seen in permanent magnets, which pull on magnetic materials and attract or repel other magnets. Magnetic fields surround and are created by magnetized material and by moving electric charges such as those used in electromagnets. Magnetic fields exert forces on nearby moving electrical charges and torques on nearby magnets. In addition, a magnetic field that varies with location exerts a force on magnetic materials. Both the strength and direction of a magnetic field varies with location. As such, it is an example of a vector field.


A previous plan for the mission was for it to go to 4660 Nereus and do a flyby of 2019 Van Albada en route. [2] In January 2000 it would rendezvous with Nereus but instead of staying it would visit multiple asteroids and comets. [2] Some of the choices that were discussed were 2P/Encke, 433 Eros (that became the mission's primary target), 1036 Ganymed, 4 Vesta, and 4015 Wilson–Harrington. [2] The Small-Body Grand Tour was a plan for visiting two asteroids and two comets over a span of a decade with the spacecraft. [2]

4660 Nereus asteroid

4660 Nereus is a small asteroid. It was discovered by Eleanor F. Helin on February 28, 1982, approximately 1 month after a near pass by the Earth.

433 Eros near-Earth asteroid

Eros, provisional designation 1898 DQ, is a stony and elongated asteroid of the Amor group and the first discovered and second-largest near-Earth object with a mean-diameter of approximately 16.8 kilometers. Visited by the NEAR Shoemaker space probe in 1998, it became the first asteroid ever studied from orbit.

1036 Ganymed asteroid

1036 Ganymed, provisional designation 1924 TD, is a stony asteroid on a highly eccentric orbit, classified as a near-Earth object of the Amor group. It was discovered by German astronomer Walter Baade at the Bergedorf Observatory in Hamburg on 23 October 1924, and named after Ganymede from Greek mythology. With a diameter of approximately 35 kilometers, Ganymed is the largest of all near-Earth objects. The S-type asteroid has a rotation period of 10.3 hours. In October 2024, it will approach Earth at 56,000,000 km; 35,000,000 mi (0.374097 AU).

Mission profile

Near-Earth asteroid Eros as seen from the NEAR spacecraft. Eros - PIA02923 (color).jpg
Near-Earth asteroid Eros as seen from the NEAR spacecraft.


The primary goal of the mission was to study the near-Earth asteroid 433 Eros from orbit for approximately one year. Eros is an S-type asteroid 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 30 April 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.

S-type asteroid asteroid spectral type

S-type asteroids are asteroids with a spectral type that is indicative of a siliceous mineralogical composition, hence the name. Approximately 17% of asteroids are of this type, making it the second most common after the carbonaceous C-type.

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-Shoemaker did not prove or disprove this link to the satisfaction of scientists.

Between December 1999 and February 2001 NEAR Shoemaker used its gamma-ray spectrometer to detect gamma-ray bursts as part of the InterPlanetary Network. [3]

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 GRB in the sky is improved by increasing the spacing of the detectors, and also by more accurate timing of the reception. Typical spacecraft baselines of about one AU and time resolutions of tens of milliseconds can determine a burst location within several arcminutes, allowing follow-up observations with other telescopes.

The journey to Mathilde

Launch of the NEAR spacecraft, February 1996. NEARlaunch.jpg
Launch of the NEAR spacecraft, February 1996.

After launch on a Delta 7925-8 (a Delta II launch vehicle with nine strap-on solid-rocket boosters and a Star 48 (PAM-D) third stage) 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. [4]

Delta II American space launch system

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 variants. The rocket flew its final mission ICESat-2 on September 15, 2018, earning the launch vehicle a streak of 100 successful missions in a row, with the last failure being GPS IIR-1 in 1997.

253 Mathilde main-belt asteroid

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 has a relatively elliptical orbit that requires more than four years to circle the Sun. This tumbling asteroid has an unusually slow rate of rotation, requiring 17.4 days to complete a 360° revolution about its axis. It is a primitive C-type asteroid, which means the surface has a high proportion of carbon; giving it a dark surface that reflects only 4% of the light that falls on it.

