Nuclear: The most promising option for mid-range manned space flight.

The space shuttle awaiting launch: the shuttle depended on conventional rocket technologies, but future manner spacecraft may rely on nuclear-enabled rockets for their extra-atmospheric portions of their journey. Drawing by the author.

I don't know if the rest of you have been following the exciting work related to the Nuclear Cryogenic Propulsion Stage project down at Marshall Space Flight Center or not, but NASA is doing some exciting things that are promising for the concept of a nuclear-powered rocket one day perhaps propelling a manned spacecraft to Mars or other targets of exploration. The concept is that a nuclear cryogenic rocket with liquid-hydrogen propellant super-chilled to very low temperatures at the point of its launch (and making use of conventional chemical rocket technology for its atmospheric travel stage immediately after launch) would, once outside of the mesosphere, engage its nuclear reactor which would in turn super-heat the liquid hydrogen fuel, burning it for the source of trans-solar system propulsion. Thus, the reactor itself would be cold and not emitting hardly any radiation whilst in the atmospheric launch phase and would only be powered up once outside of the atmosphere; at that point, the power-saving advantages of nuclear fuel over conventional chemical rocket fuel would allow a much greater range for the spacecraft and also would produce speeds that would be in excess of what conventional chemical rockets can reasonably provide using current technology and pragmatic size constraints. 

The dream of this approach is nothing new: the concept for a nuclear-powered rocket able to go beyond the abilities in terms of speed and range of chemical conventional rocket technology has been an object of our space program since around 1955 and something that was investigated in earnest up to the mid-1970s. The main reason it didn't go further in earlier years was that the core technologies for it were not yet viable; also, the general plan for a manned mission to Mars came to an end for NASA in the 1970s and the US Air Force's efforts to design a nuclear-powered bomber also fell short of producing such an aircraft and discouraged the drive at NASA and elsewhere for further research on nuclear-enabled propulsion technologies for space travel. Now, we have the technologies not only to design and build a viable nuclear rocket, but the necessary technologies to test the materials and concepts involved. NASA's labs at Marshall currently are making use of the Nuclear Thermal Rocket Element Environmental Simulator (NTREES) technology to test non-nuclear materials for thermodynamic properties essential to the design of the Nuclear Cryogenic Propulsion Stage rocket itself. The NTREES simulations, NASA has reported, are very encouraging and are answering the core questions they have been designed to address. Aside from the real-world lab-based NTREES simulations, computer simulations also are demonstrating the promise of the project and are being used to investigate other aspects of specifics germane to designing the rocket system itself. 

NASA has prepared a great informative PDF available here regarding the Nuclear Cryogenic Propulsion Stage and NTREES:

I've always been a huge fan and advocate of space exploration for the sheer sake of exploration and science, but I know that Congress and many taxpayers like to also know what "real-world" benefits any NASA project may offer, and I know that NASA loves to tell us of such benefits, too. While NASA has yet to say a lot that I'm aware of related to technology transfer and data-sharing from NTREES, it certainly seems to me as a software designer as well as a journalist that the project is ripe for data-mining: after all, the very advanced nature of the simulation experiments being performed on non-nuclear materials that stand in for nuclear ones could carry over into other areas of simulation and modeling for the nuclear industry and I could see the material-specific data garnered from the NTREES experiments also holding further uses beyond the immediate questions it answers for NASA. If we have the specifics of materials used in NTREES and the correlated specifics of the nuclear materials these test materials represent, we should be able to learn a lot about high-variable temperature and pressure performance (along with many other things) of such materials as well as comparison studies between such materials. We probably could, if the datasets are specific and nuanced enough, even build an in-computer software simulation of NTREES itself to work with various materials in a simulation environment prior to even going into the cost of lab experiments. I plan to speak with NASA's communications people about this in the near future and will report back whatever they can say. Any time we do lab-based testing of this nature and the data is collected in a manner that leaves no parameter unaccounted for, we will have datasets (providing they can be shared) that could be the basis for some very awesome approaches to materials theory simulations in the software realm, too. 

But for now, I'm very content with the idea we may have a nuclear-enabled spacecraft to get people to Mars in coming decades. I cannot think of much that would be more exciting.

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