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Comment by mr_toad | Hacker News Reader

The trouble is you need to keep the elements of an optical telescope very very precisely aligned - a precision on the order of the wavelength of light, which is impractical in space.

Or you could do computational interferometry, but only if you could accurately measure the phase of light in visible wavelengths, which is an unsolved problem.

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I think LISA Pathfinder showed that it's possible to phase lock lasers over very long distances as long as they are in a stable orbit. It's basically a metal cube in freefall surrounded a proximity sensor, so that as the sensor drifts toward the cube, but long before making direct contact, the apparatus can adjust it's position. The experiment demonstrated that the system can be used to keep mirrors precisely separated over large distances in support of gravitational wave detection. I would think something like this could be adapted to align lots of things that are in a stable orbit.

Correct me if I'm wrong, but doesn't this interstellar swarm scheme require onboard clocks accurate to 1/frequency of the the light being used? Which is equivalent to the accurate measurement of phase.

They don't, see https://arxiv.org/abs/2309.07061 . The basic idea is to use "picosecond-level" synchronization to improve the signal-to-noise ratio. They mention that a truly phase-coherent swarm would perform much better but they consider that a longer term prospect (section 2.1.4).

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