ESA-backed researchers from Delft University of Technology in the Netherlands and SCALE Nanotech in Estonia have demonstrated the laser-propulsion of graphene sails in microgravity.

As demonstrated first by JAXA's mission IKAROS (2010) and recently by The Planetary Society's LightSail 2 (2019), using light sails as propulsion system is among the most promising ideas to enable fast and affordable space trips. Not only sails do not require fuel to move, but they save its corresponding costly weight and that of its containing tanks.

Unfortunately, the light radiation pressure (momentum transfer of photons) only confers relevant acceleration when the sails are sufficiently large (from few to thousands of squared meters) with a minimal mass, and currently used materials are limited when scaling up their size.

"Graphene is part of the solution", says Dr. Santiago J. Cartamil-Bueno, SCALE Nanotech's director and leader of GrapheneSail team. "We demonstrate a novel sail design that reduces the overall sail mass by using perforated films. By covering the holes with CVD graphene, the full area of the sail is again available for optical performance at minimal mass cost. The fabrication is relatively simple and could be easily scaled up to squared kilometers, although the in-space deployment of such a giant sail will be a serious challenge".

With the support of ESA, the researchers gained access to the ZARM Drop Tower in Bremen (Germany), in order to test the graphene sails in space-like conditions. Here, experiments are performed in a free-fall capsule that ensures a high-quality microgravity environment (<10-6 g) for few seconds. When the sail prototypes of small sizes were weightlessly floating, they were irradiated by 1W lasers and started to move with accelerations up to 1 m/s2.



Dr. Thorben Konemann, Dep. Scientific Director, ZARM Drop Tower Operation and Service Company, remarked: "It is always a great pleasure for us to support visionary and promising experiment concepts. The success of the GrapheneSail team underlines again the capabilities of the Bremen Drop Tower - offering not only an excellent microgravity environment for fundamental research, but also being a first stepping stone and testbed for space technology without the complexity of in-orbit operations".

Accessing this type of facilities is not trivial, even for such a breakthrough initiative. Luckily, Dr. Astrid Orr, ESA's Physical Sciences Coordinator at ESTEC, saw it different: "this project is a wonderful example of scientific research that can be performed with the support of ESA on a ground-based space-analogue platform - in this case microgravity - and which also has high potential for ESA's future spaceflight and exploration programs".

"We want to set sails to Mars before SpaceX," jokes Dr. Santiago J. Cartamil-Bueno, "but for now we keep our feet on the ground. Currently, the graphene sails are being developed through the European Space Agency Business Incubator Center Hessen and Baden-Wurttemberg and we look for more strategic partners that allow us to scale the technology up for an eventual test in space".

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