Nuclear salt-water rocket

Chemical rockets use heat energy produced by a chemical reaction to heat the gas products. The hot products exit through a propulsion nozzle at a very high speed, creating thrust. In a nuclear thermal rocket (NTR), thrust is created by heating a fluid by using a nuclear fission reactor. The lower the molecular weight of the exhaust (hydrogen having the lowest possible), the more efficient the motor can be. However, in this engine the propellant can be any of many fluids having suitable properties as it does not participate in generating heat. In a NSWR, the nuclear salt-water would be made to flow through a reaction chamber and out of an exhaust nozzle in such a way and at such speeds that critical mass will begin once the chamber is filled to a certain point; however, the peak neutron flux of the fission reaction would occur outside the vehicle. ==Advantages==

There are several advantages relative to conventional NTR designs. As the peak neutron flux and fission reaction rates would occur outside the vehicle, these activities could be much more vigorous than they could be if it was necessary to house them in a vessel (which would have temperature limits due to materials constraints). The fission reaction in an NSWR is dynamic, and because the reaction products are exhausted into space, it does not have a limit on the proportion of fission fuel that reacts. In many ways, NSWRs combine the advantages of fission reactors and fission bombs. One design would generate 13 meganewtons of thrust at 66 km/s exhaust velocity (6,730 seconds ISP), compared to about 4.5 km/s (450 seconds ISP) exhaust velocity for the best chemical rockets as of February 2023. The design and calculations discussed above are using 20%-enriched uranium salts. However, it would be plausible to use another design which could achieve much higher exhaust velocities (4,725 km/s) and use a 30,000-tonne ice comet along with 7,500 tonnes of highly enriched uranium salts to propel a 300-tonne spacecraft up to 7.62% of the speed of light and potentially arrive at Alpha Centauri after a 60-year journey. ==Limitations==

The propellant used in the initial design would contain a rather large amount of the relatively expensive isotope U, which would not be very cost effective. However, if the use of NSWR began to rise, it would be possible to replace this with the cheaper isotopes U or Pu in either fission breeder reactors or (much better) nuclear fusion–fission hybrid reactors. These other fissiles would have the right characteristics to serve nearly as well, at a relatively low cost. Another major limitation of the Zubrin's nuclear salt-water rocket design included the lack of a material to be used in the reaction chamber that could actually sustain such a reaction within a spacecraft. Zubrin claimed in his design that the apparatus was created so that the liquid flow rate or velocity was what mattered most in the process, not the material. Therefore, he argued that if the proper velocity was chosen for the liquid traveling through the reaction chamber, the site of maximum fission release could then be located at the end of the chamber, thus allowing the system to remain intact and safe to operate. These claims are unproven due to no such device having ever been built or tested. It is also not certain that fission in a NSWR could be controlled: ==See also==