14 DAY TRIAL // Astronauts John Grunsfeld and Andrew Feustel have just recently begun performing their fifth and final maintenance spacewalk on the Hubble Space Telescope, aiming to install new batteries and another insulating layer on the aging observatory. The batteries have never been changed since the instrument was first delivered into orbit in 1990, and today's is the second set to go in. They will be positioned just above the Wide Field Planetary Camera 3. The FGS-2 Fine Guidance Sensor will also be replaced, and mission controllers hope that, with it, they will be able to better designate new targets for the tool.
The new spacewalk began at 8:20 am EDT (1220 GMT) and will hopefully conclude faster than the fourth, which lasted for more than eight hours. If everything goes according to plan today, then the Hubble will later be completely repaired, all its instruments and sensors operational again, and its “skin” upgraded. The telescope was in surprisingly good condition when the astronauts got to it a few days ago, despite the fact that more than seven years had passed since the last service mission.
Still, pressure is high today for Grunsfeld and Feustel, because the two astronauts are the last people to get to the space telescope. Any of the objectives they miss on today during the spacewalk could result in the premature destruction of the observatory, if it leaves orbit, or if its instruments malfunction again on account of temperature glitches and other similar factors. With the Wide Field Planetary Camera 3 (WFPC3) installed and the STIS instrument repaired, the observatory can now continue to work for at least another five years, astronomers hope. All of its gyroscopes have been replaced as well, and, today, all the batteries will too.
The imaging spectrograph STIS is a very important and unique instrument on Hubble, because it can act like a camera as well – and that's one of the main reasons why astronauts did not abandon their last spacewalk before the task was completed. Its basic operating principle is fairly simple – it breaks down light into its composing wavelengths, it can thus detect supermassive black holes in the distant Universe, and can also analyze the atmosphere around distant exoplanets. During the repairs, the instrument initially powered on in a test, but soon broke down again, due to temperature variations.