How long would it take to get to Alpha Centauri using a solar sail? The fastest travel time I’ve seen calculated is 1000 years. Imagine a reflective sheet only nanometers in thickness attached to the payload with diamond strength cable. A close pass by the Sun (the classic ‘Sun-diver’ maneuver, first called this, as far as I know, by Gregory Benford) is followed by sail deployment as close to the Sun as possible. Assume a sail of perhaps 100 kilometers in diameter, a payload of several million kilograms, and accelerations of a few g. After acceleration, the sail would be wound around the habitat for cosmic ray detection, and later re-deployment for deceleration.
Gregory Matloff presents these ideas in an essay with the fetching title “The Reenchantment of the Solar System: A Proposed Search for Local ET’s,” available online (thanks to Larry Klaes for the tip on this). As you can see from the title, the sail mission to Centauri is only the beginning of the possible wonders discussed here. For Matloff goes on to show that an advanced civilization whose star is leaving the main sequence could use identical techniques to reach much higher speeds. Replace the Sun with a giant star a thousand times more luminous and you cut travel time to Centauri down to about 320 years.
And while Centauri Dreams has often considered possible targets for interstellar probes, Matloff turns the story around. His paper discusses stars in the solar neighborhood that might be home to migrating interstellar civilizations. To fit the bill, the stars need to be subgiant or giant class, like Procyon (11.3 light years from the Sun), Beta Hydri (21.3 light years) or Pollux (35 light years). Could such stars have produced interstellar arks that might have reached the vicinity of our Sun? If so, wouldn’t the logical place to look for them be in the outer Solar System?
From the paper:
If we are indeed within such a “Dyson Sphere” of artificial worldlets, we could detect their presence through astronomical means since a space habitat will emit more infrared radiation than a like-sized comet or asteroid. Interestingly, several Kuiper-Belt objects have recently been found to have an unexpected and substantial red excess. It is argued that, in opposition to the assumptions of current SETI searches, the very advanced occupants of this possible local Dyson Sphere may have as little interest in beaming radio signals in our direction as we do in communicating with termites. A research program is proposed whereby large and small college observatories would routinely monitor the spectral irradiances of Near Earth and Kuiper Belt objects while a concurrent theoretical effort models the spectral characteristics of various proposed space habitats.
This paper, a winner in the National Institute for Discovery Science essay competition, is nicely followed up by Matloff’s recent work in the Journal of the British Interplanetary Society, including specifics on how to study hypothetical Kuiper Belt Objects of artificial origin. The author’s The Starflight Handbook (New York, John Wiley & Sons, 1989) remains an essential book for students of interstellar flight.