The spacecraft provides the power, pointing and telemetry for the photometer. Other than the four reaction wheels used to maintain the precision pointing and an ejectable cover, there are no other moving or deployable parts on the spacecraft.
Image Credit:
NASA Ames/Ball Aerospace
NASA is now looking for a new mission for Kepler. This mission would use only two reaction wheels now that attempts to revive one of the failed wheels has not succeeded. Reaction wheels two and four had failed and the spacecraft needs at least three to operate normally. Engineering tests showed that one of the wheels was possibly viable but has now ended attempts to restore the wheel. NASA has concluded that the wheel is not healthy enough to continue the mission, therefore Kepler as we knew it is done and the mission will end. There is some good news though, NASA is looking for white papers to resume some level of science data collection using two reaction wheels and thrusters. This will not allow the spacecraft to resume normal pointing accuracy but may allow some new, slightly different mission to be executed.
Schematic view of two possible point-drift mode observations on a
CCD. During a ~4 day period, the spacecraft can hold a target to within a jitter of ~0.5-1.0 arcsec along a drift line that is estimated to be ~1.4 degrees in length. A reset of the pointing brings the observation back to near the start point. The rate of drift is estimated to be approximately 0.9 arcsec/minute (~1 pixel in ~5 minutes) or possibly less. The path of a target during this time period will inscribe
an arc shape on the focal plane.
The diagram to the left gives you an idea of how a new mission could work, allowing more error or drift on the pointing of the spacecraft. This is based on an early analysis by Ball Aerospace.
“At the beginning of our mission, no one knew if Earth-size planets were abundant in the galaxy. If they were rare, we might be alone,” said William Borucki, Kepler science principal investigator at NASA’s Ames Research Center in Moffett Field, Calif. “Now at the completion of Kepler observations, the data holds the answer to the question that inspired the mission: Are Earths in the habitable zone of stars like our sun common or rare?”
There is no other spacecraft capable of looking for planets the way Kepler did and we need to remember it was an outstanding success. Kepler had actually completed it’s normal mission life and was in an extended mission which took advantage of the fact that the spacecraft could still obtain good science data.
