Sabre is usually described in the context of the Skylon SSTO design but, would it make more sense to use such engines for the first stage of a two stage design?

Basically, would the air breathing capability of Sabre be a worthwhile advantage over a pure rocket to perform the launch to the upper atmosphere phase in a staged design.

(Presuming the full recovery of the mooted Sabre first stage, here).


The Reaction Engines Ltd (REL) web site has this to say:

"The resulting increased system performance enables aircraft-like horizontal take-off and landing operations, which reduce cost, infrastructure, and mission timelines while increasing responsiveness and system reusability. SABRE class engines are applicable in both multi-stage and single-stage architectures."

REL have been distancing themselves from SSTO as the first application for several years - you'll be hard pressed to find any mention of Skylon on their site now. A 30th Anniversary tweet showed a badge/patch including their current TSTO concept -- complete with (the other sort of) aerospike:

TSTO 30 years

They have participated in a number of studies using SABRE engines as the first stage, including those with the Air Force Research Laboratories AFRL SABRE TSTO fully reusable

and Paris University/CNES

SABRE TSTO options

Latest REL TSTO concept : REL TSTO concept 2019


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