Scientists of Samara National Research University, together with their colleagues from the City University of New York, has been developing a space solar sailing vessel to be able to overtake the currently existing fastest probes and reach the most remote areas of outer space.

The researchers are convinced that, without using even a gram of terrestrial fuel, these spacecrafts can become a serious alternative to traditional spaceships, engines of which consume tons of rocket fuel. For flying in outer space, such a sailing vessel needs only thin pressure of photons emitted by the Sun.

Sunlight particles have an impulse and transmit it to any illuminated surface, creating pressure that carries the spacecraft with it. The thrust generated depends on the sail area and the weight of the ship itself - how light it is. The sail unfolds and focuses on the sun. Accelerating, it is potentially capable of moving at a speed of 120,000 km/s and more. For comparison, the fastest speed of “Voyager 1” is 17.2 km/s.

The key advantage, of course, is obvious. Chemical-fuel engines can run for hundreds of seconds, plasma engines can run for thousands of hours, but both are limited by the working substance reserve. But sails can give thrust while their surface is simply illuminated by the Sun. And, according to astronomers, the Sun will do it for about 5 billion more years.

The ability to fly indefinitely makes sails ideal for exploring the inner Solar system, where sunlight is abundant.

Previously, the American University’s scientists participated in developing NanoSail-D and NEA Scout frame-type solar sails. The spacecraft were launched into outer space in 2010 and 2022. The first one successfully unfolded and functioned in the Earth orbit, but the second one was lost, and obtaining data from it failed.

The device, which is being developed now, is a round inflatable structure in the donut shape. Its middle part is covered with a thin membrane: this is the solar sail. According to the developers, at the right moment, the inert xenon gas will inflate the entire structure, and the sail will unfold.

The hull will be covered with special substance that will begin evaporating as it gets closer to the Sun. The additional impulse will provide acceleration, as if this were a jet engine. According to preliminary estimates, the new sailing vessel will be able to develop the speed sufficient for reaching even the Oort cloud at the edge of the Solar System in 20–30 years.

The Oort cloud is located 2,000 times away from the Sun than the Earth. The same star long-distance runner “Voyager 1” will take about 300 years to get there.

“This means that we or the next generation will be able to getnew information from the Oort cloud, presumably generating all comets, and study the matter that has remained unchanged since the Solar System formation about 4.6 billion years ago,” says Professor Olga Starinova, Head of Samara University’s Department of Flight Dynamics and Control Systems.

Scientists have estimated options for flying a sailing vessel to all the planets of the Solar System. So, small sailing vessels can stay in orbits near the Jupiter, the Saturn or the Mars for a long time, transmitting scientific data to the Earth. By the way, a sailing vessel will be able to reach the Jupiter in just a year instead of four or five years by traditional spacecraft.

The developers have already calculated the trajectories for travelling to the Sun, which will allow getting as close as possible to the star, using solar energy to gain speed, without burning down the device. And in the near future, they want to test another way of gaining speed, suitable for deep space missions.

According to Olga Starinova, the Americans are now focused on testing another sail in outer space. It’s about NASA’s Advanced Composite Solar Sail System (ACS3), which is demonstrating the technology for manufacturing and unfolding solar sails for future small spacecrafts. Launching the experimental cubesat satellite took place on April 24 this year from New Zealand. The main objective of the mission is testing composite masts made of flexible polymer and carbon fiber, which are capable of unfolding from small structures into rigid and lightweight struts of 7 m long each. Herewith, the sail, thickness of which is only two microns (thinner than a sheet of tissue paper) must withstand loads without breaking.

“If the ACS3 flies successfully, then the next one should be ours. This is in about three years,” noted Olga Starinova.

By the way, solar sails can be used for scientific research not only in deep space, but also in near-Earth orbits. For example, for lighting cities or floating platforms in polar latitudes.

