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

The primary tool in the search for exo-Earths may return to service. Recently the second of four reaction wheels failed on the Kepler Telescope. At least three wheels are needed in order to point the observatory and search for planets. These devices, called reaction wheels, are basically flywheels which simply spin to point the spacecraft. Reaction wheels 2 and 4 failed due to increased bearing friction. During recent tests engineers attempted to characterize the failures of these wheels. If the friction was not to high, and also constant the wheels may be usable. If the friction was variable the wheels would not be capable of achieving the fine pointing accuracy needed for the mission. In these tests both wheels were spun in both direction with reaction wheel 4 having higher friction.

Kepler finds three planets possibly in Habitable Zone in one solar system

High-precision pointing of the Kepler spacecraft is controlled by reaction wheels, which are small electric motors mounted on the spacecraft that control the three axes of motion: up/down, forward/back and left/right.
Image Credit:
Ball Aerospace

Engineers today are starting performance testing using reaction wheel 2 as it seems to be healthier. There are no current plans to test reaction wheel 4 any further. In these tests they will first test he wheel in a coarse-point mode using RW1, 2 and 3. This mode is regularly used during normal operations, but has insufficient pointing accuracy to deliver the high-precision photometry necessary for exoplanet detection. coarse-point mode using RW1, 2 and 3. Coarse-point mode is regularly used during normal operations, but has insufficient pointing accuracy to deliver the high-precision photometry necessary for exoplanet detection. This test will however let the engineers know they can prevent the spacecraft from entering safe mode. This degree of pointing accuracy would be equivalent to keeping an imaginary Kepler telescope pointed at a theatre-size movie screen in New York City’s Central Park from San Francisco.

The second test will determine if the wheel can maintain pointing accurately enough to download data using the deep space network. This level of pointing is more accurate than that of simply preventing safe mode entry used in the first set of tests

The final test will enable fine-point mode, or the mode used for collecting science data. In this mode pointing is controlled to within a few milliarcseconds. Using our imaginary Kepler telescope example, this degree of pointing accuracy would be equivalent to pointing at a soccer ball in New York City’s Central Park from San Francisco.

Planets found in the Habitable Zone

Once testing is done it will take a few weeks for engineers to determine if Kepler can begin collection full science data again. With the bounty of new planets it has found lets hope Kepler can once again search for planets. Even if only for a short time the data it gathers is of immense value in the search for planets outside our own solar system.