The project team GrapheneSail confirmed working capacity of the developed graphene solar sails, which could significantly accelerate under the action of laser radiation under conditions of high vacuum and microgravity. Thus, graphene can be considered as a promising material for the fabrication of solar sails for spacecraft. Article published in the journal Acta Astronautica, a brief account of the work described on the ESA website.
The principle of acceleration of the spacecraft using light sails is based on the pressure exerted by the photons on any surface, transferring her momentum. As a light source can be a terrestrial or orbital laser system or, if to speak about the interplanetary environment, the Sun. The advantages of this method of acceleration apparatus lies in the unlimited duration and lack of flow of the working fluid. It is believed that the use of sails may allow for a relatively short time to reach the closest planetary systems, however, is fraught with difficulties. To date, solar sail was successfully tested on the spacecraft IKAROS and LightSail 2.
The sail should be relatively large, light, have a high reflectance and be sufficiently robust to withstand the process of deploying and the impact of cosmic radiation. In their design, mostly use a thin film of Kapton or Mylarwith a thickness of several micrometers, coated aluminum coating of nanometer thickness to increase reflective abilities. However, there are other engineering solutions, such as films of aluminum, magnesium or beryllium or carbon fiber.
The project GrapheneSail, developed by the European company SCALE Nanotech and supported by the European space Agency, offers the option of a solar sail consisting of double-layer graphene covering the copper lattice, accelerated by the laser beam. This structure allows to reduce the average density of the sail and make it hard enough.
The project team, headed by Santiago Cartmel Bueno (Santiago Cartamil-Bueno) published the results of tests of model sails the high vacuum and microgravity. Model sail weighed 0,25 milligrams and consisted of a circular copper mesh with a diameter of 3.05 mm and a thickness of about 30 micrometers, on which were placed two layers of CVD graphene. Samples were loaded in a vacuum chamber to which was supplied from two fiber lasers with continuous wave radiation with a power of one watt operating at wavelengths of 450 and 655 nm. The camera was also a tracking system based on optical microscope. The entire installation together with battery and control system housed in a capsule that has a fold down inside 100-meter tower ZARM Drop Tower in Bremen, thus, by 4.7 seconds inside the capsule was a regime of microgravity through freefall.
Experiments have confirmed the efficiency of the sail. The value of thrust and acceleration for the sample without graphene in the power range of the laser radiation from 0.1 to 1 watt, respectively 31 millimeter per second squared and 8 nanonewtons, while for samples with graphene, these values amounted to 47-992 millimeters per second squared and 12-248 of nanonewtons depending on the power and the operating wavelength. The obtained thrust values one order of magnitude greater than the results of theoretical calculations, which requires further work and is of great interest in graphene as a material for solar sails.
Earlier we talked about how interstellar asteroid suggested to catch up on a laser sails and looked like our planet from a space sailing ship Lightsail-2.