Graphene sets sail in microgravity

image: Graphene light sail of 3mm in diameter with a mass of 0.25 mg 'sets sail' when pointed with a 1W laser. The prototype has a graphene micromembrane design that reduces the overall mass while keeping functional the complete area of the sail. view more 

Credit: Dr. Santiago Jose Cartamil-Bueno

Overseas exploration and trade during the Age of Discovery (15th-17th centuries) were possible by sail technology, and deep-space exploration will require the same for the coming Age of NewSpace. This time, however, the new sails shall move with light instead of wind, for which these light sails need to be extremely large, thin, lightweight, reflective and strong.

In a light-hearted leap for humankind, ESA-backed researchers demonstrate the laser-propulsion of graphene sails in microgravity. In an article recently published in Acta Astronautica, they report a scalable design that minimizes the overall sail mass and hence increases their thrust upon light irradiation. In addition, they prove the new sail concept by accelerating prototypes in a free-fall facility with 1W-lasers, reaching up to 1 m/s2. This milestone paves the way for lightweight ultralarge sails and eventually may help us to reach other star systems in a human lifespan.

Let me play among the stars

Physical exploration of deep space became a reality when NASA's Voyager 1 left our Solar System in 2012, after a trip of 35 years and 121 AU (18,100,000,000 Km, 11,250,000,000 mi). Were Voyager 1 traveling to Alpha Centauri Cb, the exoplanet of our closest neighboring star system at 260,000 AU, humanity would have to wait dozens of millennia and hope that the shuttle kept some power to reach us then.

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".

Völlig losgelöst, von der Erde

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 (