Jeff Foust, for SpaceNews:
The PGA engine — its name taken from the initials of Stratolaunch’s founder, billionaire Paul G. Allen — will use liquid oxygen and liquid hydrogen propellants with fuel-rich staged combustion and a thrust of 200,000 pounds-force.
Stratolaunch is currently working on the preburner for the PGA engine, the smaller of two combustion chambers in a staged combustion engine. In a fact sheet, Stratolaunch said it plans to perform a “full-scale” test of the preburner by the end of this year at NASA’s Stennis Space Center in Mississippi.
It’s encouraging that they chose to develop a hydrolox engine for their architecture, and 200,000 pounds-force puts it right about what a Merlin 1D is pushing these days.
Even me, the Stratolaunch skeptic, is quite pleased with these early details.