(AmaraGraps) There’s no denying that satellites and communication have become inseparably linked as vehicles of human progress. We use satellites every day for location and timing services, for security in financial transactions, global navigation satellite systems, weather monitoring, and more. Satellites, like any transportation vehicle, have a lifetime, however, and our space vehicles with their associated debris from humans’ last six decades, litter our near-Earth environment. Conventional Satellite Internet through its mega-constellations pose additional debris dangers.
What if moving forward in our human communication endeavors cripples our existing space capacity? The Kessler Syndrome, has already begun, according to its author. But there’s one potential solution with quantum technology.
Internet has been a powerful force for good in our global societies, but only about 60% of the world has Internet access today. That business case is behind the Internet mega-constellation satellites: many fly at low-Earth orbit, with an optimization towards high bandwidth. Can the same Earth coverage and bandwidth be provided with fewer satellites? Quantum satellite Internet has that potential. The new research by Khatri et al, 2021 to optimize satellite orbital configurations for a global quantum Internet, is exciting for its potential to meet an urgent society and economic need.
There are 34,000 debris objects larger than 10 cm currently in orbit around the Earth. In low-Earth-orbit (LEO), where are many navigation, experimental and observation satellites, even a tiny 1 cm debris particle can damage, or destroy a satellite, due to the orbital particle’s typical 10 km/s collision speed. Space debris fragmentation, which is the runaway process behind the Kessler Syndrome, generates more debris particles.
Therefore, avoiding collisions in this near-Earth space is part of today’s satellite operations. Take Starlink, the constellation of 1700 conventional Internet satellites. From December 2020 to October 2021, Starlink made about ~4900 collision avoidance maneuvers, with numbers growing each month. There were ~610 collision avoidance maneuvers in October 2021, alone, an average of about 20 per day. These are avoidance maneuvers are with other space objects, not with its own constellation. Such effort is costly.
From the clydeco.com report, the OECD estimates that the economic expense of protecting missions from space debris amounts to at least 5 to 10% of the total mission costs for LEO satellites, which could be hundreds of millions of dollars. The economic arguments are growing quickly with the debris.
These Starlink collision avoidance numbers were before the widely criticized November 2021 Russian ASAT Weapons Test, where at least 1500 new debris pieces were generated. Starlink is one of the many space operators, including those agencies running the ISS and the Chinese Space Station, which are now necessarily acting to avoid more collisions from the new ASAT debris. The work of these space operators is more expensive now, with a discussion in the space community if Space-X can sue Russia.
The irony of such a potential litigation is that Space-X is itself contributing to the expenses of others’ space work with its own mega-constellation. There are more mega-constellations planned by other vendors, as well. A large concern of the space debris community is about the number: 21,441 satellites to provide Internet communication, that is still planned to be launched by about 2025. According to the Economist, of the filings made with the International Telecommunication Union, 100,000 non-SpaceX communication satellites could be launched into low orbits by 2030. The risk of collisions and the exponential growth of space debris cannot be ignored.
A Quantum satellite Internet could potentially buy societies some time. While human creativity proceeds with a decades-long space debris cleanup effort, a Quantum satellite Internet could meet the society need with more secure Internet and fewer satellites for the same Earth coverage, if the research demonstrates such potential. A milestone work reported in early 2021 by Chen et al, established that satellites could be used to overcome a distance limitation of near-term quantum networks. By integrating the fiber and free-space Quantum Key Distribution (QKD) links, the QKD network could be extended to a remote node more than 2,600 kilometers away, enabling any user in the network to communicate with any other, up to a total distance of 4,600 kilometers.
The research by Khatri et al, 2021 goes further, seen here in their Summer 2021 presentation. They find that satellite links are optimal for longer distances; and ground links for shorter distances. Their first simulation asks: “Given two ground stations on the equator separated by a distance d, what is the best rate that can be achieved using the least number of satellites in the constellation, while maintaining 24 hour coverage?”
With the answer, copied from their summer presentation:
The research by Khatri et al, finds a minimum and maximum satellite altitude that begins at 500 km and reaches to 5000 km with a constellation of 100-400 satellites in polar orbits, with reasonably high satellite-to- ground entanglement-distribution rates. See table below and their paper, for more details.
Table by Khatri, et al, in their Summer 2021 presentation.
Future research steps to be considered will take into account different local conditions, different satellite constellations, with different scheduling strategies, their presentation says. I hope they continue full speed ahead. We need such approaches. Quantum Satellite Internet has a bright future.