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Old 04-23-2008, 08:49 PM   #1
Notebook
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Default Herschel spacecraft assembly complete.

http://www.esa.int/esaCP/SEM0Z0QJCFF_index_0.html

Quote:

Primary mirror:
3.5 m in diameter.

Launch:
Herschel will be launched in 2008 together with another
ESA scientific mission, Planck. Both satellites will separate shortly
after launch to operate independently.

Orbit:
Herschel will orbit a the L2 virtual point in the Sun-Earth
system, located 1.5 million km from Earth.

Instruments:
HIFI (Heterodyne Instrument for the Far Infrared), a
high-resolution spectrograph; PACS (Photoconductor Array Camera
and Spectrometer); and SPIRE (Spectral and Photometric Imaging
REceiver). These instruments cover the 60–670 micron waveband. They
will be cooled to temperatures very close to absolute zero.

Launch mass:
about 3 t.

Dimensions:
about 7.5 m high and 4.5 m wide.

Operations:
Herschel will be operated as an observatory. About two-thirds of its observing time will be available to the world’s scientifi c community. The rest is guaranteed time mainly belonging to the instrument consortia.

Primary ground station:
New Norcia, Australia.

Operational Lifetime: a minimum of 3 years for routine science observations.
N.
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Old 04-23-2008, 09:03 PM   #2
Whatu
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Has any previous mission been to a Lagrange point and stayed there?

What are the advantages of having a satellite in a Lagrange point?
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Old 04-23-2008, 09:40 PM   #3
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Good questions Whatu!

I don't think there have been any missiions to the Earth-Sun L2 yet, looks like it is going to get crowded though:-

Quote:
L2 will become home to ESA missions such as Herschel, Planck, Eddington, Gaia, the James Webb Space Telescope
Maybe the ISS will end up there as a first-line maintenance base...

More info about L2 here:-

http://www.esa.int/esaSC/SEMO4QS1VED_index_0.html

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Old 04-23-2008, 10:36 PM   #4
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If I have understood the article correctly, one of the main advantages is that the satellite is not orbiting earth, and not going through a cycle of heating/cooling, and this makes observations more stable.
This could be a good place to put the hubble telescope .
Also this point is always at 1.5 million kilometers behind the earth, in the imaginary sun-earth line. So the satellite put in there will never see the sun, and would be.. kind of... in an orbit with a radius: "earth radius + 1.5 M km".

I guess that if there are already plans for missions to that point, the benefits from it are greater than the difficulty to bring (and make it stay) it to the point.

I just re-read the article and it seems that theyre gonna put the "James Webb" telescope there.

But another question arises.. As there is only one L2 point, how do they think they are going to put various missions in there? just guess they wont be in the same time-frame.
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Old 04-23-2008, 10:55 PM   #5
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Yea but how small is Earth at this distance? I've tried looking for a distance vs. size calculator, but you have to know too much about the actual conditions there to figure it out.
I'm thinking that this thing won't be in Earth's shadow as the Sun is just too big.
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Old 04-23-2008, 10:57 PM   #6
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Quote:
Originally Posted by Zatnikitelman View Post
 Yea but how small is Earth at this distance? I've tried looking for a distance vs. size calculator, but you have to know too much about the actual conditions there to figure it out.
I'm thinking that this thing won't be in Earth's shadow as the Sun is just too big.
Yea I think you are right... kinda forgot how big the sun was >.<
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Old 04-24-2008, 03:20 AM   #7
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If the orbital radius is more than about 4 times the Moon's orbital radius, then the Sun will not be completely eclipsed (since the Earth is almost 4 times the Moon's size).
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Old 04-26-2008, 07:30 AM   #8
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Technically these satellites are not exactly at the Lagrangian point, but they are in a quasi-periodic orbit around the Lagrangian point, since an object sitting exactly at the Langrangian point won't be stable for very long.
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