COLUMBIA, Md. -- NEAR, the spacecraft that became the first manmade object to land on an asteroid, may continue sending its signal for months, but after Wednesday nobody will be listening.
The spacecraft, which was designed for orbiting and not landing, astounded even the experts on Monday by touching down so gently on the asteroid Eros that its radio beacon continued to send a strong signal to Earth.
Mission director Robert Farquhar said that if the craft's solar panels continue to generate electricity, the signal could last at least three months.
But on Wednesday, Valentine's Day, the five-year mission officially ends, said Farquhar, and NASA's Deep Space Network will no longer relay signals from Eros, some 196 million miles away.
"We could still speak to it, but we won't be able to," he said. And, in any case, NEAR will eventually be silenced when the craft's landing point on Eros moves out of sunlight and the solar panels can no longer make electricity. The craft's signal then would slowly fade as its batteries died.
NEAR's signal carries almost no information, so there is little likelihood of getting new scientific data from the spacecraft, which had been orbiting Eros for the past year and relaying photos and other information to Earth, officials said. The signal is little more than a hum that lets mission control known that NEAR is still alive -- not of a quality high enough to send data or photos.
The featherlight landing of the 1,100-pound NEAR -- for Near Earth Asteroid Rendezvous -- surprised even the most optimistic of mission officials.
"I just figured something had to go wrong, but it didn't," said Farquhar, the official who had first proposed the landing. He had estimated that the odds of NEAR being able to send a signal after landing was less than 1 percent.
Some NASA officials even warned that it would be "a controlled crash" and not a landing on Eros, a potato-shaped object about 21 miles long.
Instead, NEAR precisely fired its rockets to drop from a 15-mile orbit over the asteroid and then drifted down, slowed by four more rocket firings. It hit the asteroid, with rockets still firing, and bounced back up, before alighting firmly on the surface.
Some engineers said the bounce may have carried NEAR more than 300 feet up in the low gravity of Eros, where an object dropped from six feet could take seconds to fall.
"This was a landing, not an impact," said Farquhar. He said the landing speed, relative to the surface of Eros, was about 3.5 miles an hour, a fast walk.
The mission was controlled by the Johns Hopkins University Applied Physics Laboratory and funded by the National Aeronautics and Space Administration.
"They made a spacecraft that was only designed to orbit and then they put it down on an asteroid and it's still working," said Ed Weiler, NASA's chief scientist. "That is amazing."
NASA administrator Dan Goldin said Monday he first doubted NEAR's chances for a successful landing.
"I was dubious that we would ever get a signal back," he said. "They pushed the boundaries. Wonderful, bold, courageous, brilliant -- those are the words to come to mind."
Goldin said he called the Mission Control Center in Houston, which is commanding the flight of space shuttle Atlantis to the International Space Station.
"I told them to tell the astronauts that we have just landed on an asteroid," said Goldin.
After the news was relayed to the Atlantis crew, spacewalking astronaut Thomas Jones radioed back: "I hope we'll have some astronauts following to the asteroids in just a few years."
The United States does plan to send more robot missions to asteroids and to eventually land a craft on a comet and bring back samples. But no manned missions to an asteroid are planned.
Putting a spacecraft on the asteroid was a major first for the United States. Never before had an American craft made the initial landing on an outer space body, NASA officials said. The first robot landings on the moon, Mars and Venus were all Soviet craft.
Weiler said the NEAR landing taught valuable lessons that will help in future exploration of asteroids and comets. Such missions, he said, could be important if an asteroid such as Eros ever threatens the Earth. A similar space mountain is thought to have killed the dinosaurs 65 million years ago.
"This landing gives us a lot of practice," said Weiler. "We'll eventually want to land on comets."
NEAR achieved orbit of Eros, an asteroid named for the Greek god of love, on Valentine's Day last year. The landing completes a five-year, 2-billion-mile mission for NEAR and boosts the cheaper-faster-better philosophy pushed by NASA for exploring outer space.
Developed by scientists at Johns Hopkins, NEAR was designed, built and launched in just 26 months, far shorter than most NASA missions.
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