Debris Assessment Software to predict lifetimes of satellites in low Earth orbit. “We do not know at this time if there are any plans to change that program to address the changes in atmospheric composition predicted in the paper,” he said. “The F.C.C. periodically reviews its rules and regulations and updates them consistent with developments in the marketplace and in scientific knowledge.”

SpaceX did not respond to a request for comment.

Dr. Lewis said that he suspected that some of the modeling, however, relies on outdated data, and that more needed to be done to actively remove satellites and debris from orbit rather than relying on the passive atmospheric effect. “Operators have to make this aspect of the mission a priority,” he said.

Even a moderate increase in lifetimes for large constellations could pose significant problems. “If SpaceX’s spacecraft re-enter passively in 10 or 15 years, would you argue that’s good enough?” Dr. Lewis said. “Given the fact that it’s a large constellation, lots of people would say probably not.”

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