NASA’s Dawn spacecraft experiences reaction wheel malfunction
During preparations for observing Ceres’ Occator Crater, NASA’s Dawn spacecraft’s remaining reaction wheels stopped functioning. The probe controls its orientation in space by changing the speed these gyroscope-like devices spin.
Dawn is preparing to observe Ceres on April 29, 2017, from an “opposition” position, meaning the spacecraft will pass directly between the dwarf planet’s Occator Crater and the Sun. This unique vantage point may provide new insights about the bright spot at the center of the crater.
When the reaction wheel stopped working on April 23, the spacecraft entered safe mode and assigned control of its orientation to its hydrazine thrusters. The mission team discovered the situation during a scheduled communication session on April 24. After diagnosing the problem, they returned the spacecraft to its standard flight configuration, still under hydrazine power, on April 25.
The reaction wheel failed after Dawn had completed its five-hour period of ion thrusting to adjust its orbit on April 22, but before a shorter maneuver scheduled for April 23–24.
Dawn’s current orbit will still allow it perform opposition observations. According to the mission team, the reaction wheel’s malfunction will not significantly impact the remainder of the spacecraft’s extended mission at Ceres.
The spacecraft is equipped with four reaction wheels. One of the wheels failed in 2010, a year before the spacecraft entered orbit around Vesta, and another in 2012, as it was finishing its explorations of that asteroid. For most of the time since Dawn left Vesta, including the first year of operations at Ceres, all four wheels were turned off.
Launched on Sept. 27, 2007, from Cape Canaveral Air Force Station in Florida, the spacecraft arrived in orbit around Vesta on July 15, 2011, and departed for Ceres on Sept. 4, 2012. Dawn arrived at Ceres in 2015 and completed its prime mission in June 2016. It is now on an extended mission.
Video courtesy of NASA
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.