SpaceX is asking the FCC to approve modifications to its license to launch and operate a constellation of non-geostationary (NGSO) satellites, reducing the altitude from 1,150 kilometers to a new altitude of 550 km.
The change in altitude will result in lower latency for the satellites—as well as allow SpaceX to speed up the deployment of its constellation.
This past March, the FCC approved a SpaceX plan for a satellite system comprised of 4,425 satellites and granted it the authority to use frequencies in the Ka (20/30 GHz) and Ku (11/14 GHz) bands for providing global internet connectivity.
The revised plan calls for 16 fewer satellites—to 4,409. It would also allow for SpaceX to surpass the deployment milestones laid out in its license. Under commission rules, it’s supposed to begin operation of at least half of its authorized satellites no later than March 29, 2024. But the new target calls for launching its first batch of satellites before the end of 2019.
As GeekWire points out, SpaceX needs to convince the commission that the revised plan would create no more interference for ground-based networks and geosynchronous satellite networks than the original plan would have.
The changes are being proposed in part as a result of the work SpaceX did with two experimental satellites, identified as Microsats 2A and 2B, that were launched earlier this year. GeekWire reported in May how SpaceX founder Elon Musk tweeted that the latency displayed by the satellites, dubbed TinTin A & B, was "Good enough to play fast response video games."
In its Nov. 8 FCC filing, the company explained that at 550 km, the Earth and its atmosphere act like a vacuum cleaner—atmospheric drag naturally removes objects from orbit, including loose debris. But that drag also forces satellites to work harder to remain in orbit. In addition, satellites operating at low altitude see less of the Earth, usually requiring more satellites to serve a given area.
However, SpaceX proposes to separate itself from most other NGSO constellations and operate at the lower altitude based in part on feedback gained from its experimental satellites, which have conducted extensive testing in the lower 500 km range.
The company explained that by operating closer to the Earth, SpaceX would be able to 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.” Under the previous altitude plan, the latency was expected to be on the order of 25-35 milliseconds.
The FCC is due to consider SpaceX’s plan at its open meeting on Thursday. An important component of SpaceX’s plan is the impact on space debris, which has been identified as a priority for the commission. An updated space debris mitigation plan is also on the commission’s Thursday agenda. SpaceX said improved orbital debris mitigation is a significant advantage of its proposed modification.
Moving to the lower altitude also increases the space between its satellites and those of other large proposed NGSO constellations, including OneWeb, Boeing and Telesat. The commission authorized those companies to operate NGSO systems at altitudes between 1,000 kilometers and 1,200 kilometers. By modifying its constellation to operate at 550 km, SpaceX would reduce potential conflict with those other constellations and improve the safety profile for everybody, the company said.