LANDING ON EROS: FEBRUARY 12, 2001
NASA Press Release: The first spacecraft to orbit an asteroid has become the first to land on one. At 3:07 p.m. EST today, NEAR mission operators at the Johns Hopkins University Applied Physics Laboratory confirmed that the NEAR Shoemaker spacecraft had touched down on the surface of asteroid 433 Eros, 196 million miles from Earth.
NASA's NEAR Shoemaker spacecraft traveled its last mile, cruising to the surface of asteroid Eros at a gentle 4 mph (1.9 meters per second) -- finally coming to rest after its 2-million-mile journey.
Cheers and congratulations filled the Mission Operations Center at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., 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."
The last image snapped by NEAR Shoemaker was a mere 400 feet (120 meters) from the asteroid's surface and covered a 20-foot (6-meter) area. As NEAR Shoemaker touched down it began sending a beacon, assuring the team that the small spacecraft 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, which will monitor the spacecraft until Feb. 14.
NEAR Shoemaker's final descent started with an engine burn at 10:31 a.m. (EST) that nudged the spacecraft toward Eros from about 16 miles (26 kilometers) away. Then four breaking maneuvers brought the spacecraft to rest on the asteroid's surface in an area just outside a saddle-shaped depression, Himeros. When it touched down, NEAR Shoemaker became the first spacecraft ever to land, or even attempt to land on an asteroid. The success was sweetened by the fact that NEAR Shoemaker was not designed as a lander.
The spacecraft spent the last year in a close-orbit study of asteroid 433 Eros, a near-Earth asteroid that is currently 196 million miles (316 million kilometers) from Earth. During that time it collected 10 times more data than originally planned and completed all its science goals before attempting its descent to the asteroid.
NEWS STORY ON NEAR LANDING FROM SPACE.COM
12 February 2001
By Leonard David Senior Space Writer
LAUREL, MARYLAND - What goes down, may come back up again.
Engineers at APL are looking at the prospects for relaunching the NEAR Shoemaker spacecraft from the surface of asteroid Eros. A command is already built into the probe as it rests upon the space rock's surface.
The liftoff from the asteroid is on tap for this Wednesday, roughly 2:00 p.m. Eastern time, according to David Dunham, NEAR's mission designer at APL.
The launch from Eros would be after nine rotations of the asteroid following today's NEAR Shoemaker landing, Dunham said.
"Since we've got a lock on the signal, it's got to be pretty much in the right position" for the liftoff, said Dunham.
Dunham said the probe may rise upwards well over 1,300 feet (400 meters) above Eros. "It could sit in the dirt and wiggle a little bit before liftoff. These are weaker thrusters on the spacecraft," he said.
Some thought has been given to sequencing a double boost of thrust from the asteroid, hurtling it perhaps as high as a kilometer above the asteroid.
Dunham said that if the camera has not been damaged in the first landing, more images above the asteroid could be taken. However, pictures of the first landing spot on Eros are not likely to come into view, he said.
The spacecraft would then settle down to a new landing spot.
"The whole thing is just more icing on the cake," Dunham said.
The NASA probe had already happily surprised scientists earlier today, when it made space history with a successful landing atop an asteroid more than 196 million miles (316 million kilometers) from Earth.
"I'm happy to report the near spacecraft has touched down on the surface of Eros. We're still getting some signals, so evidently it's still transmitting from the surface itself. This is the first time that any spacecraft has landed on a small body," said Robert Farquhar, NEAR mission director at The Johns Hopkins University Applied Physics (APL) Laboratory in Laurel, Maryland.
NASA Administrator Dan Goldin was among the first to congratulate the team.
"I'm just overwhelmed with the courage and talent it took to get to this point," Goldin said shortly after the landing.
The car-sized NEAR Shoemaker probe has been orbiting Eros since February 14, 2000. Since it began looping the tumbling space rock almost a year ago -- at a range of high and low-altitudes over Eros -- the craft has amassed an asteroid photo gallery made up of 150,000 snapshots.
Touchdown took place shortly after 3:05 p.m. Eastern time. The spacecraft fell onto the dust-laden, cratered, and rock-piled surface of Eros. While the vehicle is a fully equipped science spacecraft, NEAR Shoemaker is without landing legs or airbag.
"We're right on the money," cried out mission controllers as the craft drifted closer and closer to Eros. Images relayed on the way down to the surface showed what appears to be ancient craters buried below the thick, dusty face of Eros.
"We're seeing things really well," said Joseph Veverka, NEAR's imaging team leader from Cornell University in Ithaca, New York. "The pictures are absolutely fantastic. This is a great experience to just sit here and accompany a spacecraft down to the surface."
In one image, a giant boulder could be clearly seen fractured in at least six pieces. As one image after another reached Earth, the spacecraft appeared to be headed toward a smooth landing surface.
