The 457mm (18-inch) diameter hybrid rocket is the largest hybrid to be developed outside the US and uses Hydroxyl‐Terminated Polybutadiene (HTPB), a synthetic rubber, as the primary fuel and HTP, highly concentrated hydrogen peroxide (H202), as the oxidising agent. HTP is non‐toxic although it can cause burns; it was used extensively in the UK space programme of the 1950s, 60s and 70s in rockets such as Black Knight and Black Arrow, which used liquid fuel engines burning kerosene. The Falcon pump-fed, 457mm hybrid was static-tested in the UK in October 2013; it was the largest rocket to be fired in the UK for around 20 years. In the process of developing the hybrid rocket, Falcon also produced the largest silver catalyst packs ever made in the UK and reverse-engineered and uprated the Stentor large HTP pump, shown in cut-away below. Falcon also reverse-engineered the turbine so, combined with experience in HTP : kerosene bi-propellant rockets, Falcon has the capability to rapidly redevelop the Black Arrow engine technology.