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Operators of satellite constellations are constantly forced to move their satellites due to encounters with other spacecraft and space debris. And, thanks to by SpaceX Starlink satellites, the number of such dangerous approaches will continue to increase, according to estimates based on the available data.
by SpaceX Star link satellites alone are involved in about 1,600 close encounters between two spacecraft each week, according to Hugh Lewis, head of the astronautics research group at the University of Southampton, UK. These encounters include situations where two spacecraft pass within 0.6 mile (1 kilometer) of each other.
Lewis, Europe’s leading space debris expert, makes regular assessments of the situation in orbit based on data from the Socrates database (Satellite Orbital Conjunction Reports Assessing Threatening Encounters in Space). This tool, managed by Celestrack, provides information on the orbits of satellites and models their trajectories in the future to assess the risk of collision.
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Lewis posts regular updates on Twitter and has seen a disturbing trend in the data that reflects the rapid deployment of the Starlink constellation.
“I looked at data going back to May 2019, when Starlink first launched to understand the burden of these mega-stellations,” Lewis told Space.com. “Since then the number of matches recorded by the Socrates database has more than doubled and we are now in a situation where Starlink accounts for half of all matches.”
The current 1,600 close passes include those between two Starlink satellites. Apart from these encounters, the Starlink satellites approach the spacecraft of other operators 500 times a week.
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In the July update of conjunctions involving #Starlink & #OneWeb as predicted by #SOCRATES (https://t.co/CjUGwoALuU), we can see the continued (exponential) increase in the number of close passes August 2, 2021
By comparison, Starlink’s competitor OneWeb, currently flying over 250 satellites, is involved in 80 close passes with other operators’ satellites each week, according to Lewis data.
And the situation can only get worse. So far, only 1,700 satellites of an expected constellation of tens of thousands have been placed in orbit. Once SpaceX launches all 12,000 satellites in its first-generation constellation, Starlink satellites will be involved in 90% of all close-range approaches, Lewis’s calculations suggest.
And another for @ cosmos4u: the number of conjunctions on August 3, 2021
The risk of collision
Siemak Heser, CEO and co-founder of Boulder, Colorado, based at Kayhan Space, confirms the trend. His company, which is developing an autonomous commercial space traffic management system, estimates that on average, an operator managing about fifty satellites will receive up to 300 official conjunction alerts per week. These alerts include encounters with other satellites as well as debris. Of these 300 alerts, up to ten would require operators to perform avoidance maneuvers, Hesar told Space.com.
Kayhan Space bases its estimates on data provided by the American Space Surveillance Network. This network of radar and telescopes, managed by the US Space Force, closely monitors approximately 30,000 living and missing satellites and debris up to the size of 4 inches (10 centimeters) and provides the most accurate location data objects in orbit.
The size of this catalog is expected to increase tenfold in the near future, Hesar added, partly due to the growth of mega-stellations, such as Starlink, and partly as sensors improve and allow detection of even smaller objects. The more objects there are in the catalog, the more dangerously close the encounters.
“This problem is getting really out of hand,” Hesar said. “The processes currently in place are very manual, non-scalable, and there is not enough information sharing between the parties that could be affected in the event of a collision.”
Hesar likened the problem to driving on a highway without knowing that there was an accident a few miles away from you. If two spacecraft collide in orbit, the cloud of debris generated by the crash would threaten other satellites traveling in the same area.
“You want to have that situational awareness for the other actors who are flying around the neighborhood,” Hesar said.
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Bad decisions
Despite concerns, only three confirmed orbital collisions have occurred so far. Earlier this week, astrophysicist and satellite tracker Jonathan McDowell, who is based at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, found evidence in Space-Track data that the Chinese weather satellite Yunhai 1-02, which disintegrated in March of this year, was actually hit by space debris.
The worst known space collision in history took place in February 2009 when the US communications satellite Iridium 33 and the late Russian military satellite Kosmos-2251 crashed at an altitude of 789 kilometers. The incident created over 1,000 pieces of debris larger than 4 inches (10 cm). Many of these fragments were subsequently involved in other orbital incidents.
Lewis is concerned that with the increase in the number of close passes, the risk of operators making a bad decision at some point will also increase. Avoidance maneuvers cost fuel, time and effort. Therefore, operators always carefully assess these risks. A decision not to perform an avoidance maneuver following an alert, such as that taken by Iridium in 2009, could however clutter the orbital environment for years and decades.
“In a situation where you get alerts on a daily basis, you can’t maneuver for everything,” Lewis said. “The maneuvers use thruster, the satellite can’t provide service. So there has to be a certain threshold. But that means you accept a certain risk. The problem is that at some point you might take a risk. bad decision. “
Hesar said there are still considerable uncertainties over the positions of satellites and debris. In the case of operational satellites, the error can be up to 100 meters (330 feet) wide. In the case of debris, the uncertainty of its exact location can be on the order of a mile or more.
“This object can be anywhere in this bubble several miles away,” Hesar said. “At this point, and for the foreseeable future, avoidance is our best recourse. People who say ‘I’m going to take the risk’, IMHO, it’s an irresponsible thing to do.”
Starlink’s monopoly
Lewis is concerned about the growing influence of a single player – Starlink – on the safety of orbital operations. All the more so, he says, since the space flight company only recently entered the world of satellite operations.
“We trust one company to do the right thing,” Lewis said. “We’re in a situation where most of the maneuvering that we’re seeing will involve Starlink. They were previously a launch provider, now they’re the biggest satellite operator in the world, but they’ve only been doing that for two years so there is a number of inexperience. “
SpaceX relies on an autonomous collision avoidance system to keep its fleet away from other spacecraft. This, however, could sometimes introduce other problems. Automatic orbital adjustments change the predicted path and therefore make collision predictions more complicated, according to Lewis.
“Starlink doesn’t publish every maneuver they perform, but it is believed that they perform a lot of small fixes and adjustments all the time,” Lewis said. “But it causes problems for everyone because nobody knows where the satellite is going to be and what it is going to do in the next few days.”
Follow Tereza Pultarova on Twitter @TerezaPultarova. follow us on Twitter @Spacedotcom and on Facebook.
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