Transistor May Be Key to Probe’s Failure : Space: Crucial component of Mars Observer came from same batch that caused a weather satellite’s breakdown, NASA scientists say.

A broken transistor in a small but crucial clock aboard the Mars Observer may have doomed the first U.S. mission to Mars in 17 years, NASA officials said Thursday.

The part came from the same manufacturing batch of microcircuits that also caused a pre-launch breakdown of a weather satellite at Vandenberg Air Force Base in June, space agency officials said.

The Observer has been out of communication since Saturday, when it was preparing its final approach to Mars. NASA flight controllers have no way to know if it is safely in orbit around the fourth planet or spinning out of control in interplanetary space.

As engineers at the Jet Propulsion Laboratory continued their search Thursday for the missing Mars Observer spacecraft, Glenn E. Cunningham, project manager for the $980-million mission, said the possibility of the failed transistor was “receiving considerable attention.”

If the theory is correct, “it would be a non-recoverable situation,” he said.

The transistors are manufactured by Frequency Electronics Inc. in Uniondale, N.Y., a NASA spokesman said. Company officials could not be reached for comment late Thursday.

Cunningham aired the suspicions of his engineering team as NASA Administrator Daniel S. Goldin in Washington, announced an outside investigation of the apparent loss of the Mars Observer spacecraft. A mission review board will be led by Timothy Coffey, director of research at the Naval Research Laboratory in Washington, NASA officials said.

NASA officials said they first learned that the transistors might be defective when a problem developed aboard the NOAA-13 weather satellite as it awaited launch in June. Although transistors from the same batch were used in the Mars Observer, officials said they were not at first concerned because two of these transistors would have to fail to jeopardize the Mars spacecraft.

NASA engineers at JPL in Pasadena now say they suspect that the defective transistors may have caused the spacecraft’s central clock, which controls the operation of its on-board computer and other essential systems, to fail. Failure of the clock, called the RXO, would mean the computer could not turn on the probe’s radio transmitter or perform any of its pre-programmed recovery functions.

The Mars Observer has two clocks, one a backup to take over in case of emergencies. Both clocks would have to fail for the spacecraft to become helpless. The transistors fail when a tiny weld between an aluminum wire and a gold post gives way.

“This failure could have been induced by the shock of pressurant valves operating during the propulsion tank pressurization event on Aug. 21, after which communications were not restored,” Cunningham said in a statement.

“The spacecraft is not designed to automatically protect itself against more than a single failure in any piece of hardware,” he said.

The backup clock had last been tested on launch day, when it was found to be working perfectly, NASA officials at JPL said.