Page "Tripropellant rocket" Paragraph 8

The concept was first explored in the US by Robert Salkeld, who published the first study on the concept in Mixed-Mode Propulsion for the Space Shuttle, Astronautics & Aeronautics August 1971.

He studied a number of designs using such engines, both ground based and a number that were air-launched from large jet aircraft.

He concluded that tripropellant engines would produce gains of over 100 % in payload fraction, reductions of over 65 % in propellant volume and better than 20 % in dry weight.

A second design series studied the replacement of the Shuttles SRBs with tripropellant based boosters, in which case the engine almost halved the overall weight of the designs.

His last full study was on the Orbital Rocket Airplane which used both tripropellant and ( in some versions ) a plug nozzle, resulting in a spaceship only slightly larger than a Lockheed SR-71, able to operate from traditional runways.