Engineers restored regular communications with the spacecraft Magellan last night after it had sent its controllers into a state of high anxiety by sending only erratic radio signals for more than 14 hours after collecting its first raw radar echoes from the surface of Venus.
When radio contact was finally restored late last night, "we jumped up and clapped," said Tommy Thompson, Magellan science manager at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif. "It was just like the home team scored a touchdown."
Flight controllers had spent the day playing radio tag with the robot craft and trying to figure out what was going on 145 million miles from Earth.
At midday, the spacecraft "phoned home" and reported itself to be in apparently good health, but its orbit almost immediately took it behind Venus again, leaving controllers in suspense. When it emerged, they failed to detect the signal immediately, engineers said. But at 4:03 p.m. EDT, they reestablished what one spokesman described as "a good solid lock."
But they lost communication again 25 minutes later and said the pattern was probably the result of a cone-shaped sweeping motion in the spacecraft, known as "coning," which it was programmed to perform to search for Earth in an emergency. Transmissions from a medium-gain antenna on the craft were sweeping Earth and then moving on.
The good news was that Magellan's first images of the Venusian surface, produced during its Thursday night test run, "look pretty damn good" and will be released early next week, a few days earlier than planned, according to project manager Tony Spear of JPL, which manages the mission for NASA.
The test run -- the first for the $744 million mission -- produced more pictures than expected showing hardened ancient lava flows and volcanic cinder cones topped with craters, faults and fractures on Earth's sister planet along strips of surface 1,000 miles long by 15 miles wide, project scientist Steve Saunders said.
On Aug. 29, Magellan was scheduled to begin 243 days of work collecting such strip maps, which would be assembled into a mosaic expected to be the most detailed and complete map of Earth's sister planet.
Last night, JPL officials restored communication with Magellan by sending it a signal to put it in continuous contact with Earth but at a low rate of data return while they check its memories to determine the cause of its problem. Magellan's computer will be asked to return data at a high rate, which is required for transmitting the radar mapping data, probably sometime next week, JPL officials said.
Spacecraft handlers said the loss of signal occurred because the highly automated craft apparently had gone into what is known as a safe mode -- a protective posture ordered by an onboard computer -- because "something scared it" Thursday night.
At that point, Magellan had just completed the second of two mapping test runs and had pivoted toward outer space to scan stars to calibrate its exact position, as it does routinely on each orbit. It was expected to resume transmission of the radar data to Earth at 11:52 p.m. EDT Thursday. Controllers first became concerned when it failed to do so.
In a safe mode, the spacecraft is designed to turn its solar arrays toward the sun to maintain its power supply, hunker down in orbit for some period of time, from a few hours up to 18 hours, unless instructed otherwise, and then search for Earth and contact its handlers, JPL officials said.
The signal was initially reacquired by NASA's Deep Space Network's Goldstone, Calif., tracking station less than 15 hours after it had first been lost. The word arrived at JPL about 10 minutes into a news briefing in which Magellan officials were explaining the loss of signal, when their colleague Steve Wall rushed into the room with a piece of paper.
"It was wild, and totally confusing," said JPL spokesman Jurrie van der Woude. "But at least we knew the spacecraft was not dead. It was joyful to hear a signal and to have it confirmed that it was Magellan's voice."