Connect the dots | Improving Satellite Collision Predictions for Space Efficient
Helping operators steer satellites away from potential collisions in increasingly crowded orbits is a key factor in improving space traffic management, but it’s also important to know when fuel drain detours aren’t necessary.
Current surveillance and tracking systems cannot determine the exact location and trajectory of the vast amount of objects in near-Earth orbit.
Instead, they rely on probabilities that feed into conjunction alerts sent to operators, who then take action if the risk of collision is high enough for them.
The frequency of collision avoidance maneuvers performed by satellites in low Earth orbit (LEO) depends on their size, the population density at the specific altitude, the accuracy with which objects are currently being tracked, and the threshold of operator risk.
“Depending on those factors for a given operator, they could perform anywhere from just a few [collision avoidance] maneuvers per year, up to several maneuvers per week, via satellite,” said Darren McKnight, Senior Technical Researcher at Space Situational Awareness (SSA) provider LeoLabs.
According to Stefan Frey, CEO and co-founder of German startup Vyoma – which plans to use satellites to improve SSA measurements – LEO operators now perform an average of two satellite collision avoidance maneuvers every year.
And if a decision is made to move a satellite based on a 0.01% collision probability, he says, “you could argue that in 9,999 out of 10,000 cases the maneuver was in fact not necessary”.
Analysts predict that tens of thousands of satellites will be deployed in LEO over the next decade. Vyoma, LeoLabs and others looking to improve SSA accuracy, reliability and coverage say the proliferation of LEO satellites will increase the number of close approaches.
Recent debris-causing events don’t help either. In the first four months of 2022, debris from Russia’s anti-satellite weapon test in November “caused about a 50% increase in statistical collision risk” with satellites between 370 and 570 kilometers away, according to McKnight.
LeoLabs is expanding its SSA ground-based radar network to track LEO objects more accurately and more frequently, which McKnight says will improve the accuracy of calculated collision risk and reduce unnecessary evasive maneuvers.
“As the space environment is rapidly changing, so are the SSA capabilities needed to support that growth,” McKnight said. Legacy government systems are not equipped to handle this long-term growth, he said.
Robert Sproles, senior director of constellation planning and operations at Spire, which operates more than 100 small satellites in LEO, said the company receives an average of 12 conjunction data messages every day from the unit. surveillance of the Space Force’s 18th Space Defense Squadron.
Sproles did not specify how often Spire maneuvers satellites in response to collision threats, but said its risk classification system has three categories:
• GREEN when the probability is less than 0.1% and no action is required.
• YELLOW when it is between 0.1 and 1% and requires further investigation to see in which direction the alerts are moving. If necessary, Spire contacts other operators to initiate coordination procedures, but no maneuver is yet planned.
• RED when the probability of a collision is greater than 1% and requires action, which begins with coordination with the other operator and may or may not result in action by either or both.
Sproles said making collision probabilities more accurate would allow operators to save fuel or even downsize a satellite’s propulsion capabilities from the outset to reduce overall system costs.
This article originally appeared in the June 2022 issue of SpaceNews magazine.