High Quality Content by WIKIPEDIA articles! SABRE (Synergistic Air-Breathing Rocket Engine) is a concept by Reaction Engines Limited for a hypersonic precooled hybrid air breathing rocket engine for propelling the proposed Skylon launch vehicle into low Earth orbit (LEO). SABRE is the logical continuation of Alan Bond`s series of liquid air cycle engine (LACE) and LACE-like designs that started in the early/mid-1980s for the HOTOL project.