OK, these are just cheap on my part… NERVA artwork simply downloaded from various places on the Net. Meh, what are you gonna do…
Anyway, here are two paintings (essentially the viewgraph artwork of the day… feel free to compare to modern Powerpoint art and weep) of the early Aerojet 1963 Nerva design:
And here’s a much later (circa 1970) rendering of a NERVA engine. Note the long nozzle extension, which appears to be some sort of non-metallic composite. NERVA engines could get away with uncooled nozzle extensions for one simple reason: they weren’t really all that hot. Conventional hydrogen/oxygen chemical rockets have amazingly hot core combustion temperatures… and this is ok, because there are no solid structures within the cores of the engines. A considerable amount of cooling is required to keep the surrounding structures from melting, however. But solid-core nuclear thermal rockets like NERVA *do* have solid structures within the core of the rocket… that structure being the nuclear reactor. As a consequence, the sort of temperatures that a chemical rocket engine deals with regualrly would cause the nuclear reactor in a NERVA to simply melt and flow out the nozzle. So NERVA engines have much cooler exhausts than their chemical bretheren. The reason why even dull NERVA engines still produce higher specific impulses than the most advanced chemical engines is because the exhaust, while relatively cool, has an extremely low molecular weight. Running pure hydrogen, the molecular weight of the H2 exhaust is just… 2. But a hydrogen/oxygen engine running a mix ratio designed to produce a pure H20 exhaust has an exhaust molecular weight of 18. The Isp of a LOX/LH2 engine can be increased by running it fuel (hydrogen) rich… while this lowers the exhaust temperature, it also lowers the average exhaust molecular weight. Still, this can’t approach what a NTR can do.
Whoops, this image is hugenormous (2-point-something megabytes). Click on the link if you want to see it.
5 Responses to “NERVA art”
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Has NERVA ever been the subject of a book? There’s a place for a book on nuclear rocket history.
“To the End of the Solar System: The Story of the Nuclear Rocket ”
“The Nuclear Rocket: Making Our Planet Green, Peaceful and Prosperous ”
“Gas-Core Nuclear Rocket Design”
“Role of Nuclear Power And Nuclear Propulsion in the Peaceful Exploration of Space”
Only the design book is within my price range. I suspect that first one is the one I’d like to put on my shelf.
Well, maybe not. Someone I missed the one with “green” in the title. Usually I avoid anything with “green” in the title.
I rather like the solar thermal rocket idea; biggish inflatable/deployable mirror concentrates sunlight through a quartz? window into a receiver cooled with hydrogen gas boiled off from a liquid supply. Isp around 800 seconds and maybe 50 pounds (max) thrust, but no radiation or shields.
Falls somewhere between electric drives and serious nuclear thermal, but lots simpler. Boeing, and likely others, were batting it around a few years back.
Gas core NTR seems like a really fun engineering challenge.