Thursday, October 8, 2009

Telescopes in Space

At first the idea of a telescope floating around in space is absurd, but any marginally knowledgeable astronomer can profess that it's a fantastic idea. Astronomy at the most fundamental level is the study of space, everything and anything that's not Earth, and it's one of the oldest realms of intrigue known to humankind; it was popular long before the scientific method wandered onto the scene, despite being very much a scientific pursuit. On one hand, that space is an old interest isn't surprising--anyone that has turned their sight to the sky on a clear, dark night knows exactly why. A gaze into what might as well be the infinite unknown, the act itself as simple as a glance at our own hands, has a way of inspiring speechless profundity in even the most uninterested amongst us. On the other hand our primal fascination with space is surprising for its distance, simply far removed from our experience and altogether relatively bland to the naked eye for its expansive empty darkness excepting the occasional tiny point of light. I find it interesting that this practical void drew fascination more readily than the exceptionally vibrant and astonishing diversity of phenomenon on Earth which we can easily approach and examine. I suppose it's another case of obscene acclimation leading to an almost humorous misplacement of gratitude (or the frog in slowly heated water, though I'm not a fan of the literal part of the notion when put that way). Nonetheless, space is a fascinating place, especially when explored with our modern technologically augmented senses, the subject of this post.

As it turns out, Earth is a lousy place from which to explore everything that's not Earth. The telescope, primary instrument of astronomers, is often incapacitated by the humble cloud, and it is increasingly difficult to find a spot where light pollution (that light from the ground which obfuscates the much fainter light from billions of miles away) isn't a problem. But even on the highest, most remote mountain on the clearest night, a telescope on Earth is substantially limited by a variety of factors, and thus the idea for a telescope in space. Space telescopes were proposed by at least the 1920's; the first (Hubble) was funded in the '70s but took about twenty years to get into space, in 1990. Of course, 20 years from paper to space is ok by me, given that it's a hulking monstrosity, nearly 25,000 lbs of technical wizardry. It may have launched as early as 1986 if it weren't for the Challenger disaster, which put Hubble in cold storage but to the tune of $6 million a month, not your everyday storage unit. Nonetheless, the time investment seems to have paid off, as the Hubble is very near entering its 20th year of functionality.

Despite the near 20 years of development, shortly after launch the images Hubble was transmitting indicated a serious issue, with quality far less than expected to the extent that it performed similarly to ground telescopes. Before long it was discovered that the main mirror was shaped incorrectly. Telescopes depend almost wholly upon the precise shape of the main mirror, and the precision of the Hubble's is astounding--it was perhaps the most precisely manufactured mirror ever made, with a deviation from the intended curve never more than 10 nanometers. In other words, the shape was at most off by a length about 40 times shorter than the shortest wavelength of visible light (the color violet, at 400 nm). To give you some kind of perspective, nothing skinnier than about 400 nm can be seen with our eyes, no matter how powerful a microscope you can find: the problem is that for something under 400 nm, visible light can't hit it, which means it can't bounce back and into our eyes. So given a mirror so amazingly precise, how could it possibly have been so bad? Well, the mirror was very precisely manufactured to the wrong shape!

Here's a question: how do you fix a ~7ft diameter mirror that took 5 years to manufacture, stuck in the middle of a technological marvel which is hurtling through space at 17,000 mph?? There were two backup mirrors made, but replacement wasn't an option. Fortunately, the Hubble had a strength, a unique design choice: it was built so that it could be serviced by astronauts. After extensive analysis of the problem, a surprising solution was conceived--new sensor instruments, something like the chip in any digital camera, would be  specifically designed to be flawed in a way that would be the anti-flaw of the mirror, thus cancelling out the effects! It reminds me very much of doing the same thing to both sides of an equation in math; you can do whatever you want, as long as you do it to both sides (note that this isn't always true). This story is one that I find informative and inspiring, I hope you can find similar value in it. I also recommend taking a look at the Hubble Space Telescope page on wikipedia, as there's a lot more generally interesting stuff to know. Surprisingly, the Hubble is just one of around 100 space observatories past, present, and future. ~45 of them have been terminated, ~15 are planned for the future, and this year alone stands to see the launch of 8 new observatories!

1 comment:

Kim Griesemer said...

Well-written, Cole, as always. I never saw the Milky Way until we were on Bora Bora. I remember finally feeling there what Carl Sagan was famous for saying--there ARE billions and billions of stars. I'm so glad we got to share that time together.