Vary that thrust: longer hot-fire of rocket engine demonstrator

The Throttleable Liquid Propulsion Demonstrator (TLPD) is a Łukasiewicz Research Network – Institute of Aviation rocket engine demonstrator that will be ideal for use as part of upper stages on small rockets and could be used on spacecraft, kick-stages or exploration missions. The engine can vary its thrust down to 10% and up to 110% of its ideal operating conditions, making it a good candidate for use on landing on other planets. It is restartable and runs on non-toxic easily-storable propellants.

The first test-firing phase last year proved the engine’s operations at different thrust levels in steady states, but kept the engine running at set power levels from startup to the end of each firing. These tests validated the high-tech valves that regulate the flow of the propellants to the engine.  

The team used a passively-cooled combustion chamber during the first phase of testing since the short test duration didn’t require active cooling. As the tests proceeded the team saw that the engine heated up less than the hottest temperatures predicted, so they decided to conduct a first batch of throttling tests ahead of schedule. These tests saw the engineers change the thrust – or power of the engine – while still firing. The results continued to be very promising.

Engine dynamics – new combustion chamber

The second phase of the test campaign in November 2024 had the engine firing up and running at varying thrusts for up to a minute at a time – over seven times longer than in the first tests.

To achieve this, a new combustion chamber was designed and made with additive manufacturing techniques that added water-cooling to allow longer tests while also varying the thrust. It is one thing to keep a rocket engine running at different levels of power, but an extra difficulty to throttle between the different levels. During the throttling the engine runs in so-called transient phases that are by definition dynamic and thus hard to predict or control. The complete engine design worked perfectly with very stable combustion for all engine operating points tested over the 14 hot-fire runs.

Flight-like phase

The success of the Throttleable Liquid Propulsion Demonstrator so far has earned the project to be continued. Over the next two years – with a budget of €5 million – the demonstrator will be upgraded to a flight-like engine adapted specifically for European space transportation needs.

The new engine demonstrator will include technical improvements and optimisations and be designed so it could be integrated into a lander for another planet or moon or for inclusion on tugs and operational spacecraft to remove space debris or refuelling orbital depots.

The project is part of ESA’s Future Launchers Preparatory Programme (FLPP) with prime contractor ‘Łukasiewicz Research Network – Institute of Aviation’ (Lukasiewicz-ILOT) based in Poland and partners Astronika and Jakusz SpaceTech.  A Łukasiewicz spin-off company, Thaliana Space, will join the project in this second phase, working with potential customers to integrate their needs into the engine design.