NEAR

Aborted rendezvous
Cause of problem
Near-Earth asteroids
Experiments
End of mission
 Eros (15K)

Near Earth Asteroid Rendezvous (NEAR) was the first of NASA's Discovery series of spacecraft. Built inexpensively from of the shelf technology it was launched by a Delta 2 rocket in February 17, 1996 for a three year journey to the asteroid belt. The probe passed within 1,200 kilometers of the asteroid 253 Mathilde in June 1997. It measured mass and volume of the body and transmitted back high resolution images from the flyby. In December 1998, NEAR approached it's primary target, near-Earth asteroid 433 Eros (near-Earth asteroids are asteroids that come within 1,3 AU's of the sun, Earth is 1 AU from the sun). On December 20 1998, it was supposed to do the first of four engine burns to put it on course for a rendezvous with Eros on January 10, 1999. The 20 minute burn was not accomplished and Mission Control lost contact with the probe. 27 hours later at 8 p.m. on December 21, when the probe activated a preprogrammed 360-degree sweep looking from a signal from Earth, Mission Controll managed to lock on to the signal during a 10 minute window and immediately started to upload commands. Communications were regained but the scheduled redezvous with Eros had to be put of for a year.
Instruments (7K)

The reason for the abort was traced back to sensors that had detected an acceleration increase that exceeded the limits programmed into it's onboard computers. The aborted burn left the probe with 30 kilograms less fuel, this leaves the probe with 1/3 of the fuel it would have had if the rendezvous burn on December 20 had been successful. On January 3 1999, a 24 minute large burn was executed, using 57 percent of it's remaining fuel to increase the probe's speed by 932 meters per second. This was done to almost match the speed of NEAR and Eros and leave them in almost identical orbit.

The near-Earth asteroids orbit the sun inside the main asteroid belt which is located between Mars and Jupiter. Scientists are interested in these objects because some of them cross Earths parth. An asteroid about 10 kilometers wide is thought to have slammed into the Earth 65 million years ago, killing the dinosaurs. Scientists want to find out what these body's contain and how they are built up. Eros is the second largest of the known near-Earth asteroids. Eros is 40 kilometers long and 14 kilometers wide, it does not cross the Earths path.

If all goes well Near will be studying Eros from a distance of 35 kilometers in February 2000. The probe will map the asteroid which is covered with craters and strange grooves. The magnetometer will determine if Eros has a magnetic field and other instruments will measure distribution and thickness of the different materials on it's surface. Scientists want to find out if materials on Eros match the materials found in meteroites. The mission may also shed some light on the beginning of the solar system. Readings from Earth indicate that Eros used to be a part of a much larger object.

Near will orbit Eros for about a year. The mission will not be extended. Mission Controll will instead maneuver the probe closer to Eros to get better pictures of the asteroid and test techniques for flying a probe very close to the surface of an irregular body. They may also decide to let the probe make a soft landing on Eros. NEAR's antenna has no pointing capability so they would have to try to land the spacecraft on it's side so that it can transmit data back to Earth. The scientists would measure the deceleration of the probe as it hits Eros. That would hopefully shed some light on the build-up of the asteroid, if it's a solid rock or a pile of rubble held together by the week gravity. Even if the probe survives the impact it's antenna would soon be carried out of alignment with the Earth, causing the loss of comunications. If they don't land and the spacecraft is left in an altitude from 100-200 kilometers of Eros it may orbit the asteroid for many years before it will most likely wander away and enter an orbit around the sun. It may also crash into the asteroid, but it is very unlikely.