In low-altitude mapping orbit, Dawn will prolong its hydrazine supply by switching to a "hybrid mode" of pointing, where it will use its two remaining functional
reaction wheels in combination with hydrazine thrusters to point itself.
The redesigned
reaction wheels were successfully launched last year on the Transition Region and Coronal Explorer, a satellite mission that is studying the sun's coronal region with the TRACE satellite in April 1998.
Kepler was knocked out of commission last spring when the second of its four
reaction wheels stopped working (SN Online: 5/15/13).
L-3's Space and Navigation Division is a premier supplier of Momentum Exchange devices, including Momentum Wheels,
Reaction Wheels, and Control Momentum Gyroscopes for space applications.
Scientists found the telescope in safe mode, on investigation that one of the
reaction wheels was found broken.
Last summer, the possibility of a scientifically productive mission for Kepler after its
reaction wheel failure in its extended mission was not part of the conversation," said Paul Hertz, NASA's astrophysics division director at the agency's headquarters in Washington.
Millennium manufactures the RWA1000 small satellite
reaction wheel under exclusive license from Sinclair Interplanetary of Canada.
This instrument got a new lease on life when NASA engineers managed to compensate for the failure of its
reaction wheels.
During that first mission, the craft lost the functionality of one of its
reaction wheels.
Once separated from the launch vehicle, the 18 thrusters on the GEO Flight 3 satellite provide stationkeeping, three-axis control and de-spinning of the
reaction wheels throughout the mission.
However, they have ruled out both the maneuvers and the craft's orientation-adjusting
reaction wheels as the cause.
On January 10, engineers sent a command to spin Philae's
reaction wheels, which helped stabilize the lander during its descent.
