SpaceX halves altitude of broadband satellites to avoid space debris

SpaceX has received permission from the Federal Communications Commission to halve the orbital altitude of more than 1,500 high-speed satellites planned to reduce the risk of space debris and improve latency.

The SpaceX satellite project, called Starlink, aims to provide broadband broadband and low latency around the world. In a statement on the new FCC approval, SpaceX said, "Starlink's production is on track and the first group of satellites has already arrived at the launch site for processing."

Last year, SpaceX received FCC approval for the launch of 4,425 satellites in low Earth orbit at several different altitudes, ranging from 1,110 km to 1,325 km. However, the FCC's approval depended on SpaceX's filing of a more detailed plan for debris mitigation.

As part of its plan to prevent space debris, SpaceX then requested permission to operate 1,584 of these satellites at an altitude of 550 km instead of the 1,150 km previously authorized. The FCC approved the request Friday in an order, but pointed out that SpaceX still has to file a detailed resolution plan for the rest of the satellites.

"Given the atmospheric resistance at this lower altitude, this relocation will dramatically improve space security by ensuring that any orbital debris will return and disappear rapidly into the atmosphere," SpaceX told the FCC. November 2018 in its license amendment application.

At a lower altitude, "all orbital debris will experience rapid atmospheric reentry and death, even in the unlikely event that a spacecraft fails in orbit." (SpaceX is designing its satellites to completely burn when entering the atmosphere to prevent physical damage from falling objects.)

Satellites in orbit at 1,150 km will take "hundreds of years to penetrate the Earth's atmosphere," but a SpaceX satellite "will take less than five years (even in the worst-case scenario) it starts at 550 km altitude. I said.

The low altitude will bring an advantage to broadband users, explained SpaceX. "By operating closer to Earth, SpaceX would also reduce the latency of its communications signals up to 15 milliseconds, a point at which it would be virtually invisible to almost all users," the company said. (SpaceX said that a latency of an altitude of 1,150 km would be 25 ms to 35 ms.)

Compromise at low altitude

There are however disadvantages to using a lower altitude.

"The same atmospheric drag that helps to sweep the orbit of debris also forces satellites to work harder to stay in orbit," wrote SpaceX. "To stay high, the satellite must be able to overcome a greater atmospheric drag, and satellites operating at low altitude are seeing less of the Earth, which requires more satellites to serve a given area."

SpaceX said it performed tests showing that it could solve these problems. SpaceX has announced its intention to "operate at this altitude, though relying in part on information provided by its experimental satellites, which have conducted extensive testing of SpaceX's capabilities to operate in the lower 500 km zone. therefore, SpaceX has learned to mitigate the disadvantages of lower altitude and continue to enjoy significant and significant benefits. "

SpaceX also plans to reduce the number of satellites in the low-orbit constellation from 4,425 to 4,409. The forecast orbital heights of the remaining 4,409 satellites have not been modified. Under its FCC authorization, SpaceX must launch at least half of these satellites no later than March 29, 2024 and the others by March 29, 2027.

The FCC is satisfied with the SpaceX debris mitigation plan for 1,584 satellites subject to change in altitude. But SpaceX has to submit a more detailed plan for the rest of the satellites.

"Although we find that the orbital debris mitigation plan is sufficient with respect to the space stations that SpaceX proposes to operate with its modification, SpaceX has not provided any new information regarding the plans for reducing the orbital debris. orbital debris from other satellites in its proposed system, "said the president. FCC said. "SpaceX has only partially satisfied the condition of its authorizations requiring SpaceX to submit and approve an updated orbital debris mitigation plan by the Commission prior to the launch of the service."

The new altitude of 550 km is not the lowest that SpaceX plans to use for its broadband service. SpaceX received a separate license in November 2018 to deploy 7,518 broadband satellites at altitudes ranging from 335 km to 346 km. These lower satellites are intended to increase capacity and reduce latency in heavily populated areas. In total, SpaceX has been approved by the FCC for the launch of nearly 12,000 broadband satellites.