TAMPA, Fla. — SpaceX called on the Federal Aviation Administration to correct a report back to Congress warning that, by 2035, falling debris from U.S.-licensed constellations in low Earth orbit (LEO) could injure or kill someone every two years in the event that they deploy as planned.
In an Oct. 9 letter to the FAA and Congress seen by , SpaceX principal engineer David Goldstein said the report relied on “deeply flawed evaluation” based on assumptions, guesswork, and outdated studies. The letter got here 4 days after contacted the corporate with questions on the report, published Oct. 5 on the FAA’s website.
Within the report, the regulator said 28,000 hazardous fragments from de-orbiting satellites and the rockets that launch them may very well be surviving reentry every year by 2035 — particularly if SpaceX’s rapid Starlink expansion plans remain on course.
SpaceX has launched 5,000 Starlink satellites since 2019, has permission from the U.S. Federal Communications Commission to grow the constellation to 12,000, and is looking for international approvals to eventually expand to 40,000 Starlinks in orbit. In response to the FAA report, Starlink represents greater than 85% of the expected risk to people on the bottom and aviation from falling debris within the timeframe.
The FAA was directed by Congress in 2020 to issue a report on the risks related to the reentry disposal of satellites from LEO megaconstellations. In 2021, the FAA commissioned the Aerospace Corp., a federally funded nonprofit focused on space, to supply a technical assessment of the rise of LEO constellations and the risks posed to aviation and folks on the bottom by unplanned and controlled reentries of those satellites and the upper stages that launch them.
The FAA told Aerospace Corp. to deal with non-geostationary satellites launched by america under FAA licenses, so the evaluation excluded constellations comparable to China’s proposed 13,000-satellite Guowang network.
The Aerospace Corp. also concluded the probability of “an aircraft downing accident” in 2035 at 0.0007 per yr because of this of falling debris, which might likely kill all onboard.
“By 2035, if the expected large constellation growth is realized and debris from Starlink satellites survive reentry, the entire variety of hazardous fragments surviving reentries every year is anticipated to achieve 28,000, and the casualty expectation, the number of people on the bottom predicted to be injured or killed by debris surviving the reentries of satellites being disposed from these constellations, could be 0.6 per yr, which suggests that one person on the planet could be expected to be injured or killed every two years.
“Some debris fragments would even be a hazard to people in aircraft. Projecting 2019 global air traffic to 2035 and assuming that a fraction that may injure or kill an individual on the bottom also could be able to fatally damaging an aircraft, the probability of an aircraft downing accident (defined within the Aerospace report as a collision with an aircraft downing object) in 2035 could be 0.0007 per yr.”
Excerpt from FAA report back to Congress: Risk Related to Reentry Disposal of Satellites from Proposed Large Constellations in Low Earth Orbit
Nonetheless, the FAA conceded any “rise in reentry risk is minimal over the present risk” if SpaceX is correct in reporting zero surviving Starlink debris so far, and that their components are fragile enough to burn up entirely within the atmosphere.
In response to satellite tracker and astrophysicist Jonathan McDowell, 358 Starlink satellites have de-orbited. There have been no reports of their debris reaching the bottom.
“To be clear, SpaceX’s satellites are designed and built to completely demise during atmospheric reentry during disposal at end of life, and so they accomplish that [emphasis in original],” Goldstein wrote within the letter.
“Extensive engineering evaluation and real-world operational experience confirm this basic fact.”
The FAA based its conclusions on a claim that the space industry has not met the 90% success rate for post-mission disposal, he added, whereas he said SpaceX’s post-mission disposal success rate is larger than 99%.
Goldstein also said the evaluation improperly leveraged a 23-year-old NASA study that found roughly one piece of debris survives reentry for each 100 kilograms on Iridium Communications satellites — a much smaller LEO constellation.
“The evaluation is inapplicable to SpaceX satellites because — amongst other things — Iridium satellites weren’t even built to be fully demisable,” he said, and are “not similar in material, construction, design, orbit and operation from SpaceX or some other modern satellite in LEO.”
