Testing graphene in space-like microgravity

A team of students working at Delft Technical University (TU Delft), the Netherlands, are preparing an exciting experiment to test graphene in space-like microgravity, for potential future use as a light sail in space-craft propulsion.

The GrapheneX team successfully submitted their experiment proposal to ESA Education’s Drop Your Thesis! Programme in October 2016. The team members – Santiago Cartamil-Bueno, Rocco Gaudenzi, Davide Stefani and Vera Janssen – travelled to Bremen, Germany between 6-17 November 2017 to perform their experiment at the 146 m ZARM Drop Tower.

Light sails can be used in space as a method of propelling spacecraft using light from the sun or from Earth-based lasers. When light is reflected from or absorbed by a surface, it exerts a force that pushes the surface away from the light source. This radiation pressure can be used to propel objects into space without using fuel or gases.

However, the thrust generated by radiation pressure is very low. For effective propulsion, the light sail must have a large surface and be as light as possible. Graphene is very light and strong, and could be a good candidate for solar sails. The GrapheneX team plan to investigate how graphene could work as a light sail in an experiment that simulates the low-gravity and high-vacuum conditions of space.

The sails to be tested by the GrapheneX team are graphene membranes, supplied by Graphene Flagship partner Graphenea. The radiation pressure from shining high-power laser light onto the graphene membranes should cause the sails to move approximately 2mm. This displacement will be measured with a simple microscope to determine the thrust on the graphene sails. The team plan to use different colours of laser light, to investigate the exact mechanism of how momentum is transferred to the graphene from light.

At the ZARM Drop Tower, the experiment – including graphene sails, lasers and cameras - will be loaded into a capsule and catapulted the height of the tower. Inside the tower, vacuum conditions allow the capsule to rise and fall without friction or air resistance, so that the capsule experiences apparent weightlessness down to one-millionth of the Earth’s gravitational force. As the capsule accelerates, the graphene sails will be released into almost gravity-free free-fall. At this point, the laser will be allowed to shine onto the graphene chip, and the pressure generated by the laser falling onto the graphene will be detected. A key challenge of this experiment is automating the experiment procedures to initiate and record the results in the 9.3 seconds of free fall.

All preparatory work for this experiment is being carried out by the GrapheneX team at TU Delft, with support from Herre van der Zant (TU Deflt), Angelo Cervone (TU Delft) and Jian Rong Gao (Delft Space Institute, the Netherlands). As part of the Drop Your Thesis! programme, the team are also mentored by Pekka Janhunen (Finnish Meteorological Institute, Finland). This experiment is supported by ESA Education, the Graphene Flagship, and the Delft Space Institute.