Cassini probe restarts troubled maneuvering system

larger   Two of Jupiter's four major moons, Europa (above) and Callisto (below), aligned with each other and the center of the planet in this picture taken by Cassini on December 7

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(CNN) -- A spacecraft flying by Jupiter was to resume using its main maneuvering system Friday, days after NASA engineers suspended scientific observations because of a malfunction.

The Cassini probe had been sending back images and other data about Jupiter as it travels on a $3.5 billion U.S.-European mission to Saturn and its moon Titan.

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

Encouraging preliminary tests late this week convinced NASA engineers to restart the reaction wheels.

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"The results are all normal. It's encouraging but we need to proceed cautiously," Bob Mitchell, NASA's Cassini program manager at the Jet Propulsion Laboratory, said in a statement.

Cassini's wheels can point the spacecraft in any desired 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 one of the reaction wheels began to need extra force to turn, and the spacecraft reacted by automatically switching from electricity to a hydrazine thrusting system to maneuver.

Computer-generated image of the Cassini spacecraft

The hydrazine must be conserved for the primary mission at Saturn, according to JPL, which manages the mission for NASA and and the European and Italian space agencies.

JPL engineers speculate that a tiny piece of material, perhaps from one of the motor's magnets, moved out of place and created friction in the motor.

"If that's what happened, maybe centrifugal force threw it out or the motor ground it up," Mitchell said. "It doesn't seem to be there now."

Cassini will pass Jupiter at a distance of 10 million km (6 million miles) on December 30, gaining a boost from its gravity that will allow the spacecraft to reach Saturn in July 2004.

Reuters contributed to this report.

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Cassini-Huygens Mission to Saturn and Titan
  • Cassini Jupiter Flyby Science
NASA
NASA Jet Propulsion Laboratory

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