Nasa's Chandra space telescope has shut itself down, just days after a similar problem hit the Hubble space telescope.
The cause of the latest problem is unclear and investigations are continuing, the space agency said.
It has now entered a safe mode that aims to ensure it is kept protected and powered up until the mysterious problem is solved.
Chandra is an X-ray observatory, which collects emissions from the very hot parts of the universe. In the time that it has been scanning the sky from orbit, the sophisticated telescope has helped spot the beginnings and ends of black holes and galaxies, helping us understand the central processes of the universe.
The issues came just days after the Hubble space telescope, responsible for some of the most iconic space images ever taken, also put itself into safe mode. That happened because of problems with the on-board gyroscopes, which are used to ensure that it is pointing in the right direction.
Like its fellow space telescope, Chandra has managed to survive much longer than engineers had promised when it first launched. It has now been around for 19 years – despite being originally designed for just five – and Nasa said that it expects it to continue its work in the years to come.
"At approximately 9:55 a.m. EDT on Oct. 10, 2018, NASA’s 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," Nasa wrote in a statement.
"Analysis of available data indicates the transition to safe mode was normal behaviour for such an event. All systems functioned as expected and the scientific instruments are safe. The cause of the safe mode transition is under investigation, and we will post more information when it becomes available."
As well as Hubble and Chandra, the Kepler space telescope – which looks for distant planets by watching for them passing in front of stars – has also run into issues because of a lack of fuel. The various issues with Nasa's hardware are not thought to be related.
Astronomers joked that now would be the perfect time for strange events to happen in space. "Both Hubble and Chandra in extended safe modes," wrote the University of Alabama's William Keel on Twitter, saying that we should now anticipate "galactic supernova", an "alien fleet", "comet disruption/impact with one of giant planets" or a range of other phenomena.