RFA One

The first stage is powered by nine Helix engines, each producing 100 kN (22,000 lb_f) of thrust.^[3][10] The second stage will use a vacuum-optimised version of the Helix engine.^[10] The Helix engine uses rocket grade kerosene, known as RP-1, fuel and liquid oxygen oxidizer.^[3] During 2020 the company redesigned Helix from a gas-generator cycle to an oxygen-rich staged combustion cycle.^[3] Some components used in early engine versions, such as the turbopump, were procured from the Ukrainian company Pivdenmash to shorten development time.^[11] Later versions of these components have been developed internally.^{[citation needed]}

The third (or "orbital") stage, named Redshift, will function as an orbital transfer vehicle (OTV). Powered by an RFA-developed Fenix engine, with propellants of nitromethane fuel and nitrous oxide oxidizer^[5] the engine can be restarted multiple times on orbit. This allows the vehicle to achieve different orbits within a single flight and complete various missions for particular customers.^[3]

The rocket is designed for serial production and is aiming to use a large number of COTS components to reduce production and launch costs. Major components of the engines of the first two stages are to be 3D printed.^[12]

In August 2021 RFA performed a cryogenic pressure test on a prototype first stage, during which the prototype burst.^[13][3] Three hot fire tests for performed with the Helix rocket engine with a total duration of 74 seconds in July 2022. The second stage was approved for flight operations in May 2023 through the integrated system test with 280 seconds of hot fire.^[14]

In April 2024, RFA reported successful installation of five of nine Helix engines onto RFA One's first stage in preparation for transport to SaxaVord Spaceport for hot-fire stage testing.^[15]

The first stage of the RFA One arrived in SaxaVord Spaceport in May and successfully performed its first hot fire test with five Helix engines that same month.^[16][17]

On Monday, 19 August 2024, a static fire test of the first stage with all nine engines, the stage that was slated to fly on the maiden flight of RFA One, experienced an anomaly that resulted in a fire, subsequent explosion, loss of the stage, and major damage to the launch mount.^[18][19][20] Ground testing of a new RFA One launch vehicle is slated for 2025, which is also the revised estimate for a first orbital launch attempt.^[9] A launch license was granted by the Civil Aviation Authority on 16 January 2025, limiting the company to 10 launches per year as well as no more than two in any given month, and requires 60 days' notice for range safety purposes.^[21]