NEAR-EARTH ASTEROID RENDEZVOUS - MISSION OVERVIEW

The Near-Earth Asteroid Rendezvous (NEAR) mission, the first launch of NASA's Discovery Program, will be the first mission to orbit an aster oid. NEAR will make the first comprehensive scientific measurements of an asteroid's surface composition, geology, physical properties, and internal structure. NEAR launched successfully on February 17, 1996, a board a Delta II-7925. It will orbit the 20-km-diameter near-Earth ast eroid 433 Eros for about 1 year, at a minimum orbit radius of about 35 km from the center of the asteroid. The NEAR is a solar-powered, thre e-axis stabilized spacecraft with a launch mass including propellant o f 805 kg. NEAR uses X band telemetry to the NASA Deep Space Network, w ith the data rates at Eros up to 8.8 kbits/s using a 34-m High Efficie ncy (HEF) dish, and up to 26.5 kbits/s using a 70-m dish. A solid-stat e recorder is accommodated with a memory capacity of 1.8 Gbytes. Attit ude control is to 1.7 mrad, line-of-sight pointing stability is within 50 mu rad over 1 s, and post processing attitude knowledge is within 50 mu rad. NEAR accommodates 56 kg of instruments and provides them wi th 84 W. The instruments are a multispectral imager (MSI), a near-infr ared spectrograph (NIS), an X ray/gamma ray spectrometer (XRS/GRS), a magnetometer (MAG), and a laser rangefinder (NLR), while a radio scien ce (RS) investigation uses the coherent X band transponder. NEAR will make a flyby of the C-type asteroid 253 Mathilde in June 1997 and will rendezvous with 433 Eros in February 1999. It will execute an initial slow flyby of Eros, with a flyby speed of 5 m/s and a closest approac h distance of 500 km. Subsequently, its orbit will be lowered to 35 km . The NEAR Mission Operations Center and the Science Data Center are a t the Johns Hopkins Applied Physics Laboratory. The Science Data Cente r will maintain the entire NEAR data set on-line, and data from all in struments can be accessed by every member of the NEAR Science Team. Da ta, including images, are released over the Internet as soon as they a re validated.