Two satellites almost crushed. Here's how they dodged him



The first alert arrived on January 27th. Two small satellites, rotating through the Earth's low orbits, had "the potential for a conjunction".

These are the words used by Major Cody Chiles, spokesperson for the joint force space component command, to designate the risk of collision. The satellites, one from a company called Capella Space and the other from Spire Global, could touch each other.

It is up to 18 Air Force Spacecraft Squadron to issue alerts on possible collisions, when it believes that these events are sufficiently probable. In this case, the chance of a direct hit was, depending on who you ask, either really small or rather scary. Based on its data and a somewhat generic model, the squadron estimated the probability between 0.2 and 10% over a 72-hour period. But it's a guessing game.

If the satellites collided, fragments of satellite (years of work, dollar signs) would be projected, lost, in space. They would turn into even more elements fueling the already large swirl of space debris putting other orbits at risk.

Spire, which operates about 60 small satellites that track ships and the weather, was not worried about this warning.

Capella, who has only one satellite, was.

But since the squadron tracks more than 24,000 space objects, these messages arrive as often as junk mail. In 2016, the unit sent nearly 4 million of these "Conjunction Data Messages", whose severity ranges from "paying attention" to "considering to shirk." systems, so that they can not eat away from the danger. In potential encounters like this, the other party sometimes becomes the one who has to move. But if no satellite can escape, the situation is complicated.

Capella has only recently launched its first satellite, Denali named after the national park, orbiting a rocket called SmallSat Express, which launched more than 60 others at the same time. Founded in 2016, Capella has a history that goes back to a crash. The founder, Payam Banazadeh, like everyone else in 2014, was puzzled by the disappearance of the Malaysian flight 370, the plane that had disappeared in the direction of China. "We asked ourselves the following question:" Why can not we find this huge 777 aircraft on this planet we call our homeland? Banazadeh, a former NASA Jet Propulsion Laboratory engineer, said, "We do not have enough to monitor our planet."

That's part of the answer. His reasoning says that satellites that see visible light can not look through the clouds or the darkness of the night. Much of the world, a lot of the time, is lost to them. Instead of passively collecting light, Capella sends radio waves to the ground. They bounce, altered by everything they encounter, and the satellite detects them, creating a radar system based in space. "We send energy and signals from our own satellite, instead of waiting for light to reach us," says Banazadeh. "It's like we have our own flashlight."

With such a system, you can monitor vessels, monitor crops, identify floods and even conduct government oversight. You can maaaaaybe help find a missing throw. In any case, Denali was only a demonstration satellite and was not part of the fleet of dozens of users that will be launched in the coming years. But it was their first experience and therefore their precious test bed.

So, when Capella received the 18 Fighter Squadron's conjunction warning, the atmosphere in his California Mission Control Room was tense. Over time, the company said the probability of collision was increasing. They did not want to think about the relative speed (about 34,000 km / h) and the violence of this hypothetical accident, or what it meant to Denali. So they decided to move it.

Spire engineers, meanwhile, were preparing data: its satellites, which collect the GPS signals that have crossed the atmosphere, have precise meanings of their own positions, a better proprioception than what the Air Force has been able to provide since the ground. "So, when someone contacts us and says," Hey, there's a conjunct event happening; we are more attentive to these satellites and are starting to download data, "says Nick Allain, brand manager at Spire. It makes it a routine. The company receives several such messages each week for its 60 satellites.

Spire satellites can not propel themselves. Data collection is therefore the most important task that society can do. In a disastrous situation, Spire can tilt the solar panels of a satellite to modify the drag, hoping to protect it from danger. ("Imagine how a flying squirrel flies," says Allain.)

Avoiding this potential collision, however, fell on Denali, who had boosters on board, but they were not tested. On Tuesday, January 29, they launched the system. To their relief, it seemed to work. Then they used it, shooting four times, aiming to lift the Denali orbit about 50 meters at each push. "If we did not have the ability to maneuver, the situation would have been very scary," Banazadeh said.

They did not know that it was enough. On January 29, the team observed whether a collision would occur.

Shortly after lunch, the air force "confirmed that the event was minimal … after the passage safely between the two satellites".

Allain, the numbers supporting him, seems confident that this would have always been the case. "You tend to take on big risks before you start," he says, mapping the main obstacles in orbit and defining the trajectory of a satellite accordingly.

But with a growing population of objects surrounding the Earth, many of which can not cope, the number of small risks continues to grow. Neither Spire, which owns one of the largest private herds in orbit, nor Planet, which has the largest current fleet, have installed propulsion systems on their small satellites. Both have passive ways of changing their course, although their use to avoid a collision may require a more advanced warning. Allain also cites some propulsive disadvantages: it can make tracking these instruments in orbit harder, and placing a lot of little things filled with fuel on a rocket is risky. In addition, small satellites, being smaller and shorter in life than larger satellites, are less likely to crash into objects than objects with a larger surface area and life expectancy. longer.

But luck is not nil. And not everyone thinks passive systems are enough. Banazadeh, for example, suggests that there should be regulations requiring satellites to have some kind of propulsion system or other anti-collision system. Building satellites that can go together, in this logic, is not just for the sake of these satellites. This is for the common good of the satellites and for the protection of the space itself. The space is big … but not so big that the debris of an accident disappear.


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