Hybrid propulsion offers a cheap and performing solution to power future operational space transportation systems. It combines the benefits of solid and liquid propulsion.
Initiated in 2010, the Unitary Motor propulsion demonstrator was developed within ESA's Future Launchers Preparatory Programme.
Following several small scale tests the first large scale hot fire test was successfully achieved in 2014. A final static firing in July 2018 proved the motor for its suborbital launch.
On 27 September 2018, the motor powered the Nucleus demonstrator, a single stage sounding rocket developed around the engine for in-flight testing. Nucleus, launched from the Andøya Space Center, reached an altitude of 107 km in less than 3 minutes, deployed 6 payloads and then splashed down in the Atlantic Ocean.
The hybrid engine combines liquid hydrogen peroxide with solid HTPB fuel and reaches a thrust level of 30 kN. For greater performance, single motors can be clustered while using a common oxidiser supply.
A future version of the motor is planned to have an increased thrust of 75–100 kN, harnessing advanced turbopump technology. This is an important step towards using hybrid propulsion on orbital rockets, such as microlaunchers.