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Successful Launch of ESA's Herschel and Planck
rgarbacz writes "Today at 13:12 GMT, the ESA launched successfully new and long-awaiting spacecraft: Herschel, the infrared telescope with a 3.5m mirror, and Planck, the CMB mapper. The spacecraft were carried by the Ariane-5, which lifted off from Kourou in French Guiana. They will stay in L2 to perform the research. This launch is one of the most expensive and important missions of the European Space Agency. Planck will measure the CMB with an accuracy more than 10 times better than the previous mission, WMAP. Because of this high sensitivity, both spacecraft are cooled to temperatures close to absolute zero by on-board liquid helium; staying in L2 is very helpful to maintain this state. Both spacecraft are designed to observe the Universe at its infancy: Herschel by observing the first stars and galaxies (whichever came first), and Planck by scrutinizing the first photons that were set free, making up the cosmic microwave background radiation."
The correct term would be inaccuracy. Calling it accuracy is misleading, but very common.
What is "L2"?
Plural of "spacecraft" is "spacecraft".
English, do you speak it?
Herschel is supposed to complete its mission in three years, Planck in only 15 months. After the helium supplies have evaporated, their missions end. They won't be repaired / serviced, because they are too far away to be easily reached with a shuttle. That's what local news here say.
I hope I didn't brain my damage.
It seems like the summary writer didn't understand TFA. Quoting from ESA:
The older measurements that Planck is trying to improve already are accurate to 0.1%.
It seems like someone got confused with the coincidence that the temperature of the universe, 2.7 K, is about 1% of the temperature of freezing water, 270 K.
During the launch commentary they mentioned that the scopes are launched with a 3 year supply of helium. I'm pretty sure repair missions to L2 would be pretty impractical.
Well, that's because the space is too hot.
Even without the sun.
They are trying to measure the CMB. If you are not colder than outer space, most of the radiation would just come from the telescope itself...
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
"In order to study the coolest places in the Universe the Herschel instruments must be cooled to just above absolute zero. A large cryostat surrounds the instruments maintaining an operational temperature of 1.7 K for a nominal mission lifetime of 4 years." ESA has some great info on their site.
I hope I didn't brain my damage.
Because what they're trying to measure is, in some senses, the temperature of space itself - the ~3K CMB. So they need the detector to be colder than that.
Isn't there some way to use one or more of the three forms of heat transfer to keep the instruments cold enough to work without having to rely on a limited source of helium?
No. The radiative coolers (can't really use conduction or convection in space) will keep the craft cold enough for the low frequency instrument to work, even after the helium* runs out, but to get the 0.1K that the high frequency instrument needs, there's no (good) alternative to this active cooler.
* Well, not after the helium in its own refrigerators runs out. But it's not actively venting that, so we only have leakage to worry about there.
I am trolling
I realize we, as in all space agencies, use helium or something else to keep these instruments cold, but why can't we use the coldness of space to do the same thing?
Space isn't really "cold", or rather, the terms "cold" and "hot" lose much of their meaning when you're talking about incredibly low densities like you have in space.
If you have an atmosphere then you transfer heat by radiation and conduction. You can cool your instruments by putting them in the shade (so they don't get the radiated energy from the sun) and ensuring the atmosphere is cool so that it will conduct the heat away. The atmosphere on Earth is actually not a great conductor, but because it is a fluid you can keep the air moving so that as soon as some of the heat has been conducted to the surrounding air you move that (warmer) aid out of the way and replace it with cool air - this can be done naturally by convection or by forcing the air to move with a fan.
In space you have practically no atmosphere, so the heat transfer is almost entirely by radiation - your instruments are essentially in a giant vacuum flask. Your satellite needs to reflect away the energy radiated by the sun, and the cosmic microwave background radiation, etc. and also radiate away its own heat (remember, these satellites contain lots of electronics and like all electronics they will generate heat). This is a pretty tall order - surfaces that radiate well are also really good at absorbing energy. - I imagine it's much cheaper and lighter to send up a load of liquid helium and dissipate the heat by letting it boil away.
http://blog.nexusuk.org
I realize we, as in all space agencies, use helium or something else to keep these instruments cold, but why can't we use the coldness of space to do the same thing?
According to this PDF the Planck mission does not use liquid helium coolant (although Herschel does). Also the upcoming James Webb telescope will not use it.
Space radiates. If we were to put a black body in space at absolute zero, after a while it would be about 2.7 Kelvin. This is because of the cosmic microwave background (which is what they're trying to measure here).
If you have a distractor (radiation from the craft itself) as big as the thing you're trying to measure, you won't get good results.
The NASA/GSFC Solar Dynamics Observatory (SDO) also uses RTEMS on some of its support processors. The main processor on SDO runs the closed source VX/Works OS.