At a time when the race for satellite constellations is in full swing, NASA is particularly worried about a future communications satellite project. In an official letter addressed to the US FCC or Federal Communications Commission and dated October 30, 2020, the US space agency evokes their fear regarding the risks of collisions that could be caused by the constellation in question.
The satellites at the heart of the matter are those which will eventually be launched by the firm AST & Science based in Texas. It is a constellation called SpaceMobile composed of 243 elements at most and which will orbit at an altitude of 720 km. According to information, the satellites will be equipped with a very large antenna with an area of around 900 m², which could increase the probability of conjunctions or very close crossings with other devices in orbit.
According to AST & Science officials, SpaceMobile is a project that aims to deliver a broadband connection service directly to users' cell phones.
The bottom of the problem
What worries NASA the most about SpaceMobile is that the area where the constellation is planned to orbit matches the area used by what they call the "A-Train." The latter is a group of 10 Earth observation satellites operated by NASA, the US Geological Survey, and several international partners. The particularity of the A-Train is that its elements follow the same path in orbit.
The A-Train satellites travel at an average altitude of 705 km, but they can sometimes descend to 690 km or even climb up to 740 km. According to the letter from NASA signed by Samantha Fonder, representative of the agency within the Commercial Space Transportation Interagency Group, the constellation of AST & Science will thus be essentially located in the same area as A-Train, at least if the proposed altitudes by the company are ultimately used.
By doing the math, NASA scientists concluded that to navigate safely through SpaceMobile's satellites, A-Train officials would need to plan 1,500 mitigation measures and avoidance maneuvers, as well as 15,000 activities. planning per year. This would equate to 4 maneuvers and 40 planning activities per day.
What AST & Science says
So, what NASA is asking is that AST & Science consider other alternatives to the orbit that will be used by the constellation, including an orbit below that of the A-Train. However, the managers of the telecommunications company are not of this opinion. According to them, SpaceMobile will pose no risk of collision.
AST & Science has indeed made its own calculations and according to the results, each satellite in the constellation has only a 1 in 5,000 chance of colliding with another craft, even without any mitigation measures. With 243 elements, the probability of a random collision would thus be 1 in 20.
In relation to the letter from NASA, Abel Avellan, the founder of AST & Science, indicated that they know what they are doing. “We're not a bunch of cowboys wanting to launch satellites. It is a serious project and one which is well funded, ”he said.
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In any case, let's wait to see the response of the FCC concerning this project to know if the Texan company will be finally authorized to launch its constellation in the orbital zone which they propose.