IHT - Worry Rises Over Silence Of NASA's Mars Probe

Craft Fails to Contact Earth Despite Flurry Of Efforts by Scientists

Paris, Monday, December 6, 1999

By John Noble Wilford - New York Times Service

PASADENA, California - Concern over the fate of the Mars Polar Lander deepened Sunday after flight controllers, having repeatedly failed to receive any radio signals from it on the planet's surface, were forced to fall back on alternative tactics in an effort to re-establish communications.

But when the lander failed to communicate with Earth for the fifth time in 48 hours, speculation increased that the mission might be doomed.

The lander, following instructions programmed in its computer, was supposed to relay a radio transmission Sunday during a brief communications window through another spacecraft, the Mars Global Surveyor, which has been orbiting Mars since 1997.

Once again, however, there was only silence, as there has been since Friday, when the $165 million craft was to have landed on Mars.

It was the first time that scientists had tried to get the craft to use its UHF antenna, which is not powerful enough to communicate directly with Earth but is capable of sending a stream of data to the orbiting surveyor for relay to Earth. The hope had been that if the lander's main antenna, which scientists had been using in their previous attempts to communicate with the lander, had failed for some reason, then the UHF might succeed as a backup.

The window of opportunity stretched from 10:50 A.M. to 10:56 A.M. California time, but because it takes 15 minutes for a signal to travel the 145 million miles (232 million kilometers) from Mars to Earth, it was about 11:15 A.M. before scientists knew that their latest attempt had failed. Sunday's only other communications opportunity, using the original radio, was scheduled for 9:40 P.M. to 11:55 P.M.

Richard Cook, project manager at the Jet Propulsion Laboratory in Pasadena, said flight controllers were ''still upbeat'' and had many contingency plans for trying to get a signal.

Even though the procedures have so far been unsuccessful, he said, ''we will continue to look beyond Sunday.''

But after the anxious wait, there was a growing fear that the spacecraft might be disabled or could have crashed, dooming a $165 million mission critical to exploring Mars for evidence of conditions that could support some simple forms of life, past or present.

Compounding the concerns was the fact that flight controllers had failed so far to make radio contact with two small probes the spacecraft was supposed to have released before it entered the Martian atmosphere. The probes were to slam into the Martian surface and penetrate the frigid ground as part of the search for evidence of ice on the planet.

The basketball-size probes should have started sending radio messages through the Global Surveyor on Friday night. Several attempts to pick up signals produced nothing but silence.

The last flight controllers heard from the main spacecraft before its landing attempt was, as planned, 11 minutes before it was to touch down at 12:01 P.M. Friday. All systems appeared to be operating normally then.

An analysis of tracking data just before the communications blackout, scientists said, indicated that the lander, if it survived, would have come to rest on smooth ground at a site that on maps looks like an amphitheater. A low ridge is nearby, but the angle of the slopes appeared to be no more than 2 degrees.

A similar analysis showed that the two probes should have hit on a somewhat more hazardous landscape, said Suzanne Smreker, a scientist at the Jet Propulsion Laboratory.

The lack of communications from both the lander and the two probes raised speculation that their troubles might be related. Asked if a single malfunction could have been the cause, Mr. Cook said that the only possibility that readily came to mind would have occurred five minutes before the spacecraft entered Mars' atmosphere. At that time, the spacecraft was to have jettisoned a section that had supplied power and other services during the cruise toward Mars. The two probes also rode piggyback on that section. They were to be released 18 seconds after the section's separation.

If for some reason the separation never occurred, engineers said, that could have destabilized the lander's descent with possibly catastrophic consequences. And the probes might not have been properly deployed. But engineers said that this was speculation.

In any event, the first three times tracking stations on Earth listened for signals from the lander on Friday they heard nothing. Commands were sent to the lander to cast its radio signals over a wider sweep of the sky in the hope of linking with Earth. But controllers had no way of knowing if the lander had received the commands or could act on them.

Mission officials held out hope that the polar lander's troubles might prove temporary. Perhaps it came down at an odd angle, or it sank a few inches into a crusty surface. In either case, its position might be preventing the antenna programmed for the initial radio contact from establishing a ''downlink.'' The wider Earth-seeking broadcasts of signals might eventually bring results.