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Old 17th July 2016 | 06:46
  #106 (permalink)  
t43562
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There may be applications for cryogenic fuel / atmospheric oxidiser engines and high-speed / very high altitude wingborne flight but, the efficient upward path to orbit is via the route of minimum time/drag as, I think, was illustrated by the Saturn V.
Fortunately Reaction Engines has plenty of people who know what they're doing and has had the US AFRL and ESA check their work.

Even a non-expert like me knows that SABRE's advantage is that its precooler is so light compared to the amount of cooling it does - this is the main item of new technology after all. The other great realisation was that air need not be liqufied - it just has to be cold enough to compress.

We also know that oxygen is relatively heavy so that you get a great advantage (in payload) from not having to carry enough to reach Mach 5 after which SABRE behaves like a rocket.

Presumably the engineers that have done the sums don't think drag has a significantly negative effect on this outcome. After all the complete launch is only something like 15-20 minutes of engine use if I remember correctly.

I don't know how efficient these different schemes are as I am not a rocket scientist. But I do know that the aim is cost per kilo to orbit, not efficiency.
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