> Pointing a telescope at something bright and nearby is easier than something very distant and dim, so the precision requirements are obviously in the opposite direction.

You're wrong. Between 1979 and 1998 the MMT Observatory used six repurposed spy satellite mirrors that had been donated by the NRO, manufactured for the cancelled KH-10. Furthermore in 2012 the NRO donated two unflown spy satellites to NASA, the mirrors from which may be used for the upcoming Roman Space Telescope. Spy satellite mirrors make great telescope mirrors.

> "manufactured parts from intelligence programs [...]"

As I point out above, the NRO has donated at least eight primary mirrors that were specifically manufactured for cancelled or unused spy satellites. The Hubble mirror may be another example of such, or it may have merely been fabricated by the same people.

> that were the rejects from those production lines".

That's the only dodgy part of his claim, but it's not that strange of a claim when you recall that Hubble's primary mirror infamously had a spherical aberration. I presume NASA didn't know about the aberration before they launched HST, otherwise they should have corrected for it on the ground instead of having astronauts correct it in space. But it doesn't seem completely outlandish that the NRO gave NASA mirrors they had previously deemed unsuitable for their own use.

> Especially the strong implication that Hubble is made out of lower tolerance parts, since they are rejects, is a claim that need significantly more evidence than what you provided here.

Well, it did ship with a faulty mirror after all :)

Just joking, I know this was a manufacturing error specific to Hubble which kinda proves it wasn't a reused part. I think the mirror would have a slightly different focal length anyway? But maybe 400k is far enough to be "infinity" even at that scale.

For the most part, yes, with adaptive optics and corrective measures being taken to deal with more satellites in orbit, ground telescopes are superior or at least comparable to space telescopes given their ability to be much larger.

Space telescopes these days are primarily being designed for observations that simply can't be done while in the atmosphere (eg the wavelengths JWST and NGR look at). The value of a space telescope in the same wavelength range as what ground based telescopes usually use would mainly benefit in terms of being able to have much longer exposures.

My understanding is ground based telescopes imaging in the same wavelengths also have to deal with distortion in the atmosphere, star link interference would be easier to filter out compared to the other stuff (which is why locations for these mega ground based telescopes are chosen with utmost care )

Disclaimer. Not a physicals or astronomer, just a enthusiastic backyard amateur astronomer who reads a lot about telescopes .

Yes, there are many kinds of science which can be done more cheaply from the ground.

Even considering the effect of Starlink.

Yes they are very much possible, and cheaper than space too.

What starlink does is ruin part of the images, and if the thing you were interested in observing happens to be blocked by a starlink trail you're hosed: a thing literally blocked what you tried to see and you lost the nigh (because usually you get just a bit of the a night for your observation). Other things that ruins your night is clouds, so starlink effectively makes the weather at a site worse, only you find out after the night that it was all a waste.

To some extent you can plan around it, but as the mega constellations grow they'll have to avoid each other more frequently and there's no rules for how that shits coordinated, so you maybe you can know in advance that the night is wasted.

But the risk that a satellite is in an undocumented orbit by the time you try to observe will likely be very high in the future.

You'd almost certainly want to launch several. You get one data point per half-orbit, when you're at opposite sides of the Sun. This is tolerable for the Earth, where an orbit is one year. But a full orbit out at 20AU takes eighty four years! Collecting a useful number of samples with one spacecraft would take centuries, while two spacecraft in opposition on the same orbit can measure parallax instantly.

I understood perfectly.

Starship is 9 meters wide.

JWST folded is about 3 tiles wide, in a housing 4.7m in diameter, unfolding to 6.5m. So a JWST style fold in a Starship would be double. A one-mirror-segment-per-flight would be something like 36m, in the same arrangement. But since you would be constructing from separate sections, the diameter is theoretically limitless.

Just stack the mirrors inside Starship, and assemble them in space. Below, an example of a 300m diameter telescope using 8-meter mirror segments assembled in-orbit

https://caseyhandmer.wordpress.com/2021/11/17/science-upside...

Making it not need to fold, or spend years testing and re-testing all the unfolding, would solve a very great deal.