NEAR Shoemaker

Lore & Background

NEAR was the first robotic space probe built by Johns Hopkins University's Applied Physics Laboratory. A previous plan for the mission was for it to go to 4660 Nereus and do a flyby of 2019 van Albada en route, with some choices discussed including 2P/Encke, 433 Eros (which became the mission's primary target), 1036 Ganymed, 4 Vesta, and 4015 Wilson–Harrington. The Small-Body Grand Tour was a plan to visit two asteroids and two comets over a decade with the spacecraft.

After launching on a Delta 7925-8 on February 17, 1996, NEAR flew by the asteroid 253 Mathilde on June 27, 1997, returning over 500 images and gravitational data. A first attempt at orbital insertion around Eros on December 20, 1998, failed due to an anomaly that caused the spacecraft to tumble and expend 29 kg of propellant, reducing the propellant margin to zero. The root cause has not been determined, but software and operational errors contributed. A new plan allowed a flyby of Eros on December 23, 1998, and orbital insertion was achieved on February 14, 2000.

NEAR spent about a year in various orbits around Eros, gradually decreasing to a 35 km circular polar orbit and later shifting to retrograde orbits. The mission ended with a slow controlled descent and touchdown in Eros's saddle region on February 12, 2001, at an estimated speed of 1.5 to 1.8 meters per second, becoming the first spacecraft to soft-land on an asteroid. After landing, the gamma-ray spectrometer was reprogrammed to collect data from about 4 centimeters (approximately 1.6 inches) from the surface, where it was ten times more sensitive. The last data signals were received on February 28, 2001, before the spacecraft was shut down.

Reader's Guide

NEAR Shoemaker's primary scientific objective was to return data on the bulk properties, composition, mineralogy, morphology, internal mass distribution, and magnetic field of Eros. Secondary objectives included studies of regolith properties, interactions with the solar wind, possible current activity, and the asteroid spin state. This data was used to help understand the characteristics of asteroids in general, their relationship to meteoroids and comets, and the conditions in the early Solar System. Some scientists claim the mission's ultimate goal was to link Eros to meteorites recovered on Earth, but NEAR did not prove or disprove this link to the satisfaction of scientists.

The spacecraft was equipped with an X-ray/gamma-ray spectrometer, a near-infrared imaging spectrograph, a multi-spectral camera with a CCD detector, a laser rangefinder, and a magnetometer. A radio science experiment used the tracking system to estimate the gravity field. The total mass of the instruments was 56 kg, requiring 80 watts of power. Between December 1999 and February 2001, NEAR used its gamma-ray spectrometer to detect gamma-ray bursts as part of the InterPlanetary Network. The mission demonstrated the feasibility of close-proximity operations around small bodies and provided foundational data for asteroid science.