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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 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. It was the first spacecraft to orbit an asteroid and land on it successfully. In February 2000, the mission closed in on the asteroid and orbited it. On February 12, 2001, Shoemaker touched down on the asteroid and was terminated just over two weeks later.
The primary scientific objective of NEAR was to return data on the bulk properties, composition, , 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 was used to help understand the characteristics of in general, their relationship to and , 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 gravitational field of the asteroid. The total mass of the instruments was , requiring 80 watts of power.
Some scientists claim that the mission's ultimate goal 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 can be 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 as part of the InterPlanetary Network.
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 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. The camera took images of Eros, data were collected by the near Infrared 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 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.
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 kelvin) conditions the probe experienced while on Eros.
The craft was three-axis stabilized and used a single bipropellant (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 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 solar panels, which could produce 400 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 resonators and accelerometers. Four (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.
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. Ronald K. Burek. "The NEAR Solid-State Data Recorders". Johns Hopkins APL Technical Digest. 1998
The solid-state recorders are constructed from 16 Mbit IBM Luna-C . One recorder has 1.1 of storage, and 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.
target="_blank" rel="nofollow"> NEAR Shoemaker Profile by NASA's Solar System Exploration
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