Herschel Space Telescope Opens For the First Time 84
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."
it is not the "largest evel launched into space" (Score:5, Informative)
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.
Lid Release Video (Score:2, Informative)
While not completely obvious from the wording, the slow motion video [youtube.com] that most sites seem to be using of the lid opening is actually from a test on an identical cover after it had been sealed for 2 years and not from the actual telescope in space. On the actual telescope, opening was only initially confirmed via gyro sensors and temperature changes afterwards. It won't be fully confirmed until they do light tests.
Re:Repair? (Score:3, Informative)
It's not repairable. It'll orbit around L2 and is placed 1.5 millions km away from earth. We cannot currently send humans at that distance. As for repairbots, I don't know.
Re:it is not the "largest evel launched into space (Score:2, Informative)
I'm not sure who "we" is here, but note that it is mostly a European project, not a US one. It's good to see more international missions because it means more science and different ways of approaching designs and management. Russia's Keep-It-Simple and incremental improvement approach to manned-mission designs have been a fine lesson for NASA, for example. Hopefully NASA will learn new tricks from others' unmanned missions also, as they are learning from our stuff. Plus, more science.
Re:it is not the "largest evel launched into space (Score:5, Informative)
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.
Re:it is not the "largest evel launched into space (Score:5, Informative)
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.
Re:How far out is 1.5 million miles? (Score:5, Informative)
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 [heavens-above.com]. 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 [wikipedia.org] 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.
Re:it is not the "largest evel launched into space (Score:2, Informative)
It is actually the largest telescope every launched into space. It has a larger mirror than Hubble. It is also true that it is the largest infrared telescope launched into space, but then a square is also a rectangle.
Re:Repair? (Score:5, Informative)
The upside of it being in orbit around L2 is that it never has to face either the earth or the sun, so every second of every day is useful observation time. Hubble is in LEO which makes it accessible, but also shielded by the bulk of the planet almost half of every day for any given target. This is fine for scheduled observations, but not so good for staring at one point or homing in on something in progress. Also, some time is inevitably lost making sure it doesn't stare into something bright as it swings around the planet, which is not an issue at L2.
Even if it does not live as long as Hubble (and it probably won't if there is no servicing), it has the potential to produce more data per unit of time. Also, with the bigger reflector, exposures should not take as long, also freeing it up to do more science. This also has the nice side effect of reducing the effects of thermal noise and cosmic rays, since they just don't have as much time to do their damage to any given picture.
Mal-2
Re:Outgassing... (Score:4, Informative)
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.
Re:Repair? (Score:3, Informative)
It will live three to five years, so it will not outlive Hubble. After that it has run out of the coolant (helium).
By that time it has scanned the whole space a couple of times.