WASHINGTON — Reaction Engines Ltd., a British company that has worked for decades on an air-breathing rocket engine for spaceplanes and other hypersonic vehicles, has filed for bankruptcy.

The company formally entered administration, a process under United Kingdom law to allow for the restructuring or liquidation of companies in financial distress, on Oct. 31 after attempts to raise additional funding fell through. PricewaterhouseCoopers has been appointed as administrators of the company during the process, and under U.K. law has eight weeks to develop a plan to restructure or sell the company, or else liquidate its assets.

As part of the company’s administration process, most of its approximately 200 employees have been laid off. An industry source said that, given the company’s struggles to raise money, the most likely course of action will be liquidation.

The company, founded in 1989, is best known for the Synergetic Air Breathing Rocket Engine (SABRE), an engine concept proposed by the company intended for use on spaceplanes that would allow them to reach orbit without the need for boosters. SABRE would use hydrogen and oxygen, taking oxygen from the air through a unique “precooler” design at lower altitudes and speeds and switching to onboard supplies of liquid oxygen as it ascended towards orbit.

The company proposed using SABRE on a spaceplane called Skylon, a single-stage vehicle that could carry 17 tons to low Earth orbit. Work on Skylon did not advance beyond the conceptual stage, and the company acknowledged that development of Skylon would have cost more than $10 billion.

Reaction Engines continued to work on key technologies for SABRE, securing relatively modest government awards like an $11 million grant from the European Space Agency in 2016. Large aerospace companies, including BAE Systems and Rolls-Royce, invested in the company as it sought other applications for SABRE and its technology, such as for hypersonic vehicles.

The company established an American subsidiary, Reaction Engines Inc., which set up a facility at the Colorado Air and Space Port, an airport east of Denver, for testing elements of SABRE technology like its precooler. That subsidiary is also included in the administration.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...