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Herschel Space Telescope Opens For the First Time
davecl writes "The Herschel space telescope, the largest ever launched into space, has opened its instrument cover, allowing its three instruments to observe for the first time. BBC news has the main coverage, while there is more coverage on the SPIRE instrument team website, and on the mission blog. I'm part of the SPIRE instrument team and the excitement as we move towards our first observations is building fast. The PACS and SPIRE instruments will see first light in the next few days."
In an effort to contribute something to the thread that isn't irrelevant, stupid, or hateful assholery, this is very cool. I'm looking forward to its first images. Maybe it'll be sensitive enough to image extrasolar planets.
"I disapprove of what you say, but I will defend to the death your right to say it." - Evelyn Beatrice Hall, re Voltaire
The entry should clarify that it is the largest infrared telescope ever launched. Actually, the adjective large should not be used. Space is not porn. To most people.
It would also be very helpful for the public to know how will Herschel and Hubble complement each-other. Otherwise, the general public may believe that humanity has launched two different things to accomplish the same task.
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I wonder if they designed any of it to be repaired in space, learning from Hubble. (It's not a direct competitor to Hubble because it "sees" in longer wavelengths.)
I wonder if it would have been cheaper to build *multiple* Hubbles rather than repair them in space, which costs about a half-billion per mission. However, they'd have to decide that path in advanced to take advantage of bulk assembly procedures. Or build them to be remotely serviceable thru a repair-bot? But that's mostly untried technology, which usually means expensive or unpredictable overrun risk.
Table-ized A.I.
Infrared can pass through dust, such as that which composes nebulae, that would block other wavelengths.
"I disapprove of what you say, but I will defend to the death your right to say it." - Evelyn Beatrice Hall, re Voltaire
There are several good reasons to concentrate on infrared radiation. A few, off the top of my head, are: the relative transparency of the interstellar medium in the infrared compared to optical and UV; the optical design of infrared telescopes is closer to that of the familiar optical types compared to X-ray and gamma-ray telescopes; the presence of strong emission lines in the infrared from ionization species unavailable in the optical; the fact that UV and optical emission from distant objects is seen in the infrared due to their high redshifts; and that the thermal emission of circumstellar dust peaks in the infrared. Similar lists exist for the other bandpasses, but screw them :)
Good reasons for placing infrared telescopes into space include the high opacity of the Earth's atmosphere in the infrared, the high thermal emissivity of the Earth and atmosphere in the infrared, and the low temperatures at which the detectors need to be kept.
"I guess the moral of the story is, don't paint your airship with rocket fuel." -- Addison Bain
There is no one "right" spectrum frequency. They each offer different information; different clues. For example, an animal that can see 3 colors has more potential information than an animal that can only see 1 or 2.
And while Hubble and Herschel may be able to overlap somewhat, they are specialized (optimized) for different frequencies. It's difficult to make a single scope that can see every frequency well, so they send up different scopes for different spectrum ranges. Different materials make for better reflectors, conduits, and sensors for different frequencies. That's just life on the Spectrum Highway.
Think how AM radios need a long wire (coiled in practice) for an antenna. FM radios and traditional TV need about a meter-long antenna(s), and cell-phones have about a 3-inch antenna. No single antenna works best for all. Same with light-based scopes.
Table-ized A.I.
The atmosphere is a lovely IR absorber. So, if you're gonna launch a telescope into space, why not look at a band of frequencies you can't see thru the atmosphere? Whatever you see, it'll be something you can't see from the ground (more or less).
So that works pretty well, if the criteria is to see whats never been seen before, discover new things, etc.
http://en.wikipedia.org/wiki/Infrared_astronomy
"Science flies us to the moon. Religion flies us into buildings." - Victor Stenger
Hubble and Herschel's orbits are not even comparable to each other.
As pointed out earlier in a separated thread, Hubble is in a low, circular orbit about 560 km above the Earth. It has has a low inclination -- about 28 degrees with respect to the equator. You can actually see the orbital details and where it is in the sky on Heavens Above. The low Earth orbit was chosen so that the space shuttles could service it as they can't reach very far orbits basically due to limitation i how much fuel they can carry (bear in mind that at launch the shuttle engines are powered by the huge orange tank attached to it). It would have to be double checked but I think that the low orbital inclination was decided because it's was easier to launch -- Hubble is one of the most massive payloads ever carried by a space shuttle -- since you benefit from the fact that the Earth rotates so it effectively adds up to your velocity whereas for a polar orbit the contribution is basically null.
On the other hand, Herschel is orbiting 1.5 million km away from the Earth at the L2 point, in a direction opposite to the Sun -- the Sun - Earth - Herschel system forms a straight line. To give you an idea of the scale, the Earth-Moon distance is about 385 000 km so Herschel is located 3.9 times further. Therefore it's easy to understand why the mission is a one-hit wonder because there is no way someone is gonna go there fix it. To be more precise, Herschel is actually "orbiting" about the L2 point (see this diagram on Wikipedia) otherwise its orbit around the Sun-Earth-Moon system would be too unstable. The main reason for sending Herschel so far away from Earth is to optimize its infrared performances. Herschel observe at very long infrared wavelengths compared to, say, the the infrared camera of Hubble and near the Earth, even though you are in space, there is still a lot of thermal radiation coming from the Earth as well as the radiation belts that add up on top of what you want to detect. By being further away, passive cooling helps you and the liquid helium that keeps you cryostat cold heats up slower so your instrument has a longer life time. Also, "temperature" fluctuations are much smaller out there whereas they can be quite large near the Earth depending if your in the Earth shadow, crossing a radiation belt, etc. More stable environment means smaller systematics, which, in turns, imply better telescope sensitivity.
Finally, note that Hubble's successor, JWST will also hang out around L2 for similar reasons.
NASA uses a variety of explosive bolts.
Manganese/barium chromate/lead chromate: time delay mix, used for sequencing. Gasless burning.
Zirconium/potassium perchlorate: NASA standard initiator (NSI). Rapid pressure rise, little gas but emits hot particles, thermally stable, vacuum stable, long shelf life. Sensitive to static electricity.