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Comment by __tg__ | Hacker News Reader

Not sure about the Starship numbers but if its is $2m per Hubble mass, then launching 200 hubbles would be $800m, not $43m. This however is not about sending bricks into orbit. The ELT mirrors are segmented and need precise alignment with each other to micron precision. Deploying a segmented mirror in orbit has still not been done (the James Webb Telescope launches in 2021); the engineering involved adds orders of magnitudes of complexity over a single-piece primary mirror such as Hubble has. Add to this maintenance costs: a mirror the size of ELT in orbit needs a huge maintenance program behind it to work at all. The lifetime cost for such a mirror would be in tens of billions, if not hundreds. This is why such large telescopes keep getting built on Earth.

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> the James Webb Telescope launches in 2021

The JWT has been re-scheduled many times with the latest attempt scheduled for 2021. I'm sure that'll get pushed, yet again.

Manditory XKCD: https://xkcd.com/2014/

I still think that 2026 remains a reasonable estimate.

$2m is the cost on Starship's Wikipedia page, which implies 10 Hubble masses. Now, I am not talking about taking 216 mirrors and combining them into a single mirror pointed at a single camera, but actually 216 self-contained mirrors and cameras. That is, whether they're put closer together or further apart, they'll be interferometry based. What's important isn't how well-aligned they are, but how well they know how they're aligned.

I think the reason these things keep getting built on Earth is because until now no one has dared to dream of putting that much mass in orbit for that cheap.

Self-contained cameras are not good enough. You need to actually quantum-interfere the photons from one optical path with those from the other paths to get the effect of the larger resolution.

You can do this with optical fiber, a pixel at a time, for sufficiently slowly changing scenes. Each big mirror is then responsible for collecting enough photons so they can all interfere constructively and deliver a useful brightness level.

The output goes through a diffraction grating to get a spectrum for each pixel, so they need it pretty bright.

Is this what they did to bring us the high resolution picture of a black hole? If not could that method be used by these hypothetical hubbles?

>> Is this what they did to bring us the high resolution picture of a black hole? If not could that method be used by these hypothetical hubbles?

That was using radio waves, something that can be measured in each telescope, saved as data, and then combined in a computer. At optical wavelengths we cannot record the data as accurately/quickly and so must instead use extraordinarily precise mirrors and fiber optics to join the light from each telescope in real time. These links must be accurate in distance to within a wavelength.

It sounds like the parent is referring to a specific type of interferometer, because yes, this is what they used on the EHT and it did not have any such entanglement or quantum effects.

Actually regular light-wave interference suffices, but it's quantum anyway, just because that's how light is.

Yeah. The money in the space business was never in launchers but in satellites.

Satellites need to be incredibly well built because they are ridiculously expensive to deliver. If we can deliver them for a fraction of the cost, it no longer makes sense to build them so expensively.

True! The way microcomputers supplanted mainframes.

If you launch cheaper satellites more often: - you get to iterate so you can make improvements at a much faster pace - there is less problems from a single failure - more scale effects

You can enter a virtuous cycle.

There are limits! It can be that it's hard to make a useful satellite once you go below some certain size. And reliability suffers if you try to skimp on good practices.

On many scientific satellites, the instruments are one off anyway and are complex, hard and hand built with astronomical costs, so it might not save so much even if the launch and the bus were a lot cheaper.

I understand the analogy, but this one is bad.

Microcomputers came about because, at some point, we could make small computers with just enough processing power that they could be useful.

Mainframes didn't really go anywhere - they are still doing heavy lifting in large corporations, and modern mainframes employ every trick we use to make x86's fast and then a couple that would make x86's prohibitively expensive.

I'm not sure that holds true, at least for the big telescopes.

The lifetime cost of the hubble is about 10 Billion and the development cost of the James webb telescope is approaching 10 Billion. James Webb will launch on an Ariane 5 rocket, which costs about 140 million per launch. This is about 1-2% of the development costs.

JWT launch = $CURRENT_YEAR + 1

It doesn't even matter because you know when it does launch, there will be some one in a million malfunction that destructively aborts the mission.

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