NEAR Shoemaker phones home for the last time
Posted: February 28, 2001
At 7 p.m. EST Wednesday, NASA's Deep Space Network antennas pulled down their last data signals from the spacecraft resting on the surface of Eros, concluding an extended mission of NEAR after it survived an extraordinary descent and landing on the surface of the space rock 196 million miles away.
The Deep Space Network, managed by the Jet Propulsion Laboratory for NASA, consists of large antennas at three complexes located in Goldstone, Calif., near Canberra, Australia, and near Madrid, Spain. Each complex houses several radio antennas of different sizes, including giant 70-meter (230-foot) telescopes, used to communicate with interplanetary satellites.
"NEAR has raised the bar," says Dr. Stamatios Krimigis, Space Department head at The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., which built the spacecraft and managed the NEAR mission.
"The Laboratory is very proud to have managed such a successful mission and worked with such a strong team of partners from industry, government and other universities. The team had no weak links and the result was an historic mission that surpassed everyone's expectations."
"This mission has been successful far beyond what was in the original mission plan," says NEAR Mission Director Dr. Robert Farquhar of APL. "We got the first images of a C-class asteroid when we added a flyby of asteroid Mathilde in 1997; we added two low altitude series of passes over the ends of Eros this past October and January that gave us spectacular images from 2.7 kilometers above the surface; and we achieved the first landing of a spacecraft on an asteroid on Feb. 12. All this at no extra cost. When you talk about ' faster, cheaper, better,' this is what 'better' means."
On Feb. 12 at 3:01:52 p.m. EST, NEAR Shoemaker made a gentle, picture-perfect 3-point landing on the tips of two solar panels and the bottom edge of the spacecraft body. But the mission wasn't finished yet. Much to the amazement of the mission team and millions of observers around the world who were following the descent, the touchdown was so elegant that the craft was still operating and sending a signal back to Earth even after landing.
Jumping at the chance to get "bonus science" from the spacecraft, which had already collected 10 times more data than originally planned, the mission team asked for and got a 10-day extension and then four more days of DSN antenna time, enabling NEAR Shoemaker to send back data through Wednesday. The extension was granted to allow the gamma-ray spectrometer to collect data from an ideal vantage point about four inches from the surface. The spectrometer team quickly redesigned software and uploaded it to the spacecraft so they could begin collecting elemental composition readings.
The results were spectacular. "This is the first gamma-ray experiment that has ever been done on the surface of a body other than Earth," says Dr. Jacob Trombka, of NASA's Goddard Space Flight Center, in Greenbelt, Md., who heads the gamma-ray spectrometer team. "In fact, we can say it's the first feasibility study of how to design an instrument to be used on a rover that could select samples from the surface, look for the presence of water, or map the surface for the purpose of future mining."
The gamma-ray spectrometer team was able to retrieve data for a period of seven days after the spacecraft landed. "Right now we know we have good data with strong signatures," Trombka says. "But it will take months to scrutinize what we've collected. What we're looking for is information that will help us more precisely classify Eros and determine the relationship between the asteroid and meteorites that have fallen to Earth."
NEAR Shoemaker now rests silently just to the south of the saddle-shaped feature Himeros as the asteroid twists more and more away from the sun with each rotation, moving the southern hemisphere into its winter season and temperatures as low as minus 238 degrees Fahrenheit (minus 150 centigrade).
Project Scientist Dr. Andrew Cheng of APL, says the glamorous part of the mission is over but now scientists can get down to studying the data, including the more than 160,000 detailed images taken by the spacecraft. "We solved mysteries, we unveiled more mysteries. Now we're sharing the amazing amount of data that we collected with scientists all over the world, to sort through and debate and hopefully to help us discover facts about Eros and our solar system that no one knows today."
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Images from the descent:
Last view before landing
Extreme close up!
View from 2.5km
Closest view yet
Views of Eros: 1 2 3 4
View of the horizon
A preview of landing:
The landing site on Eros
Illustration showing NEAR's drop from orbit
Graph shows descent in altitude vs. time
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