As satellite constellations expand, NASA is concerned about orbital debris

Several aerospace companies, including SpaceX and OneWeb, have promised to launch one day thousands of satellites in low Earth orbit, but these mega-constellations could make space a more congested and dangerous place. This is why NASA recommends in a new report that these companies ensure that their future satellites are out of their orbit once they have completed their missions.

Currently, approximately 4,000 intact spacecraft live in orbit around the Earth, of which only 1,800 are operational. Yet many companies want to significantly increase this number. Satellite operators are eager to launch thousands of sensors capable of transmitting Internet connectivity to Earth, thus ensuring global coverage. SpaceX has filed applications with the FCC for launching nearly 12,000 satellites over the Internet – first, an initial constellation of 4,425 probes, followed by a constellation of 7,518. Meanwhile, the European company OneWeb has received approval to launch up to 720 FCC satellites, and recently requested permission to launch an additional 1,260 satellites.

If all these constellations were successfully launched at about the same time, the number of operational satellites in orbit would quadruple, which would increase the risk of catastrophic and cascading satellite collisions. NASA wanted to know the potential impact of such an environment. Thus, in a new study, the space agency considered future scenarios in which huge constellations of thousands of satellites dominate the low Earth orbit to determine what kind of effect would have. Based on their research, NASA scientists say that almost all these satellites – 99% – will have to be removed from the orbit as soon as they have completed their time in space. This should prevent the number of satellite collisions from increasing over the next few centuries.

"Because of the number of spacecraft involved in large constellations, [these companies] Jer-Chyi Liou, chief orbital debris scientist at NASA who spearheaded the new study, said that one must pay attention to certain areas to make sure they do not pollute the planet. 39, near space environment with significant orbital debris. The edge.

The aerospace industry is particularly concerned about collisions with spacecraft, as these accidents can create several debris that move in space at thousands of kilometers at the time. And these fragments may threaten other spacecraft in orbit, causing new accidents and damage. Many fear that these collisions will cause a cascading effect, where accidents are becoming more frequent, so that the low Earth orbit becomes too crowded to support the satellites safely – a hypothetical future called Kessler's syndrome. Fortunately, collisions have been rare until now. But in 2009, an abandoned Russian satellite struck an American communications probe, creating thousands of debris.

To determine the risks, Liou and his team estimated how many additional satellites could be deployed in space over the next few years, as well as how much space these probes would take. The team assumed that between 6,700 and 8,300 additional probes could be added. They also thought that the spacecraft would weigh about 330 and 660 pounds each and that these probes would run for about five years in orbit. "We have tried to use the information available in the public domain from companies offering large constellations to obtain sizes for these large constellations," says Liou.

These hypothetical futures eventually led the team to propose a 99% recommendation. The advice: for 100 satellites, 99 must be unsubscribed as soon as their mission is over, usually within five years of its completion. This involves lowering the satellite's altitude so that it quickly succumbs to the gravity of the Earth and burns during the descent into the atmosphere of our planet. If this does not happen, the population of spacecraft in low Earth orbit will begin to grow considerably over the years.

Image: SpaceX / YouTube

The more objects in orbit, the greater the chance that spacecraft will have unplanned accidents. For example, the NASA team tested what would happen if only 90% of these large constellations were de-orbited in time. In this situation, the number of collisions would be about 260 over the next 200 years. But if 99% are removed in time, then only 34 accidents would occur in the same period. It's just a little higher than the current risk.

Liou recognizes that 99% is a pretty high number to respect, but it is necessary to keep a low Earth orbit safe for spacecraft. "If you do not reach 99%, the population increase in the environment is important," he says. In addition, similar studies have come to the same conclusion. Scientists at the European Space Agency suggested last year that large constellations should be eliminated at a rate of 95%.

Beyond the need to desorb spacecraft, the NASA study listed some other recommendations for satellite operators. For example, these probes will have to be hardened to withstand any collision with debris in space, including micrometeorites. Thus, if a small rock strikes one of these satellites, the vehicle is not damaged to the point that it can not desorb in time. In addition, these satellites can not explode easily. Since humans began sending space ships into orbit, nearly 200 accidental explosions have occurred in space, according to Liou, which can create debris that endangers other spacecraft. Liou recommends that satellites of this mega-constellation should be built so that their probability of explosion is less than one in 1000.

These recommendations will increase the time and money needed to manufacture these spacecraft and operate satellite networks. But respecting these rules would ensure that near-Earth space remains usable for the foreseeable future. When the FCC approved SpaceX's license for its Internet satellite constellation, it said the company will need to provide an "updated description of orbital debris mitigation plans for its system," although it provides details and analysis. when it is filed. SpaceX told the FCC that it would desorb its satellites in five to seven years. Meanwhile, OneWeb has also boasted that its deorbitation plans are very reliable and will take them out of their orbit in five years. OneWeb declined to comment The edge, and SpaceX did not respond with a statement in time for publication.

Image: OneWeb

There are other backup options that would also allow these satellites to come out of the orbit faster. It is possible that these satellites may be equipped with a "deorbitation kit", such as a balloon or a sail; These tools increase the surface of a satellite, allowing it to be bombarded by more particles in the upper atmosphere, ultimately driving the satellite down. This can be difficult if the satellites are too high and far from the atmosphere. The addition of such kits can also be expensive. "The cheapest solution will rely on satellite propulsion and make the fuel tank bigger," said Jonathan Goff, president and CEO of start-up Altius Space Machines. The edge.

Whatever the case may be, what happens if a spaceship dies and can not move to a lower altitude? This is a plan B, says Goff. "You make your plan A as reliable as possible, but you also have a plan B," he says. That's why many engineers, like Goff, have come up with other ways to clean inoperative spacecraft and get them out of the orbit. Some proposals include vehicles equipped with harpoons, nets or lasers, all of which can help bring down the missing satellites.

But there are also plans for vehicles that can catch up with satellites and seize them, either to make repairs or to place them on an accelerated descent to Earth. It's the kind of spaceship Goff works on at Altius. He proposes that these companies want to add some sort of grappling hook so that future service machines can grasp them more easily. In this way, future service satellites could even repair or refuel missing satellites instead of eliminating them. Then, satellite operators would not need to replace the satellite with a subsequent launch. "We need tow trucks, but we would also like to be the towing service that says," Well, let's see if we can restart your car, "says Goff. "So you can go from providing orbit backup services to broadcasting through" Can we do things to repair or upgrade to extend the life of these constellations? "

We are still far from the years when these constellations become fully operational in orbit. OneWeb is targeting its first launch for the end of the year or the beginning of next year, and SpaceX is in charge of launching a few thousand satellites by 2024 in order to maintain its FCC license. But in the end, Liou hopes that these companies will go ahead safely with their mega-constellations. "They started discussions with the orbital debris community right from the start," he says. "They have a good understanding of the key areas we need to address."

Goff says that the problem of collisions is an extremely important thing to consider if we want to carry out more ambitious missions in low Earth orbit, such as private space stations. "I want to see this future, but that future can not happen if we destroy the low Earth orbit environment or at least significantly degrade it."