The successful review of the hypersonic engine, which is designed to act as both a jet and a rocket, means that the company can move on the major testing milestones in the next 18 months.

It's been more than 30 years since the ancestor of the SABRE engine began development, with significant investments by Boeing, Rolls-Royce, ESA, and UKSA to the tune of tens of millions of pounds. This may seem like a long time, but SABRE, which is the power plant of the Reaction Engine Skylon spaceplane , is a significant step forward in orbital launcher design.

SABRE is a hypersonic hybrid engine. It draws in air to act like a conventional jet while accelerating to speeds of up to Mach 5 (3,704 mph, 5,961 km/h), then converts to a pure rocket engine burning hydrogen and liquid oxygen, making speeds of up to Mach 25 (17,521 mph, 29,808 km/h) possible.