[QUOTE=Measure for Measure]
The Economist Magazine once discussed ultra-light spacecraft. They would be tethered to solar sails and powered by lasers cannons which would remain in this solar system. Thus, the need for propellant is minimized.
This webpage discusses Starwisp, which uses a 1 kilometer sail weighing 16 grams, powering a 4 gram spacecraft. The whole thing weighs less than an ounce, and is pushed by beamed microwaves.
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A “4 gram spacecraft” is nothing more that a message in a bottle; there is no way that you could build a useful payload of that mass with anything like conventional technology, much less protect it from ablation, impact, and radiation. Now, a payload that is critically self-replicating and self-organizing, i.e a Von Newmann “Universal Assembler” or Bracewell probe might a possibility, albeit one requiring the capability of autonomous molecular assembly that is way into the realm of science fiction-y “grey goo” at this time. (See Greg Bear’s Queen of Angels or Neal Stephenson’s Diamond Age for examples.) And the amount of power required for the Starwisp is nothing short of incredible; given the difficulty we have in even keeping a space station powered and supplied in Low Earth Orbit, I’d say that maintaining a multi-gigawattt orbiting laser or maser is well beyond current capability.
[QUOTE=Quartz]
I’m not sure that this is correct: we would already know the habitable zone before launching the probe, plus we can detect the presence of some major planets by the wobble they cause in the stars they orbit. Equally, finding planets within a star system is relatively trivial: take a photograph when pointing at the star and take another a day or two later. If something has moved, it’s not a star. Perhaps, though this might be something for a path-finder probe, with other probes following it by a year or so, so they can adjust trajectories in time.
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Having spoken with a couple of mission planners and a number of engineers at NASA Jet Propulsion Laboratory regarding a variety of planetary exploration missions, I have at least a small bit of insight as to what it takes to successfully execute a program of this type. It is one thing to lay out a mission plan, but the plan usually evolves significantly even after the mission is launched and on its way, based upon operational difficulties with the equipment, new information and insights about the target, et cetera. For instance, the Voyager 2 spacecraft, like its sister, was originally intended only to visit Jupiter and Saturn in a regrettably abbreviated version of the original Grand Tour mission to visit all outer planets; however, by the time Voyager was approaching Jupiter, the mission operators had enough experience from Voyager 1, and faith in the beyond-design-limits reliability of the on-board systems, to plan a gravity assist around Saturn to take them to Uranus and Neptune, completing nearly all of the Grand Tour objectives for chump change. (I suspect they held the possibility of doing this as pocket kings until the rousing success of Voyager 1 gave them a full house in aces.) However, this took the extensive judgment of experience programmers, engineers, orbital ballisticians, and planetary science Ph.Ds to make the most of the tiny window of opportunity to thread the needle, and this is using information about the movements of the planets that we can determine from Earth observations down to a few kilometers. We may have, relatively soon, software capable of making those kinds of trades on a limited open-ended basis, but we’re not there yet, and we certainly don’t have the kind of synthetic cognition capable of making the complicated judgements of what mission is scientifically most worthwhile for the risks it poses, which is why we pay Ph.Ds the [del]big[/del]reasonably-good money.
[QUOTE=Quartz]
Can I also ask for expansion on one topic? My though is that for the bulk of the journey, the probe would be off - completely unpowered - and then at the appointed time something would switch it on. This way there would be no issue of failure through use. Do we have that that technology? Some sort of switch operating through radioactive decay, perhaps? Or perhaps a solar cell - once it gets sufficiently near the target star, it would generate sufficient energy to switch on the rest of the probe.
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You would not want a probe to be completely unpowered; for one, if may need to make course corrections, and the further away it does this the less energy it takes. It would also be nice to have some kind of telemetry feedback from it so you don’t waste a couple hundred years of effort on a probe that got smashed up in a random collision (however unlikely) passing through the Oort cloud. The energy to do this would be prohibitive given current power sources–the radioisotope thermoelectric generators used for interplanetary missions with durations of less than a decade would be wholly inadequate for interstellar transit–and so you’d be stuck not really knowing whether it was working or not. Of course you would want to keep many systems powered down, both to conserve energy and reduce wear, but the fact is building any complex and delicate electrical or mechanical system intended to work after a century or more without maintenance is way beyond our experience.
If you did have some kind of feasible Starwisp system as discussed above, the smart thing to do would be to build thousands of them (the energy requirement is the same and at the light weight you could boost hundreds of them per rocket launch) and send them out knowing that at least a few would survive. But again, we’re going on about virtually indistinguishable-from-magic technology compared to extant capabilities. Something like this will probably be the way that we explore other star systems–by proxy, rather than running around in red spandex with phasers set to ‘stun’–but it’s not going to be for a long time yet.
Stranger
