For the second time in less than two weeks, NASA's Hubble Space Telescope is in safe mode after an external power supply failed. As a precaution, astronauts on the ISS will remain in space for 24 hours to come up with a system workaround.
According to NASA's statement, the problem with Hubble is that it does not actually have a backup source for its external power supplies. So while a satellite would have one alternative path to the space station, Hubble does not.
Because the ISS astronauts are still in space, they will install a new power supply that will keep Hubble in safe mode at least until Monday at 6:35 pm (10:35 a.m. GMT). Hubble will then go into shut down mode and the ISS astronauts will return to the space station.
If Hubble reverts to safe mode on the ground, the astronauts will bring back the ISS, put Hubble in a simple cryogenic safe mode, and restart it to see if anything else went wrong. So far, the power supply failure seems to have been caused by a sensor failure, which meant the outside power supply suddenly gave out, shorting out the antenna, and causing it to burn off.
Since its launch in 1990, Hubble has saved humans from space shuttle disasters twice, and has been instrumental in providing data about the universe for 26 years.