WASHINGTON -- NASA is declaring dead an 18-year-old sun satellite that completed highly successful studies of interplanetary space and once served as a radiation sentinel for Apollo astronauts.
Pioneer 9 refused to awaken from a long 'coma' and a last-ditch effort to receive radio signals from it has failed, Project Manager Richard Fimmel said Wednesday.
'The result was nothing,' Fimmel said in a telephone interview from NASA's Ames Research Center in Mountain View, Calif. 'On the basis of that and many other attempts, we have decided we can no longer communicate with Pioneer 9.'
'Think of it as having been in a coma,' said NASA spokeswoman Linda Blum. 'Now it's officially dead.'
Fimmer said the 148-pound spacecraft's last radio signal was received in May 1983 and engineers have been unable to raise it since.
Eighty command sequences were radioed to Pioneer 9 Tuesday from the National Aeronautics and Space Administration's Goldstone, Calif., tracking center, but highly sensitive receivers heard no response.
Fimmel explained that Pioneer 9 and its three predecessors have not been tracked regularly for years because NASA's communications antennas are now concentrating on newer and more important missions.
But every once in a while, scientists turn their attention to the Pioneers to gather data from instruments that still are operating.
'They outlasted the ability of NASA to keep up with them as other programs came along,' said Project Scientist Harold Collard.
Pioneer 9 circled the sun 22 times and covered 11 billion miles of space, studying radiation from the sun along with magnetic and electric fields in interplanetary space.
Pioneer 9 was launched from Cape Canaveral, Fla. Nov. 11, 1968. Pioneers 6, 7 and 8 were launched in 1965, 1966 and 1967 and are still operating in similar solar orbits, Collard said.
He said Pioneer 8 was last tracked in April 1985, Pioneer 7 was heard from last March and Pioneer 6 reported Jan. 7 and is 'healthy and doing fine,' Collard said.
He said all four spacecraft has provided a wealth of data on the nature of the solar processes, the sun's influence on Earth and on the great outbursts of radiation called solar flares.
Because of their ability to detect solar flares before the radiation reached Earth, the Pioneers were dubbed 'interplanetary weathermen.'
Pioneer 9 and its sister craft played valuable roles during the Apollo moon landing program between 1969 and 1972 by looking for solar flares in time to warn astronauts who might be outside Earth's protective magnetic field going to or from the moon.
Fimmel said Pioneer 9's solar cells, which degrade over time, apparently weakened to such an extent that they were unable to power the craft's transmitter. But he said there is no way to determine for sure what led to the probe's demise.