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The OP of the question Would a lunar telescope provide a significant improvement over terrestrial based equipment? got slightly trounced for asking "the wrong question", but this answer does address both the question and "(t)he real question (which) is what advantages, as well as disadvantages, does a telescope on the Moon have over a telescope somewhere else in space, e.g. in Earth orbit or at a Lagrange point?

When I saw the bit about interferometry being done in space via:

precision formation flying

I became really interested! For example, the individual telescopes of the Atacama Large Millimeter Array (ALMA) are moved around to different mounting sites (by trucks) to reconfigure the array, but the location of those mounts is known to essentially millimeter accuracy. This is important because the 3D configuration of the elements of the array must be known to do the correlation properly.

I understand that "known" does not also mean fixed. Once characterized, orbits in space can be incredibly well known or at least predictable, especially if "double checked" at regular intervals.

And I'm a firm believer in "Space and Optics were made for each other."

So I am wondering, how will "precision formation flying" likely be first demonstrated?

enter image description here

above: an ALMA dish moving in precision, albeit deeply sub-orbital motion. "The first successful movement of an ALMA antenna took place at the Operations Support Facility (OSF) on 8 July 2008..." From here.

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  • $\begingroup$ Are you asking for information on a specific mission or...? $\endgroup$ – Chris Oct 25 '16 at 2:22
  • $\begingroup$ @Chris if there is a specific mission, or two, that can be pointed to, then that would indeed be a great answer. If there is a research effort, or study, but no mandated mission yet, that would also be good. Since I am not familliar with what has been done, I don't want to pre-specify. $\endgroup$ – uhoh Oct 25 '16 at 3:53
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    $\begingroup$ Does interferometry between a spacecraft and a ground-based observatory work for you? Spektr-R is a space-based radio telescope using interferometry operationally. en.wikipedia.org/wiki/Spektr-R $\endgroup$ – Hobbes Oct 25 '16 at 15:21
  • $\begingroup$ Great question. I've been hearing ideas about flying a constellation of satellites in a formation to do just that. With launch costs going down and small sats being able to share launches, I won't be surprised if we see those ideas come true in the near (few years) future. $\endgroup$ – ventsyv Oct 25 '16 at 16:40
  • $\begingroup$ @Hobbes Wow that's quite interesting as well! But it's not formation flying. I used "How will..." future tense because I have a hunch interferometry demonstrated using formation flying will happen but perhaps in 5 to 10 years. $\endgroup$ – uhoh Oct 25 '16 at 22:29
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The first precision formation flying mission is ESA's Proba-3, slated for launch in 2018.

Proba-3 is ESA’s – and the world’s – first precision formation flying mission. A pair of satellites will fly together maintaining a fixed configuration as a ‘large rigid structure’ in space to prove formation flying technologies.

The mission will demonstrate formation flying in the context of a large-scale science experiment. The paired satellites will together form a 150-m long solar coronagraph to study the Sun’s faint corona closer to the solar rim than has ever before been achieved. Beside its scientific interest, the experiment will be a perfect instrument to measure the achievement of the precise positioning of the two spacecraft.

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    $\begingroup$ Well, the physics of formation flying are identical, no matter what application. I think the first application will be eLISA (en.wikipedia.org/wiki/…). Leave the question as is for now. $\endgroup$ – Hobbes Oct 25 '16 at 15:19
  • $\begingroup$ sure, go ahead. $\endgroup$ – Hobbes Oct 27 '16 at 6:59
  • $\begingroup$ Aha, ELISA is a laster interferometer, formation-flier, and a telescope of sorts! It looks like it's a bit further out in time. Wasn't there some recent demonstration of some cube inside of a satellite very precisely controlled? I can't remember if precision formation flying was involved. It was in the news within the last year but I can't find it now. $\endgroup$ – uhoh Oct 27 '16 at 7:14
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    $\begingroup$ That's LISA Pathfinder, one satellite with two test masses inside that have to fly freely within a cavity in the satellite. $\endgroup$ – Hobbes Oct 27 '16 at 7:58
  • $\begingroup$ OK thank you for that!! Technically each mass was (almost) in it's own orbit, but I am stretching it a bit. $\endgroup$ – uhoh Oct 27 '16 at 8:12

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