Single-Loop Coolant: Heat carrier fluid for spacecrafts

Candidate coolant mapping and thermal physical properties screening

© Fraunhofer UMSICHT

Dispersion as heat carrier fluid

One of the first samples of the Phase Change Slurry for a single-loop thermal system in spacecraft.

Project aims

Space vehicles need thermal control systems to provide cooling for the technical equipment and the crew cabin. Radiators outside the spacecraft are used for heat rejection. Hydraulic loops connect inner heat sources with the radiators outside. Due to specific safety and physical requirements, a dual-loop structure with two different heat carrier fluids is commonly used. A single-loop system would have the potential to reduce complexity, weight and auxiliary energy demand, but there is no suitable heat carrier fluid available so far.

Fraunhofer UMSICHT with AIRBUS Defence and Space have been selected by the European Space Agency (ESA) to investigate the possibility to use a Phase Change Slurry (PCS) as heat carrier fluid in a single-loop system. Objectives of the project are the development of a suitable dispersion, the determination of the most important fluid properties and operational tests of the dispersion in test rigs. The dispersion bases on commonly used heat transfer fluids used in spacecrafts and an additional phase change material dispersed into the fluid.


The challenge for a single loop system is to manage with the highest heat load in the hottest environment and the lowest heat load in the coldest environment, which requires a high turndown ration of the system. A fluid of a single-loop thermal control system must meet two performance characteristics: good thermal properties and low viscosity at low temperatures. Furthermore, the fluid shall not risk jeopardizing the health of the crew in the event of leakage.

Project partner


Duration: Since Summer 2018