One of the images from the flyby of 253 Mathilde (253) mathilde crop.jpg
One of the images from the flyby of 253 Mathilde

On 27 June 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, [5] as well as gravitational data allowing calculations of Mathilde's dimensions and mass. [6]

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 from 0.5 to 10.2 degrees, and the aphelion distance from 2.17 to 1.77 AU, nearly matching those of Eros. Instrumentation was active at this time. [4]

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. [7]

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's orbital speed to that of Eros. A 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. [4]

Orbital insertion

Trajectory graphic depicting the voyage of the NEAR spacecraft. NEARtrajectory.jpg
Trajectory graphic depicting the voyage of the NEAR spacecraft.
Animation of NEAR Shoemaker trajectory from May 31, 1996 to February 12, 2001.
NEAR Shoemaker; 433 Eros; Earth;   253 Mathilde ; Sun; Animation of NEAR Shoemaker trajectory.gif
Animation of NEAR Shoemaker trajectory from May 31, 1996 to February 12, 2001.
NEAR Shoemaker; 433 Eros; Earth;    253 Mathilde ; Sun;
Animation of NEAR Shoemaker's trajectory around 433 Eros from April 1, 2000 to February 12, 2001
NEAR Shoemaker *   433 Eros Animation of NEAR Shoemaker trajectory around 433 Eros.gif
Animation of NEAR Shoemaker's trajectory around 433 Eros from April 1, 2000 to February 12, 2001
   NEAR Shoemaker ·   433 Eros

Orbital insertion around Eros occurred on 14 February 2000 at 15:33 UT (10:33 AM 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 4 and 9 February; 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 26 October. [4]

Orbits and landing

Eros asteroid from approximately 250 meters altitude (area in image is roughly 12 meters across ). This image was taken during NEAR's descent to the surface of the asteroid. Erosregolith.jpg
Eros asteroid from approximately 250 meters altitude (area in image is roughly 12 meters across ). This image was taken during NEAR's descent to the surface of the asteroid.

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' composition from a vantage point about 4 inches (100 mm) from the surface where it was ten times more sensitive than when it was used in orbit. [8] 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. [3] The impact of cosmic rays on the sensor was also reduced by about 50%. [3]

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. [9]

Spacecraft and subsystems

NEAR spacecraft inside its Delta II rocket. NEARCraft.jpg
NEAR spacecraft inside its Delta II rocket.

The spacecraft has the shape of an octagonal prism, approximately 1.7 m on a side, with four fixed gallium arsenide solar panels in a windmill arrangement, a fixed 1.5 m X-band high-gain radio antenna with a magnetometer 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. [3] A bismuth germanate shield was used although this proved only moderately effective. [3]

The craft was three-axis stabilized and used a single bipropellant (hydrazine / nitrogen tetroxide) 450 newton (N) main thruster, [10] and four 21 N and seven 3.5 N hydrazine thrusters for propulsion, for a total delta-V 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. [4]

Power was provided by four 1.8 by 1.2 meter gallium arsenide solar panels which could produce 400  watts at 2.2  AU (329,000,000 km), NEAR's maximum distance from the Sun, and 1800 W at one AU (150,000,000 km). Power was stored in a nine ampere-hour, 22-cell rechargeable super nickel-cadmium battery. [4]

Diagram showing location of NEAR science instruments. NEAR Spacecraft Configuration.jpg
Diagram showing location of NEAR science instruments.

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 gyroscopes and accelerometers. Four reaction wheels (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 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. [4]

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 is the first APL spacecraft to use significant numbers of plastic encapsulated microcircuits (PEMs). NEAR is the first APL spacecraft to use solid-state data recorders for mass storage—previous APL spacecraft used magnetic tape recorders or magnetic cores. [11]

The solid state recorders are constructed from 16 Mbit IBM Luna-C DRAMs. One recorder has 1.1 gigabits of storage, the other has 0.67 gigabits. [4]

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. [1]

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