h a l f b a k e r yRenovating the wheel
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This works on the same concept as a solar sail, except the light source is supplied by colonies of glowworms. They live in spheres attached to the spacecraft, with one half reflective and the other half (the back half) transparent, so the accumulated photons are ejected out the rear.
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Is this for an unmanned probe? You do realize what you're up
against: |
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The Plutonium-238 cells in the Voyager probes are
projected to keep powering them until 2025 at the earliest,
meaning a lifespan of almost 50 years. |
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utilizing the power of paradoxical propulsion. |
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Apart from the novel source (ie glowworms), there isn't anything new here, this is just another flavour of photonic drive. |
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Other designs utilise nuclear reactors or other energy sources, and lasers/other directional light sources. Not very powerful, but I think the specific thrust is very high IIRC?? |
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it doesn't work if the light source is on the ship. If it did work you would need to be prepared for a very slow journey, glow worm metabolism is a very low energy/weight fuel. |
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Sound like they'd make a good diet food, then. |
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Normally you eat solid fuel rockets? |
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Gloworms are a very inefficient store of light. A fuel cell/LED combo would have a much better energy/weight ratio. As would a plain ol' rocket. |
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//it doesn't work if the light source is on the ship// Yes it does. If you utilise a miror so the outgoing light is travelling in one direction, the resultant recoil will propell the mirror (with ship attached) in the other direction. |
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Bearing in mind that the thrust produced from light is rediculously low. |
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And on the sides of the spacecraft we need some fireflies for directional control... |
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// Bearing in mind that the thrust produced from light is rediculously low |
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//Gloworms are a very inefficient store of light. A fuel cell/LED combo would have a much better energy/weight ratio. |
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Wrong, glowworms are extremely efficient, close to 100% light:energy ratio compared to 20% for LEDs |
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I still think that there is a conservation/paradox problem with producing the light that pushes a solar sail on board. Anybody out there able to give me a yea/nay on that? Also, although the light production bits on a glow worm may be quite efficient the (Kg Thrust)/(Kg Fuel) is a joke. Even if their food is 100% conserved (!) and 100% converted into light (!) the final result is simply not that much energy. Solar sails only work because they do not have the mass of fuel slowing them down. Strap any extra weight on them and their terminal velocity is to low to even consider using them for any mortal purpose. E=MV still applies in space. |
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no paradox at all...the light that is reflected imparts momentum, the light that passes out the rear through the transparent cover does not. |
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/Strap any extra weight on them and their terminal velocity is to low to even consider using them for any mortal purpose// |
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Uh, Que? Whilst there actually is a terminal velocity for solar sails (hint - the only drag factor is pertaining to the density of random molecules in space, and of course the cross-section of the sail of course assuming you're outside of any local gravity wells) - how is the mass of the sail+craft in any way relevant to it's terminal velocity? Mass only affects acceleration. Terminal velocity is determined by a force balance, thrust versus drag. Both are independant of mass. |
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There is no paradox in the glow-worm and mirror device. You're thinking it's the same as the fan-and-sail boat, which it's not. |
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Imagine a boat, with a metal plate at one end, and a pintle mounted machine gun at the other. if you programmed this fictional gun to spray out bullets in every direction, most of which simply fire out into space, but a few of which hit the metal plate, bounce back and careen off toward the rear. This produces a net thrust. All the forces are ballanced, except that in the end, more bullets are coming off to the rear of the boat than to the front. This is a net change in the boat's momentum, ballanced by the fact that proportionately more bullet mass is going "backwards" than forwards. Now optimise the plate placement to reflect more bullets. Then change bullets to photons of light, polish the plate 'till it's a mirror, and use a handful of glowworms instead of the gun. Bingo schmingo, you have a nett thrust. |
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Just a very low thrust, but a thrust nonetheless. |
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Oh yeah, what exactly do you mean by E=MV ?? |
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Most people would assume you mean E=1/2 MV^2 |
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...But what did you really mean? |
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well of course it weighs nothing, it's in space!! But seriously, the glowworm effect is cumulative, so it starts of tiny but is constant. eventually the craft would reach very high speeds, if you could keep the buggers alive that long. |
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Bun to [CustardGuts] for introducing the all-too-rarely-used word "pintle" to the discussion. |
