NASA's Chandra X-Ray Observatory, observing the universe in high-energy light since 1999, is back in action after suffering a glitch due to the failure of the gyroscope and going into safe mode last week.
The cause of Chandra's safe mode on October 10 has now been understood and the Operations team has successfully returned the spacecraft to its normal pointing mode, according to the US space agency.
"The safe mode was caused by a glitch in one of Chandra's gyroscopes resulting in a 3-second period of bad data that, in turn, led the on-board computer to calculate an incorrect value for the spacecraft momentum. The erroneous momentum indication then triggered the safe mode," NASA said in a statement late on Monday.
The team has completed plans to switch gyroscopes and place the gyroscope that experienced the glitch in reserve.
Once configured with a series of pre-tested flight software patches, the team will return Chandra to science operations which are expected to commence by the end of this week, NASA said.
On October 10, Chandra X-ray Observatory entered safe mode, in which the observatory is put into a safe configuration, critical hardware is swapped to back-up units, the spacecraft points so that the solar panels get maximum sunlight, and the mirrors point away from the Sun.
Chandra is 19 years old, which is well beyond the original design lifetime of five years. In 2001, NASA extended its lifetime to 10 years.
The US space agency said that it was also continuing to work towards resuming science operations of the Hubble Space Telescope that on October 5, entered safe mode after one of the three gyroscopes (gyros) being used to point and steady the telescope failed.
Gyroscopes help spacecraft maintain proper orientation.
Scientists are currently performing analyses and tests to determine what options were available to recover the gyro to operational performance.
Till that time, science operations with Hubble have been suspended.
Besides Chandra and Hubble, NASA's planet-hunting Kepler space telescope is also almost out of fuel. Kepler has found about 70 per cent of all known alien worlds to date.
NASA's Dawn spacecraft, which has been orbiting the dwarf planet Ceres since March 2015, is also nearly out of fuel and might run out as early as October.
The space agency's Mars rovers Opportunity and Curiosity too have faced issues of late.