National Aeronautics and Space Administration flight controllers had no way of knowing whether the planetary probe had safely reached a planned Martian orbit on its own. They had nothing except a faith in their own skill to sustain the belief that the spacecraft still existed.
Engineers at the Jet Propulsion Laboratory, which is running the mission, listened in vain through the antennas of the agency's Deep Space Network for any sign of the lost spaceprobe. There was only silence.
At about 5:40 p.m. EDT -- the critical moment of the scheduled rendezvous with Mars -- a silence fell over the space center. Attention centered on a simple computerized graph projected on television monitors throughout the JPL campus.
Any movement on the red, white and blue graph would have signaled the resumption of transmissions from the lost probe. After seven minutes of silence, the voice of the NASA flight controller crackled on the intercom: "We have come up negative in our search for a signal."
The flight controllers maintained their vigil last evening. But they could not stem growing suspicions that the probe might have been destroyed Saturday when it lost contact with Earth.
"I'd like to believe the spacecraft is in orbit around Mars. We will continue to try and re-establish communications with the lTC spacecraft, assuming it is in orbit," said Project Manager Glenn E. Cunningham.
"We are not giving up. I need to emphasize that very strongly."
The nearly $1 billion Mars Observer project was the first U.S. mission to the solar system's mysterious fourth planet in 17 years.
NASA officials held out the faint hope late yesterday that the Observer might have automatically performed the delicate series of rocket firings that would place it in the proper orbit.
NASA engineers and space scientists said the spacecraft -- one of the most sophisticated and independent planetary probes ever designed -- could still establish communications on its own with Earth this afternoon. Officials said there was a remote possibility that the Observer might have suspended operations in an emergency mode designed to conserve its systems.
If that is true, the probe will attempt to contact JPL no later than 5 p.m. EDT today.
"Either it is going to come on the air after five days, or they all are going to get drunk," said John Pike, director of the space policy project at the Federation of American Scientists.
"I think it's gone," said space historian James Oberg in Houston, who has written authoritatively on Mars and the missions to explore it during the past 30 years. Mr. Oberg said yesterday that JPL officials "are really avoiding the fact that it was probably a catastrophic failure."
When the spacecraft lost contact Saturday, it was preparing to pressurize its fuel tanks before a series of orbital maneuvers. Mr. Oberg said he suspected the fuel tank simply exploded. "Something violent occurred during the blackout," he said.