Another gap in mapping Venus.

Another gap in mapping Venus

NASA blames an engineer at its Jet Propulsion Laboratory (JPL) for incorrectly sending a series of computer commands late last week, an error that shut down the mapping of Venus by the Magellan spacecraft for four complete orbits of the planet. Flight-controllers at JPL in Pasadena, Calif., eventually corrected the problem, which spokesman James J. Doyle calls Magellan's first mapping loss due to a human programming error.

Though blank spaces should have separated each of the commands sequentially radioed to the spacecraft on Nov. 23, the JPL engineer inadvertently omitted them. Magellan's computer, functioning correctly, responded to this irregularity by automatically turning off the craft's radar transmitter and receivers, its two tape recorders, and one of the transmitters that sends data to Earth, says Doyle. When the error was corrected, the mapping resumed.

Five times since Sept. 15, when Magellan began its mapping mission, scientists have failed to receive expected images of Venus' cloud-shrouded surfaces, resulting in the loss of data from 11.8 mapping orbits. (A "mapping orbit" designates the 37 minutes of actual mapping that occurs during each of Magellan's 3-hour, 15-minute circuits of Venus.) As of Nov. 26, Magellan had completed 423 mapping orbits and charted about 23 percent of the planet's surface.

Aside from the most recent incident, project engineers remain uncertain what caused the data losses. However, they suspect such things as static in onboard electronic equipment, loose wires, and problems at NASA's tracking stations in Australia and Spain that may have prevented data reception. Twice during its checkout phase in August, Magellan also lost radio contact with Earth -- again inexplicably -- for more than half a day each time (SN: 9/1/90, p.135).