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Can it be done with solar sails?
by dd36 5y ago
Can it be done with solar sails?
- goldenkey 5y agoSolar sails only absorb enough energy for tiny crafts in space, a frictionless environment. You overestimate photon flux momentum from the sun.
- Akronymus 5y agoSolar sails indeed only absorb a tiny amount of energy, BUT per given area. They can theoretically made to be extremely large without much weight relative to the size. Which in turn allows you to accelerate even quite large payloads in a reasonable amount of time.
- goldenkey 5y agoThe mirrors are extremely heavy and solar sails are exclusively used above our atmosphere, in space, where more flux from the sun is received. The flux even at earth orbit is a measly 47e-7 Newtons per square meter. That's 0.00016905632 pounds per square inch. You still stand by what you just stated? It's not feasible to do below clouds, in an environment with constant friction, air or water resistance. The only reason you can do it in space is because that tiny slow acceleration can accumulate over a long period of time. This precludes frictional losses that would normally be incurred within atmospheres.
- Akronymus 5y agoIt seems I misunderstood the thread. I somehow thought we were talking about sails in space rather than in atmo.
- goldenkey 5y agoSo what were you originally referring to? Solar wind in space? I'm honestly confused now.
- Akronymus 5y agoI was actually. I rhought the parent I originally replied to was saying that solar sails aren't useful for large payloads in space.
- andrewflnr 5y agoThey overreached a tiny bit in reaction, but they were responding to someone who seemed to be proposing solar sails inside the atmosphere.
- goldenkey 5y agoI didn't overreach at all. Nearly all the creatures of HN just try to save face after they make invalid statements. This involves acting confused, changing the subject, or a barely clever combination of both. The desire to be correct and win what barely even counts as a debate is a contagion deeply plaguing these creatures.
- sopooneo 5y agoNot an expert, but I'm going to say no. There is no medium in space, moving relative to the solar wind, against which the "keel" of a solar sail ship could push.
- adolph 5y agoGravity? I guess something with enough mass to use gravity might be too large to use solar sails.
- Tuna-Fish 5y agoGravity does not actually provide a force in the sense that a sailboat would require. (It acts on all parts of the vessel equally.) There is some work on the idea of using both a photon sail and a magnetic sail on a single vessel. In many interesting locations, these would push in different directions, allowing you to sail.
- xaedes 5y agoThis is similar to flying in air. I suppose when your craft is big (or long) enough you could leverage differences in luminous flux (or intensity?) to generate some thrust. The differences will be tiny and the necessary craft size big. One would have to run the actual numbers, but it _could_ work in principle. Compressing air by moving through it to leverage the resulting difference in velocities sadly won't work =( The steady state is then just the speed of air. I guess for light this also applies in a similar way.
- lambdatronics 5y agoNot exactly, but you can do a crazy 'sun dive' maneuver: https://aapt.scitation.org/doi/full/10.1119/10.0002178 https://aapt.scitation.org/doi/full/10.1119/10.0002178 It takes advantage of two things: 1) The Oberth effect, where thrust is more effective the deeper you go into a gravity well 2) The thrust from a solar increases as you get closer to the Sun