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Comment by rtkwe | Hacker News Reader

There's a lot of limitations with an on orbit satellite you don't run into with ground based systems. Hubble is pretty old and it's mirror pretty small at this point so there are hard limits on it's usefulness for viewing very faint objects, it's mirror simply doesn't gather as much light because it's relatively small at just under 8 feet. Another thing you can't do anywhere nearly as easily are upgrades or adding new experiments. With ground based telescopes it's relatively easy to add new experiments on the side mirror to measure new spectra or measure in a different way. That just can't be done with a space based telescope, even if the design allowed for it the costs sky rocket.

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With a telescope integrated into Starship, you could potentially land the whole telescope from orbit and do repairs and upgrades on the ground. Whether the main mirror can withstand launch and reentry is a question though

EDIT: found a counterargument: https://www.scientificamerican.com/article/elon-musks-starsh...

That also depends on how Starship can actually open which they've been pretty vague on for larger payloads. It seems difficult for it to open in a way that gets the bottom half of the front of the ship out of the way (because of the heat shield). If you can't fully clamshell that open you might still need expensive and delicate origami to unfold the main mirror and any sun shields to get them a clear view of the sky.

That's setting aside the costs of actually running it too as brought up in the article. Maybe that can be brought down but there's necessarily going to be more complexity and more specialized workers required to run a space telescope vs a ground telescope. It'd be interesting to see where the extra costs come from; the specialized people monitoring the satellite, downlink time, etc. Some could get brought down but seems difficult to make it cost competitive with having a similar telescope on the ground.

Dont starlink constellations have to be replaced every few years, maybe a decade tops? So theyre being launched constantly. Just throw your new fangled sensor on the next one, no need to upgrade.

That's completely unworkable... Starlink sats are tiny and by being replaceable you don't want to put extra expensive equipment on them. There's not the space to put the primary and secondary reflector you need. So far we don't have a way to do the same kind of synthetic array with visible light we can do with radio waves. Even once we get past that issue you still have the light gathering issue of small reflectors where the kind of extremely dim objects astronomers are most interested in can't be imaged properly with small reflectors.

Starlink sats also want to keep their bottom pointed at the ground at all times because that's where all the fancy radios live while telescopes need to freely point and track their targets.

It doesn't gather as much light as ground based telescopes, but the background (for example, from airglow) is also much lower, so the SNR is pretty good.

That's one of the reasons for building in the Atacama desert. Also, the adaptive optics technology has pretty much removed the majority of the negatives from the atmosphere.

What's SNR?

An abbreviation for “signal-to-noise ratio” that imo should have been StNR or simply S/N. (Thus I sympathize with not parsing it immediately — it is widely used, though, so it is good to know.)

https://en.wikipedia.org/wiki/Signal-to-noise_ratio_(imaging...

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