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NASA Unloads Magellan Memory to Diagnose Venus Orbiter’s Woes

August 18, 1990

PASADENA, Calif. (AP) _ Engineers worked Saturday to strengthen their radio link to Magellan and unload the spacecraft’s memory banks to try to find out why the orbiter temporarily lost contact with Earth while circling Venus.

They already know the malfunction made one of Magellan’s computers stop sending signals called ″heartbeats″ to another computer Thursday night, said David Okerson, a Magellan engineer assigned to Jet Propulsion Laboratory.

That spurred Magellan to put itself into a series of protective safety modes that cut off contact with Earth, then sent radio signals across the heavens in a long, balky but successful effort to restore its radio link with controllers.

A steady hookup was re-established Friday night after nearly 15 hours of no radio contact followed by eight hours of intermittent contact.

″The spacecraft administered CPR to itself,″ Okerson said. ″These protection mechanisms just saved our bacon.″

Laboratory spokeswoman Mary Beth Murrill said the time needed to diagnose and fix the original problem likely will delay the start of Magellan’s mission to use radar to make the best pictures and maps yet of Venus’ cloud-covered surface. Okerson said he couldn’t predict the likelihood of delay, but said engineers are still aiming to start mapping Venus on Aug. 29 as planned.

The engineers lost contact with Magellan on Thursday night just after it bounced radar waves off Venus for a test and sent the information to Earth. The data were assembled into Magellan’s first pictures of Venus, which displayed ″Venusquake″ faults, volcanic cinder cone and broad plains covered by old lava flows.

The pictures will be released Tuesday, the National Aeronautics and Space Administration said.

Magellan was launched from the shuttle Atlantis on its $744 million Venus exploration mission on May 4, 1989. It went into orbit around Venus Aug. 10 after a circuitous trip of 948 million miles.

Magellan remained in a safety mode on Saturday, following simple computer instructions meant to keep it in contact with Earth by pointing its secondary antenna at its home planet.

To obtain information needed to learn what went wrong Thursday, engineers commanded the spacecraft to transmit all of the information in its computer memories back to Earth, Murrill said.

Magellan’s secondary antenna sends a much broader radio beam to Earth than the main antenna. But it sends data at a painfully slow 40 bits per second, so unloading Magellan’s memory banks proceeded at a crawl.

Okerson said engineers were working to increase the speed 30-fold, to 1,200 bits per second. But at that rate, the secondary antenna’s signal is weak because Magellan and Venus are nearing their most distant point from Earth, on the other side of the sun some 147 million miles away.

To receive the high-speed data, officials of NASA’s Deep Space Network were arranging to link a 112-foot antenna dish at a Goldstone, Calif., tracking station to a 230-foot dish that normally tracks Magellan, Okerson said.

Similar steps also may be taken at the network’s tracking stations in Australia and Spain, he added.

Normal contact with Magellan should be restored sometime during the week when it is ordered to leave the safety mode, point its main antenna at Earth and send data at a higher speed.

That will allow NASA to unload the contents of a tape recorder on Magellan that contains much more detailed information about Thursday’s malfunction than is stored by the computer memory banks, Okerson said.

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