A rchive Date
[ 10-06-2000 ]
Category
[ Science ]
sub-Categoy
[ Astronomy ]

An artist's rendering shows the Mars Polar Lander spacecraft at its landing site, with a robotic arm extended.

Big ears listen for signals from Mars

Astronomers sift through data, seeking Polar Lander’s beep

MSNBC

Feb. 4 — Astronomers in three countries are sifting through hundreds of gigabytes of radio data as part of the world’s most ambitious effort to detect faint signals from the lost

Mars Polar Lander probe

. “We’ll be working flat-out this weekend,” said British astronomer Ian Morison.

AFTER A WEEK of preparation, two listening sessions were conducted Friday at the Westerbork Synthesis Radio Telescope in the Netherlands and the Lovell Telescope at Jodrell Bank in England. The telescopes were optimized to detect the equivalent of an interplanetary cellular-phone call from Polar Lander.

This week’s global dragnet was conducted because the faint signature of Polar Lander’s UHF transmissions appeared in data gathered Dec. 18 and Jan. 4 by a 150-foot (45-meter) radio telescope at Stanford University, known as “the Dish.”

NASA’s

Jet Propulsion Laboratory

had given up hope for the lander, which disappeared Dec. 3 just before it was to touch down near Mars’ south pole. But the faint signals, which came to light in late January only after weeks of computer processing, were greeted like the sound of tapping from beneath the rubble of an earthquake.

“The

NASA

people are very excited about this,” said Willem Baan, director of the Westerbork telescope facility. “They hope that it is real.”

The signal’s polarity and frequency, as well as its timing, tend to support the view that Polar Lander is using what is essentially a backup of a backup communication system. But NASA wants to confirm that the signal was coming from Mars rather than from a terrestrial source or another spacecraft.

A NEW LEVEL

Last week, NASA and Stanford were unsuccessful in their attempt to pick up fresh signals, but this week Westerbork and Jodrell Bank — two of the world’s most sensitive radio receivers for the Polar Lander signal — took the search to a new level.

NASA sent up commands ordering the spacecraft to transmit Friday during specified half-hour communication windows. NASA has cautioned that the signal would be as faint as the glow of a Christmas tree light or a cell-phone call placed from Mars, but the European astronomers said that they could eventually detect even that faint a signal.

“Things are going well,” Baan told MSNBC. “We have a wonderful system, and it’s working perfectly.”

Morison had similarly good news at Jodrell Bank: “The (UHF) band looked very clear of interference. We think we got very good data.”

NASA had hoped that an Italian telescope array would be able to participate in Friday’s exercise, but JPL spokeswoman Mary Hardin said the Italians couldn’t listen in. However, Stanford spokeswoman Dawn Levy said the Dish was able to put previously scheduled projects on hold and listen once again for Polar Lander.

Astronomers cautioned that it would take hours or days to coax the signal out of the background noise, depending on how faint the signal turned out to be. Each round of analysis would delve deeper into the gigabytes of radio data to seek the signal’s characteristic signature at 401.5 MHz. “It takes a long time to prove there’s nothing there,” Morison said.

“We’re trying to look for a needle in a very large haystack,” Baan said.

The plan called for the two observatories to compare notes, then consult with the Jet Propulsion Laboratory, where scientists would review the results.

“We want to make sure we have checked and double-checked these data before we can confirm whether or not there is a signal,” Richard Cook, project manager for Polar Lander, said in a status report released by JPL. “I don’t think we’ll know anything either way until sometime next week.”

As for future observations, Morison said a long-planned, Europe-wide radio telescope session would probably rule out a Polar Lander repeat on the same scale next week. But he noted that late this month Mars would come into the area of the sky covered by the Arecibo Observatory in Puerto Rico, the world’s largest single radio telescope.

WHY IT’S A BIG DEAL

Mission managers say the signal pattern detected earlier by the Dish would indicate that the lander can’t use its main radio transmitter — and that it can’t send UHF signals in a normal mode for relay to Earth via Mars Global Surveyor, which is currently circling the Red Planet. In this scenario, the lander would be limited to transmitting a continuous-wave UHF signal to Earth.

Under such conditions, there’s little hope of receiving any data of scientific value, NASA says. But even the faint signals could help the space agency figure out what went wrong with the $165 million mission.

At least two panels are investigating the mission’s failure — an internal team at JPL and an independent review board organized by NASA headquarters. Members of the independent panel paid a visit to JPL this week, and the initial findings of the investigation are due by mid-March.

If the lander was able to transmit even a weak signal, that would tend to support the hypothesis that the mission failed not because of a catastrophic mechanical failure, but because it came down in an unfortunate locale — perhaps on a steep incline or in rough terrain.

Scientists acknowledge that the landing zone included some areas where the three-legged lander could have conceivably tumbled sideways, restricting its ability to communicate. But they say the risk of that happening was unavoidable.

December’s failure was particularly embarrassing for NASA because it came less than three months after the $125 million flop of its sister mission, Mars Climate Orbiter. In that case, investigators quickly figured out that the orbiter was sent on a fatal plunge through Mars’ atmosphere because of a miscalculation: English-scale measurements were not converted to the metric equivalents used by JPL.

Polar Lander was supposed to analyze Mars’ lower atmosphere and layered soil, while Climate Orbiter was supposed to function as a communications relay as well as a weather satellite — all in an effort to trace Mars’ climate history and figure out what might have happened to the water that scientists believe once flowed on the planet.

As a result of last year’s double failure, NASA is rethinking its plan to send a lander, rover and orbiter toward Mars next year.

]

Cross-Indexed:

Antennas Around World Listen For Mars Signal

Some pages may require Adobe Acrobat Reader^™