Kepler Down But Not Out

NASA’s Kepler Space Telescope has lost a second reaction wheel, but top officials with the project stressed today that they are not calling it quits yet.

The hastily called teleconference with reporters this afternoon suggested a dire situation, but Kepler principal investigator Bill Borucki and Deputy Project Manager Charlie Sobeck, both with NASA’s Ames Research Center, insisted that while the news was not so good, it did not mean the Kepler mission is over.

They stressed two points.  First, although Kepler cannot produce the type of scientific data on planets around other stars — exoplanets — for which it has become famous with only two of its four reaction wheels functioning, they have not given up on ultimately getting one of the two malfunctioning wheels to operate once again.  Reaction wheel 2 was turned off last year when it showed signs of failure; reaction wheel 4 failed yesterday.  Second, even if Kepler no longer can produce new exoplanet data, two years of archived data await investigation so new discoveries are likely anyway.

Borucki said repeatedly that Kepler was designed to operate for four years, and it has operated for four years.  It has done what it was designed to do — search for Earth-size planets around other stars within the star’s habitable zone (and thus candidates for harboring life) and determine whether such planets are frequent or rare.  Kepler uses the transit method to detect planets by searching for a dimming of a star as the planet passes in front of it.   Borucki said that few astronomers believed it was possible to detect exoplanets in this manner and he had to submit his idea for funding again and again and again.  Ultimately he succeeded.  When asked what he is feeling today, with two malfunctioning reaction wheels that could mean the end of new data acquisition, he said he was “elated with how much we’ve accomplished.”  While it would be “frosting on the cake” if it lasted another four years, “we have an excellent cake” already, he exclaimed.

Sobeck said that Kepler has cost about $600 million to date, and the current spend rate is $20 million per year.   Kepler has completed its primary mission and now is an extended mission phase for an additional two years.  NASA holds “senior reviews” every two years where experts decide which missions to continue funding, since there is a finite amount of money for mission operations.  NASA astrophysics division director Paul Hertz said at today’s teleconference that the next senior review for Kepler is in 2014 where a decision will be made as to whether the spacecraft continues to return scientific data that warrants continued funding.  The agency will be conducting studies over the next several months to determine what science can be obtained from Kepler if the two reaction wheels remain out of commission as well as alternative methods for pointing the telescope with the extreme precision required to obtain the exoplanet data.  The spacecraft has thrusters, but all of that fuel would be quickly consumed if it was used to maintain pointing accuracy instead of using the reaction wheels.

Hertz stressed that this is NASA’s “first, not our last, exoplanet mission.”  Next is the recently-approved Transiting Exoplanet Survey Satellite (TESS), scheduled for launch in 2017, which will search for the exoplanets that are closest to our solar system.   Then the James Webb Space Telescope, to be launched in late 2018, will study the atmospheres of selected exoplanets to determine if life might exist there.  Both will build on the data from Kepler. 

Sobeck conceded that the Kepler team is “saddened” by the news that a second reaction wheel failed, imperiling the telescope’s mission, but the mood of the teleconference was upbeat.  He said Kepler is “not down and out,” though they do not know yet what its performance level will be in the future.  Borucki agreed: “I wouldn’t be a pessimist here.  I wouldn’t write it off at this point.”

If the spacecraft’s precision pointing capability cannot be regained, they stressed repeatedly that there are two years worth of data yet to be mined and more exoplanets to be discovered.