Reaction Wheel Failure Ends Kepler Data Collection, But Analysis Continues

By Frank Morring, Jr. morring@aviationweek.com
Source: AWIN First
May 15, 2013

Failure of a second reaction control wheel on NASA’s Kepler planet-finding space telescope has ended data collecting with the spacecraft, but not analysis of the “terabytes” of data already captured.

Scientists have a calendar quarter of data still to analyze for the telltale flickers in the light of distant stars as planets pass in front of them, and perhaps two more years of work in all conducting additional analysis and confirming their findings with ground-based observations, according to William Borucki of NASA’s Ames Research Center, the principal investigator on Kepler.

Hidden in that data is likely to be the “Goldilocks” rocky planet the same size as Earth, in the habitable zone where liquid water can exist around a star like the Sun, he said. “We’re very optimistic the data we have will allow us to accomplish that,” Borucki said.

But four years into its mission, the apparent loss of reaction control wheel No. 4 is likely to will additional data collection. A second wheel — No. 2 — shut down last July, and without at least three of the high-rpm stabilizers it is not possible to maintain the extremely precise pointing necessary for detecting planets with the transit method, Borucki said during a Wednesday teleconference with reporters on the mission status.

The spacecraft went into a safe mode May 12 because it lost attitude control, apparently because of the wheel failure. When controllers attempted to move the wheel on May 14, it wouldn’t budge, according to Charles Sobeck of Ames, the deputy project manager.

Sobeck said there remains a chance the wheel can be restarted by applying more torque, or trying to run it backward. Similar efforts may be made with the other failed wheel, he said. Controllers also may be able to operate the spacecraft in a less-accurate mode, using its onboard fuel to counteract the effects of solar wind on its solar arrays. There is enough fuel on board for several months of operation using the thrusters alone to maintain attitude, and the less-accurate approach could keep the spacecraft arrays pointed at the Sun for “years,” Sobeck said.

The mission’s engineering team will work on ways to keep using the spacecraft in the weeks ahead, as the science team continues to analyze the data already collected. The mission is spending about $20 million a year, and isn’t due for another review until the spring of 2014, according to Paul Hertz, the astrophysics director at NASA headquarters.

To date, Kepler has cost about $600 million, and has discovered more than 2,700 candidate planets around other stars — most of which Borucki believes will be confirmed as planets and enough to demonstrate that most of the stars in the galaxy have planetary systems.

“Two hundred eighty of these planetary candidates are the size of Earth,” Borucki said. “Another 850 are twice the size of Earth. Now these are small enough that we might expect many of them to be rocky planets. Several of the planets that we’ve found are around binary stars, so when you look up at the sky at night and you think I’m going to wish upon a star, about 50% of the time you’re going to wish upon a binary star or a triple star, and so finding planets around them indicates almost all of the stars in our galaxy have a good chance of having planets.”


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