For the first time, a real solar sail to appear in outer space was not anyone’s else, but Russian: It was tested in the early 90s of the last century as part of the orbital experiment “Znamya 2”. Oleg Saprykin, General Director of the Consortium “Kosmicheskaya Regata”, told “Rossiyskaya Gazeta” about unknown or already forgotten details, “In 1989, the international competition on creating spacecrafts with solar sails and their flight to Mars was announced. Applications for participation were submitted by the USA, Canada, Great Britain, Italy, China, Japan and the Soviet Union. But it was not easy to build a light and reliable spaceship with a big sail. Foreign applicants provided for one or another frame structure to maintain the shape of the sail, and the total mass of the spaceship became unacceptably large. in our project, there was no frame: the solar sail was a disk made of the 5 micron thick polymer film with the aluminum coating. Two such disks rotating in opposite directions were to be installed on the spaceship. This created centrifugal forces that stretched the film, ensuring its flat shape. The project turned out to be the best and received the highest rating from the competition jury.”

But the race under solar sails did not take place, because the organizers had no financial support. Despite its cancellation and the collapse of the Soviet Union, work on the domestic project did not stop. In 1993, the Russian sail was brought in folded form into low-Earth orbit by the “Progress M-10” transport spacecraft and unfolded in working condition.

The diameter of the sail-disk formed by eight sectors of a thin mirror film was 20 meters. The purpose of the experiment was testing the method of unfolding a thin-film structure in outer space and maintaining its stability due to rotation. The option of illuminating the Earth with sunlight reflected from the sail was also studied. This has become the second, very promising area of use of the technology being created.

The experiment was generally successful, although some design flaws were revealed. Then the project of the improved reflector “Znamya 3” was launched, and preparation of the intermediate project “Znamya 2.5” began. The latter was launched into space in October 1998 by the “Progress M-40” spacecraft.
However, everything was prematurely terminated due to an error in the automatic control program.

But the third project, “Znamya 3”, in which it was supposed to unfold a large mirror with its diameter of 60–70 meters and for which other material with increased radiation resistance was chosen, did not take place. According to experts, its inclusion in the long-term program of space experiments did not save it either.

“Financing has not been opened,” notes Oleg Saprykin, “the program has been revised several times, but this one has always been present in it. During the operation of the “Mir” Space Station, and, after its drowning, the ISS, the project “Znamya 3” remained an important component of the planned scientific and technological work on board. However, the money has not allocated yet.”

The developments remained. Scientists believe that flight tests of the solar sailing vessel in the “Znamya 3” experiment are of not only applied, but also of fundamental importance. The results will open up prospects for developing unique spacecrafts capable not only of carrying out long-term flights within the Solar System without fuel, but also illuminating our country’s northern regions by using space mirrors, regulating solar radiation directed at the Earth to “compensate” for climate change, as well as serving as “space beacons”, and performing other important scientific and technical tasks that require a long stay in outer space.

By the way, there was one more interesting project in Russia. In 1999, the Lavochkin NGO accepted an order from the US Planetary Society for the design of the solar sailing vessel “Kosmos 1”. For accelerating, it had to use the 30-meter mirror film consisting of eight separate segments.

The first operational solar sailing vessel was the Japanese IKAROS spacecraft, launched in 2010. This device was equipped with the sail measuring 14x14 meters. In 2015, the “LightSail-1” nanosatellite with the 32 square meter solar sail was launched in its test flight from the American spaceport at Cape Canaveral. Another similar spaceship was launched in 2019.

Scientists believe that solar sails can be used for exploring two promising icy moons in our Solar System: Jupiter’s moon Europa and Saturn’s moon Enceladus. They are considered the key objects for searching extraterrestrial life due to the likely presence of the salty ocean beneath their surface.

The geysers of water emitted by the Enceladus and the plumes observed on the Europa will provide unique opportunities for exploring the composition of these oceans without having to land on them, according to the paper published in the journal “Acta Astronautica”. According to estimates made by the authors of the study, a 100-kilogram solar sail can reach the Europa in just one to four years, and the Enceladus – in three to six years. Modern technologies demonstrate their capacities for ensuring interstellar missions and exploring new horizons.

After materials of “Rossiyskaya Gazeta”: rg.ru