About the only realistic engine other than the above gradient fusion and NPTR that has both high ISP and (reasonably :P) high acceleration is the direct drive fusion one. Not quite the exhaust velocity, but still. Or, if nothing else, you could approximate an Epstein drive with a nuclear pulsed thermal engine. all the billions poured into that approach only lead to use realising how even micro-scale instabilities dramatically affect the performance of the reaction. I really don't like using lasers for fusion. 16 times the needed energy to fuse means 4 times the nugget velocity, all things being equal. The study also used D-T fusion, but higher energy is probably possible with D-He (well, useful energy you don't lose 80 percent of it to neutrons). Either way, I guess that even if that were less optimistic, one could include a particle of fissile material in the core of such a nugget to be compressed into criticality and start a chain reaction (americium or U233 would do nicely good neutronics). 10 km/sec is around 100 times less than needed for impact fusion. Though, I must say, the speed estimated for the fuel nugget in that study was far lower than I had anticipated. Reply DeleteĪctually, the similar Gradient Field Imploding Liner approach seems to be a better match: You want the field to as closely approximate a sudden stop as possible. Or, you could use the heatshield to anchor the coils (carbon has both exceptional thermal properties, and exceptional strength properties).ģ) For lack of a better term.how "flexible"is a magnetic field, and how does that flexibility scale with distance from the coil and field strength in Teslas? We can already do 40 T of field strength, but all magnetic fields are "bendy". The tape material used would probably be some kind of REBCO with a nanotube backing. Depending on the temperature the coil can handle before it quenches, the rate of fire and the size of the pellet, it seems somewhat doable.Ģ) Your coils would need backing, so they don't burst from the strength of their magnetic field. That means that between your superconducting coil and the reaction chamber, you'll want some kind of heatshield. Some issues:ġ) You still need to absorb the waste heat from the reaction. The fusion products are expelled the other way, providing thrust. From the POV of the pellet, the magnetic field slams into it, heats it and compresses it, and just as the particle crosses the crux of the field, it fuses. A pellet of Deuterium/He-3 is wrapped in a lithium foil, then shot out the back towards the magnetic field at say 1000 km/sec (I've heard that as a ballpark for impact fusion). Perhaps, they use extremely powerful magnetic fields around a loop as their exhaust port. I've thought about this myself, but reached a somewhat different conclusion given the numerous problems encountered by laser-driven fusion on Earth: impact fusion. In other words, the fusion output can be increased 10 times and all the performance falls back in line with what was calculated so far. The 'multiplier' mentioned earlier jumps from 46,300 to 461,300, just over 10 times better than before. To adjust for this while maintaining the same performance, we would simply state that the fusion reaction is ignited 10^0.5: 3.16 times further away, or 948m. If we assumed a ten times greater density for the Rocinante, for example, we would have an empty mass of 2500 tons. A stronger field allows for fusion products to be redirected from further away, so that an even smaller portion of the harmful energies are intercepted. The variable will be the ignition point distance from the spaceship and therefore the magnetic field strength of the coils in the 'nozzle'. This proposed design can be easily scaled to adjust for different figures for mass, acceleration and deltaV. Of 21.2 thousand kilometres in about 10 minutes, and 0.76 million kilometres in
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