Innovation in the use of technology, and the search for effective solutions to make space exploration more efficient and sustainable never stops. In the case of solar sails, this revolutionary technology can be the alternative to engines and fuel for spacecraft. In this article, we explain what they are, how they work, which missions are working with them and why they may represent a turning point in space travel.

How solar sails work in space

A spacecraft with a solar sail has huge reflective sails that capture the energy of the Sun’s light and uses it to propel the spacecraft. It is a question of using external sources for power and movement, and these sources will depend on the type of solar sail.

One of the best known and highly developed types are photon solar sails, which use the pressure of light from solar radiation. It works as follows: light reflects off the solar sail, which has a mirror-like shiny surface, so that the photons rebound off of it. When this happens the momentum of the photons is transferred to the sail, giving it a tiny push. These tiny impacts are very small indeed, but there is no friction in space, so that each hit continually adds velocity to the craft that is attached to the sail.

Navigation and steering are similar to how we control a sailing ship, except that the force comes from the light instead of the wind. When a sail is facing the Sun, the photons are moving outwards, away from the source, so we can change direction by modifying the angle of the sail.

But what happens where there is no source of solar energy nearby? In theory, it would be possible to focus powerful lasers on the solar sail to give it some additional momentum when the energy source that the spacecraft needs is far away. This technology has not yet been developed, but in principle it would provide better acceleration than the energy from the Sun.

Advantages of solar sails

The fact that it relies on external sources is one of its main advantages, so that when the technology is more fully developed, the spacecraft will not require motors or even fuel. This is bound to reduce the problem of space debris, because there will be fewer elements floating in space when the mission has ended.

Besides, the fact that the craft or probes do not need either motors nor fuel makes them lighter, so they can reach higher speeds and can other loads.

What is more, spacecraft powered by solar sails can navigate in unstable orbits because they can use the sail’s acceleration power as a balancing force. This enables them, for example, to get closer to the Sun because they are better equipped to face solar storms.

Solar sails can also enable faster space exploration at much greater distances, arriving at more remote planets and solar systems because, despite their low speed when starting, continuous acceleration over time will allow them to reach enormous speeds.

For all the above, and research which is still ongoing, solar sails can represent a real revolution in space exploration.

Some space missions that are already using solar sails to navigate

Although this technology is still not fully developed, and has a long way to go, there are space missions that are using solar sails in space today.

There is the Japanese Space Exploration Agency (JAXA), which has built and successfully launched solar sails with its IKAROS spacecraft, which was the first to demonstrate controlled navigation with solar sails. The sail used by IKAROS is an enormous square measuring 196 m2. It is the largest solar sail built to date, taking the spacecraft to Venus and followed a trajectory to the other side of the sun.

NASA has also worked on this with its small NanoSail-D2 satellite, which was the fifth of its prototype solar sails to achieve a successful deployment. Its solar sail has a surface of 10 m2 and only needed five seconds to deploy.

The Planetary Society, an international not-for-profit organization dedicated to space exploration, has also launched two projects to study the feasibility of this technology for space exploration: LightSail 1, which focuses on testing the method for deploying the sail, and LightSail 2, which is a vessel with a fully operational solar sail of 32 m2 whose goal is to demonstrate the feasibility of solar sail systems for navigating.

The full development of this technology is still a long way off, but it has huge potential and may mark a turning point in space exploration.

(IKAROS photography. Author Andrzej Mirecki)