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ok, just so i don't look the idiot: terminal velocity in a solar sail system is the velocity achieved before the distance to the sun reduces the light input to a negligible level. The more massive the craft the larger the sail needs to be to achieve a workable terminal velocity. As mass rises light from the sun, even while nearby, is not enough to get you up to speed, (that damn square root) and we tool off out of the solar system still accelerating slowly on our glowworms. But they have a limit and as they produce light they use themselves up, furthermore, as i vaguely recognized, we can only harvest less than 1/2 that output for velocity (far less than 1/2 actually). Now, no matter how efficient the glow worm is as a light source, my seat of the pants math tells me that, given a healthy sun launch, the fewer glow worms on board the faster the terminal velocity with the maximum a 0. (all that matters is the size of the sail/mass). Looking at it another way, if you released the craft in space with no sun boost what final speed would it achieve? Would it get significantly higher the more glow worms you added? I think not. |
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//glowworms are extremely efficient, close to 100%// |
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Only in terms of energy used to make light. A lot of their energy will be spent growing or making baby glow worms. And the food they eat will not have the energy/weight ratio that hydrogen/oxygen tanks would have. Also note that while the heat generated by an LED is usually considered wasted, it would nonetheless radiate from the back of the spacecraft and would still give useful thrust. |
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Now I think about it though, I believe I can improve on 100% efficiency. Use peltiers to pump heat from the front of the craft to the back. Not only will all the power radiate from the back of the craft, but other heat from background radiation/instruments etc will also be drawn to the back end and radiate out. |
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ah but the beauty of this system is that it's renewable. With rocket ful once you use it, it's gone for good. Glowworms breed in their own little ecosystem, providing a potentially infinite source of power. |
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[WcW] there is no sail on this system, just in case you didn't realise. The glowworms act on the front half of their ecosphere, so it's all pretty much self-contained. |
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// Glowworms breed in their own little ecosystem, providing a potentially infinite source of power// |
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You have just failed physics. Living things do not and cannot circumvent the laws of thermodynamics. |
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//close to 100% light:energy ratio// That refers to the light-producing chemical reaction in isolation; (net production of light) : (food energy input) will be much less, as the insect has metabolic overheads apart from light production. |
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(Edit) Like [Bad Jim] said. |
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I can't believe this thread has continued. I just assumed it was a joke. If it isn't a joke, here are at least the major issues: 1. visible light is not the only radiation from a craft, the magical system that keeps the worms warm will bleed IR in all directions this is a net loss of energy over time that must be included in the original craft so this would not go on infinitely. 2. Glow worms are are not clear, so by using a mirror means that you are spacing them out enough so they don't absorb the light that they eminate. This and their weak thrust would mean that the ships massive frontal area and negligible thrust wouldn't overcome even the drag of hitting the unbelievably rare gasses of deep space. 3. And here's the big one POOP. Till someone shows me a closed ecosystem that produces light, I think the worms will drown in their own feces. If you can show one, then forget space propulsion, I have a Noble Prize here for you as that could be used right here on Earth for more things than I can list. I would buy one today and hang it in my basement. |
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// I just assumed it was a joke//
[marked-for-tagline] |
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It *is* a joke. We can also hope it was intended so. |
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brilliant. Kafka would be proud. |
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//You have just failed physics. Living things do not and cannot circumvent the laws of thermodynamics. |
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And you've just failed biology. Ecosystems can and do exist, why I belive we have one right here on Earth. |
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And that ecosystem must get energy from somewhere, namely a large nuclear reactor called "the sun". And even it obeys the laws of thermodynamics; it does not create energy, it is merely a battery with about 10 billion years of shelf life. |
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//It's inevitable that we will lose many of the cockroaches to space// |
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I'm all for sending cockroaches. It's got to be cheaper. And they would quickly colonize other planets, providing later human arrivals (bred specifically to subsist entirely on insects) with a nutritious and tasty snack. |
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//...failed physics// //...failed biology// now if we can just get one of the social sciences, we'll have all the halfbaker prerequisites covered |
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lurch, you have just failed social dynamics. There are plenty of other types of ignorance yet to be represented. No-one has failed computer science yet. And correct me if I'm wrong, but no-one has completely failed to understand the idea either. |
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<hits gong, mashes thumb> |
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Only the sphere of glow worms is actually needed, and the worms don't need to glow, although that is a definite aesthetic advantage. A sphere of hamsters would also work, as the infrared photons would provide an effective (though exceeding small) thrust. Eventually, given some mysterious source of food and thousands of hamster generations, the sphere of interstellar hamsters would reach a fair fraction of light speed. Entering the atmosphere of a far flung planet, they would explode like a small nuclear bomb. |
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Tourist: Australia's the arsehole of the world. |
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Australian: So you're just passing through? |
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