Limits to telescope size

Just seen some pictures of Hubble, and The "Very Large Telescope"
(original name) in Chile. It made me think.

With a reasonable space based industry, moon mining, metal working,
aluminium and glass production, precision engineering, how big an
optical telescope could be built in zero-g?

What are the limits? Could a 100m diameter optical telescope be built?
what would it see?

As for radio telescopes, what are the limits are baseline inferometry?
what would a few telescopes, each say 3km across, in solar orbit, say 1
billion km apart be able to achieve?

wrote:

Just seen some pictures of Hubble, and The "Very Large Telescope"
(original name) in Chile. It made me think.

With a reasonable space based industry, moon mining, metal working,
aluminium and glass production, precision engineering, how big an
optical telescope could be built in zero-g?

What are the limits? Could a 100m diameter optical telescope be built?
what would it see?

I don't see any reason in principle (as opposed to the actual
engineering) why you couldn't make a parabolic mirror of almost any
size.

Of course, where any planetary surface is involved, sooner or later
there will be deformity and sag issues. And a sufficently massive mirror
(with associated framework and/or tube up to the focal point) in free
fall would be difficult to steer and track. Espically if orbiting deep
in some gravity well, where there would be a tendency to line itself up
with the planet's center of mass.

But you'll likely have observed plenty of neat new stuff (including,
I would think, direct imaging of extrasolar planets) well before
reaching those limits...


As for radio telescopes, what are the limits are baseline inferometry?
what would a few telescopes, each say 3km across, in solar orbit, say 1
billion km apart be able to achieve?

Problems here are somewhat similar to those in optical, except that
minute deformations of the parabolic surface are less critical at these
wavelengths.

--

You know what to remove, to reply....

wrote:
Just seen some pictures of Hubble, and The "Very Large Telescope"
(original name) in Chile. It made me think.

With a reasonable space based industry, moon mining, metal working,
aluminium and glass production, precision engineering, how big an
optical telescope could be built in zero-g?

What are the limits? Could a 100m diameter optical telescope be
built?
what would it see?

Heck, they are seriously looking at doing this on the ground, including
exactly the studies you describe:

http://www.eso.org/projects/owl/publ..._Messenger.htm

Several times larger, at the very least, should be possible in space.

As for radio telescopes, what are the limits are baseline
inferometry?
what would a few telescopes, each say 3km across, in solar orbit, say
1
billion km apart be able to achieve?

Good question. We know from pulsar studies that coherence is
maintained at the microsecond level all the way around the earth's
orbit. We can't measure any better now, but there is no obvious reason
why a humongous interferometer would not give resolution roughly equal
to wavelength/spacing (in radians).

We have done correlation from high orbit to earth, and it works as
expected, so single dishes up to 36,000 km diameter (!) would work.
Two of these on opposite sides of the sun would be a rather powerful
facility.

Lou Scheffer

On 20 Feb 2005 15:24:38 -0800, in a place far, far away,
made the phosphor on my monitor glow in such a
way as to indicate that:

Just seen some pictures of Hubble, and The "Very Large Telescope"
(original name) in Chile. It made me think.

With a reasonable space based industry, moon mining, metal working,
aluminium and glass production, precision engineering, how big an
optical telescope could be built in zero-g?

What are the limits? Could a 100m diameter optical telescope be built?

Possibly, but there'd be little point, since you can get equivalent
resolution with multiple-mirror systems.

wrote in news:1108941878.780319.37180
@z14g2000cwz.googlegroups.com:


What are the limits? Could a 100m diameter optical telescope be built?
what would it see?

Here's a project for a ground-based 100 meter telescope (that's about
328 feet!).

http://www.eso.org/projects/owl/

High angular resolution can be, and is being, achieved with arrays
of optical telescopes. This is probably more practical than a
mirror of some arbitrary maximum size. The OWL barely looks practical
at all.

--Damon

In article ,
Rand Simberg wrote:
What are the limits? Could a 100m diameter optical telescope be built?

Possibly, but there'd be little point, since you can get equivalent
resolution with multiple-mirror systems.

Actually, there are groups working on concepts for a 100m ground-based
telescope, notably the European OWL project. The main mirror *is*
segmented, but apparently there are practical advantages in having a
single filled aperture rather than a wide scattering of smaller mirrors.

There's no reason why you couldn't build an OWL in space, although it
would be an expensive project if it used current infrastructure.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

In article . com,
wrote:


What are the limits? Could a 100m diameter optical telescope be built?
what would it see?

Look into the OWL, the OverWhelmingly Large telescope, a 100 meter
ground-based telescope.

http://www.eso.org/projects/owl/

--
David M. Palmer (formerly @clark.net, @ematic.com)

Damon Hill wrote:

High angular resolution can be, and is being, achieved with arrays
of optical telescopes. This is probably more practical than a
mirror of some arbitrary maximum size. The OWL barely looks practical
at all.

There's a 30 meter telescope project (a kind of a small OWL) that would
cost about $600 M to build. Hey, that's less than one shuttle launch.

Paul

wrote in message
ups.com...

With a reasonable space based industry, moon mining, metal working,
aluminium and glass production, precision engineering, how big an
optical telescope could be built in zero-g?

What are the limits? Could a 100m diameter optical telescope be built?
what would it see?

I remember Gerard O'Neill (of High Frontier fame) once wrote a paper on such
a concept. He suggested a vast array of multiple mirror segments 1 meter
across each. He recommended an independent RCS on each segment. It might
seem tempting to just attach them all to some kind of framework, but he
insisted that with temperature differences, etc. that would be the last
thing you'd want to do.

I forget now what size array he was talking about, but I remember him saying
you would not only be spotting extrasolar planets, you'd be charting weather
systems on them.


--


Regards,
Mike Combs
----------------------------------------------------------------------
Member of the National Non-sequitur Society. We may not make
much sense, but we do like pizza.

Henry Spencer wrote:
Actually, there are groups working on concepts for a 100m ground-based
telescope, notably the European OWL project. The main mirror *is*
segmented, but apparently there are practical advantages in having a
single filled aperture rather than a wide scattering of smaller mirrors.

Light buckets on Earth have historically been spectrometry
workhorses. Two excellent cases in point being extra-solar
planet hunting and high-Z supernova searches (both of which
have produced ground breaking science within the last
decade). For that you very much want a whole heck of a lot
of light gathering area and you really don't want to mess
around with futzy issues like nulling and whatnot. With
adaptive optics and the bleeding edge of interferometry it
has become possible to compete at the high end (with space
based observatories) in more than just spectrometry, but
that's still their bread and butter.


There's no reason why you couldn't build an OWL in space, although it
would be an expensive project if it used current infrastructure.

However, there is a realm of space access cost where
constructing something like a 100m telescope in space
would actually be cheaper than doing so on Earth.
Probably somewhere around an order of magnitude cheaper
than today's launch costs, though that's just a SWAG.