The Prime rocket was a British light launch vehicle under development by Orbex. Its booster (first stage) was planned to be reusable. The rocket's diameter was , and would use a non-toxic bi-propellant consisting of liquid oxygen and propane. First stage reuse was planned to be achieved by a combination of a parachute and four 'petals' which would fold out prior to atmospheric reentry to induce drag and passively reorient the vehicle. It would be capable of launching payloads up to to a standard 500 km Sun-synchronous orbit (SSO).
In February 2026, the project was cancelled as Orbex ceased operations.
One cited advantage of using propane is that it remains liquid at cryogenic temperatures, which enables a design where a central carbon-fibre tank of propane is surrounded by an outer tank of liquid oxygen, creating a light structural mass.
In 2022, the maiden flight of Prime was expected to occur in late 2025, subject to the availability of SaxaVord Spaceport and a Civil Aviation Authority launch licence, for Surrey Satellite Technology Ltd. In 2025, the first flight was planned for early 2026. Orbex also announced it was chosen by nanosatellite company Astrocast to launch their communications satellites and by Italian in-orbit logistics company D-Orbit for two other launches.