Hubble Servicing Mission is Go!
Published on Oct 31, 2006 at 12:12 pm.
No Comments.
Filed under NASA, space telescopes.
A little earlier today, NASA Administrator Michael Griffin made the long awaited and hoped for announcement that one more servicing mission will be sent to the Hubble Space Telescope (HST). After the Columbia accident, plans for another servicing mission were dropped. Missions to the International Space Station have the option of hanging around there until help arrives if the shuttle is seriously damaged in liftoff. That is not an option for missions to HST, though. NASA administrators, fearing the devasting loss of another shuttle, which would end the entire program, decided to let HST die. The astronauts, however, were willing to take the risk, and there was a huge outcry from the scientific community and the public to save the Hubble telescope. So, after careful study, weighting the costs, benefits, risks, and so forth, NASA has decided that it is worth it to send another Space Shuttle Mission to HST. The mission is planned for about two years from now. The way that it stands, this mission will occur about the time that one of the two launch pads at Launch Complex 39 (Kennedy Space Center) is taken out of service to be modified for the new Ares rockets. The Vehicle Assembly Building is large enough to support operations needed to prepare two shuttles for launch. NASA may choose to delay slightly the modifications necessary to pad 39B until after the HST servicing mission. That would permit a backup shuttle could be ready to launch on a rescue mission if needed. It is technically possible to launch two shuttles from the same launch pad in just a couple weeks time, but that is difficult, and it would be more prudent to have the other pad available.
The mission to the HST is not simply a repair mission, as it is often portrayed in the media. Rather, HST was designed from the very beginning with the idea of regular servicing missions. Parts do wear out, and the gyroscopes needed to stabalize the spacecraft are in serious need of replacement. But there were other servicing requirements that were part of the design. In addition to repair, the Shuttle is needed to boost HST into a higher orbit. Earth’s atmosphere does not have a sharp edge. Though HST, the ISS, and the Space Shuttle are considerred to be in “outer space” when they are in orbit around Earth, the fact of the matter is that they are really in the uppermost parts of the Earth’s atmosphere: the thermosphere. This layer of the atmosphere is so thin that the pressure is more of a vacuum than the best vacuum pump on Earth can possibly achieve. But, still there is something there. The relentless bumping into atoms and molecules has a tiny effect of slowing the spacecraft, causing them to drop to lower and lower orbits. The lower the orbits, the more they bump into things, and the faster the process happens, until finally they fall too low and cascade down, breaking up and burning up on reentry. This is the ultimate fate of all Low Earth Orbit (LEO) satellites. So, the ISS needs occasional boosting to higher orbit. So does HST. However, the exhaust from jets need to do the job can damage the optics of the telescope, not to mention the dangers inherent in storing propellant onboard. So, HST has no mechanism to adjust its own orbit. It relies on the Shuttle for that. Furthermore, it was known when the telescope was built that technology would keep changing to produce more powerful and capable computers, detectors, and instruments. So, all the scientific instruments and computers are in modular compartments that can be slid out and replaced with compartments containing the new equipment. This is part of the plan — to upgrade the telescope with every servicing mission. With all this going on with each servicing mission, the plan was to have such a mission every three years. But, with the servicing missions on hold after Columbia loss, there have been no missions to HST since the year 2000. The telescope is in dire need of servicing right now. and it will be in even more desparate need when the mission finally happens (if it really does happen).
Most of the instruments to be installed on the next mission have already been built, planned for a mission a couple of years ago that never flew. The new instruments include a new spectrograph (the Cosmic Origins Spectrograph, COS), and a new wide field camera (Wide Field Camera 3, WFC3).
So, astronomers everywhere are letting out a sigh of relief over this announcement. It looks like NASA will save HST. If everything gets done that is planned for the mission, and if nothing bad happens to the telescope in the following years, then this mission may well extend the life of HST long enough to last until the James Webb Space Telescope is launched, NASA’s planned replacement of the Hubble Space Telescope.
-Astroprof
(Images courtesy of NASA)
