NASA Halts Spacecraft’s Observation of Jupiter

NASA suspended the Cassini spacecraft’s observations of Jupiter on Wednesday because of a problem with a maneuvering system, officials at the Jet Propulsion Laboratory in Pasadena said.

Cassini, heading toward Saturn and its moon Titan on a $3.4-billion, U.S.-European mission, had been sending back images and other scientific data about Jupiter along the way.

Observations were halted after one of the spacecraft’s four reaction wheels experienced problems, causing Cassini to switch to a different maneuvering system.

The wheels can point the spacecraft in any direction by taking advantage of the law of physics that each action has an opposite reaction. When an electric motor spins one of Cassini’s wheels, the spacecraft rotates in the opposite direction.

The problem surfaced Sunday when the No. 2 reaction wheel began needing extra force to turn. The spacecraft reacted by switching from electricity to a hydrazine thrusting system to maneuver.

The hydrazine must be conserved for the primary Saturn mission, according to officials at JPL, which manages the mission for the National Aeronautics and Space Administration and the European and Italian space agencies.

Cassini program manager Bob Mitchell said the situation was improving because the wheel functioned properly in a test Tuesday.

“If things go favorable for us from now on for the rest of the testing that we’re doing, it’s conceivable that we’d be back up and running in a week to 10 days,” he said.

Engineers don’t know what caused the problem, but speculation has centered on the possibility that something got into the wheel mechanism and then was either worn down or spit out, Mitchell said.

Since its 1997 launch, Cassini has flown by Earth once and Venus twice, each time using gravity to gain speed and change direction as it heads for Saturn. Its closest approach to Jupiter--at 6 million miles--will occur Dec. 30.

Cassini is scheduled to arrive at Saturn on July 1, 2004.