Zero gravity graphene promises success in space

Working as part of a collaboration between the Graphene Flagship and the European Space Agency, researchers from the Cambridge Graphene Centre tested graphene in microgravity conditions for the first time while aboard a parabolic flight – often referred to as the ‘vomit comet’. The experiments they conducted were designed to test graphene’s potential in cooling systems for satellites.

“One of graphene’s potential uses, recognised early on, is space applications, and this is the first time that graphene has been tested in space-like applications,” said Professor Andrea Ferrari, who is Director of the Cambridge Graphene Centre, as well as Science and Technology Officer and Chair of the Management Panel for the Graphene Flagship.

Graphene – a form of carbon just a single atom thick – has a unique combination of properties that make it useful for applications from flexible electronics and fast data communication, to enhanced structural materials and water treatments. It is highly electrically and thermally conductive, as well as strong and flexible.

In this experiment, the researchers aimed to improve the performance of cooling systems in use in satellites, making use of graphene’s excellent thermal properties. “We are using graphene in what are called loop-heat pipes. These are pumps that move fluid without the need for any mechanical parts, so there is no wear and tear, which is very important for space applications,” said Ferrari.

“We are aiming at an increased lifetime and an improved autonomy of the satellites and space probes,” said Dr Marco Molina, Chief Technical Officer of the Space line of business at industry partner Leonardo. “By adding graphene, we will have a more reliable loop heat pipe that can operate autonomously in space.”

In a loop-heat pipe, evaporation and condensation of a fluid are used to transport heat from hot electronic systems out into space. The pressure of the evaporation-condensation cycle forces fluid through the closed systems, providing continuous cooling.

The main element of the loop-heat pipe is the metallic wick, where the fluid is evaporated into gas. In these experiments, the metallic wick was coated in graphene, improving the efficiency of the heat pipe in two ways. Firstly, graphene’s excellent thermal properties improve the heat transfer from the hot systems into the wick. Secondly, the porous structure of the graphene coating increases the interaction of the wick with the fluid, and improves the capillary pressure, meaning the liquid can flow through the wick faster.

After promising results in laboratory tests, the graphene-coated wicks were tested in space-like conditions onboard a Zero-G parabolic flight. To create weightlessness, the plane undergoes a series of parabolic manoeuvres, creating up to 23 seconds of weightlessness in each manoeuvre.

“It was truly a wonderful experience to feel weightlessness, but also the hyper-gravity moments in the plane. I was very excited but at the same time a bit nervous. I couldn’t sleep the night before,” said Dr Yarjan Samad, a Research Associate at the Cambridge Graphene Centre.

During the flight, the graphene-coated wicks again demonstrated excellent performance, with more efficient heat and fluid transfer compared to the untreated wicks. Based on these results, the researchers are continuing to develop and optimise the coatings for applications in real space conditions. “The next step will be to start working on a prototype that could go either on a satellite or on the space station,” said Ferrari.

The research was supported by the Graphene Flagship and the European Space Agency, as a collaboration between researchers from Université libre de Bruxelles, Belgium; the University of Cambridge, UK; the National Research Council of Italy (CNR), Italy; and industry partner Leonardo Spa, Italy.

Inset image: Professor Andrea Ferrari onboard the parabolic flight.