Updated A proposed constellation of 243 satellites, designed to beam internet connectivity to smartphones and under consideration by America's comms watchdog, will triple the existing risk of a potential collision with ten Earth science spacecraft in low-Earth orbit, NASA warned.
AST & Science, a Texas-based company, has applied for approval to build SpaceMobile, which claims to be the “first and only space-based cellular broadband network to be accessible by standard smartphones.” Its proposed network is under review by the FCC. However, NASA reckons it will heighten the risk of contact between spacecraft within a region that is already crowded.
The space agency is particularly concerned about the gap between 690 and 740km above Earth, an area home to the so-called A-train. The A-train consists of ten spacecraft used to monitor Earth, operated by various groups including NASA, the United States Geological Survey, France’s National Centre for Space Studies, and Japan’s Aerospace Exploration Agency. AST wants to place its satellites across 16 orbital planes at an altitude of 700km, a distance that’s too close for comfort.
“The AST constellation would be essentially collocated with the A-Train if the proposed orbit altitude is chosen,” Samantha Fonder, NASA’s Representative to the Commercial Space Transportation Interagency Group, and a member of its Human Exploration and Operations Mission Directorate, wrote in a letter [PDF] addressed to the FCC.
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What’s more the area is also particularly risky since it contains chunks of debris leftover from a previous orbital crash. “Additionally, this is an orbit regime that has a large debris object density (resulting from the Fengyun1-C ASAT test and the Iridium33-COSMOS 2251collision) and therefore experiences frequent conjunctions with debris objects,” she continued.
Fonder reckons that placing another 243 satellites near the A-train will increase the chances of a space smash. NASA has arrived at that conclusion by taking into account various factors, including the size of the AST’s SpaceMobile birds. They are much bigger than the spacecraft in the A-train and carry 900-square-metre antennas.
“Based on the results of a NASA [Conjunction Assessment Risk Analysis] simulation tool, the number of mitigation actions required for a 30m hard-body radius object in this orbit regime increases from [about two to six per year] - almost a tripling of what is observed presently,” Fonder said. The proposed constellation of 243 raises that figure to about 1,500 possible “mitigation actions” needed per year.
NASA has recommended AST’s satellites undergo a full risk analysis to the same level conducted by the space agency. The simplest way to mitigate problems in the future, however, is to simply move the SpaceMobile fleet in an orbit beneath the space occupied by the A-train. That way their orbits won’t coincide, and if any of the mobile internet satellites were to fail it’d be out of the harm’s way too.
The Register has asked NASA and AST & Science for further comment. ®
Updated to add
NASA has responded and it looks like there may be a fix for the A-Train issue:
"The A-Train occupies the space between 700 and 730 kilometers. A safe distance for the placement of a satellite constellation would be several kilometers below the A-train," the agency said.
"If the constellation were placed above, the vehicles would need to transit through the A-train on the way up and down, raising significant risk of conjunction. NASA’s technical recommendations are intended to promote a mutually acceptable path forward that will allow the company’s activity to be conducted in a safe and successful fashion."