WASHINGTON — NASA’s Kepler spacecraft has suffered no long-term effects from an anomaly last month that threatened the mission, and the spacecraft should be able to operate for at least two more years, the mission’s manager said May 10.
At a press conference to announce new exoplanet discoveries in data collected by the spacecraft, mission manager Charlie Sobeck said the spacecraft had fully recovered from an “emergency mode” in April that disrupted science observations for more than two weeks.
“It looks at though it was a transient event,” he said of the incident that triggered the emergency mode April 7. “We don’t see that the spacecraft is operating any differently today than it operated before the emergency mode.”
Controllers found the spacecraft had gone into emergency mode during a scheduled communications session then, around the time the spacecraft was to begin the latest in a series of observations. The cause of the anomaly remains under investigation, but Sobeck said last month that the spacecraft likely went into emergency mode after a series of false alarms overwhelmed the spacecraft’s computers.
Controllers worked in the days after the incident to recover the spacecraft, first taking it out of emergency mode and then gradually restoring Kepler to normal operations. It resumed its regular science observations April 22. “Right now, everything is looking good with the spacecraft,” he said.
Emergency mode uses more of the spacecraft’s fuel than normal to stabilize the spacecraft, raising the possibility that the extra fuel consumption might shorten the spacecraft’s life. However, Sobeck’s comments indicated that the additional fuel consumption was not a major concern for Kepler’s extended mission, known as K2.
“The K2 mission is ultimately going to be constrained by fuel, and right now my estimate is going to be something over two more years of fuel,” he said. “So, some time in the middle of summer of 2018 is when I think we may run out.” That is not significantly different than mission planning prior to the anomaly, which projected mission operations to the middle of 2018.
Sobeck’s comments are more optimistic than in a May 3 interview published on NASA’s website. “It appears to me as though we lost more fuel than I had hoped, but less than I had feared,” he said then.
He noted in that interview there was a “noticeable” drop in pressure in the spacecraft’s fuel tank but that the decrease was not linear, so he couldn’t draw conclusions about how much fuel the spacecraft used during that emergency mode. “I suspect it will take a few months of normal usage to recalibrate our fuel estimates.”
Kepler, a NASA mission to search for exoplanets, launched in 2009, aiming its telescope at a single region of the sky. Its primary mission ended in 2013 when the second of four reaction wheels on the spacecraft, used to maintain accurate pointing, failed.
Spacecraft engineers developed an alternative approach to point the spacecraft using the remaining reaction wheels and solar pressure. In this alternate mode, Kepler cannot study the same region of the sky continuously as in the past, but can look at different regions for about three months at a time. Kepler was about to start the ninth of these observing campaigns of the K2 mission at the time it went into emergency mode.
Although Kepler’s primary mission has ended, analysis of the data it collected continues. Sobeck spoke at a press conference where scientists announced the discovery of 1,284 exoplanets in data from the spacecraft’s primary mission. Astronomers used a new statistical analysis technique to verify that dips in brightness observed in stars in Kepler’s field of view were caused by orbiting planets passing in front of the star.
Kepler has discovered a handful of planets so far in the K2 mission, but astronomers are using the observing campaigns for other research as well. While continued operations are pending the outcome of an ongoing senior review of extended NASA astrophysics missions, Sobeck said in the earlier interview he expected Kepler to operate until it ran out of fuel.
“It has been our plan to continue operating the K2 mission until the fuel runs out,” he said. “Meaning that at some point we will begin a campaign and will never hear back from the spacecraft.”