"Damon Hill" wrote in message
31...
Andrew Nowicki wrote in news:4216D559.B6CA6011
@nospam.com:


If JWST is launched into the L2 point, it will
sizzle in the sunlight almost as much as the
Hubble Space Telescope.

Which is why it has its own sunshade. Also, it's
away from Earth's thermal radiation, which is the real
reason for that orbit. What's the problem with this?


Absolutely right. It's thermal radiation from the Earth, not from the Sun,
that causes problems for infrared telescopes in low orbits, where the 300K
Earth fills nearly half the sky. The problem is general heating of the
spacecraft, which makes it use up helium coolant much faster. It is very
hard to reflect away this infrared radiation, which is mostly at wavelengths
of about 0.01mm. Most of the Sun's radiation is visible and near-IR light,
which is easily reflected by a sunshade.

If something goes wrong
with the JWST, the telescope will be difficult to
repair because the L2 point is far away from the
Earth. Worse yet, JWST has a monolithic design
not suitable for telerobotic repair or upgrade.
My conclusion: James Webb Space Telescope
should be redesigned to improve its thermal
insulation and compatibility with telerobots,
and then launched into low Earth orbit.

What telerobots?

You may have noticed they're not going to repair
Hubble, either. If JWST breaks, well, that's too
bad...and no upgrades.

We aren't going to have a Shuttle much longer and
it's not clear that CEV will be able to provide similar
support at even slightly lower mission cost.

--Damon

--
Mike Dworetsky

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