Tag Archives: reaction wheel

Kepler is back in operation after a ten day rest to safe the mission.

Kepler is back in operation after a ten day rest to save the mission.

When Kepler launched in March 2009, it had four reaction wheels — three for immediate use, and one spare. But one wheel (known as number two) failed in July 2012, so a major problem with the currently glitchy wheel (called number four) could spell the end of the $600 million Kepler mission. It’s unknown at the moment if the 10-day rest period will bring wheel number four back into line. “Over the next month, the engineering team will review the performance of reaction wheel #4 before, during and after the safe mode to determine the efficacy of the rest operation,” Hunter wrote.

Kepler shut down for ten days to save the mission.

Uh-oh: Kepler has been shut down for ten days to save the mission.

The spacecraft was launched with four so-called reaction wheels that spin to help keep the telescope pointing at its target fields of stars. One of these, reaction wheel No 2, failed in July 2012, leaving three to do the maneuvers, including a quarterly roll to a new orientation. Now reaction wheel No 4 has shown early indications that it might fail, prompting its NASA controllers to attempt some long-distance maintenance. They hope that by resting the wheels, their lubricant will spread to ease increased friction.

If this wheel fails permanently, the Kepler mission would be over, as it would be impossible to orient the spacecraft with enough precision with only two wheels.

An update on Dawn’s reaction wheel failure.

An update on Dawn’s reaction wheel failure.

Essentially, this will delay the journey to Ceres for about nine days. The spacecraft is left with two working reaction wheels, with which it can complete all its science work. However, if they cannot get the failed wheel working again, Dawn will be left with no backup should another wheel fail.

One of Dawn’s reaction wheels, used to orient the spacecraft, shut down last week.

Uh-oh: One of Dawn’s reaction wheels, used to orient the spacecraft, shut down last week.

During a planned communications pass on Aug. 9, the team learned that the reaction wheel had been powered off. Telemetry data from the spacecraft suggest the wheel developed excessive friction, similar to the experience with another Dawn reaction wheel in June 2010. The Dawn team demonstrated during the cruise to Vesta in 2011 that, if necessary, they could complete the cruise to Ceres without the use of reaction wheels.

That the spacecraft can get to Ceres without reaction wheels is good. However, can it be oriented precisely to do science without these wheels? The JPL press release does not say.

One of Kepler’s reaction wheels — used to orient the space telescope — has failed.

Bad news: One of Kepler’s four reaction wheels — used to orient the space telescope — has failed.

Kepler only needs three wheels to function – one to control the probe’s motion along each axis – and the probe resumed its observations on 20 July. “Kepler is functioning very well on three reaction wheels,” says mission manager Roger Hunter of NASA’s Ames Research Center in Moffett Field, California. If the glitch can’t be fixed, though, Kepler will be left without a backup wheel. “This is reducing the odds of making the mission go as long as we can,” says Kepler chief scientist William Borucki of NASA Ames, who doubts that Kepler could point accurately enough to look for transiting planets if reduced to two reaction wheels. “It was a disappointing surprise to find this wheel stopped so early.”

Engineers have successfully tested a spare reaction wheel on Mars Odyssey in their effort to bring the spacecraft back into full operation.

Engineers have successfully tested a spare reaction wheel on Mars Odyssey in their effort to bring the spacecraft back into full operation.

After more than 11 years of non-operational storage, the spare reaction wheel passed preliminary tests on Wednesday, June 12, spinning at up to 5,000 rotations per minute forward and backward. Odyssey engineers plan to substitute it for a reaction wheel they have assessed as no longer reliable. That wheel stuck for a few minutes last week, causing Odyssey to put itself into safe mode on June 8, Universal Time (June 7, Pacific Time).