Risk Associated with Reentry Disposal of Satellites from Proposed Large Constellations in Low Earth Orbit.
Public Law No. 116-260, Consolidated Appropriations Act, 2021 2021
Transportation Housing and Urban Development Joint Explanatory Statement.
Executive Summary
The Federal Aviation Administration (FAA) submits this report in response to the 2021 Transportation, Housing, and Urban Development explanatory statement for the Consolidated Appropriations Act of 2021, Public Law No. 116-260. The report informs Congress of ways that the FAA’s launch and reentry licensing process may be leveraged to address the risk from reentering space debris. This report provides the results of the FAA’s analysis.
The dramatic rise of non-geostationary satellites, particularly those in low Earth orbit (LEO), poses an increased risk to people on Earth and aviation due to reentering debris. To support the FAA technical and policy review of the issue, the FAA contracted The Aerospace Corporation (Aerospace) to provide a technical report that assesses the following: 1) The rise of non-geostationary satellites (launched by the United States under FAA licenses and otherwise); 2) The risks associated with random and controlled (targeted) reentries of the satellites identified in part 1; and 3) Current FAA licensing processes that may be applicable to addressing reentry risks identified in part 2. The final Aerospace report is attached to this FAA report.
This report evaluates the risk to people on the ground and in aircraft due to debris from random and controlled (targeted) reentries of non-geostationary satellites located in LEO, as well as the launch vehicles that deliver those satellites to orbit. The FAA limited its review to the reentry of objects from LEO constellations since the current disposal practice for satellites launched into medium Earth orbit (MEO) and above does not include reentry. Additionally, while the launch and disposal of all non-geostationary satellites present risk from debris (from both the satellite and any launch vehicle components), for the reasons discussed in this report, it is the launch and disposal of large satellite constellations, not individual satellites, that poses the most significant risk to people on the ground and in aircraft. Since large constellations are responsible for the “exponential rise of non-geostationary satellites,” this report focuses on the debris risks associated with debris reentering from large satellite constellations in LEO. The report bases its estimates on the assumption that 12 large constellations proposed in applications to the U.S. Federal Communications Commission (FCC) as of March 2021 will be fully constituted and functioning in orbit in 2035 and will deorbit satellites for disposal according to the design lifetime of their satellites.
This report identifies how the FAA launch and reentry licensing process might be leveraged to address the risk to people on the ground and in aircraft. The FAA currently regulates the launch and reentry of a launch or reentry vehicle, including the safety of the vehicle’s upper stage at the end of the launch on an individual launch basis. Although the FAA’s current regulations address risks posed by the controlled reentry of launch and reentry vehicles and their components, the FAA would need to pursue notice and comment rulemaking to adequately address the risks associated with satellite constellations reentering from LEO. Specifically, the FAA could amend its payload review to address the reentry risk of large constellations through a rulemaking activity. Consistent with the authority granted under Title 51 Page 3 Risk Associated with Reentry Disposal of Satellites from Proposed Large Constellations in LEO of United States Code (51 U.S.C.) § 50904(c),1 the FAA reviews payloads to ensure that all necessary authorizations have been obtained and the launch or reentry of the payload will not jeopardize public health and safety, safety of property, U.S. national security or foreign policy interests, or international obligations of the United States. 2 Through notice and comment rulemaking, the FAA could amend its payload review regulation to address the public health and safety implications of cumulative payloads reentering Earth’s atmosphere. However, as discussed in greater detail in this report, since the FAA does not conduct a payload review for aspects of payloads subject to FCC or Department of Commerce regulation, the FAA would not amend the payload review regulation in this manner if either of these agencies were to begin regulating debris impacts from reentering satellite constellations.
Even if the FAA amended its regulations through rulemaking, the FAA’s requirements would fall short of addressing all reentry risks to people on the ground or in aircraft since the FAA’s authority does not extend to payloads launched from outside the United States by a person who is not a U.S. citizen or an entity organized under the laws of the United States. This could result in the FAA only authorizing a portion of a full constellation of satellites if an operator launches part of its constellation from the United States and another part outside the FAA’s jurisdiction. At this time, the FCC regulates the reentry risk of a constellation of U.S. spacecraft to people on the ground on an individual spacecraft basis, which does not account for cumulative risk.
In evaluating the debris risks associated with satellite constellations reentering Earth’s atmosphere, the FAA assessed the debris risks associated with the satellites themselves, as well as the launch vehicles that deliver those payloads to orbit. Increased launches of satellite constellations mean increased launches of launch vehicles capable of leaving large pieces of debris (i.e., upper stages of launch vehicles) in orbit for eventual reentry into the atmosphere. A stack of 60 Starlink first generation satellites has a mass of just over 17 tons, whereas the upper stage that placed those satellites in orbit has a mass of over 25 tons. Therefore, the FAA notes in this report that a safety assessment of large constellations must consider all reentry risks, including both satellite and launch vehicle stages. The FAA regulates purposeful, controlled disposal of upper stages at the end of a launch operation when it is planned, but the controlled disposal is not mandated in FAA regulation. A rulemaking is in process to address the risks associated with reentering debris and more closely align the FAA’s orbital debris mitigation regulations with the U.S. Government Orbital Debris Mitigation Standard Practices (USG ODMSP).
1 51 U.S.C. § 50904(c) (“The Secretary of Transportation shall establish whether all required licenses, authorizations, and permits required for a payload have been obtained. If no license, authorization, or permit is required, the Secretary may prevent the launch or reentry if the Secretary decides the launch or reentry would jeopardize the public health and safety, safety of property, or national security or foreign policy interest of the United States.”). 2 14 CFR § 450.43(a).
Risk Associated with Reentry Disposal of Satellites from Proposed Large Constellations in LEO
Since over 85 percent of the expected risk to people on the ground and aviation from reentering debris in 2035, as predicted in the Aerospace technical report, is a result of FAA licensed Space Exploration Technologies Corporation (SpaceX) launches of Starlink satellites, it would be worthwhile to definitively evaluate if any debris from random atmospheric reentry of Starlink spacecraft survives reentry. If SpaceX is correct in reporting zero surviving debris, as SpaceX reports in FCC filings, and Starlink is a fully-demisable spacecraft, the rise in reentry risk is minimal over the current risk.
By 2035, if the expected large constellation growth is realized and debris from Starlink satellites survive reentry, the total number of hazardous fragments surviving reentries each year is expected to reach 28,000, and the casualty expectation, the number of individuals on the ground predicted to be injured or killed by debris surviving the reentries of satellites being disposed from these constellations, would be 0.6 per year, which means that one person on the planet would be expected to be injured or killed every two years.
Some debris fragments would also be a hazard to people in aircraft. Projecting 2019 global air traffic to 2035 and assuming that a fragment that would injure or kill a person on the ground also would be capable of fatally damaging an aircraft, the probability of an aircraft downing accident (defined in the Aerospace report as a collision with an aircraft downing object) in 2035 would be 0.0007 per year.
The FAA will continue to work with other government agencies and industry to improve the management of large constellations of non-geostationary satellites, particularly those in LEO, that pose an increased risk due to reentering debris. The FAA will continue to improve the launch and reentry licensing process to address this risk where appropriate.
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