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Comment by asaddhamani | Hacker News Reader

Which is much more expensive and risky, just look at the Hubble($4.7B) failure recently, or the Kepler ($600M) failures before that. How many years (decades?) has James Webb($8.8B) telescope been in development? Ground based can't be easily replaced by space based and will leave lots of people and nations out of astronomy, which will truly be a terrible loss.

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I'll just point out that not all ground-based astronomy is affected. Satellites are only visible when the sky is dark but the satellite is not in Earth's shadow, so only observations at dusk and dawn are affected.

Are you sure this is true? You can frequently see satellites in the dead of night. Further, they show up quite plainly in non-visible wavelengths like radio or infrared even during the day.

This of course only applies to visible light, they will be visible in infrared no matter what.

When can you see satellites in the Earth shadow with visible light?

The parent post said that only observations at dusk and dawn are affected. I'm pointing out that, even at astronomical midnight, large fractions of the sky aren't in earth's shadow. For other wavelengths the shadow is irrelevant, since satellites contaminate data even without the sun's direct illumination.

Well sure, at high latitudes and during certain seasons that may be true for higher altitude LEO satellites (Starlink is fairly low), but if we’re talking corner cases, sometimes the surface of the Earth isn’t in Earth’s shadow at astronomical midnight (land of the midnight sun).

Corner cases don’t really count as “frequent,” however.

That traditional space telescope cost is heavily driven by how expensive space launch used to be, which is already changing now.

Also with the upcoming RLVs in space repair or retrieval and redeployment might also become an option, this time much more affordable than with the Shuttle.

James Webb is doing observation literally impossible to do from ground

My point is that not every use case is viable for space telescopes due to cost, next to impossible repairs, required technology, etc. They can't replace ground based observations completely.

Starship (which will get its bread and butter from Starlink) actually WOULD enable much cheaper space telescopes, cheaper repairs and maintain by astronauts. Starlink satellites themselves are very inexpensive and show there’s no fundamental reason why space hardware MUST be extremely expensive compared to ground hardware.

Space telescopes could actually be cheaper than ground telescopes if SpaceX succeeds in reducing cost of human spaceflight to their goals. Space telescopes don’t need massive structures to keep the mirror from deforming under gravity, they don’t need advanced adaptive optics to adjust for seeing, they can point almost anywhere in the sky and can observe objects day and night without weather or seasonal concerns.

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