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NASA Looks At Reviving Atomic Rocket Program (newatlas.com)
Big Hairy Ian shares a report from New Atlas: When the first manned mission to Mars sets out, it may be on the tail of an atomic rocket engine. The Space Race vintage technology could have a renaissance at NASA after the space agency's Marshall Space Flight Center in Huntsville, Alabama signed a contract with BWXT Nuclear Energy to develop updated Nuclear Thermal Propulsion (NTP) concepts and new fuel elements to power them.
Today, with NASA once again considering the challenges of sending astronauts to Mars, the nuclear option is back on the table as part of the agency's Game Changing Development program. Under this, NASA has awarded BMXT, which supplies nuclear fuel to the U.S. Navy, a $18.8-million contract running through September 30, 2019 to look into the possibility of developing a new engine using a new type of fuel. Unlike previous designs using highly enriched uranium, BMXT will study the use of Low-Enriched Uranium (LEU), which has less than 20 percent of fissile uranium 235. This will provide a number of advantages. Not only is it safer than the highly enriched fuel, but the security arrangements are less burdensome, and the handling regulations are the same as those of a university research reactor. If NASA determines next month that the LEU engine is feasible, the project will conduct testing and refine the manufacturing process of the Cermet fuel elements over the course of a year, with testing of the full-length Cermet fuel rods to be conducted at Marshall.
Slashdot reader Big Hairy Ian adds: "At the very least it looks much more feasible than Project Orion."
Today, with NASA once again considering the challenges of sending astronauts to Mars, the nuclear option is back on the table as part of the agency's Game Changing Development program. Under this, NASA has awarded BMXT, which supplies nuclear fuel to the U.S. Navy, a $18.8-million contract running through September 30, 2019 to look into the possibility of developing a new engine using a new type of fuel. Unlike previous designs using highly enriched uranium, BMXT will study the use of Low-Enriched Uranium (LEU), which has less than 20 percent of fissile uranium 235. This will provide a number of advantages. Not only is it safer than the highly enriched fuel, but the security arrangements are less burdensome, and the handling regulations are the same as those of a university research reactor. If NASA determines next month that the LEU engine is feasible, the project will conduct testing and refine the manufacturing process of the Cermet fuel elements over the course of a year, with testing of the full-length Cermet fuel rods to be conducted at Marshall.
Slashdot reader Big Hairy Ian adds: "At the very least it looks much more feasible than Project Orion."
Nothing much. Until reactor is started for the first time, it doesn't contain anything that is not found in nature. It's basically more concentrated uranium, so it can be safely disposed of by letting it crash into the sea. And presumably, the reactor is designed in such a way that it won't become critical after immersion into seawater.
There are interesting developments in this area. For example, Kilopower ( https://en.wikipedia.org/wiki/... ) is aimed to replace RTGs since Pu-238 is becoming too scarce. It will produce about 4kW of thermal energy and will be completely passively regulated by natural thermal expansion of components - no moving parts required whatsoever.
Even SpaceX admits that for more distant missions (far outer planet destinations, oort cloud, etc), scaling chemical rockets is not sufficient. Nuclear rockets are also interesting for Venus, delivering crew and payload between the habitable layer (~54km) where breathable air is a lifting gas that can loft a colony, and orbit. Some of Venus's great advantages, like having nearly Earthlike gravity and thus no concerns about wasting like exist for the moon and (to a lesser extent) Mars, are also disadvantages, in that it's also nearly Earthlike difficulty to get to orbit. Furthermore, unlike Mars where your rocket rests on the ground, with Venus you have to support its fully fueled mass. While it's possible to get out with two-stage chemical rockets and re-dock the returning stages, you get much better mass fractions with nuclear. Even though nuclear pretty much only works with hydrogen propellant (the ISP drops in linear proportion to the atomic mass of the propellant), and hydrogen is not particularly common on Venus, the low propellant requirements mean that a nuclear rocket can use less hydrogen than most low-hydrogen rocket propellants that could be used were the ascent vehicle a two-stage chemical rocket.
I'm sure lots of people are going to be discussing NERVA in this comments section. It's important to realize that NERVA is obsolete technology, and there are much better designs available at present. NERVA's biggest problem was its awful thrust to weight ratio. One of the first realizations since then was that you can make a nuclear rocket with a LOX "afterburner"; at liftoff, you use LOX to vastly augment the thrust (the resulting ISP, while nothing like pure hydrogen nuclear-thermal, is still well above that of normal hydrolox). Once the high liftoff thrust requirements are no longer needed, the rocket transitions to pure hydrogen thrust for much higher specific impulse.
A variety of airbreathing modes have also been investigated which can strongly increase thrust and/or specific impulse further - thrust augmentation, nuclear scramjets, nuclear-driven turbojets, etc. Also, there have been general improvements in nuclear technology to allow for transferring higher energies to the hydrogen steam since then, as well as a number of yet-to-be-proven concepts. For example a fission fragment reactor can theoretically get the hydrogen much hotter than the reactor itself; in such a system, the goal is to (as much as possible) capture only neutrons in the fuel and only thermalize fission fragments (which carry most of the energy) in the hydrogen. But you definitely wouldn't pursue a fission fragment reactor with LEU....
He's really very... gentle... and fuzzy. We're becoming fast friends.
For high-mass, Hohmann-transfer spacecrafts bound to Mars, nuclear really isn't the best propulsion option even in the long run. It's basic physics. At the low delta-Vs required for the flight, the mass ratios and volumes required are disadvantageous for nuclear, as is mined mass usage from all hydrogen sources with the exception of perhaps mining hydrogen directly from Saturn or one of the other smaller gas giants.
Ezekiel 23:20