At just after 3 p.m. on Feb. 12, the NEAR Shoemaker spacecraft cruised to the surface of asteroid Eros at a gentle 4 mph, finally coming to rest after its 2-billion-mile journey. Cheers and congratulations filled the Mission Operations Center at the Applied Physics Laboratory--which built the spacecraft and manages the mission for NASA--when NEAR mission director Robert Farquhar announced, "I'm happy to say the spacecraft is safely on the surface of Eros."
Not only safe but also operational. NASA announced Feb. 14, NEAR's scheduled end date, that it would extend the mission for up to 10 days to gather data from the spacecraft's gamma-ray spectrometer, a scientific instrument that could provide unprecedented information about the asteroid's surface and subsurface composition. Late last week, mission operators at APL commanded the instrument to begin collecting and recording data.
The landing marked not only the end of a five-year journey--the last year spent in a close-orbit study of Eros--but the first time such a feat had ever been tried or accomplished. The success was sweetened by the fact that NEAR Shoemaker was not designed as a lander.
NEAR Shoemaker's final descent started with an engine burn at 10:31 a.m. that nudged the spacecraft toward Eros from about 16 miles away. Then a set of four braking maneuvers brought the spacecraft to rest in an area just outside the asteroid's saddle-shaped depression, Himeros.
As the small spacecraft touched down, it began sending a beacon, assuring the team that it had landed gently. The signal was identified by radar science data and about an hour later was locked onto by NASA's Deep Space Network antennas.
The soft landing turned out to be a mission planner's dream. "We put the first priority on getting high-resolution images of the surface and the second on putting the spacecraft down safely, and we got both," Farquhar said. "This could not have worked out better."
Mission operators say it may have been one of the softest planetary landings ever. They were also able to assemble a picture of what happened in the moments after the landing: What they originally thought was the spacecraft bouncing may have been a short hop or "jiggle" on the surface; the thrusters were still firing when the craft hit the surface but cut off on contact. NEAR Shoemaker came down only about 650 feet from the projected landing site.
"It essentially confirmed that all the mathematical models we proposed for a controlled descent would work," said Bobby Williams, NEAR navigation team leader at NASA's Jet Propulsion Laboratory. "You never know if they'll work until you test them, and this was like our laboratory. The spacecraft did what we expected it to do, and everyone's real happy about that."
During the final three miles of its descent NEAR Shoemaker snapped 69 detailed pictures, the highest resolution images ever obtained of an asteroid. The camera delivered clear pictures from as close as 394 feet showing features smaller than a golf ball. The images included several things that piqued the curiosity of NEAR scientists, such as fractured boulders, a football field-sized crater filled with dust and a mysterious area where the surface appears to have collapsed.
"These spectacular images have started to answer the many questions we had about Eros," said Joseph Veverka of Cornell University, NEAR imaging team leader. "But they also revealed new mysteries that we will explore for years to come."
NEAR Shoemaker--the first in NASA's Discovery Program of low-cost, scientifically focused planetary missions--was launched on Feb. 17, 1996, and on Feb. 14, 2000, became the first spacecraft to orbit an asteroid. The car-sized spacecraft gathered 10 times more data during its orbit than originally planned, and completed all the mission's science goals before Monday's controlled descent.
"NEAR has raised the bar," said Stamatios M. Krimigis, head of APL's Space Department. "The Laboratory is very proud to manage such a successful mission and work with such a strong team of partners from industry, government and other universities. This team had no weak links--not only did we deliver a spacecraft in 26 months, we were ready to launch a month early, and that efficiency continued through five years of operations. This is what the Discovery Program is designed to do."
To see images from the mission, go to the NEAR Web site at http://near.jhuapl.edu.