"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," Charlie Sobeck, Kepler mission manager, said in an update posted online today.
Engineers discovered Thursday that Kepler was operating in emergency mode, forcing it to burn more of its precious fuel supply. Kepler needs its fuel to ignite its thrusters and also to orient the spacecraft so it is able to check-in with the Kepler team on Earth.
Kepler entered emergency mode 14 hours before it was set to orient itself toward the center of the Milky Way for a gravitational microlensing study that would allow it to potentially detect extremely distant planets by using the gravity of massive objects, such as stars and planets, and studying its effect on other nearby objects.
NASA engineers will now examine a trove of data downloaded on Sunday to determine a possible cause for the emergency event. Sobeck said the team had ruled out the aforementioned maneuver and the spacecraft's reaction wheels as a potential cause of Kepler slipping into emergency mode.
This isn't the first issue for Kepler, which launched in 2009. Two of the reaction wheels that allow the spacecraft to orient itself stopped working in 2013. Since then, Kepler has been operating in K2 mode, which makes up for the loss of the wheels by leveraging pressure from sunlight.
Despite the glitches, Kepler has had tremendous success in space; NASA says Earth 2.0 may soon be discovered.
Last year, NASA announced it had located a planet and star closely resembling Earth and the sun. The newly discovered planet, which NASA has named Kepler-452b, is believed to be 6 billion years old -- making it about 1.5 billion years older than the Earth and our sun. NASA said the star, Kepler-452, also has the same temperature as our sun and has a diameter 10 percent larger.
What makes the discovery especially intriguing is that the planet is orbiting the habitable zone of the solar system, the "Goldilocks" region where it's not too hot or too cold, so that the surface of the planet could sustain liquid water.
During its prime mission, which ended in 2012, Kepler detected nearly 5,000 exoplanets -- more than 1,000 of which have been confirmed.