Hope for Hubble

Space.com reminds me of an upcoming event that, to me as an astronomer, holds a great deal of excitement and tension. On October 10, 2008, Space Shuttle Atlantis will lift off on a mission to the Hubble Space Telescope, there to perform a series of repairs and upgrades that will, we hope, keep it operating for years to come (a minimum of five more years is the goal), and even improve on its capabilities.

Follow up:

Why is Hubble so important? The main mirror of this telescope is a mere 2.4 meters, modest by modern standards. However, because Hubble orbits above most of our atmosphere, it does not have the atmospheric smearing and distortion that astronomers call seeing. From the ground, optical telescopes can make out details a little less than half an arcsecond apart, on a very good night. A technique called adaptive optics can improve on this, but has yet to reach the full capability and flexibility of Hubble. Hubble's suite of instruments are designed to take advantage of this clarity in various ways. Thus, when you want do discern fine details at great distances, Hubble is one of the key tools to which astronomers turn. Indeed, competition for use of the telescope is fierce - maybe one in six, or even one in nine (depending on the year) proposed programs actually goes through.

Hubble has been in orbit since 1990, and I think it isn't much of an exaggeration to say that in many ways it has revolutionized astronomy. I am one of many, many astronomers who have found Hubble an invaluable tool for research. I study supernova remnants (exploded stars) in the Magellanic Clouds, a pair of mini-galaxies that orbit our own Milky Way Galaxy. That means I'm looking for details in objects that are over 150,000 light-years away! Not only are these images incredibly informative, though, they can also be amazingly beautiful. I'm pleased that two objects from my program were chosen as Hubble Heritage images - the supernova remnants with unromantic names N63A and N49.

The upcoming mission (Service Mission 4) will:

• replace the gyroscopes used to keep the telescope precisely pointed at target objects, the refurbished Fine Guidance Sensor which helps control this process, as well as necessary features like batteries and thermal insulating blankets;
• repair two instruments, the Space Telescope Imaging Spectrometer (STIS) and Advance Camera for Surveys (ACS), which failed in 2004 and 2007, respectively;
• install two new instruments, the Wide Field Camera 3 (WFC3), and the Cosmic Origins Spectrograph (COS); and
• add the Soft Capture and Rendezvous System, a docking port so that, when Hubble is no longer operational, a spacecraft can attach to it and bring it out of orbit safely.

This is the fifth time Hubble has been repaired and upgraded, and it will, alas, be the last, due to the retirement of the Space Shuttle fleet. This one almost didn't happen at all. Service Mission 3B took place in 2002, but in 2003 the tragic loss of the Columbia shuttle led to a re-evaluation of Space Shuttle missions. In 2004, it was declared that there would not be another service mission to Hubble - it was simply too risky. What followed was a practically unprecedented outcry from astronomers, and from the general public. I was at an American Astronomical Society meeting where poor Michael Griffin, the new NASA chief at the time, was bombarded with questions and demands from the astronomical community regarding Hubble. In 2006, it was decided that the continuation of the Hubble mission would go ahead with Service Mission 4. It can't have been an easy decision - besides the risk factor, it also meant that money had to be diverted from other projects to sustain this one spacecraft.

You can see that "hope" in the title of this article has two meanings here. On the one hand, this mission has such great promise - a renewal of Hubble, perhaps even a better and more powerful Hubble than before. Thanks to advances in technology, for instance, the new Wide Field Camera (WFC3) will have many times the sensitivity of previous versions, and we may be able to get back the Advanced Camera for Surveys, which can cover larger swaths of sky. We've missed the opportunity to get spectra from STIS - now we not only have the chance to get STIS back, but to add the much more sensitive Cosmic Origins Spectrometer as well. The replaced structural parts could keep Hubble going well into the future.

On the other hand... we are always mindful of the risks involved, to the shuttle crew in particular. One is that Hubble's high orbit exposes it to a lot of orbiting space junk, although the chances of a major hit are still low (Hubble's still up there, after all). Then too, for the first time NASAS plans to have another shuttle on standby, in case a rescue mission is needed.

Then too, keep in mind that this is the most ambitious Hubble mission yet planned. It will last 11 days and include 5 spacewalks. It will mean astronauts working in space to repair instruments while they remain on the telescope - which those instruments were never designed for! Even if the mission is successful, they may not make it through the entire to-do list, given the challenging conditions. We here on the ground will be extremely grateful for as many improvements as the astronauts can manage.

Here's hoping!