FOR members of the Mars Observer mission team, losing communication with their spacecraft is a major disappointment. Yet they are far from conceding defeat. They note that other American planetary mission teams faced similar challenges, yet went on to success.
Voyager 2, which surveyed distant Neptune, lost contact with Earth for a week shortly after launch. And controllers lost communication with the highly successful Magellan Venus explorer several times.
At press time, however, Mars Observer had not yet answered the urgent calls from Earth. Because of that "there's some disapointment" here, said Glen Cunningham. Mars Observer project manager. He spoke at a press conference at the California Institute of Technology's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
Under these circumstances, Mr. Cunningham said that the Mars Observer controllers "plan to continue to try to establish communications assuming that [the spacecraft] is in orbit [around Mars]." He noted that "the emotional attachment of these people to the project is high" so they are putting everything they can into this effort.
Contact with the $400 million spacecraft was lost Aug. 21 when the propulsion system was pressurized prior to firing rocket engines to insert the craft into Martian orbit. Mars Observer radios were turned off as part of this routine. No signal has since been received from the craft.
Asked how he could assume Mars Observer has gone into Martian orbit and not just missed the planet, Cunningham said, in effect, that it is a matter of an engineer's faith in the system. The spacecraft computers had complete instructions for orbit insertion. "The best information we have is based on what was loaded into the spacecraft," he said. He explained that this fact plus his knowledge of what the spacecraft can do are the reasons for "optimism."
At press time, there was a possibilty that the spacecraft itself might take action to try to contact Earth Wednesday afternoon. Cunningham explained that the craft has a five-day countdown timer that resets itself every time the craft receives a signal from Earth. If no signal is received for five days, the timer initiates a procedure in which the craft makes sure its antenna is pointed toward Earth and takes other action to facilitate contact with Earth.
If Mars Observer has indeed heard nothing from Earth since Saturday, the timer should have taken this action Wednesday afternoon. However, Cunningham noted that "it's quite possible that it is hearing us and we're not hearing from it."