The FAA was unable to comment because Oct. 9 is a federal holiday in america.
Tricky work
Determining the precise risk from reentering satellites is difficult resulting from the uncertainties in reentry survivability calculations, Marlon Sorge, executive director of Aerospace’s Center for Orbital and Reentry Debris Studies, told via email Oct. 5.
“The phenomenology is sort of complex and the available ‘ground truth’ data is proscribed,” Sorge said, and the precise results are also highly depending on the specifics of satellite designs.
“As you’ll be able to imagine it is vitally difficult to get ‘ground truth’ data on what survives reentry by observing actual reentries as they occur randomly everywhere in the world, not often in convenient locations,” she added.
Relatively than attempting to predict the long run, she said the evaluation sought to grasp how behaviors result in reentry consequences, so motion may be taken to scale back potential risks.
“This type of information helps in planning for possible future rule changes given the increased traffic that is feasible in the long run,” she said.
In response to Goldstein, Aerospace Corp didn’t seek to review Starlink’s demisability evaluation, and its “errors can have been avoided if Aerospace had simply made basic inquiries with SpaceX, however it elected to not accomplish that.”
Goldstein also slammed Aerospace Corp. and the FAA for failing to update figures within the 2021 evaluation for the dimensions of constellations before submitting it to Congress.
While the report assumes 54,902 FCC-licensed satellites are in space across 12 filings from nine operators, updated regulatory filings have reduced this number by 7,518.
Along with excluding constellations licensed by China and other foreign governments, Goldstein highlighted how the evaluation failed to think about U.S.-based Amazon’s plans to start launching its proposed constellation of greater than 3,200 satellites next yr.
“The very fact FAA simply accepted the Aerospace report without query or scrutiny raises concerns regarding FAA’s technical competence to responsibly assess and regulate on this area,” Goldstein wrote.
Rocket debris risk
In addition to satellite reentries, the FAA report highlighted the increasing risk of falling debris from the rise in launches needed to deploy and sustain large LEO constellations.
The U.S. business rockets that launch large constellations typically leave their upper stage in orbit, which the report noted often has more mass than individual satellites “and due to this fact poses a greater reentry risk to people on the bottom.”
Whereas 60 Starlink first-generation satellites have a complete mass of just over 17 tons, an upper stage of the Falcon 9 that launched them to LEO is over 25 tons.
The report also pointed to the reentry of a Falcon 9 upper stage in March 2021 following a Starlink launch that “could have landed anywhere from 53 degrees south to 53 degrees north latitude.”
Wreckage from the core stage of a Chinese Long March 5B rocket that reentered into Earth’s atmosphere two months later was widely criticized within the U.S. and elsewhere.
Although the debris fell into the ocean, where most random reentries find yourself because water covers 70% of the Earth, the FAA said the chance of huge objects reentering over populated areas stays.
“Despite guidelines recommending purposeful reentry, large space objects reenter the Earth’s atmosphere roughly once every week,” the report added.
“Some are recently launched, and lots of more were launched prior to any agreed-upon disposal strategies.”
The U.S. government tracks reentries, however the FAA said it may possibly’t predict them accurately enough to supply meaningful warnings to those in peril.
“As a rule of thumb, a reentry time may be off by ten percent of the orbital time remaining,” the report warned. “Which means that 10 hours before reentry, the expected reentry time may be off by one hour.”
Goldstein’s letter to the FAA didn’t touch on the chance of injury or death from rocket reentries.
The FAA published draft regulations in September that may require U.S. business launch providers to deorbit spent upper stages post-launch, primarily to scale back risks of orbital debris but additionally to limit risks to people on the bottom from uncontrolled reentries.
Nonetheless, the FAA said it doesn’t have the authority to adequately address the risks related to satellite constellations reentering from LEO.
An FAA rule-making on this matter will depend on whether other agencies — the FCC or Department of Commerce — decide to begin their very own process for regulating the reentry of constellation-related debris.