[X] My Assistant

[tacitus]

A subject which has been fascinating me recently is the nature of interstellar space exploration at some far off point into the future. It would seem to me that even if one day decades or centuries from now interstellar spacecraft (unmanned or manned) become a practical proposition, the most efficient way of exploring the galaxy around us will continue to be bigger and better telescopes in space, on the Moon, on Mars, etc.

While there is no substitute for being on the spot, it will certainly be many centuries before we have the technology and resources to visit planets and fully explore them more than a few light years in any direction from Earth. But we already know, in principle, how to build ginormous space telescopes that can capture the trickle of reflected photons from exoplanets many light years away, and the odds are we will have the ability to do so within decades, not centuries.

It's all very interesting speculation, though since I am but a mere amateur, I have a few questions about the practicalities and limitations of such an enterprise, assuming the funds and technologies are available. Remember, we're not talking about the near future here. Assume we already have a dozen space elevators around the Earth, colonies on the Moon and on Mars, and regular missions to the asteroids, Jupiter, Saturn, and beyond. Perhaps 200, 300, even 400 years hence.

- Is there a point where bigger or sharper scopes won't help resolve further detail in the images of exoplanets?
- At what point will we have to send the telescopes into the outer system beyond the effects of zodiacal light?
- How far will we be able to probe before interstellar gases and dust become a problem?
- Any guesses as to the absolute limit of reliable observations where we can examine the nature of a planet and its atmosphere--i.e. enough to detect signs of life and civilization--(excluding chance events like gravitational lensing)? Is it tens, hundreds, or thousands of light years?
- If there are planets in, say, the Beta Centauri system, how much detail on their surfaces could we potentially resolve. Could we ever see Beta Centauri b as well as we can Mars from Earth through a thousand dollar telescope?

There are some very interesting mission designs already on the drawing board for the decades ahead, but how much further can we go in exploring the galaxy around us before we would have to leave our own solar system to continue the work?

[jasedm]

I love the idea, but feel that the major challenge would be keeping all the elements cohesive.
The sun's radiative pressure would make the whole assembly flex like a soap bubble (or a planet's magnetosphere). When today's mega-mirrors are affected by an imperfection of a few nanometres, this telescope would spend it's entire budget on station-keeping propellant.

[NGC3314]

I love the idea, but feel that the major challenge would be keeping all the elements cohesive.
The sun's radiative pressure would make the whole assembly flex like a soap bubble (or a planet's magnetosphere). When today's mega-mirrors are affected by an imperfection of a few nanometres, this telescope would spend it's entire budget on station-keeping propellant.

Or maybe not. For some interferometric applications, precise knowledge of the baselines is needed, but control of the baselines can be rather less exact. That is, if you have adequate compensation techniques (such as "optical trombones"). drift can be tolerated as long as it is known in real time exactly enough for compensation. And some of the exoplanet interferometer projects have already counted on using differential sunlight pressure to assist with attitude and stationkeeping, since it can be controlled at a level much finer than anything else available in deep space (where the geomagnetic field isn't available; I gather the solar wind field is too unsteady for this).