For over four-and-a-half hours, as engineers and scientists here at The Johns Hopkins University Applied Physics Laboratory (APL) cheered close-up images the probe sent back during its descent, the probe drifted down toward the rock of ages.
APL built and managed the NEAR mission for NASA, one of the Discovery-class of probes that signals a cheaper, better, faster approach to space exploration.
Price tag for this long-term survey of an asteroid by the econo-class spacecraft: $223 million.
NEAR's mission control at The Johns Hopkins University's Applied Physics Laboratory reported the craft blasted its hydrazine-fueled motors for 20 second starting at 10:31 a.m. Eastern time.
The burst of rocket thrust moved the NASA probe out of its current orbit 22-miles (35-kilometers) above Eros.
The spacecraft immediately began dropping toward Eros. In the next four-and-a-half hours, a series of braking maneuvers led to the spacecraft making contact with Eros.
Small body, big hopes
The craft has relayed a bounty of scientific data about the asteroid, including some 160,000 images that covered all of the 21-mile-long (34-kilometers) asteroid's surface.
Eros is moving in a clockwise direction as it spins on its axis.
NEAR Shoemaker drifted onto the surface of Eros, softly touching down in an area bordering Himeros - a distinctive saddle-shaped depression. On the way down to the landing zone, the highest-resolution images ever taken of Eros' boulder-strewn, cratered terrain were transmitted to Earth.
NEAR Shoemaker was not designed specifically for the touchdown, with the daring dive called for as the mission drew to a successful close on February 14.
"It's a very nice way to end this mission," Louise Prockter, a member of the NEAR imaging team at the Applied Physics Laboratory (APL) told SPACE.com.
"At least we'll know exactly where the spacecraft is and what happened to it. So if there's a future mission out that way, we'll be able to look for it," Prockter said.
Remaining fuel a question
When the spacecraft was launched February 17, 1996, its fuel tanks were filled with 715 pounds (325 kilograms) of fuel. After five years, exactly how much propellant remains is unknown. Precious bursts of fuel were needed to prod NEAR Shoemaker lower and lower to the surface of Eros and mission director Robert Farquhar was not sure the probe would have enough gas to the end.
"The primary thing is to get high-resolution images. The closer we get the more success we have," Farquhar said.
After plopping down on Eros, the spacecraft was healthy enough to transmit science data. Over the next two days, ground stations on Earth will keep an active ear to transmissions from NEAR Shoemaker.
Roundtrip communications time between NEAR and Earth is 35 minutes. At Goldstone, California, a Jet Propulsion Laboratory (JPL) Deep Space Network antenna is to keep a lock on NEAR, with another big dish in Madrid, Spain also at the ready.
Landing on an asteroid is no cakewalk, Farquhar said, particularly when the spacecraft is not built for such a task.
Any number of things could have gone wrong. Engines could misfire; the camera could be pointed the wrong way; or the landing site terrain could have proved impossible for NEAR to navigate successfully.
From a distance
Scientists are delighted that the spacecraft relayed high-quality, close-up images of Eros.
The telescopic camera, built for remote distance viewing, stayed in focus down to an altitude of about 0.3 mile (0.5 kilometer) above the surface.
"The camera should reveal things on the surface, down to as small as a tea cup," said Clark Chapman, member of the NEAR Shoemaker science team from Southwest Research Institute in Boulder, Colorado.
"The close-up images are what we're after," said Lucy McFadden, NEAR science team member from the University of Maryland in College Park. "We're going to microscopic views relative to where we started. It's just tremendous."
Prockter said the spacecraft's last in-focus snapshots may help quell considerable debate between scientists working on the project. The nature of the regolith -- broken up bits of rock and dirt that cover the asteroid -- as well as how deep and how much is there, and the origin of that material, are all questions being argued.
"Looking close up might help us answer some of those questions," Prockter said.
Chapman said a head-scratcher for him is understanding why so many giant boulders populate Eros.
"We've been arguing between ourselves about what it means geologically," Chapman said. "Why is it so different than the Moon? I've just got to believe that the higher resolution images are going to give us a whole bunch of additional clues as to what's really going on. There's lots of speculation."
Survivor for science?
Now that the craft has touched down on the surface of Eros, hopes run high that NEAR's onboard magnetometer can relay measurements directly from the asteroid.
To date, the magnetometer has not seen anything that can be attributed to Eros. Why that's the case is a little puzzling, said Andrew Cheng, NEAR project scientist, because most of the meteorites that are thought to be related to Eros are magnetized.
But whether or not the magnetometer ever picks up data from Eros, researchers are still constrained by finances. Money for mission operations runs out on February 14, 2001.
Prior to the landing, McFadden was wistful.
"It's really sad the whole thing is going to end Monday," she said.
