SpaceX Satellites Will Fly Low to Prevent Space Junk

JIM WATSON/AFP/GETTY IMAGES

SPACEX HAS RECEIVED Federal Communications Commission approval to halve the orbital altitude of more than 1,500 planned broadband satellites in order to lower the risk of space debris and improve latency.

SpaceX’s satellite project, named Starlink, aims to provide high-speed, low-latency broadband around the world. In a statement on the new FCC approval, SpaceX said that “Starlink production is well underway, and the first group of satellites have already arrived at the launch site for processing.”

SpaceX last yearreceived FCC approval to launch 4,425 low-earth-orbit satellites at several altitudes from 1,110 kilometers to 1,325 kilometers. However, the FCC approval was contingent on SpaceX filing a more detailed debris-mitigation plan.

As part of its plan to prevent space debris, SpaceX later asked for permission to operate 1,584 of those satellites at an altitude of 550 kilometers instead of the previously authorized 1,150 kilometers. The FCC approved the request in an order on Friday but pointed out that SpaceX still has to file a detailed debris-mitigation plan for the rest of the satellites.

“Given the atmospheric drag at this lower altitude, this relocation will significantly enhance space safety by ensuring that any orbital debris will quickly re-enter and demise in the atmosphere,” SpaceX told the FCC in November 2018 in its application for a license modification.

At the lower altitude, “any orbital debris will undergo rapid atmospheric re-entry and demise, even in the unlikely event that a spacecraft fails in orbit.” (SpaceX is designing its satellites to burn up completely during atmospheric re-entry in order to prevent physical harm from falling objects.)

Satellites orbiting at 1,150 kilmoters will take “hundreds of years to enter the Earth’s atmosphere,” but a SpaceX satellite “will take less than five years (even under worst-case assumptions) if it starts at an altitude of 550 kilmoters,” the company said.

The lower altitude will bring an advantage to broadband users, SpaceX explained. “By operating closer to the Earth, SpaceX would also reduce the latency of its communications signals to as low as 15 milliseconds, at which point it would be virtually unnoticeable to almost all users,” the company said. (SpaceX has saidlatency from an altitude of 1,150 kilmoters would be 25 milliseconds to 35 milliseconds.)

Low-Altitude Trade-Offs

There are downsides to using a lower altitude, though.

“The very same atmospheric drag that helps to sweep the orbit clean of debris also forces satellites to work harder to remain in orbit,” SpaceX wrote. “Staying aloft requires the satellite to be able to overcome more atmospheric drag. In addition, satellites operating at low altitude see less of the Earth, requiring more satellites to serve a given area.”
SpaceX said it has conducted tests that show it can solve these problems. The company intends to “operate at this altitude nonetheless, based in part on feedback gained from its experimental satellites, which have conducted extensive testing of SpaceX’s capabilities to operate in the lower 500 kilometer range. Consequently, SpaceX has learned to mitigate the disadvantages of operating at a lower altitude and still reap the well-known and significant benefits.”

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