The heart of space missions: Propulsion

Successful handling of cryogenic propellants paves the way for future space exploration

More than half a century after humanity's first steps on the moon, we are entering a new phase of space missions, including the return to the Moon and the journey to Mars. Achieving this will require a rethinking of propulsion systems. With the participation of ZARM, a review article has been published in the Nature Portfolio Journal "Microgravity" in which cryogenic liquids, in particular liquid hydrogen and methane in combination with liquid oxygen, are seen as the most effective and promising propellants for these space missions. So far, propellants still account for the majority of a spacecraft's transportation mass, so refueling in space is crucial to extend the range of space missions. The work is the result of collaboration between researchers in a European Space Agency (ESA) Topical Team and is dedicated to the physical principles of propellant handling. It will serve as a basis for future investigations and experiments, such as an experiment with liquid hydrogen on a research rocket.

The cryogenic challenge

Cryogenic propellants such as methane or hydrogen become liquid at extremely low temperatures. The extremely complicated handling of these media in space poses a significant scientific and technological hurdle. The article addresses the essential requirements for handling cryogenic propellants, including conditioning, storage, control and transfer. The work also aims to identify gaps in our physical understanding that need to be addressed to enable future exploration missions. Interdisciplinary research in the fields of thermodynamics, fluid dynamics and structural mechanics is required to solve this task.

Stepping stone into space

The refueling of spacecraft beyond our orbit is essential for extending the range and duration of space missions. ZARM Director Marc Avila is co-author of the review article and underlines the relevance of filling stations in space: "The ability to refuel spacecraft after they have overcome the Earth's gravitational field and have already used up most of their fuel en route is a necessary prerequisite for reaching Mars. But to actually make a space filling station a reality, we need strategies that combine scientific and technological progress."

Link to Microgravity article: www.nature.com/articles/s41526-024-00377-5

Contact for scientific questions:
Prof. Dr. Marc Avila
directorate[at]zarm.uni-bremen.de

Contact for media inquiries:
Birgit Kinkeldey
birgit.kinkeldey[at]zarm.uni-bremen.de
0421 218-57755