The Next Generation of Human Spaceflight

[djolds1]

The nuke rockets were joint NASA AEC things under Project Rover. Solid core tests were done from 1959 through the last one in 1973, I think it was. By 1973, they had pretty well worked the bugs out of NERVA, although its T/W was less than desirable.

The DUMBO NTR-Solid variant was far superior to NERVA in terms of T/W.

There were also gas core design studies and experiments being performed as part of Rover. Just not actual engine tests. These were more scientific bench tests of feasibility. It actually looked pretty good for the open cycle gas core design, right up to termination in 1972. They were then about two years from doing their very first gas core engine test article, with the 15 year interval from 1972 to a planned Mars mission in 1987 to "get it right".

I was unaware progress beyond NTR-solid had gotten that far before the programs were killed. Thanks.

The "other" gas core design was the "nuclear lightbulb". This featured zero plume radiation, but was limited by temperature of the lightbulb material to about 1300 sec Isp or so. It was projected to have much better T/W than NERVA, and so was being considered for Earth surface launch application. NERVA was only useful as an upper stage engine, such as for doubling the payload of a Saturn-5. But, at 0.38 gee on Mars, NERVA is "good enough", and requires no real development, just re-creation.

Its been re-researched and redesigned several times, the latest being Timberwind's Particle-Bed variant, IIRC.

We're going to need something better than chemical if we really want to send men to Mars.

Depends on mission parameters. NASA/Von Braun style explore-returns, yes. "A rocket a day" philosophy one-way private ventures, no.

[Skipjack]

There have been some recent developments with Thungsten based fuel rods that are very promising. They dont have the ISP of gascore reactors, but they are also much simpler and have less problems.
They solved the fuel rod cracking problem that earlier solid core NERVA designs experienced. They also allow for higher temperatures increasing the ISP quite a bit.

[GW Johnson]

I knew about DUMBO. It's actually pretty close to what I had in mind. That's a completely different fuel element design geometry, and as I understand it, requires a different nozzle design as well. That's OK, it's a good solid core design, and needs a few tests to verify effectiveness, with NERVA as the default backup. One way or another, we have a solid core engine we can build.

I know less about Timberwind, but I had been classifying particle bed and fluidized-bed machines as solid core.

I always thought of "nuclear light bulb" as a gas core fireball separated from the propellant flow by a transparent envelope. This envelope was usually double-walled, and had its own cooling flow between those walls.

The open cycle gas core machine had several geometric possibilities. The one favored by NASA and AEC back about 1969 was a spherical engine chamber with tangential wall injection of propellant (LH2), and a solid rod feed of uranium through a gland fitting, once fission was started. I have heard this was subject to enhanced uranium losses under acceleration, but a semi-reentrant nozzle design would have fixed that.

[GIThruster]

I know less about Timberwind, but I had been classifying particle bed and fluidized-bed machines as solid core.

Timberwind was designed around VERY short term use, for ballistic missiles. As "Vanilla" over at NSF has shown, it cannot be expected to hold together for more than a very short period of time. It will necessarily melt down and go critical. Vanilla showed very conclusively that Timberwind was really very reckless in design, and should never be built for any reason. It WANTS to go BOOM.

[GW Johnson]

Timberwind sounds about as bad as the Pluto nuke ramjet. The core assembly supports ran about 10 F from meltpoint. Nonmaneuvering low altitude M3 cruise missile. It spewed a lot of hard radiation in ground tests. The jet was pretty loud, too. Its shock wave plus jet noise was calculated to be lethal to those on the ground right under the flight path. Between that and the radioactive exhaust, they estimated more casualties from those two effects than the nuke warhead.

[CaptainBeowulf]

I remember seeing an illustration of Pluto somewhere. Might have been in, or on the cover of, an old popular mechanics or something like that. It looked pretty cool, but I remember the article discussing that it wasn't really nice - and thinking about it, I figured out that it would be pretty lethal. Your description backs that up.

[GW Johnson]

As I recall, Pluto was a belly-scoop ramjet with wings and conventional tail group. It resembled a very large Snark, Matador, or Mace. My father remembered this project at what used to be Chance Vought in Dallas. They were the airframe prime for it. That was substantially before my time.

Some but not all, of the old connected-pipe test facility for Pluto is still out on the Nevada nuclear test site. I think it is at, or near, Jackass Flats, where some of the old Rover nuclear rocket stuff still is.