This video of Jupiter's surface spans 24 rotations between October 31 and November 9 (refresh browser to replay animation)

Revived Cassini preps for Jupiter flyby, shoots color movie

Computer-generated illustration of the Cassini spacecraft

In this story: Video captures Red Spot, possible thunderstorms Probes to conduct joint Jupiter study RELATED STORIES, SITES

By Richard Stenger
CNN.com Writer

(CNN) -- The troubled Cassini probe will resume making scientific observations of Jupiter before flying by the giant planet to conduct joint studies with another spacecraft, NASA said Thursday.

Mission engineers shut down instruments on Cassini after its maneuvering system malfunctioned eleven days ago. After more than a week of tests, they determined that the craft could move around without any problems.

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"Everything has been working smoothly, so we're planning to send up commands today to resume all scientific observations," said NASA scientist Bob Mitchell in a statement.

Before its instruments were turned off, Cassini had been sending back thousands of images of Jupiter. The probe is flying by the planet as it travels on a $3.5 billion journey to Saturn and its moon Titan.

NASA released Cassini's first color movie of Jupiter this week. The short clip presents the entire circumference of the planet, flattened into the form of a rectangle.

Like a similar map of the Earth, the most extreme northern and southern latitudes are stretched out considerably. The smallest discernable details at the equator are about 600 kilometers (about 370 miles) across.

The Great Red Spot swirls, orange and white storm bands slide against each other and momentary black dots reveal the shadow of passing moons in the video, which spans 24 Jupiter rotations between October 31 and November 9.

To the east (right) of the Red Spot, oval storms roll over each other like ball bearings. Small, bright features appear quickly and randomly in turbulent regions, possible signs of lightning storms.

The smallest visible features at the equator are about 600 kilometers (about 370 miles) across. In a map of this nature, the most extreme northern and southern latitudes are unnaturally stretched out.

Observations were halted December 17 after one of the spacecraft's four "reaction wheels" experienced problems, causing Cassini to switch to a different maneuvering system.

The reaction wheels serve to point the spacecraft in any desired direction. When an electric motor spins one of Cassini's wheels, the spacecraft rotates in the opposite direction.

The problem surfaced 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.

The hydrazine must be conserved for the primary mission at Saturn, according to the Jet Propulsion Laboratory in Pasadena, California, which manages the mission for NASA and the European and Italian space agencies.

JPL engineers speculate that excessive friction caused by prolonged operation at low speeds caused one reaction wheel to malfunction. Testing the wheel at higher speeds may have restored a necessary lubricant.

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"That's our leading theory, but we may never know for sure," Mitchell said.

Cassini will pass Jupiter at a distance of 10 million km (6 million miles) on December 30, gaining a slingshot-like boost from the planet's gravity that will help the spacecraft reach Saturn in July 2004.

The probe will conduct the first joint investigation of Jupiter with another spacecraft, Galileo, which has orbited the planet system for five years.

The robotic duo will make observations of the Jupiter system and its magnetic fields from different locations. One will be inside and the other outside the magnetic envelope. NASA scientists hope to study the effects of the solar wind on the magnetic field around Jupiter.

Other synchronized studies of the largest planet in the solar system are in the works. Before Cassini leaves the Jupiter system, it will take pictures of the planet's night-side aurora in January.

At the same time, back in Earth orbit, the Hubble telescope will train its powerful lens on Jupiter's day-side aurora.

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

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