Reaction Engines Limited

In 1989, Reaction Engines was founded by Alan Bond (lead engineer on the British Interplanetary Society's Project Daedalus), Richard Varvill and John Scott-Scott (the two principal Rolls-Royce engineers from the RB545 engine project). The company conducted research into space propulsion systems, centred on the development of the Skylon re-usable SSTO spaceplane. The three founders had worked together on the HOTOL project, funding for which had been withdrawn the previous year, in 1988.

In 2015, BAE Systems agreed to buy a 20% stake in the company for £20.6m as part of an agreement to help develop Reaction Engines' Synergetic Air-Breathing Rocket Engine (SABRE), a hypersonic engine designed to propel the Skylon orbiter.

In April 2018, Boeing announced an investment in Reaction Engines, through Boeing HorizonX Ventures, with a $37.3 million Series B funding alongside Rolls-Royce. Rolls-Royce and REL announced a strategic partnership in August 2020, with a £20m investment.

In January 2023, the company announced that it had raised a further £40m from backers including the United Arab Emirates Strategic Development Fund.

At the end of October 2024, after unsuccessful attempts to raise more money from investors, the company ceased operations, laying off the majority of staff and entering administration.

Skylon

Skylon was a design for a single-stage-to-orbit combined-cycle-powered orbital spaceplane.

SABRE

Skylon, and the SABRE engine by which it was to be powered, were being developed as a private venture which aimed to overcome the obstacles that were imposed on further HOTOL development due to the British government classifying the HOTOL engine as an official secret, and keeping the engine design classified for many years afterward.

The company's development effort was focused on developing a ground demonstration of the SABRE air-breathing core, with additional funding gained from the sale of consultancy and spin-off applications from its heat exchanger expertise.

In February 2009, the European Space Agency announced that it was partially funding work on Skylon's engine to produce technology demonstrations by 2011. With this funding, Reaction Engines completed a non-frosting sub-zero heat exchanger demonstration program, Bristol University developed the STRICT expansion/deflection nozzle, and DLR completed an oxidiser-cooled combustion chamber demonstration. Reaction claimed this work moved the Skylon project to a TRL of 4/5.