Friday, November 06, 2020

Satellite and space debris tracking as a service

All spacefaring nations must work together on common issues, such as tracking the thousands of pieces of space debris that could stifle the commercialization of space.
Commerce Secretary Wilbur Ross

On February 2, 1989, the Soviet Union launched its Cosmos 2004 satellite and the Chinese launched a rocket on December 15, 2009. Cosmos 2004 is now defunct as is the third stage of that Chinese rocket, but both remain in orbit. They were long forgotten until recently when LeoLabs, a satellite tracking service, predicted that they had a good chance of colliding at 971 km over the sea near Antarctica.

It turns out that they did not collide but they came within 11 meters of each other. The two objects have a combined mass of 2,800 kg and were traveling at a relative velocity of 52,900 km/h. Imagine what would have happened had those massive objects collided at that speed. Since they are in a vacuum, the collision would have been silent, but large and small fragments would have been scattered into their own orbits, exponentially increasing the likelihood of future collisions.

The Chinese rocket scientists were not thinking about the possibility of a collision with Cosmos 2004 when they launched their rocket in 2009, but today, with SpaceX and others planning to launch thousands of broadband-service satellites into relatively crowded low-Earth orbit, the debris problem is obvious and daunting, but there are some promising developments. (For more on the extent of space debris click here and here).

Governments have been tracking the orbits of satellites and debris larger than 10 cm for some time but a new company, LeoLabs, is using phased-array radar antennas to track objects as small as 2 cm. In a recent interview, LeoLabs CEO and Co-Founder Daniel Ceperley, said their phased-array radar antennas are capable of tracking the approximately 250,000 orbiting objects that are greater than 2 cm within a 100-meter margin of error.  

LeoLabs antennas can switch direction in one millisecond, but since it is difficult to locate and establish control over satellites with only one or a few observations in the first hours and days after deployment, they offer a Launch and Early Orbit service in which they focus more time on the satellites and SpaceX is using that service.

While the first hours and days after deployment are critical, the risk of a collision persists as long as a satellite is in orbit so LeoLabs also offers a Collision-Avoidance service that will report possible collisions a week in advance and follow up with increasingly more frequent and more accurate notices during the week. This will give satellite operators time to test alternative collision-avoidance maneuvers using LeoLab's interactive maneuver-simulation service.

The Collision-Avoidance service works if a satellite operator is trying to avert a collision with debris or a defunct satellite, but if two active satellites are involved, both parties must be informed and able to communicate about planned maneuvers. SpaceX says Starlink satellites will be able to maneuver autonomously to avoid collisions, but what happens if the approaching satellite also maneuvers in the same direction?

Up to this point, I've been talking about terrestrial tracking of satellites and debris, but tracking can also be done from space. A while ago, I suggested that SpaceX might equip their satellites to detect debris while in orbit and they have some autonomous collision avoidance capability, but as far as I know, they have no plans for offering collision avoidance data or service to others.

Northstar, a space-based Canadian startup, plans to track satellites from orbit. They have contracted for three satellites that will be in polar orbits at an altitude of 575 kilometers and plan to launch at least three more batches of three each in different orbits by 2024.

Like LeoLabs, Northstar plans to offer tracking as a service. While Northstar is several years behind LeoLabs, it will use different technology. If successful, Northstar plans to track satellites from low-Earth to geostationary orbits. They will be able to use optical scanners since there are no problems with the atmosphere and weather in space and will have a wide view, enabling them to revisit objects frequently and quickly and accurately predict orbits.

The investment and operating costs may also be different than those of LeoLabs, but I don't know whether it will have cost more to build and operate the 12 LEO satellites Northstar plans to orbit in 2024 or the six radar tracking stations LeoLabs will have in operation next year.

(NorthStar and ExoAnalytic, which tracks satellites and debris with terrestrial optical telescopes, announced a partnership in April 2019, evidently intending to combine their observations, but there is no further mention of that on their Web sites and Northstar has changed it's business model which initially called for dual-use satellites combining both Earth observation and satellite tracing.)

As shown below, many nations now launch, own, and/or operate satellites. (The map is as of 2016 but the database at the site included 68 nations as of August 1, 2020). Whether the tracking is done from the ground or space, it is clear that global data must be shared and collision-avoidance protocols invented, standardized, and perhaps automated. (Holger Krag, director of the European Space Agency (ESA) Space Safety Programme Office hopes to like to demonstrate automated maneuver coordination by 2023).

Achieving global space law and regulation like we have for the seas seems like an impossible technical and political challenge -- exacerbated by the fact that many satellites and tracking services, like the recently completed US "Space Fence," are operated by military and security organizations -- but it must be done. There has already been a close miss between a Starlink satellite and Aeolus, an ESA satellite, in which a software bug led to a communication breakdown between the ESA and SpaceX.

I am amazed to find myself agreeing with and quoting a member of Trump's cabinet, Commerce Secretary Wilbur Ross, who said "all spacefaring nations must work together on common issues, such as tracking the thousands of pieces of space debris that could stifle the commercialization of space."

Update 4/27/2021

The Union of Concerned Scientists has updated the satellite database mentioned above. As of January 1 2021, 72 nations have launched and/or operated satellites and there were 3,732 in orbit. The need for global regulation and collaboration will increase rapidly as SpaceX and other low-Earth orbit satellite companies and governments launch mega constellations.

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