NASA To Cryogenically Freeze Satellite Mirrors 47
coondoggie writes "NASA said it will soon move some of the larger (46 lb) mirror segments of its future James Webb Space Telescope into a cryogenic test facility that will freeze the mirrors to -414 degrees Fahrenheit (~25 K). Specifically, NASA will freeze six of the 18 Webb telescope mirror segments at the X-ray and Cryogenic Facility, or XRCF, at NASA's Marshall Space Flight Center in Huntsville, Alabama, in a test to ensure the critical mirrors can withstand the extreme space environments. All 18 segments will eventually be tested at the site. The test chamber takes approximately five days to cool a mirror segment to cryogenic temperatures."
Re:It seems off... (Score:4, Informative)
It says ~25K not -25k. The tilde (~) usually means approximately [wikipedia.org] in written English.
Re:Cryo! (Score:5, Informative)
May want to look into it more then. Freezing to death is one of the more pleasant ways to go. It does suck for a bit as you start getting too cold, but then after a while you start to feel warm again. At this point you start to feel rather detached and dreamy. Most people that have been brought back from cold water drownings or hypothermia report the same things. Having nearly frozen to death on a hike I can confirm just how pleasant it was, up to the point that it finally sank into my head I was freezing to death and managed to get to warmth. Now, I'm not recommending it to folks, even if I do know a few that would benefit from it... But, as far as death goes, it is one of the more comfortable ones.
Re:It seems off... (Score:5, Informative)
Well, at the time they came up with 0-k, they thought so as well, as that is the point that atomic motion stopped. Then they went and discovered that while atomic motion stopped at that temp, sub atomic motion did not. They went on further to discover that they could 'cool' things further and reduce/stop some of the sub-atomic motion. I think they have given up on a true absolute-zero at this point, and simply use it as an arbitrary point where one is needed.
This is really wrong. Temperature has a precise mathematical definition (relation between system energy and entropy), which is universal. Applied to most systems, this yields the concept of temperature familiar from everyday life. Indeed, some systems are such that they can be manipulated to a state of `negative temperature', in the formal mathematical sense. However it is definitely not the case that the concept of absolute zero is tied to the motion of atoms in particular, or that it is merely 'a reference point' that has later been surpassed.
(I kinda hope you're just trolling, otherwise please just STFU when you don't know WTF you're talking about. )
Getting it right (Score:3, Informative)
Unfortunately the article gets the technical aspects wrong.
NASA is not "freezing" the mirror segments to make sure they "survive" space.
The JWST will operate at a cryogenic temperature in space. The mirrors are measured at cryovac to guide the manufacturing process so they will have the correct optical prescription at the telescope's operational temperature.
Similarly, we're testing support optics, for the pre-launch JWST testing, at cryo. We'll have the first of a one set down to temp in short order.