Software "hiccup" undermines trip past Saturn moon

By Will Dunham

WASHINGTON (Reuters) - A software malfunction prevented a key piece of equipment on the Cassini spacecraft from recording data as it flew through the plume from a geyser shooting off a moon of Saturn, NASA said late on Thursday.

NASA called the problem "an unexplained software hiccup" that came at a very bad time, preventing Cassini's Cosmic Dust Analyzer instrument from collecting data for about two hours as it flew over the surface of the moon Enceladus on Wednesday.

A key objective of the fly-by was to determine the density, size, composition and speed of particles erupting into space from the moon's south pole in a dramatic plume.

Bob Mitchell, Cassini program manager, said the problem meant that the instrument did not collect data as the craft flew through the plume -- a process lasting under a minute.

"When it went through the plume, it was not working properly," Mitchell said in a telephone interview, expressing disappointment. "We had tested that software very carefully. We don't know why it didn't work properly."

The Cassini spacecraft, studying the giant gaseous planet Saturn and its moons in a joint U.S.-European mission, flew as close as 30 miles over the surface of Enceladus (pronounced en-SELL-ah-dus) on Wednesday.

"During the fly-by, the instrument was switching between two versions of software programs. The new version was designed to increase the ability to count particle hits by several hundred hits per second," NASA said in a statement.

"The other four fields and particles instruments on the spacecraft, in addition to the ion and neutral mass spectrometer, did capture all of their data, which will complement the overall composition studies and elucidate the unique plume environment of Enceladus," NASA said.