Kepler Recovered from Emergency and Stable (nasa.gov)

Here's an exciting update on NASA's Kepler, which entered "emergency mode" last week. An anonymous reader points us to a press release on NASA's official website: Mission operations engineers have successfully recovered the Kepler spacecraft from Emergency Mode (EM). On Sunday morning, the spacecraft reached a stable state with the communication antenna pointed toward Earth, enabling telemetry and historical event data to be downloaded to the ground. The spacecraft is operating in its lowest fuel-burn mode. The mission has cancelled the spacecraft emergency, returning the Deep Space Network ground communications to normal scheduling. Once data is on the ground, the team will thoroughly assess all on board systems to ensure the spacecraft is healthy enough to return to science mode and begin the K2 mission's microlensing observing campaign, called Campaign 9. This checkout is anticipated to continue through the week. Earth-based observatories participating in Campaign 9 will continue to make observations as Kepler's health check continues. The K2 observing opportunity for Campaign 9 will end on July 1, when the galactic center is no longer in view from the vantage point of the spacecraft.

Comments

Re:What OS?

[Danathar]

Wikipedia says VxWorks (confirmed..kinda)

Why Emergency Mode uses more fuel

[arielCo]

User Statistical at Ars Technica explained it nicely:

Normally Kepler (in K2 mode) uses the pressure from sunlight combined with the two remaining reaction wheels to maintain orientation. It still does need periodic thruster usage but the heavy lifting is done by solar pressure and reaction wheels which makes the propellent usage very efficient. However it is a complicated and precarious balancing act. It needs full instrumentation, computer operation, and periodic updates from Earth to work.

When it goes into emergency mode it falls back on 100% station keeping thrusters because that is simpler although far more expensive in terms of fuel. They don't know exactly why it went into emergency mode but for whatever reason Kepler believed it could not maintain orientation without it.

In emergency mode it has to expand propellent because without some station keeping it would begin to tumble uncontrollably. If you have a spacecraft millions of kms away from Earth, tumbling out of control with its communication array no longer pointed at Earth you will probably never regain control. So it is a last ditch effort to maintain proper orientation on the hope that command & control update can fix the problem. It begins "looking" for an command & control signal from Earth (using propellent to orient the spacecraft). If/when it finds it, it then tries to keep that orientation using 100% station keeping thrusters regardless of fuel consumption. It will continue to do so until standard operation is restored or it runs out of fuel.

About Kepler's K2 mode:

Kepler's Second Light: How K2 Will Work | NASA