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NEAR Shoemaker, officially named Near Earth Asteroid Rendezvous – Shoemaker, was a probe designed to study the near-Earth asteroid Eros from close orbit. The mission was successful in that it closed with the asteroid and orbited it several times before touching down on its surface in February 2001.
The spacecraft bus was an octagonal prism, approximately 1.7 m tall. Power to the nine ampere-hour, 22-cell rechargeable super nickel-cadmium battery was supplied by four fixed gallium arsenide solar panels. The spacecraft was fitted with a fixed 1.5 m X-band high-gain radio antenna with a magnetometer mounted on the antenna feed. Instrumentation also included an X-ray/gamma ray spectrometer, a near infrared imaging spectrometer, 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 and determine its mass and density.
The NEAR Shoemaker spacecraft was three-axis stabilized. Propulsion was provided by a bipropellant (hydrazine/nitrogen tetroxide) 450 N engine, and four 21 N and seven 3.5 N hydrazine thrusters, giving the craft a potential for a total delta-V of 1450 m/s. Attitude control was achieved with the hydrazine thrusters and four reaction wheels. Guidance came through the use of five digital solar attitude detectors, an inertial measurement unit(IMU), and a star tracker camera pointed opposite the instruments. The IMU contained hemispherical resonator gyroscopes and accelerometers. Four reaction wheels were arranged so that any three could provide complete three-axis control and 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.
The mission had the primary objective of returning data on the composition, mineralogy, morphology, internal mass distribution, and magnetic field of the asteroid 433 Eros. Secondary objectives were the study of the asteroid’s regolith, interactions with the solar wind, possible current activity as indicated by dust or gas, and the asteroid’s spin state. The goal of these objectives was to understand the general characteristics of asteroids, their relationship to meteorites and comets, and the conditions in the early solar system. These objectives were to be accomplished over the course of one year.
The spacecraft entered an initial circular orbit with a radius of 200 km. This orbit was slowly brought down to a 50×50 km orbit by April 2000 and then a 35×35 km radius in July 2000. As the mission came to an end a decision was made to perform a touch down on the surface of Eros, which took place on February 12, 2001. The Near Shoemaker spacecraft marked several first during its mission. It was the first spacecraft to fly close to asteroid Mathilde, coming within 1200 km and returning more than 500 images and gravitational data. It performed the first successful major deep space maneuver, which was a two-part burn of the 450 N thruster.