the French startup sets sail (solar) for space

Photonic propulsion was imagined centuries ago, but never implemented. This will be the case from October.

When you think of a space rocket, you see a mountain of technology. But few people understand just how full a launcher actually is. Because it is nevertheless the biggest problem in the world of space today. Whether electrical or chemical (with propellant), the latter is limited, and it weighs heavily on the scales. But to go into space, every (kilo) gram counts. It is therefore necessary to lighten other elements, such as the payload, or else pay more, to launch more weight towards orbit.

To respond to this fuel problem, the best would therefore be to simply remove it. And it is with this idea, as crazy as it is simple, that Louis de Gouyon Matignon launched Gama in October 2020 alongside Thibaud Elziere. Since then, this company, based in the Paris region, has been working hard to produce a “spaceship” without fuel, and therefore without an engine.

You can find the full interview with Louis de Gouyon Matignon on Presse-citron.

A centuries-old principle

Behind this feat of engineering, in fact, hides a method that is more than 300 years old, known to astronomers even before the flight of Sputnik. As sailors have done for a very long time, Gama has the objective of making a probe fly and travel, thanks to a sail. An idea that is surprising to say the least, but which does not slow down the development of the young company. Today the company announced a fundraising of two million euros, carried out, among others, with BPI France and CNES, which shows the seriousness of the project.

Imagined centuries ago by the famous astronomer Johannes Kepler, then confirmed by the work of Maxwel, the solar sail has never won over engineers and hardly anyone has sent one into space, despite our very good theoretical knowledge on the subject. As Louis Gouyon de Matigon explains. “Today there must be 10,000 satellites in space, and those with a solar sail must be counted on the fingers of one hand. » Gama’s project is therefore quite ambitious, not to say unprecedented. Indeed, only the IKAROS probe, launched by the Japanese space agency (JAXA) at the beginning of the last decade has demonstrated convincing results.

A first flight to learn from 2022

Finally, the theory behind how a solar sail works is quite simple. As with a sailboat at sea, the idea is to be pushed by the elements. But obviously in space, there isn’t the slightest gust of wind — the solar wind has no impact on thrust here — the sail will therefore reflect the light from the Sun, and it’s precisely the photons that make up the latter, which will propel the sail (which explains the name photonic propulsion).

For Gama, we therefore have the right to a sail of nearly 75 m2, built in four pedals of nearly 20 m2 each. This square veil is extremely thin – 20 to 100 times thinner than a hair – will therefore be pushed by the photons in the vacuum of space. “The great advantage of this system is that the thrust is theoretically infinite. Although it is minimal, it accumulates and over time we reach incredible speeds » explains Louis de Gouyon Matignon.

In order to carry out a first life-size test, Gama is preparing to launch into orbit, thus propelling the sail and the hopes of the whole society into space. The flight should take place next October aboard a Falon 9 from the American company SpaceX. This mission should make it possible to verify that “all is well” and ensure a first experience with the vacuum of space for the very young company and its ten engineers, all based in Île-de-France.

Lens Venus?

But as far as the young French company is concerned, the objective will be to very quickly launch into the deepspace, interstellar space. As such, the company hopes to be able to carry out a mission around 2025 “ to Venus or an asteroid. A key step in the development of Gama, which will allow us to achieve our first exploration objective. “Bringing back a photo of Venus would be really something incredible” explains Louis de Gouyon Matignon, who struggles to hide his excitement.

Built with aluminized polyimides, this sail measures only three microns thick for 11 kilograms on the scale. “Folded, it is the size of a shoebox”, once in space, it unfolds thanks to the centrifugal force of the probe itself. “Thanks to small masses, the sail will open in the opposite direction to the rotation of the probe. » Once deployed, the probe will reflect the Sun’s rays and be pushed by them.

On Earth we know only one of the two forces of the Sun. The thermal impact of its rays. But our star is also capable of moving objects with the force of its photons. These particles (which are also waves) release neither mass, nor energy, nor heat, but when it comes into contact with matter, it pushes it very slightly. It is this thrust that Gama’s sail uses to move through space.

Infinite power…on paper

If the thrust produced by photons is derisory compared to a conventional rocket engine, the sail is an inexhaustible source of energy (or almost). As Louis de Gouyon Matignon explains, photonic propulsion is perfect for low-cost distant exploration.

“By removing the fuel from the probes, we are offering a much lighter system, which therefore costs less to send into space, and which can, in addition to that, last longer over time. » Although the veil system is not eternal, radiation from space and micrometeorites will eventually get the better of this “extra-thin survival blanket”, it is possible to accelerate the probe, as the latter is struck by the rays of the Sun.

With a minimal but constant supply of power, it is then possible to imagine an even further exploration. Gama thus plans to go to Jupiter or Neptune in just a few years. Thanks to the force of the Sun, the probe, weighing a few kilograms, would be able to move at crazy speeds “which today are unattainable with chemical propulsion”. By playing with celestial mechanics and the different gravitational forces of our solar system, it would therefore be possible to travel to Neptune or the moons of Jupiter.

Missions that can be carried out with chemical propulsion probes, and which have already been carried out in the past, but only government space agencies have managed to afford such a journey. With the Gama system, the solar sail could reduce the cost of the mission, but also the duration of the latter.

The solar sail has an Achilles heel: the orbit

If photon propulsion has many advantages, this system is not perfect. It is these defects that have made the solar sail so unpopular in the world of low orbit, which is today the main playground of New Space. The first thing to remember about the solar sail is that the latter, by its very design, is not capable of having a very high reactivity.

This does not pose a problem for distant exploration missions, but for satellites or probes present in orbit, the speed of reaction is essential. “If you have a satellite in low orbit, you want to tilt it to see another region of the Earth, you press a button in your command center and it’s done. We, with a solar sail, cannot do that” recognizes Louis de Gouyon Matignon.

But this lack of reactivity is not the only defect of the solar sail. Indeed, the latter also produces a “trail” when it moves in orbit around the Earth. Hundreds of kilometers above our heads, there are still a few atoms of air, and these will bring the sail back to Earth. Due to its large size, the sail will descend more quickly than conventional satellites, which also have a propulsion system to compensate for this return to the blue planet.

Gama: solar system lens

In short, photonic propulsion is not made for the Earth, and everyone is well aware of this at Gama. Indeed, if the company aims for orbit for its first launch in October, it does not intend to stay there and hopes to be able to reach the four corners of the solar system as quickly as possible.

In any case, with such a revolutionary propulsion system, Gama is not lacking in ambition, and it hopes to be able to produce many sails in the coming years, in order to multiply launches and thus achieve a certain financial balance.

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