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Comment by spenczar5 | Hacker News Reader

Very large telescopes can achieve great resolving power, but they run up against atmospheric turbulence, particularly in many of the spectral regions we care about for checking out exoplanets. Radio light passes right through the atmosphere for the most part, which is why you see very large radio telescopes, but they're not very practical for infrared or visible light scopes.

Space-based telescopes are a better avenue. You can achieve much better resolution in practice with a much smaller telescope. There's no atmosphere to block you, and instruments can capture light of any frequency. Cost is the main disadvantage, but delivery of satellites (and maintenance) to space is getting cheaper and cheaper.

All of which is to say that I agree we should be spending more on astronomy. That was your main point, of course. I disagree with the particulars, and think we should be more willing to go to space.

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adaptive optics on earthbound telescopes have allowed them to easily surpass hubble's resolution nearly a decade ago. it's also a lot easier to service telescopes on the planet than something orbiting at the ideal L2 point, some 1.5 million km from earth.

This is extremely far from my area of expertise so I am probably wrong, but I imagine that at some point we will advance earth based telescopes to the point where we get diminishing returns when considering atmospheric disturbance.

At that point, it will make more and more sense to launch space based telescopes. But... if we wait until we reach that point in the diminishing returns curve, than we lost valuable innovation time/expertise in space based technology.

My hunch is that if we wanted to get the best telescope tech in any given period of time, we should do both and watch as the two types of technologies converge.

What do you mean by the two types of technology converging?

Launching huge telescopes (and possibly assemble them) into space...?

No, I mean ground based telescope tech and space based tech. Both have different limits and advantages.

Isn’t it size vs astmopheric noise? Or are there loads of other factors?

There is at least one space telescope that connects with ground-based telescopes using interferometry, so in some sense, they could be called one telescope: https://en.wikipedia.org/wiki/Spektr-R

Aside from turbulence, gigantic earth bound telescopes struggle with weight and fragility of the giant mirrors.

That aspect is also much easier in space. Once you get it out there, which is hard...

The James Webb Space Telescope, nicknamed the telescope that ate astronomy, has cost an enormous amount of money due to the need to get everything aligned absolutely perfect before launching because there will be no chance for repair.

In comparison, with adaptive optics ground based telescopes have a lot more leeway to be fixed and corrected.

(That said, if astronomical interferometry can achieve the same result as a 100Metre telescope, then let's do it that way! How is less important than making sure we have something in our pipeline within the next decade that can be capable of directly measuring the spectra of exoplanets.)

Extremely large telescopes use segmented mirrors to avoid this problem.

here is a telescope idea that is theoretically super scalable

http://www.pellegrino.caltech.edu/aarest1/

Telescopes exploiting quantum effects would be able to be much smaller and have higher resolution.

https://medium.com/the-physics-arxiv-blog/how-to-build-a-qua...

Nice! Thanks for making me aware of this research.

What is the practical limit for a size and weight of an object that we can realistically put into space now? I imagine that a, for example, 10meter wide lens would be extremely heavy and can not be really split into pieces for shipping. How much smaller space telescopes are for the same performance?

The James Webb Space Telescope is an example of a segmented-mirror optical scope. The deployment video (simulation) is fascinating to watch:

https://m.youtube.com/watch?v=v6ihVeEoUdo

It has a 6.4m (21ft 4in) primary mirror. Which, from a pragmatics standpoint, answers your question.

Though I suspect mission plans could be drafted for a larger scope yet.

https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope

Fascinating video, but honestly the only thought that kept going through my head is: they've overcomplicated this.

Despite it's impressive number of steps, this does not look like good engineering.

Instead, it looks like a design by committee, with engineers going drunk on complex parts coming together rather than dumbing down the unfurling of this telescope down to its most basic possible mechanism, with the fewest moving parts possible (where failure is chronically always possible).

Seeing how overcomplicated this is, it's no surprise it cost $10 billion to build.

I strongly suspect they aren't.

You're looking at a high-precision instrument, that's being fit inside a distinctly finite space and mass budget, that will have to operate for years (possibly decades), and which is beyond reach of any conceivable service mission for a very long time.

Movement, thermal control (the Webb operates in the low end of the visible spectrum, through the infrared, so its temperature itself is critical), alignment, and drift, all matter.

And every piece of equipment has to be tested and trialed to the maximum extent possible.

Yes, it's a bit Rube-Goldbergish, but then, so is the specification.

Space X's Falcon Heavy is supposed to launch in november with a 57 ton payload. I'm not sure how big the payload can be.

I wonder if you could make one with a few bits of lens that fold out? They'd have to be positioned more accurately that one wavelength of light (to ~100nm say or a 10,000th of a mm) which is tricky on earth but might be doable in space where you don't have gravity making things flop?

Seems like the moon would be a good spot. We can build it much bigger than in orbit, and there's no atmosphere to cause interference.

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