[AR] Re: MSR reactors.
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Fri, 12 Jul 2019 17:18:34 -0400 (EDT)
On Fri, 12 Jul 2019, Anthony Cesaroni wrote:
...If the reactor and particularly all of the biological shielding
didn't weigh so much, it would have been the ticket for the proposed air
breathing jet engine cycles. The USAF just had to have a nuclear bomber so
they plowed on despite all the obvious silliness of the whole concept.
In fairness, it didn't look quite so silly in the beginning, or more
precisely, all the competing concepts looked even sillier. If it was the
late 1940s and you really, really wanted an intercontinental *jet* bomber,
it was easy to think that a nuclear engine was the only option. Late-40s
jet engines not only had dismally poor T/W, they were also terrible fuel
hogs. For a short-range defensive fighter, okay, but intercontinental?
For that mission, either you had to settle for propellers, or you needed a
power source better than chemical fuels -- and there was an obvious
candidate.
Over the following 10-15 years, not only did the full extent of the
shielding problem become apparent, but also, plain old kerosene-fueled jet
engines got *enormously* better. In piston engines, it's called
compression ratio; in jets, it's "pressure ratio". Late-40s jet engines
had quite low pressure ratios, which is why they performed so poorly in
most ways (about the only thing good about them was no propeller). Then
people started experimenting with higher pressure ratios, and boy did that
ever make a difference. In 1945, a kerosene-fueled intercontinental jet
bomber was an absurdity; by 1960, Boeing was testing the B-52H, the final
B-52 variant, with an *unrefueled* range of over 13,000 miles! And at
some ill-defined point in between, the urgent need for nuclear aircraft
propulsion quietly disappeared, although it took a while for that to sink
in.
The same thing happened to ramjets, assorted concepts for ducted rockets,
etc. In 1945, they looked quite competitive with turbojets and were worth
at least serious consideration. By 1960, not so much, unless you had some
really unusual requirement.
Henry
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