Cassini probe restarts troubled maneuvering system
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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
(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.
Tests results encouraging
Encouraging preliminary tests late this week convinced NASA
engineers to restart the reaction wheels.
New European Space Agency report discusses options to fix radio
problems with Huygens, a tiny probe designed to drop from Cassini
into the murky atmosphere of Saturn's moon Titan.
Read the report
"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
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.
Conserving fuel in space
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
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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NASA Jet Propulsion Laboratory
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