NASA’s Kepler observatory enters a modified Safe Mode

keplerThe Kepler observatory has stopped it’s science data operations due to concern about a second reaction wheel issue. Reaction wheels are used to point the observatory and are critical to the mission. There are four wheels on the spacecraft, one of which is a spare. A minimum of three are needed for normal operations. One of the wheels has already failed and another wheel ( #4) is showing early signs of failure. It has been more than three-and-a-half-years since the Kepler mission launched in March 2009. The spacecraft has continued in its heliocentric, drift-away orbit and is now more than 45 million miles away from Earth.

Earlier this month an increase in the amount of torque required to spin one of the three remaining reaction wheels was detected. This increase in friction occurred before the Jan. 11, 2013 quarterly roll, and persisted after the spacecraft roll and several momentum desaturations of the reaction wheels. Increased friction over a prolonged period can lead to accumulated wear on the reaction wheel, and possible wheel failure. To minimize wheel friction, the team implemented several mitigations including increased operating temperatures, higher spin rates, and bi-directional operation following the failure of reaction wheel #2 in July 2012.

On January 17, 2012 due to the persistence of this recent event in reaction wheel #4,  Kepler was put  in a “wheel rest” safe mode for a period of ten days. Science data collection will be stopped during this period and the spacecraft solar panel orientation will be aligned with the sun to maintain positive power for Kepler. This is similar to a normal safe mode configuration, but with thrusters maintaining attitude instead of reaction wheels. In normal operations the wheels are used as they do not require fuel to execute the pointing of the observatory. Resting the wheels provides an opportunity to redistribute internal lubricant, potentially returning the friction to normal levels.

Once the 10-day rest period ends, the team will recover the spacecraft from this resting safe mode and return to science operations. That is expected to take approximately three days. Lets hope this helps the issue as Kepler has been responsible for finding a multitude of Planets in other solar systems as well as possible Earth like planets.

About the author

Recipient of many prestigious NASA Awards including the Exceptional Public Service Medal and the Robert H. Goddard award. Experience includes working for NASA, as a contractor, in satellite design, construction and operations. Expert in the satellite operations concepts and ground systems including command, control, and science data processing.