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NASA WISE Telescope Starts Taking Pics
coondoggie writes "NASA said its Wide-field Infrared Survey Explorer spacecraft successfully popped the cover off its infrared telescope and began 'celestial treasure hunt' mission of sending back what will be millions of images of space. The WISE lens cap served as a safety system keeping the ultra-sensitive lens and telescope system safe until the spacecraft positioned itself correctly in orbit. The cap also served as the top to a 'bottle' that chille the instrument and detectors. This cryostat is a Thermos-like tank of solid hydrogen."
I understand that WISE is particularly well suited for finding asteroids (its an infra-red telescope so can pick up warm objects and its a survey scope). If this telescope finds an asteroid with our name on it with enough time to do something about it, it will make all the money spent on the space program by all the countries of the world seem like spare change.
(I wonder if this is first post. If so, it'll be my first.).
Yes, they do need the hydrogen to keep things chilly. The vacuum is a nice insulator, but can't prevent all the heat from all that sunshine hitting the satellite (and other sources) heating things up- including those very, very sensitive detectors. Noise from heat is the enemy, which is why they've gone through so much trouble to keep the detectors cold and safe in a covered 'Thermos' until ready to serve.
The hydrogen is a nice heat sink in addition to the natural vacuum flask provided by Space, and is allowed to slowly boil off, carrying away what heat that makes it through. It's also why there's a definite time limit on the main part of the mission and effective lifetime; once they hydrogen is gone, the detectors begin to heat up, heat noise ruining all that lovely sensitivity.
I suspect that they'll continue to get some results after the liquid hydrogen is gone but, much like similar previous missions, the "warm" part of the mission will not achieve anywhere near the same results as the first "cold" portion.
Space, being a vacuum, does not dissipate heat all that well.
The operating temperatures will be 30–34K for the 3.3 & 4.7 m detectors, 7.8 ± 0.5K for the 12 & 23m detectors and 17K for the optical system, which are achieved using a two stage solid hydrogen cryostat providing a minimum mission lifetime of 7 months allowing for a single full coverage of the entire sky.
Update on The Wide-Field Infrared Survey Explorer (WISE).
and surely the hydrogen will now boil off?
Exactly what they want. As the hydrogen melts and boils off, it removes heat which keeps noise down and image quality up. When the hydrogen finally boils off, it'll greatly reduce the value of the telescope since the internal components will heat up. That's probably when they'll end the mission.