Improved thresholds and SSA accuracy can reduce most satellite collision risk

WASHINGTON — Improving the accuracy of space situational awareness (SSA) data and using tighter thresholds for potential conjunctions can help retire most of the risk of satellite collisions in low Earth orbit, a new study concludes.

Research presented April 8 at the 5th IAA Conference on Space Situational Awareness in Madrid by COMSPOC found that most satellite operators only eliminate 7% of the potential collision risk based on the current accuracy of SSA data and the thresholds they use for determining when a potential conjunction warrants action.

The analysis, said COMSPOC’s Daniel Oltrogge in an interview, is based on modeling of objects in orbit with estimates of their size from different databases. The 7% estimate uses the current accuracy of SSA data and a 1-in-10,000 threshold of a potential collision to take actions such as maneuvering, a threshold used by many operators.

“So that’s quite scary, and it calls into question the efficacy of using the processes they’ve been using,” he said.

One solution is to tighten that threshold. Going to a 1-in-1,000,000 threshold would retire 75% of the risk. However, he noted that greatly increases the number of potential conjunctions operators must deal with, which is why few operators, other than SpaceX, use that threshold. “It’s going to flood their system if they go to a really stringent threshold for a given accuracy,” he said.

Another approach is improving the accuracy of SSA data. A factor of 10 improvement in that accuracy of data would retire about 75% of the risk even with the current 1-in-10,000 threshold.

“And if we were to use the sort of threshold that SpaceX is using, that would be close to zero,” Oltrogge said. Using that 1-in-1,000,000 threshold with improved SSA data would reduce the remaining risk of collisions to 8%.

“It’s not that anyone is intentionally doing a bad job” at collision avoidance, he said, but they are limited by the accuracy of current SSA data and the ability to deal with large numbers of conjunction warnings using higher thresholds.

“Typical operators seem to be only retiring 7% of collision risk using the relatively easy threshold of 1-in-10,000, and if we can have a more stringent threshold and 10 times better accuracy, we can really get most of the collision risk addressed,” he said.

That is already demonstrated to some degree by SpaceX’s operation of Starlink, with the company using a threshold around 1-in-1,000,000 and having much better knowledge of the positions of its own satellites than standard SSA accuracy. “What Starlink is doing is effective,” he said, given the lack of collisions.

Oltrogge said there is a good plan to improve SSA accuracy, involving the community of companies that specialize in SSA data collaborating with government agencies and spacecraft operators. That would include fusing data from different sources and sharing maneuver data provided by satellite operators, along with information about space weather conditions.

“We think this is very doable,” he concluded. “It’s just not something that we’ve seen the government really focusing on that much in terms of this level of collaboration and using better analytics and data fusion.”

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