This should already be ringing alarm bells!Ĭharged pions are unstable, and rapidly decay into muon/antimuon and sometimes electron/positon pairs. 3c, that gives you a mass flow of ~11g of pions a second. You did not supply a spacecraft weight, but I'm sure you can rerun the simple calculations below if you felt the need.Īnyway, in order to just lift off vertically from Earth's gravity with a 100 tonne craft, you need to generate at least a meganewton of thrust. this is plucking a figure out of the air, but is a little over the maximum mass of an airbus A321 and a little under the mass of a loaded space shuttle. Lets say you have a hundred tonne spacecraft. Where $\dot$ is the mass flowing out of the nozzle and $v_e$ is the exhaust velocity. The force exerted by a reaction engine can be described by the following equation: It gives us the most conservative estimate for how destructive your rocket is. This has been used by Forward and Frisbee amongst others, and comes about through the interaction of charged pions and the magnetic nozzle of your rocket. 69c may be practical and others even suggest that >.9c might be achievable. Early simulation suggest an exhaust velocity of ~.3c, more recent papers suggest. Its exhaust velocity is that of the annihilation products, which in turn depend on exactly how your engine works and who you ask. Your suggested antimatter rocket is what might be known as a beam core rocket, or sometimes a pion drive. The faster the exhaust velocity, the more efficient the rocket is at providing thrust over a long period of time. Now, note that I mentioned exhaust velocities above. The third type has never been realised, but the closest anyone has come to it would be Project Orion, which would have used nuclear explosions to propel a spacecraft. The thrust is so low that it could not be used to lift a rocket off even from all but the most miniscule of moons, but the engine can keep running for years at a time making them ideal for deep space probes. A common type would be a liquid propellant rocket, such as those used by SpaceX.Īn example of the second type would be an electric propulsion system such as an ion thruster or perhaps a VASIMR. high thrust, high exhaust velocity "torch drives".Īntimatter engines could be any one of the above.Īn example of a modern day takeoff-type engine would be literally any rocket engine we've used over the past hundred years or more.low thrust, high exhaust velocity, high running time, good for efficient travel in space.high thrust, low exhaust velocity, low running time, good for takeoff on a planet.You can, very roughly, divide rocket engines into three types: The answer is, of course, that it depends. Possibly you could use antimatter to heat the propellant, but good luck absorbing the gamma and charged particles efficiently to do so. Apart from the less-lethal exhaust, this also has the benefit of consuming far less antimatter, and not requiring the ship to handle near as much power. You would want a much lower performance drive that heats and ejects propellant for such uses. The atmosphere is actually pretty opaque to gamma radiation, so the radiation hazard would be limited, but in absorbing the radiation it would turn into something approximating a nuclear fireball. One with enough thrust to be useful for launch from a planet would have a devastating effect on the surroundings. A beam core antimatter rocket, pretty much the (theoretically) practical approach to building an antimatter rocket that operates as you describe, would be very nearly as efficient as these. The Kzinti Lesson referred to giant laser propulsion stations and photon drives. The lesson is "a reaction drive's efficiency as a weapon is in direct proportion to its efficiency as a drive". Putting aside the issue of antimatter exploding if storage failed, would this make these spacecraft dangerous to launch from ports based near settlements, or to be nearby when one is launching? Or would it be possible to shield the engine in such a way that it poses no risk to people nearby and doesn't cause environmental damage? Could you launch a craft like this from the centre of a city or would it be too energetic/radioactive?Ĭertain events early in Larry Niven's Known Space series involve what's known as the "Kzinti Lesson", a lesson taught by a pacifist and demilitarized humanity to the invading Kzinti. I was considering having the spacecraft in my setting use antimatter-matter spacecraft, but then I realised that at least some of the annihilation of protons and electrons with antiprotons and positrons will release gamma photons, as well as the charged pions being magnetically directed as exhaust. See the tag description for more information. Answers that do not satisfy this requirement might be removed. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc.
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