For my entire professional astronomer life, Hubble has been there as a beloved icon of what scientists can accomplish technically and scientifically when they are given the opportunity to dream. The images most of us think of when we pull up a mental image of the universe came from Hubble: The Whirlpool, The Pillars of Creation, and even Jupiter during Shoemaker-Levy 9.
Today NASA is telling us how the plan to keep Hubble imaging into the next several years and keep this amazing telescope creating iconic images until James Webb is ready to replace her. After Servicing mission 4, scheduled for roughly August 2008 (I suspect we’ll see delays), Hubble will have 90 times its original sensitivity.
While capable of unparalleled imaging, Hubble has always been a troubled little telescope with great potential. Hubble was â€šÃ„Ãºbornâ€šÃ„Ã¹ in April of 1990, with a stigma that was corrected with the first Hubble Servicing Mission in 1993. It has suffered from gyroscope failures, making steering hard, and its instrument NICMOS ran out of coolant that was replaced on servicing mission 3. It seems that every talk Iâ€šÃ„Ã´ve ever heard about about the Hubble Space Telescope involved a discussion of â€šÃ„ÃºHubble will be so much better after the next servicing mission.â€šÃ„Ã¹ That is true today, as NASA and the astronomical community holds its breath waiting for the forth-servicing mission.
Today, Hubble is surviving on one gyroscope, old batteries, and instruments that need tune-ups. Technology has also been improved, and we can the ability to do things with digital detectors today that werenâ€šÃ„Ã´t imagined in 1990.
Space Shuttle willing (or at least Space Shuttle safety board willing), the Hubbleâ€šÃ„Ã´s forth servicing mission is scheduled for 2009. With this mission, Hubble will get all new gyroscopes, new batteries, a new wide field camera, he Advanced Camera (ACS), STIS and COS will all get redone, and the Fine Guidance System will be re-tuned as well. These new cameras will allow Hubble to see fainter objects, obtain better spectra (that can do things like discover black holes in the cores of distant galaxies), and can better measure the cosmic web of structure: light, dark, and gravitationally shaping our future.
This is going to be one of the most experienced shuttle crews to date, and they are doing what astronauts do best – construction, repair, re-engineering and doing things that no robot can do. Specifically, they’ll be climbing around (and inside!) Hubble like creative ants, pulling out tiny screws that a little robot can’t grab and remove.
And they’ll be risking their lives – there are sharp edges, ways to get snagged, ways to get caught, and a lot of risk involved in making repairs that Hubble really wasn’t designed to have done while it is in space!
This raises the question: Why keep Hubble and not just build and launch another? Because Hubble really can’t be replaced.
Problem 1) Congress really wouldn’t go for it. The astronomical community has successfully sold congress on a suite of great observatories: Hubble, Chandra, GLAST, Spitzer and now James Webb. Another optical telescope was not part of that sell. We have Hubble, and we promised we’d give it up if they would only (please, please, please) give us James Webb. That was the deal. Money is scarce. If we want to move on to the new questions, we have to eventually move away from Hubble. It will get one more tuneup, and after that, when it dies, it dies.
Problem 2) Committees. If we tried to build another Hubble I’m sure people would demand the design get upgraded. It would take FOREVER (okay, maybe not that long) to get it from concept to flight. Today, Hubble is living on 1 gyroscope. When that goes, she can’t be steered any more. We don’t have time to wait while a committee agrees on what a new Hubble needs to look like and gets around to getting to building it.
There are more problems. But these are the big 2. We made a promise, and we’re running out of time.
Now, this doesn’t answer the question of why shouldn’t we give up on Hubble and focus on the Very Large Telescope and other earth-based behemoths. Again, there are basically two reasons. 1) The wavelengths available only from space, and 2) With the adaptive optics that large telescopes use to correct for atmospheric effects you lose track of exactly where each photon came from. You can rearrange the light to look right based on stars, but it’s an imperfect system and if you really want to know where a given photon started, you just can’t get there. So we need Hubble.
We need our beloved little space telescope that can, and these men and women are going to make this little space telescope work into the future. It’s close date is nominally set by bureaucrats and budget writers, but I suspect we will keep observing until Hubble is no longer safe to fly (may it’s gyroscopes last for a long long time . . .)