Two satellites almost collided. How did they manage to avoid a crash?

The first alarm came on January 27th. Two small satellites circling around the Earth in low orbits, were in a situation of possible contact. Satellites, one of which belonged to Capella Space, and the other Spire Global, could collide. Concern about possible collisions was filed by the 18th Space Control Squadron of the United States Air Force - management does this every time when it considers the collision event to be quite likely. The likelihood of a collision can be either very small or frightening. The squadron estimated the probability in the range of 0.2-10% over a 72-hour period. But this is fortune telling on the coffee grounds.

If satellites collided, wreck satellites(years of work, a lot of money) would also be scattered across space. Then they would turn into more debris that already flies around the Earth, threatening other orbiters.

Spire, which has about 60 small satellites tracking ship and weather, did not particularly bother with this warning.

But Capella, with only one satellite, was worried.

What happens if satellites collide?

Given that the squadron tracks more than 24000 space objects, such messages end up coming as often as spam. In 2016, the unit sent out almost 4 million such reports of a possible collision, the severity of which varies from “take into account” to “consider evasion”. But some small satellites, including the Spire satellite, do not know how to dodge: they do not have motor systems, so they cannot escape from danger. In such potential collisions, the other side has to move. But if none of the satellites can leave the course, the situation becomes more complicated.

Capella just recently launched its firstThe satellite, named Denali in honor of the national park, aboard the SmallSat Express rocket, which in December launched 60 satellites into space at once. The main in 2016, the company also began with a crash. The founder, Payam Banazade, like everyone else in 2014, was puzzled by the disappearance of Malaysian flight 370, which disappeared on the way to China. “We asked ourselves a question: why can't we find a huge 777th aircraft on the planet that we call our home?” Said Banazade, a former engineer at NASA's Jet Propulsion Laboratory. "Perhaps we are not observing our planet enough."

But this is only part of the answer. According to his reasoning, satellites that see visible light cannot break through the clouds or the darkness of the night. Most of the world, most of the time lost to them. Instead of a passive collection of light, Capella sends radio waves to earth. They bounce back, changing depending on what they encounter, and the satellite picks them up, creating a space radar system. “We send energy and signals from our own satellite, rather than waiting for the light to come to us,” says Banazade. “We will carry our own flashlight.”

With this system you can observeships, follow the harvest, detect floods, even carry out some kind of espionage. It may be possible to find the missing plane. In any case, Denali was a demonstration satellite, and not part of a fully functional fleet of dozens of satellites to be launched in the coming years. But he was the first.

So when Capella received a warning,The mood at Californian flight control center was intense. Over time, the company reported that the likelihood of a collision increased. There was no point in thinking about what would happen after the accident at that speed (about 50,000 km /), so they decided to remove the satellite from the road.

Meanwhile, the engineers at Spire, prepared the data: The satellites of the company, which collect GPS signals passing through the atmosphere, accurately understand their position, even better than the Air Force. “Therefore, when someone contacts and reports: hey, a rapprochement occurs there; contact in four days, “we turn into attention and start uploading data,” says Nick Allen, head of the brand at Spire. For him, it's a routine. The company receives several messages of this kind every week for its over 60 satellites.

Spire satellites cannot move by themselves,therefore, data collection is the most important thing a company can do. In a difficult situation, Spire can tilt the satellite’s solar panels to change its resistance, hoping to take it off course.

Avoiding a dangerous collision, however,got Denali, who had the engines on board - but they were not checked. Therefore, on Tuesday, January 29, the systems were activated. To the relief of all, it worked. The engines activated four times, raising the Denali orbit by 50 meters with each thrust. “If we had not had the opportunity to maneuver, the situation would have been very terrible,” says Banazade.

No one knew for sure what would happen. On January 29, teams watched intensely for a collision. And after lunch, the Air Force "confirmed that the event was nominal and the satellites passed each other safely."

Growing population of objects revolving aroundEarth, many of which can not get out of the way, leads to increased risks. Neither Spire, which has one of the largest private clusters of satellites in orbit, nor Planet, which has the most of them, places engines on its small satellites. Both companies have passive ways to change routes, but using them to avoid collisions may require more early warning. In addition, small satellites are less likely to encounter than large ones.

But there is a chance. How we will solve this growing problem is not yet clear. The cosmos is large, but not so much that the fragments of the satellites just evaporate.

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