IAU Statement on Satellite Constellations
iau.org
iau.org
I would regret losing a natural-looking night sky, but the statement admits these probably won't be visible to the naked eye.
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.
You can lose all the systems used on Earth to compensate for atmospheric and gravitational effects, and launch it to an orbit well above any satellite constellation to eliminate satellite trails from the picture.
With the advent of heavy and super heavy launchers there will no longer be an absolute focus on reducing weight. This alone will bring the cost of space telescopes by an order of magnitude.
Space telescopes also completely avoid the problem of facility construction impinging on indigenous sacred sites.
A space telescope would by its very nature be less impactful than most satellites, since it will be placed in a high orbit away from the glare of the Earth, also ensuring that the Earth fills less of the sky to allow better access for astronomy.
Starship has a 9-meter cargo space. Musk recently proposed a successor with twice that diameter. What could we do with a space telescope that size?
The real win though is lunar telescopes. Then it is ground-based. You can build it from raw materials on the moon, which is 45% silica and also has plenty of iron and aluminum. You've got no atmosphere and 1/6 gravity; you can make it huge and get perfect clarity.
This may sound far-fetched but the whole point of SpaceX is to set up permanent human habitation on the moon and Mars, in the fairly near future.
Those are serious issues that would have to be resolved before an investment in a telescope should be made.
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?
There's presumably a way to estimate that. But you'd also want to ask if it's even useful to have 10 or 100 copies of JWST? Even if the unit cost is lower, the total program cost would still be greater than the $10b for one. The astronomical community is probably not large enough to fully utilize 10 JWSTs, let alone 100. I'm sure we could come up with enough observations to keep them all busy, but there isn't enough person-power to analyze and interpret all that data. So if one has money to build 10 JWST's, a likely better use of that money would be to build one or two and spend the rest of the money hiring people (graduate students, postdocs, faculty) to do science with the data. Or just build one JWST and use the money for a second to build something else that pushes capability in other areas (e.g., the "Origins Space Telescope" far-infrared mission concept, or the Lynx X-ray telescope concept). I suspect that would be better for how much new science you can do per dollar spent.
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.
It is commonly argued that "everyone has a right to clean, affordable drinking water", and yet New York City and China and India and etc continuously pollute waterways because business has been prioritized instead, for better or for worse.
I don't know how to measure some objective ranking of the benefits of terrestrial astronomy vs satellite internet services - I doubt there's any way to quantify those two things sensibly.
I _do_ note though, that while the existence of telescopes on the ground doesn't threaten the existence of satellite internet, satellite internet _does_ threaten the existence of ground based astronomy. Doesn't seem "right" that SpaceX(or Amazon or other constellations) can just say "Sucks to be you, we're going to fuck up your entire field of study because we think we can make a buck here".
Pretty sure we shouldn't just let Elon and Jeff decide here, without letting orgs like the IAU at least have their say, and put forward an argument against it...
More like: "Sorry to interrupt your observations, but we are trying to kickstart a space-based civilisation here".
I'm sympathetic to astronomers (I have a telescope myself), but I'd much rather go to space than just observe it.
Those facilities have resulted in lots of discoveries. But Kepler wouldn't have been such a success without lots of follow-up observations from ground-based telescopes (e.g., measuring spectroscopic radial velocities to confirm exoplanets). It's likely that many HST (and eventually JWST) studies rely or will rely on data taken with ground based facilities in order to actually interpret the data. Pardon the pun, but space based telescopes don't exist in a (scientific) vacuum. They have unique and impressive capabilities, but they don't stand alone.
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
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.
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.
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.
This is what LSST is going to do, sum the images to look deeper than just one image. There are a few commercial software packages that also do this co-addition (my friend has a large but still amateur telescope and that software does this).
The exposures aren't terribly long, so the idea is to add a bunch of them together, since the CCD wells can become saturated, and even "leak" between them. This is why the camera is cooled down by extra cryogenics.
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.
It will also irradiate back a lot of heat once they are in the shade.
You want as constant a temp as possible, that that's much easier to do with a reflective exterior than a non-reflective one.
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.