The End of the Kepler Mission?

Not Yet, but Things Don’t Look Good

NASA’s Kepler spacecraft, launched in 2009 to search out worlds around other stars, has likely reached the end of its current mission due to the failure of a critical component called a reaction wheel. The spacecraft has four of these wheels which help stabilize Kepler so that it can point steadily at its assigned area of the sky. One of them failed last year, and this new failure now leaves the spacecraft with only two reaction wheels — an unstable (to put it mildly) and unworkable situation. Still, the mission team hasn’t given up. Until the problem can be corrected (and that’s not looking good), the spacecraft is what they call “Thruster-controlled Safe Mode”.

It’s a very disheartening day for the Kepler mission team, since they and their spacecraft have been SO successful in discovering new worlds and giving us a new feel for the population of planets in the Milky Way Galaxy. Of course, the mission has always had an anticipated end point, but I think that planners were hoping that day would come when the spacecraft ran out of thruster fuel. There’s a few months’ worth of fuel left, so they will keep working to solve the problem with the wheel.

Of course, Kepler’s discoveries don’t end with these problems. In fact, some of the most exciting results are still to come. The spacecraft’s light sensors have gathered so much data about distant stars and possible planets that it will be years before it is all analyzed.  Hidden in that data are many more distant planets.  So, Kepler’s mission isn’t quite over until the last planet is wrung out of the data.  Still, the mission will lose out on at least two years of further observations of planet candidates, and that WILL be a loss to the community.

Bill Borucki — the principal investigator of the Kepler team, while echoing the team’s concerns about the spacecraft, has pointed out that the mission has been wildly successful. He ended up his statements today (at a NASA telecon) by saying, “It’s been a long journey to prove Kepler would work, see it get rejected time and time again, go back and improve the proposals, and put it all together. So today, I am delighted with all Kepler has accomplished. It gave us data like no other mission ever has. I’m just elated with what we’ve accomplished. I’m not feeling sorry at all.”

So, what has Kepler accomplished?  If you  browse the mission website, you can sample some of the many types of worlds the spacecraft has discovered. It has found 2,740 planet candidates so far and 2,165 eclipsing binary stars. Of the planetary candidates, 132 are confirmed as actual planets. Each of those worlds have unique characteristics that give tantalizing clues about how they formed and the star systems they inhabit. Just as an example, the stars called Kepler 62 and 69, are two quite different stars.

Kepler 62 is not sunlike, and has several planets that are somewhat larger than Earth and one the size of Mars. When these planets were announced in April, John Grunsfeld, associate administrator of the Science Mission Directorate at NASA, hailed the mission’s critical success. “The Kepler spacecraft has certainly turned out to be a rock start of science,” he said.

Today, Grunsfeld was a bit less upbeat, but still asserted that the Kepler mission isn’t dead—yet. I echo his thoughts and hope that the Kepler mission team can find a way around the spacecraft’s reaction wheel woes. I am reminded of the same issues that Hubble Space Telescope faced with its faulty gyros, which could be fixed by astronaut visits. Kepler doesn’t have that option because it orbits too far from Earth for a rescue mission. That distant orbit is what made this fantastic mission of planetary discovery possible. I wish the Kepler team all the best in finding a way to  make the spacecraft work a while longer.