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The Near Earth Asteroid Rendezvous - Shoemaker (NEAR Shoemaker), renamed after its launch in honor of planetary scientist Eugene M. Shoemaker , is an Unmanned Spacecraft designed to study the Near-Earth Asteroid Eros from close orbit over a period of a year. The primary scientific objectives of NEAR were to return data on the bulk properties, composition, Mineral ogy, 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. These data will be used to help understand the characteristics of Asteroid s in general, their relationship to Meteorite s and Comet s, 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 81 W power. MISSION PROFILE
Summary 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 . 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. However, it is undeniable that NEAR data advanced the field of asteroidal studies tremendously. The journey to Eros .]] After launch on a Delta 7925-8 (a 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 on 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. Orbital insertion . Orbits and landing Following the flyby NEAR moved to a 200 km circular orbit and shifted the orbit from , the spacecraft's gamma-ray spectrometer was reprogrammed to collect data on Eros' composition from a vantage point about four inches from the surface where it was ten times more sensitive than when it was used in orbit. {Link without Title} 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. {Link without Title} SPACECRAFT AND SUBSYSTEMS 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 are mounted on the inside of the decks. The propulsion module is contained in the interior. The craft is three-axis stabilized and uses 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 is achieved using the hydrazine thrusters and four reaction wheels. The propulsion system carries 209 kg of hydrazine and 109 kg of NTO oxidizer in two oxidizer and three fuel tanks. Power is provided by four 1.8 by 1.2 meter gallium arsenide solar panels which can produce 400 Watt s 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 is stored in a nine ampere-hour, 22-cell rechargeable super Nickel-cadmium battery. Spacecraft guidance is 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 contains hemispherical resonator Gyroscope s and accelerometers. Four Reaction Wheel s (arranged so that any three can provide complete three-axis control) are used for normal attitude control. The thrusters are used to dump Angular Momentum from the reaction wheels, as well as for rapid slew and propulsive maneuvers. Attitude control is 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 subsytem is 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. The solid state recorders are constructed from 16 Mbit IBM Luna-C DRAM s. One recorder has 1.1 Gigabit 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. REFERENCE
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