
IAU Statement on Satellite Constellations - Tomte
https://www.iau.org/news/announcements/detail/ann19035/
======
DennisP
I feel like the IAU is being a bit short-sighted here. The point of the SpaceX
constellation is to bootstrap a lot more activity in space than we have right
now, by providing both funding and an initial market to get Starship running
at volume. Once launch costs are down to $50/kg or so, whatever loss we have
in earthbound astronomy can be more than compensated by large telescopes in
orbit and on the far side of the moon.

I would regret losing a natural-looking night sky, but the statement admits
these probably won't be visible to the naked eye.

~~~
privong
> Once launch costs are down to $50/kg or so, whatever loss we have in
> earthbound astronomy can be more than compensated by large telescopes in
> orbit and on the far side of the moon.

I don't think launch costs are the dominant expense in space telescopes. I
think most of the expense is technology development for one-off (or small run)
instruments as well as paying the people who design and build it, write the
software, and operate the telescope. So even if the launch were free, there's
still a huge expense in building space-based telescopes. I believe the rule of
thumb is space-based costs ~10x that of a ground based telescope.

The largest astronomical mirror in space is 3.5m (Herschel). 30m optical
telescopes are being built on the ground now and 10m telescopes have existed
since the early 1990s. It would be incredibly expensive to put a 30m telescope
in space, even if the launch were free.

~~~
perilunar
Well the obvious question is how much cheaper would space telescopes be if
they mass produced and launched a standard design instead of one-offs?

What if they took the JWST design ($10 billion in development costs!) and made
10 or 100 more copies? How much would each additional copy cost to build and
launch?

~~~
chongli
I think the answer to that is “not very much.” Telescopes use a lot of highly
specialized parts made of rare and expensive materials. They use a lot of gold
for various components and the mirrors are made of gold or platinum. The
tolerances in the fabrication of the mirrors are EXTREMELY tight in order to
reduce aberrations as much as possible. This sort of high precision
manufacturing with exotic materials simply doesn’t scale.

~~~
denton-scratch
"EXTREMELY tight"

Telescope mirrors need to be polished to an accuracy of a quarter-wavelength
of whatever radiation you want to capture - so for an optical telescope,
that's a quarter-wavelength of visible light. Any greater precision than that
is spurious, and won't get you better imaging. Less precision than that == bad
mirror.

The techniques for polishing and testing small mirrors (up to say 12") are
amusingly low-tech, almost steampunk. You can get to 1/4 wavelength of visible
light with a homemade grinding/polishing rig, and a homemade optical bench
that consists of little more than a jig to hold the mirror, a lamp and a
couple of razor blades.

I'm sure the challenges in building accurate 30m optical mirrors are massively
bigger, not least because very big mirrors warp under their own weight. But I
imagine the principles are just the same.

Incidentally, I had no idea people were building 30m ground-based optical
telescopes; that's just insane. I mean, my house is only 8m high.

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bitminer
It's about time.

A recent astronomy picture of the day shows the visible impact of Earth orbit
spacecraft on astronomical imagery.

[http://apod.nasa.gov/apod/ap191013.html](http://apod.nasa.gov/apod/ap191013.html)

Astronomers will need precise orbital parameters of all s/c in their
telescopes' field of view, so they can avoid deceptive data from known s/c.
The data and processing issues will be significant. Obstructive? Destructive?
Career limiting? TBD.

The article mentions only high-profile large telescopes. In fact there's
hundreds that have scientific significance. Helping hundreds or thousands of
observers eliminate local Earth orbiting s/c interference in their
observations is hard. And, currently, unsupported by these companies.

They use the public resource, outer space, for their own good. And pollute it
for others.

~~~
denton-scratch
In radio astronomy, they build interferometers, with very large baselines, to
give resolution equal to a dish the size of the baseline. AFAIAA, they can
also synthesize a baseline by taking images 6 months apart, giving an
effective baseline the width of Earth's orbit.

I don't know how an optical interferometer works, but I believe such things
have been built.

I would have thought that an optical interforometer could be configured to
just "not see" the passing satellites. I think that seems to be a mere
technical problem for telescope builders, and not a fundamental problem that
the rocket-men have to solve.

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sega_sai
Presumably one way to deal with this problem is to make the satellite surfaces
like stealth planes, i.e. very flat reflective surfaces with sharp angles. In
that case the reflections will still happen (and they will be brighter), but
they will be visible on the ground over much shorter period of time.

