In the early days of the NERVA program (early ’60’s), there came about an associated program: RIFT. Reactor In Flight Test was the rather obvious follow-on to the development of a nuclear rocket… mount the rocket to a stage and blast around in space. Lockheed had a contract with NASA to design the basic RIFT test stage, which would serve as a third stage for the Saturn V; sometimes known as the S-N stage, operational derivatives of this stage were put forward.
Compared to later nuclear stages, the S-N stage was remarkably short in length. Long stage lengths were useful to reduce the radiation hazards to the payload (especially crew); I can only assume that these early studies either assumed lower external radiation fluxes from the reactor, or assumed a higher mass of shielding. In either event, such small stages seem like a bit of a waste of the potential of a NERVA rocket, which could run for hours. As shown, these look kinda like mounting a turbofan off of a 787 onto a Cessna, and giving it two gallons of gas.
11 Responses to “Lockheed RIFT”
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I believe Douglas was also involved in RIFT planning, perhaps as a competitor to LMSC. There are a number of Douglas RIFT documents on NTRS. Some work was planned for the old SACTO site southeast of Mather AFB/Aerojet.
This might be a little off topic, but there seems to be some question of NTR’s use in SSTOs over here:
http://selenianboondocks.com/2010/06/ssto-ntr-bad/
Long after the Martin Astroplane, The folks at Andrews once proposed a NTR to on their Gryphon first stage, so as to not have to fool with LACE if I recall. How RIFT wasn’t saddled with reusability, but they seemed to think even a small NTR was worthwhile. I was wondering what your views were on the subject.
> I was wondering what your views were on the subject.
NTRs have always suffered from dismal T/W. They’re fine for in-space use, but they suck for boosters… and are terrible for SSTO use. I haven’t run the same numbers that Kirk did over there, but assuming he ran them correctly (no reason to assume otherwise) and they show that the idea won’t work… then it won’t work. Engineering is not a matter of wanting something hard enough that things work; engineering is a matter of running the numbers.
There are ways of increasing the T/W of NTRs (such as adding oxygen to the mix, or using water or ammonia), but they almost universally add mass and complexity and reduce specific impulse.
The small size of the RIFT stage may have been due to payload constraints on the Saturn V; like Skylab, the intention may have been to put the whole RIFT stage and its payload into orbit using just the first two stages of the launch vehicle, and then let it carry the payload out of orbit to its destination.
Could either RIFT or NERVA do multiple starts? Because if it’s a single burn stage that means you can’t do the S-IVB trick of using it to help get you into orbit, then firing it up again to leave orbit.
It could restart, but those son of a guns ran HOT, so at shutdown you had to pump a lot of hydrogen through the system until the reactor semi-cooled. This meant you had to carry a lot of extra H2 for missions involving restarts.
If you look at some of the well-planned mission ideas, like EMPIRE or the Boeing IMI system (available from Scott!!) there were trade studies about how to mix nuclear and chemical propulsion phases to achieve the best overall system efficiency (often defined as lowest mass at planetary injection).
Since you were going to have to cool the reactor down anyway by bleeding LH2 through it, you might as well have stuck in a LOX tank also and run it as a cryogenic engine while cooling it down.
Did you or Kirk take into account the DUMBO reactor design?
As mentioned in the comments Over There, DUMBO was designed so that it kinda fell apart as it burned … i.e. lots of entertaining bits of fissionables in the exhaust. Not exactly an auspicious start for a ground-launched vehicle.
Not from the report I read. DUMBO had *better* containment (and had a prototype fuel element that kept going and going and….) because it was designed from a ‘clean sheet of paper’ to take into account flow whereas NERVA, Kiwi, and etc. were derivatives of known ‘tea kettle’ designs using upgraded fuel elements and holders.
The way I viewed it was that NERVA was good hard working piston engine compared to DUMBO’s gas turbine. 😉
What killed DUMBO was that it came very late in the program and OMB (or whichever bean counter) required them to use the same nozzle and etc set up to test it as NERVA to save money … and they were totally incompatible design wise so it was dropped. Shortly followed by the whole program.
DUMBO had the problem of the technology not being up to the task of cutting the fine laminar-flow grooves in the uranium fuel sheet layers when it was built; they had to run the sheets through something like a precision cardboard corrugating machine and they couldn’t get the channels small enough or regular enough to get true laminar flow. Today’s laser cutting of the channels would have removed that problem.
Another DUMBO problem was that when it was tested they were forced to use the NERVA expansion nozzle, whose design wasn’t optimized for the gas flow coming out of the DUMBO reactor.
There was a very good article about all this in a Analog magazine article from the mid-late 1970’s IIRC.
BTW, the writer of that article who worked on DUMBO was really pissed off about the whole thing and said something like: “So let’s assume the whole mass of the reactor does abrade away and ends up in the atmosphere, even though that won’t happen…for that we can put 60 Skylabs into geosynchronous orbit.”