Space Probe Asked to Phone Home; No Reply : Science: NASA races against time to contact the $1-billion Mars Observer before it is lost forever.

NASA’s hopes for restoring communications with its silent Mars Observer spacecraft came down Monday to one mission controller’s fervent prayer to the $1-billion space probe: “Talk to me, baby.” But as of late Monday, the Observer had not answered.

In an effort to revive the spacecraft, NASA engineers nervously transmitted a series of electronic pleas over and over again to the probe, which is speeding toward a rendezvous with Mars today. NASA project officials said they did not know why there was no response.

Mars Observer project manager Glenn E. Cunningham at the Jet Propulsion Laboratory, which is running the mission, had his theories: The Observer’s on-board clock might be broken, its radio could be overheated or its antenna askew. The probe might be absorbed in its own silent electronic catechism, deaf to all outside entreaties.

If they cannot attract its attention soon, National Aeronautics and Space Administration officials said the spacecraft--the first U.S. emissary to Mars in 17 years--will go spinning past Mars into space, never to be recovered.

The Observer, designed to provide the most detailed look at the mysterious fourth planet, is a pathfinder for an international armada of planetary probes to be launched toward Mars in the coming decades and an important step toward human exploration of the Red Planet in the next century.

“This would be a great blow to the planetary science community,” Cunningham said. “If we never receive another signal from the spacecraft, we will never know what happened.”

NASA officials did their best to maintain an air of stoic professionalism in the face of what they hoped was a temporary setback. Technical difficulties have plagued NASA’s other recent planetary missions, but Observer had performed almost perfectly until Saturday when it fell silent.

On Monday, with less than 24 hours to go before the craft is to reach Mars, the tension at the lab was palpable.

“It is a very difficult period. I have been working on it for 12 years and it is almost there, almost within reach. And this happens,” said Arden Albee, Mars Observer project scientist. Albee said that watching the huddled teams of engineers trying to restore communications over the weekend made him so anxious that he went home and ripped up his garden ivy.

“They have been trying to work out individual commands, then sets of commands, then anything they could hypothesize that could work, while being just as careful they don’t do something bad.”

When they lost radio contact Saturday night, mission controllers at first thought the radio had been turned off in a routine preparation for pressurizing the probe’s fuel tanks. The probe’s pre-programmed computer, they thought, might automatically turn the radio on and fire the rockets that would push it into orbit around Mars.

On the chance that the probe’s antenna was pointing the wrong way, they also radioed commands repeatedly instructing the spacecraft to switch to a wider beam, low-gain antenna and radio its status to Earth.

On Monday, however, NASA officials announced that they instead suspected that the probe’s timing clock was broken. Without a working clock, the on-board computer could then be suspended in a “wait state,” unable to process the commands the flight team at the lab had been transmitting every 20 minutes for two days.

NASA engineers pinned their hopes on the spacecraft’s backup clock. If they could get it working, the computer might pick up again in its pre-programmed sequence.

“Hopefully then we will see the spacecraft back on the air with data we can assess,” Cunningham said. “That requires, however, (that) we reload the orbital insertion sequence. We all believe there is time to do that.

“It offers us a great ray of hope,” he said. “It is based on more than a prayer. We have been able to simulate the condition that we have seen and check the hypothesis.”

Even if the ploy works, NASA will still be racing against time.

Space agency officials said that for the spacecraft to make it into orbit safely, they would have to reload the orbital insertion sequence into the Observer’s computer no later than this morning--about 12 hours before the scheduled shift into orbit around Mars at 1:42 p.m.

Contacting the Mars Observer

NASA engineers at the Jet Propulsion Laboratory see three ways the Mars Observer, with which contact was lost over the weekend, could resume normal operations before missing the Red Planet completely. The NASA flight team is:

1) Sending a radio signal that switches the spacecraft to its backup clock to jump-start the onboard computer.

2) Sending a signal that triggers the radio transmitter itself.

3) If all else fails, hoping the spacecraft has gone into “safe” mode, in which case it will resume functioning automatically.

Main antenna

Magnetometers

Solar power panels

Internal clock and radio

Camera: Detects objects as small as 10 feet across on Mars surface

Laser altimeter: Measures distance from probe to surface

Gamma ray spectrometer: Measurements allow scientists to determine chemical composition lof Mars surface

Source: NASA, Jet Propulsion Laboratory