~~~
gene-h
Even if the satellites are perfectly black they'll still interfere with radio
astronomy. Even if they don't transmit they will interfere with radio
astronomy because they're warmer than the vacuum of space and will emit black
body radiation

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xt00
In the case of digital astronomy using various opto-electronic devices to take
the light and convert to charge (CMOS or CCD sensor or whatever else they
use), I wonder how possible it is to essentially sum together lots of pictures
one after another where occasionally you would reject photos that had a
satellite passing through them? Like is that how they deal with it now? In the
case of film there is no "dark noise" that you have to deal with, so you just
leave the shutter open for hours. But with digital if you leave the charge
well open for even seconds, the dark noise starts to accumulate in the pixel.
Not totally sure though how long exposures work on digital cameras -- if its
actually a sum of shorter exposures or what..

~~~
joshvm
> In the case of digital astronomy using various opto-electronic devices to
> take the light and convert to charge (CMOS or CCD sensor or whatever else
> they use), I wonder how possible it is to essentially sum together lots of
> pictures one after another where occasionally you would reject photos that
> had a satellite passing through them?

An exposure that a satellite passes through is potentially ruined. On the plus
side, although there are lots of satellites, the odds of one of them passing
through your target is relatively slim. A lot of the time astronomers are
interested in a single star in the entire field of view.

This has happened to colleagues of mine however, so it definitely occurs.
Other things which can ruin exposures are cosmic ray hits which you have no
control over.

You could do a median sum to get rid of the offending noise. Problem is you
often don't know until after you've got the data back; it's quite rare for
astronomers to do their own observations and you get allocated a fixed amount
of telescope time. So you might get given 1 hour of time on your target, but
if you messed up the exposure calculations or a satellite happened to pass
through, there's very little you can do about it.

> Not totally sure though how long exposures work on digital cameras -- if its
> actually a sum of shorter exposures or what..

The detectors used in astronomy are extremely low noise and can be used for
fairly long exposures (10s of minutes) without stacking. That said, you can
still use stacking to get better signal to noise. It's much more commonly
performed with amateur observations though, due to noisier detectors.

You also need to take dark, bias and flat frames to compensate for detector
noise.

[https://www.eso.org/~ohainaut/ccd/](https://www.eso.org/~ohainaut/ccd/)

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tandr
If reflection is such a big problem (other problems notwithstanding), there is
that better-than-VantaBlack paint that presumably absorbs a lot of light. To
think of it... it might cause even bigger problems with "dark object flying in
a total darkness"...

~~~
jofer
The issue with having sats be black is that black adsorbs a _lot_ of heat from
the sun. Even more so with "better-than-vantablack".

Cooling is actually a huge problem in space. It may be really cold, but it's
extremely difficult to transfer heat without air/water/etc. You're limited to
direct radiation, which is much less efficient than advection or conduction.
Making things black means they'll get quite hot in the sun. That's a major
problem for most satellites.

~~~
outworlder
> The issue with having sats be black is that black adsorbs a _lot_ of heat
> from the sun. Even more so with "better-than-vantablack".

It will also irradiate back a lot of heat once they are in the shade.

~~~
AWildC182
Imagine taking your computer and blowtorching it then sticking it in the
freezer every 90 minutes for a decade. How long do you think it'll keep
working?

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avmich
Satellites can theoretically all use Sun shade - a shield which is kept
oriented to Sun and reflects most light back.

This is not ideal for many reasons. More weight to carry to orbit, another
system to be kept operational. Some satellites need Sun visibility, shield may
have some interference with satellite's radios. I'm sure more problems exist.

Another approach - also not without problems - would be to aggressively deploy
orbit-based telescopes, so they would have access to space above densely
inhabited low Earth orbits. It also costs a lot, still leaves problems with
ground-based observations, even though space-based tools have some advantages
too.

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AWildC182
If only we could actually get more space telescopes in orbit _looks angrily at
JWST_

