Romanian company ATD Aerospace RS SRL is developing a 10 kN rocket engine that can be re-ignited and adjust its thrust. This builds on the 1 kN engine they developed with support from the European Space Agency (ESA).

Before working with ESA, ATD had already created several engines in the 0.5–1 kN range, which paved the way for their later developments. This project is part of ESA’s Future Launchers Preparatory Programme (FLPP), that helps develop the technology for future for space transportation systems. By conceiving, designing and investing in technology that doesn’t exist yet, this programme is reducing the risk entailed in developing untried and unproven projects for space.

The firing test seen here shows a water-cooled version as it cycles from 100% thrust to 60% and back to 100%. The test, conducted in Romania in 2025 saw the engine perform as expected. The engine uses hypergolic propellants, which are ideal for spacecraft or rockets that need to store fuel for extended periods.

Turned upside down, the engine could suspend 1000-kg on Earth, the weight of typical hippopotamus. Used as intended it could slow the descent of a rocket stage and ensure a soft touchdown.

Various sensors were used during the test firings to characterise the engine and its functions.

The development involves three designs, starting with an uncooled engine demonstration, a next version that is cooled with water, as seen in this video, and finally a self-contained engine that incorporates its own cooling.

The European Space Agency is financing the development up to the successful test of the final regenerative cooled-engine, reaching a technology readiness level of five with a smaller-scale test firing (TRL5).