Hubble has been orbiting Earth since 1990, and in those decades, it has overhauled our knowledge of the universe around us. (It's also kept us fully stocked with astronomical eye candy.)
"Hubble's instruments still are fully operational and are expected to produce excellent science for years to come," the NASA statement reads.
The telescope went into safe mode because of a failure in one of the instrument's gyroscopes, which steer Hubble and ensure it can get a steady view of space. According to the NASA statement, the particular gyroscope that failed has been acting up for about a year.
"The gyro that failed had been exhibiting end-of-life behavior for approximately a year, and its failure was not unexpected; two other gyros of the same type had already failed," NASA officials said in the statement. "The remaining three gyros available for use are technically enhanced and therefore expected to have significantly longer operational lives."
Hubble has carried a total of six gyroscopes — three standard and three enhanced — since astronauts installed them during a spacewalk in 2009, typically using three at once. The dead gyroscope is the third standard one to fail.
But when the telescope's operators switched the instrument to running on all three enhanced gyroscopes, one wasn't working quite as well as it should have been. That's the error engineers are working to fix now, with the instrument in safe mode to allow them to run tests.
Even if that particular gyroscope stays out of order, Hubble can get back to work — while it works best with three gyroscopes, the telescope can run on just one without losing too much scientific power.