Touring SDL in Utah today, I learned a bit about the WISE satellite and scouted for infrared sensor developments that might be helpful for B612’s efforts to map all of the asteroids near Earth (imagine dark objects that can only be detected from their thermal signature).
The WISE camera sensor is quite esoteric. Instead of silicon, they use mercury-cad-tel, and to minimize noise, they have to keep it extremely cold (12 Kelvin). So for WISE, they prepared a block of solid hydrogen (not liquid, like the rocket fuel, but solid). They wait until the last minute, with the rocket erect at the pad, and then insert the hydrogen block. They flow liquid helium around it to keep it cool during the countdown, and off it goes. A launch delay in this case is very expensive.
The hydrogen only lasts about 10 months, but they had another pair of Arsenic-doped Silicon sensors that could operate over a wider temperature range (32K initially, and then 70K once the hydrogen sublimated away). So the telescope had two mission phases.
The SDL entry is festooned with amazing images from the WISE telescope, and my speaker gift is a photo book of these beauties. My favorite is the multispectral triptych of Andromeda, showing the colossal rupture from a smaller galaxy puncturing space time like a freeze frame of a bullet through butter.
Andromeda is on a collision course with our own Milky Way, but that’s not for another 4.5 billion years, so we’re good. =)
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