Another NASA space telescope is out of commission, at least for the time being.

The Chandra X-ray Observatory, which has been observing the universe in high-energy light since 1999, entered a protective "safe mode" on Wednesday (Oct. 10), NASA officials announced.

"All systems functioned as expected and the scientific instruments are safe," agency officials wrote in an update yesterday (Oct. 12). "The cause of the safe mode transition (possibly involving a gyroscope) is under investigation, and we will post more information when it becomes available." [Our X-Ray Universe: Amazing Photos by NASA's Chandra X-Ray Observatory]

Gyroscopes help spacecraft maintain proper orientation. If a faulty gyroscope is to blame for Chandra's current plight, the observatory would be in good company: A gyroscope failure knocked NASA's iconic Hubble Space Telescope into safe mode last week.

Chandra and Hubble aren't the only famous NASA spacecraft dealing with some issues. The planet-hunting Kepler space telescope, which has found about 70 percent of all known alien worlds to date, is almost out of fuel. Kepler's handlers have shut down the spacecraft multiple times over the past few months, in an attempt to ensure that Kepler has enough propellant to point itself back toward Earth and beam home data.

NASA's Dawn spacecraft, which has been orbiting the dwarf planet Ceres since March 2015, is also nearly out of fuel; it could run out as early as this month, mission team members have said. The pioneering probe circled the protoplanet Vesta before its arrival at Ceres. It's the only spacecraft ever to orbit two bodies beyond the Earth-moon system.

Then there are the agency's Mars rovers. Opportunity has been silent since June 10, when a growing dust storm blocked out so much sunlight that the solar-powered rover couldn't recharge its batteries. And the Curiosity rover's memory issues recently spurred mission team members to swap that robot over to its backup computer.

This list of ailments is not an indictment; all of the above spacecraft have outperformed their original requirements and are now well into extended missions. And it's not an obituary, either; some may bounce back (though it's hard to recover from an empty gas tank).

For example, Hubble still has two functioning gyroscopes and can operate even in one-gyro mode. Curiosity could roll with its backup brain if needed. Martian winds may blow dust off Opportunity's solar panels, finally allowing the rover to recharge its batteries. And NASA officials seem bullish about Chandra.

Chandra "is expected to continue carrying out forefront science for many years to come," the officials wrote in the statement.

Mike Wall's book about the search for alien life, "Out There," will be published on Nov. 13 by Grand Central Publishing. Follow him on Twitter @michaeldwall. Follow us @Spacedotcom or Facebook. Originally published on Space.com.