[AR] Re: Circa 1968 video about NERVA nuclear rocket program
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 14 Apr 2018 22:28:48 -0400 (EDT)
On Sat, 14 Apr 2018, Perry E. Metzger wrote:
I've long been interested in the NERVA nuclear rocket program, which
got cancelled when Congress decided in the wake of the first moon
landings to cut back federal funding for NASA...
Small historical correction: the cuts happened *before* the first
landings. The budget debates of summer 1967 were when NASA lost almost
all of its post-Apollo programs, including the ones that had actual
requirements for nuclear propulsion. (At the beginning of 1967, NASA
started organizing a third "summer study" for the lunar-science community,
to begin science planning for post-Apollo lunar missions; by the time its
report was published, that fall, it came with a preface warning that there
was no guarantee that any of it could be funded.) By the time of the
first landing, NASA's budget was plummeting, plants were closing, and
teams were breaking up.
The nuclear-rocket program staggered on for a few more years, on a
combination of political inertia and hopes that some of its customers
might manage to salvage something from the wreckage, but in the end it met
the same fate.
Specific impulse of around 900 seconds with high thrust seems like a
really useful technology, at least for off-planet use.
Unfortunately, it suffers from high dry mass, because of huge insulated
LH2 tanks and engines that are very heavy for the thrust they produce,
which hurts mass ratio badly enough to quite significantly reduce the
benefits of that appealing Isp. Isp is about *engine* performance, but
it's *vehicle* performance that actually delivers payload, and they are
not the same thing. There are still benefits, but they aren't as large as
you might think if you look only at Isp. And they come with costs.
The tank-mass problem could be cured, and the engine T/W problem at least
helped, by running on something like ammonia rather than LH2... but that
reduces Isp to the point that it's no better than competitive with
chemical rockets. (With LOX/LH2 if you're optimistic about how much
ammonia dissociation you can get; with LOX/kerosene if you're not.)
It would be useful, yes, but it has its issues too.
I was unaware that there was a short film made about the development
of the engine...
https://www.youtube.com/watch?v=VzRfPC5rSic
Cool, thanks for the pointer!
Henry
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