Copyright 2001, Space.com
NASA PRESS RELEASE (FEBRUARY 14, 2001): LANDED MISSION EXTENDED
NASA's NEAR Shoemaker spacecraft, the first spacecraft to touch down and operate on the surface of an asteroid, will not be immediately shut down after all.The mission will be extended for up to 10 days to gather data from a scientific instrument that could provide unprecedented information about the surface and subsurface composition of the asteroid Eros.
Two days after touchdown, NEAR Shoemaker is still in communication with the NEAR team at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, MD. Earlier this week, the team sent commands to NEAR and guided the robotic researcher to a 4-miles-per-hour touchdown on a rock-strewn plain on the asteroid. The spacecraft gently hit the surface at 3:02 p.m. EST, after a journey of 2 billion miles, and a full year in orbit, around the large space rock.
Yesterday, the NEAR mission operations team decided against another engine firing that could have lifted the space probe off the asteroid's surface. There were initial concerns that it might be necessary to adjust the spacecraft's orientation in order to receive telemetry from the ground. However, NEAR Shoemaker landed with a favorable orientation, and there is no problem with receiving information. Mission managers have decided it is not necessary to move the spacecraft from its resting place on the surface of Eros.
SCIENCE UPDATE FROM THE NEAR PROJECT SCIENTIST (FEBRUARY 20, 2001)
On Monday, 12 February 2001, the NEAR spacecraft touched down on asteroid Eros, after transmitting 69 close-up images of the surface during its final descent. Watching that event was the most exciting experience of my life. I was asked immediately afterwards how I felt, and I mumbled something about being tired and happy, but I missed the point. I realized afterward what I should have said: it was like watching Michael Jordan on the basketball court, when the game is on the line and he is in the groove. One miracle after another unfolds, and we are left stunned and speechless. When we learned that the spacecraft had not only landed on the surface, but was still operational, we hardly knew what to think.
Over the past week, we have started to come to our senses again and to appreciate how fortunate we are. The final weeks of low altitude operations revealed bizarre and surprising aspects of surface structures on Eros, including one type of feature we noticed for the first time in the very last image taken by the spacecraft (the incomplete image taken from a height of 120 meters, 2001 Feb 12F ). As we discussed previously, there are markedly fewer small, fresh craters on Eros than we would expect from our experience at the Moon, and an amazing profusion of boulders, likewise more than we expected. We do not know just what is happening on the surface of Eros to cover and/or obliterate craters while making and/or uncovering boulders. We have seen many examples of mass motion on Eros - loose material sliding downhill - and that is no doubt part of the story, but maybe not all of it. We also believe that at least some of the bouldery debris found on Eros is comprised of ejecta from impacts on Eros; some of these ejecta do not escape but fall back to the surface.
Some of the strange features we are beginning to think about can be seen in the low altitude images obtained during the past few weeks. The new type of feature seen in the last image returned ( 2001 Feb 12F ) can be found, for example, at the bottom of the image (just above the vertical streaks indicating loss of signal), to the left of center. It appears to be a collapse feature, formed when support is removed from below the surface, and it is about the size of one's hand. Other strange sights are clusters of boulders (e.g., the upper right of 2001 Feb 12E ) - are these cases of disintegration in place? - and extremely flat, sharply delineated areas in the bottoms of some craters (e.g., the two left panels of 2001 Jan 31 ). The mere existence of sharp boundaries, called "contacts", is surprising in itself, especially if the entire surface of the asteroid is thought to have been blanketed by debris from impacts. These boundaries can be incredibly sharp on Eros, as evidenced by the last frame, 2001 Feb 12F (compare the upper right and lower left of the image).
The images tell us a tale whose outcome we don't yet know, but there is more: the story of Eros's composition is likewise still emerging. Our orbital data from the x-ray spectrometer showed that the abundances of key elements on Eros are very similar to those in the undifferentiated meteorites called ordinary chondrites, but there was a discrepancy. The abundance of the volatile element sulfur is less than we would expect from an ordinary chondrite. However, the x-ray spectra tell us only about the uppermost hundred microns of the surface, and we do not know if the sulfur depletion occurs only in a thin surface layer or throughout the bulk of the asteroid.
Fortunately, the spacecraft is now in a position to help answer the question (on the surface, that is). The gamma ray spectrometer measures the composition to a depth of about ten centimeters, and it is much more sensitive on the surface than it was in orbit. We are now in the process of trying to obtain our best yet gamma ray spectrum of Eros. We will try to determine the abundances of the volatile element potassium and the major element iron from this spectrum, to look harder at the match between the compositions of Eros and the ordinary chondrites, and to look for evidence for bulk depletion of volatiles. The latter would suggest that Eros has undergone significant heating (a geologist would call it "metamorphism").
It is sad for me to say, but the gamma ray measurement will be the last from NEAR - one more miracle is what we ask of this little spacecraft. Its job is almost done, but ours is just beginning.
Andrew Cheng NEAR Project Scientist