June 10, 2023

Operators of satellite constellations are constantly forced to move their satellites because of encounters with other spacecraft and pieces of space junk. And, thanks to , Hesar told Space.com.

Kayhan Space bases their estimates on data provided by the , which disintegrated in March this year, was actually hit by a piece of space debris. 

The worst known space collision in history took place in February 2009 when the U.S. telecommunication satellite Iridium 33 and Russia’s defunct military satellite Kosmos-2251 crashed at the altitude of 490 miles (789 kilometres). The incident spawned over 1,000 pieces of debris larger than 4 inches (10 cm). Many of these fragments were then involved in further orbital incidents. 

Lewis is concerned that with the number of close passes growing, the risk of operators at some point making a wrong decision will grow as well. Avoidance maneuvers cost fuel, time and effort. Operators, therefore, always carefully evaluate such risks. A decision not to make an avoidance maneuver following an alert, such as that made by Iridium in 2009, could, however, clutter the orbital environment for years and decades. 

“In a situation when you are receiving alerts on a daily basis, you can’t maneuver for everything,” Lewis said. “The maneuvers use propellant, the satellite cannot provide service. So there must be some threshold. But that means you are accepting a certain amount of risk. The problem is that at some point, you are likely to make a wrong decision.”

Hesar said that uncertainties in the positions of satellites and pieces of debris are still considerable. In case of operational satellites, the error could be up to 330 feet (100 meters) large. When it comes to a piece of debris, the uncertainty about its exact position might be in the order of a mile or more. 

“This object can be anywhere in this bubble of multiple kilometres,” Hesar said. “At this point, and for the foreseeable future, avoidance is our best recourse. People that say ‘I’m going to take the risk’, in my humble opinion, that’s an irresponsible thing to do.”

In September 2019, ESA’s wind-monitoring satellite Aeolus came dangerously close to one of SpaceX’s Starlink spacecraft. The space agency had to move the spacecraft to prevent a collision. (Image credit: ESA)

Lewis is concerned about the growing influence of a single actor — Starlink — on the safety of orbital operations. Especially, he says, as the spaceflight company has entered the satellite operations world only recently. 

“We place trust in a single company, to do the right thing,” Lewis said. “We are in a situation where most of the maneuvers we see will involve Starlink. They were a launch provider before, now they are the world’s biggest satellite operator, but they have only been doing that for two years so there is a certain amount of inexperience.”

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SpaceX relies on an autonomous collision avoidance system to keep its fleet away from other spacecraft. That, however, could sometimes introduce further problems. The automatic orbital adjustments change the forecasted trajectory and therefore make collision predictions more complicated, according to Lewis.

“Starlink doesn’t publicize all the maneuvers that they’re making, but it is believed that they are making a lot of small corrections and adjustments all the time,” Lewis said. “But that causes problems for everybody else because no one knows where the satellite is going to be and what it is going to do in the next few days.”

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