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In the program NASA’s innovative advanced concepts (NIAC), the American space agency has selected a solar sailing project that can pave the way for new destinations. This innovation, called Diffractive Solar Sail, can prove to be much more efficient than existing solar sails. Thanks to the phenomenon of diffraction, it can get the most out of all the collected sunlight. A spacecraft equipped with this sail would therefore be more efficient and more manoeuvrable.
Most spacecraft today run on propellant rocket engines or ion engines. It is therefore strange to imagine a sailing ship traveling through space. However, solar sail propulsion has already proven itself. Due to the low pressure generated, this device obviously does not allow a machine to leave the ground, but it is quite applicable to devices in orbit or has reached the escape velocity.
The concept was tested in particular by the Japanese Space Agency (JAXA), which in 2010 launched its IKAROS spacecraft equipped with a 200 m² polyimide solar sail, covered with solar cells on 10% of its surface. This technological demonstration was intended to evaluate the performance of this type of propulsion. Recently, The Planetary Society – a global non-profit dedicated to space exploration – also tested solar navigation through two projects, LightSail 1 and LightSail 2, launched in 2015 and 2019, respectively. LightSail 2 continues its mission today and enables the collection of essential data on this mode of operation.
A sail based on the phenomenon of diffraction
Sunshades work because of the pressure that photons of sunlight exert (called radiation pressure) when they hit their surface. This force is relatively weak, but the larger and more reflective the sail, the more it increases (if the particle is reflected instead of being absorbed, it transmits twice its momentum). By changing the inclination of the sail, it is possible to influence the applied force – by offering more or less sail surface to the light – and thus steer the vessel (like a sailboat).
The main advantage of this propulsion method is that it makes it possible to do without fuel, which gives the ship a very long range to explore the solar system. However, the concept shows certain limitations: the thrust is only maximum when the light rays are directed directly at the sail. The maneuverability is therefore limited, as a ship equipped with such a sail can not move in any direction.
The Diffractive Solar Sail project aims precisely to circumvent this “defect”. In fact, this technology exploits the phenomenon of light diffraction. When the light waves strike the edges of an obstacle (for example, a slit or any other narrow opening on an opaque panel), they deflect from their original trajectory and propagate in different directions on the other side. This is exactly the effect that this new awning seeks: it will thus consist of several small networks, integrated into thin films, which will distribute the received light over the entire sail. In theory, this would allow the spacecraft to use sunlight more efficiently without sacrificing maneuverability.
This technology could make it possible to imagine missions to places that are particularly difficult to reach via traditional propulsion methods, such as orbiting the Sun’s poles. Scientific instruments placed at this position would improve our understanding of the Sun, as well as our ability to predict space weather.
A crucial project for heliophysical science
” Exploring the universe means we need new instruments, new ideas and new ways of getting around Jim Reuter, associate administrator of NASA’s Space Technology Mission Directorate (STMD), said in a statement. That’s why NASA does not hesitate to invest in the most creative and promising projects. ” Our goal is to change that possible, and Diffractive Solar Sail promises to turn it into a range of exciting new mission applications. added Mike LaPointe, acting NIAC presenter.
Now that Diffractive Solar Sail has been selected for Phase III of the NIAC program, the project team – led by Amber Dubill of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland – has funding of $ 2 million over two years to continue the development of its technology. .
The sail must be both strong and light. Thanks to the diffraction phenomenon, it can be smaller than the sunshades tested so far. Dubill and his colleagues have already designed, created and tested various types of materials for diffractive veils; their new funding will further optimize this material. It is also planned to conduct several ground trials to best prepare for future missions.
The team is convinced that its diffractive sails will provide unsurpassed solar observation capabilities; it also plans to place an entire constellation of diffractive awnings around the Sun to collect images and other data. “ With our teams’ combined expertise in optics, aerospace, traditional awnings and metamaterials, we hope to enable scientists to study the Sun like never before. said the project manager.