Mission Type: Flyby
Launch Vehicle: Delta 7925-8 (no. D232)
Launch Site: ESMC / launch complex 17B
NASA Center: Goddard Space Flight Center, Johns Hopkins University Applied Physics Laboratory
Spacecraft Mass: 805 kg
1) MSI multispectral imager
2) MAG magnetometer
3) NIS near infrared spectrometer
4) XRS-GRS x-ray/gamma-ray spectrometer
5) NLR laser rangefinder
6) radio science and gravimetry experiment
Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, by Asif A. Siddiqi, NASA Monographs in Aerospace History No. 24
NEAR Shoemaker (Near Earth Asteroid Rendezvous) is the first mission flown under NASA's Discovery program, a series of low-cost (less than $150 million) planetary science projects. NEAR's primary goal was to rendezvous with the minor planet 433 Eros (an S-class asteroid) approximately 355 million km from Earth, and to return data on the bulk properties, composition, mineralogy, morphology, internal mass distribution and magnetic field of Eros.
On 27 June 1997, on its way to its primary mission, NEAR performed a 25- minute flyby of the asteroid 253 Mathilde. The closest approach to 1,200 km was at 12:56 UT. During the encounter, the spacecraft photographed 60 percent of the minor planet from a range of 1,200 km. The collected information indicated that the 4.5-billion-year-old asteroid is covered with craters and is less dense than previously believed.
After a midcourse correction on 3 July 1997, NEAR flew by Earth on 23 January 1998 at 07:23 UT for a gravity-assist on its way to Eros. The closest approach was 540 km.
After the Earth flyby encounter, NEAR's previously planned mission profile had to be revised in the light of an aborted engine burn on 20 December 1998 which had prevented a critical trajectory correction to meet up with Eros a month later. Instead, NEAR was put on a backup trajectory that afforded a different flyby than originally planned. As part of this new plan, the spacecraft first flew past Eros on 23 December 1998 at 18:41:23 UT at a range of 3,827 km (distance measured from the center of mass), at which time it observed about 60 percent of the asteroid and discovered that the minor planet was smaller than expected. NEAR also found that the asteroid has two medium-sized craters, a long surface ridge, and a density similar to that of Earth's crust.
After several more trajectory adjustments, NEAR finally moved into orbit around Eros at 15:33 UT on 14 February 2000; roughly a year later than intended. Orbital parameters were 321 x 366 km. NEAR was the first human-made object to orbit an asteroid.
On 14 March 2000, a month after entering asteroid orbit, NASA renamed the NEAR spacecraft NEAR Shoemaker in honor of renowned geologist Eugene Shoemaker.
Through 2000, NEAR Shoemaker's orbit was shifted in stages to permit scientific research programs. There were a few problems before the landing on the asteroid. For example, on 13 May 2000, controllers had to turn off the NEAR Infrared Spectrometer because of an excessive power surge. By 30 April, the spacecraft was in its operational orbit at an altitude of about 50 km from the center of Eros. Later on 13 July, it entered an even lower orbit at 35 km that brought the vehicle as close as 19 km from the surface.
After about ten days, it moved back into a higher orbit. On 26 October, NEAR Shoemaker performed another close flyby of the surface; this time to just 5.3 km. In anticipation of the actual landing, the spacecraft conducted a flyby in January 2001 down to a range of 2.7 km and, in the process, returned more spectacular pictures.
The historic landing phase began at 15:32 UT on 12 February 2001, when NEAR Shoemaker fired its engines to begin controlled descent. After a total of four thruster firings, at 20:01:52 UT on 12 February, the spacecraft gingerly landed on the surface of Eros at a gentle 1.6 m per second. During its entire descent, NEAR Shoemaker snapped a series of 69 spectacular photographs, the last one was taken a mere 120 m from the surface.
Touchdown was in an area just outside a saddle-shaped depression known as Himeros. Eros was 196 million miles from Earth at the time. Although the NEAR Shoemaker spacecraft was not designed to survive landing, its instruments remained operational. Immediately after landing, NASA approved a ten-day extension that was lengthened to fourteen days in order to use the gamma-ray spectrometer.
The last transmission from the spacecraft was at 00:00 UT on 1 March 2001.
NEAR Shoemaker collected ten times more data than had been originally planned, completing the most detailed scientific profile ever of a small celestial body. NEAR's portrait of Eros -- a solid, undifferentiated, primitive relic from the solar system's formation -- has already answered fundamental questions on a common class of asteroid. NEAR's 160,000 images of Eros have shown that asteroids can be incredibly diverse objects: NEAR scientists spotted more than 100,000 craters, about 1 million house-sized (or bigger) boulders, and a layer of debris resulting from a long history of impacts. Scientists were able to determine that Eros is not a "rubble pile" of loosely bound pieces, but rather a consolidated object. Furthermore, the chemical information gleaned from the mission is helping us to understand how asteroids like Eros are linked to meteorite samples recovered on Earth.
Editor's Note: This mission profile was adapted from an originally published profile in Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, by Asif A. Siddiqi, NASA Monographs in Aerospace History No. 24.