A malfunction could force an abrupt end to the Kepler Space Telescope’s planet-hunting mission.
NASA received the unwelcome news last Sunday after discovering Kepler had malfunctioned and is currently operating in a self-protective “safe-mode” as it also did earlier this month. The US space agency made the news public this past Wednesday.
It appears at least one of Kepler’s four reaction wheels―onboard devices that precisely aim its telescopic instruments―is not working properly. Kepler needs at least three of the positioning devices to keep its aim true, allowing it to continue its mission, according to NASA.
Launched in 2009, Kepler was designed specifically to hunt for Earth-like planets that may support life elsewhere in the Universe. It has revolutionized the study of extrasolar, or exoplanets, and has discovered about 130 worlds circling distant stars. Nearly 2,700 potential planets are still awaiting confirmation.
NASA scientists and technicians are working on ways to either repair Kepler’s malfunctioning devices, or to develop alternate methods to keep the spacecraft properly oriented. If their efforts are unsuccessful, Kepler’s mission could end far sooner than planned.
NASA officials insist they won’t give up on the space telescope until it can no longer perform useful science.
Unlike the days when it could simply dispatch a space shuttle mission whenever the Hubble Space Telescope needed repairs, NASA must make the repairs and correct the problem by remote control from Earth.
The reason is because, unlike Hubble which is in Earth Orbit, Kepler is in orbit with the Sun and is about 65 million kilometers from Earth, or about the distance to Mars. That distance makes it impossible to send a manned or even unmanned repair mission to fix the ailing spacecraft.
However, there are two possible ways to salvage the spacecraft, according to Scott Hubbard, a former NASA official who helped guide Kepler throughout much of its building stage and is now a consulting professor at Stanford University.
“One is that they could try turning back on the reaction wheel that they shut off a year ago,” he said. “It was putting metal on metal, and the friction was interfering with its operation, so you could see if the lubricant that is in there, having sat quietly, has redistributed itself, and maybe it will work.”
The other scheme, which has never been tried, according to Hubbard, involves using thrusters and the solar pressure exerted on the solar panels to try and act as a third reaction wheel and provide additional pointing stability.
“I haven’t investigated it,” Hubbard said, “but my impression is that it would require sending a lot more operational commands to the spacecraft.”
There seems to be little possibility that Kepler could continue to make useful observations of the cosmos, conducting experiments that perhaps wouldn’t depend on it having to precisely aim its instruments
“People have asked about using it to find near-Earth objects, or asteroids,” Hubbard said. “Kepler carries a photometer, not a camera, that looks at the brightness of stars, and so its optics deliberately defocus light from stars to create a nice spread of light on the detector, which is not ideal for spotting asteroids.”
Hubbard said that since the space telescope wasn’t built as a camera, using Kepler as an asteroid detector will need to be studied.
Meanwhile as repair and workaround solutions are being sought, the Kepler team’s priority right now is to complete preparations to put the spacecraft into a resting state similar to hibernation that minimizes fuel usage while providing a continuous X-band downlink. The X-band is a set of microwave frequencies and portions of it have been set aside to be used exclusively for deep space telecommunications.
The software required to do this was uploaded to the spacecraft last week.