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Old June 29th 20, 03:25 PM posted to sci.space.policy
David Spain
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Default The Rocket Motor of the Future Breathes Air Like a Jet Engine

It took forever for this article to finally getting around to mentioning
the technological leader, the Sabre engine from Reaction Engines.
Almost no mention of how a "Fenris" engine works. You have to follow the
link "Fenris" which takes you to a non-patent office page of what
appears to be a patent application, but isn't? It does look different in
fundamental design from the Sabre. But the lead illustration in the
Wired article is the Reaction Engine's Sabre engine not the Fenris. I
wouldn't be too happy with that if I were from Reaction Engines. I
haven't had time yet to study the Fenris, so I have no clue as to how it
works and in what ways it is different from a Sabre engine.

As Henry Spencer points out (again and again) LOX is cheap and
plentiful. These air breathing designs are optimizing for the wrong part
of the problem. You'd have to get enormous reuse out of these systems to
compete with a single Falcon Heavy launch. And once Starship becomes
fully operational, well, maybe they could launch Skylons out the cargo bay.

I wish these designs good luck from an engineering prospective I think
they are very interesting. Will they ever compete against traditional
two stage rockets? It could be the Stanley Steamer vs. the Gasoline
Engine all over again. I suspect these systems have a much better future
as quick deploy crewed military vehicles rather than cargo lifters.
There just isn't enough oomph there. And don't forget Starship in its
two stage version is also fully reusable w/o the technical complications
of a bleeding edge engine.

BTW if you an basing your fuel around the hyper hard to handle liquid
hydrogen in order to make the Reaction Engine work at all, you are
really really up against the fuel density issue.

Or as Ben Rich called them, Wide-Bodied Dogs....

Dave