SpaceX is warning that retired Starlink satellites might not always disintegrate upon reentry in the Earth’s atmosphere. Small remnants of the debris can actually survive and land on the Earth.
The company made the statement on Thursday as SpaceX has been de-orbiting and retiring hundreds of older Starlink satellites by plunging them back into the Earth’s atmosphere, which can incinerate the hardware. All Starlink satellites were designed to orbit for about five years.
SpaceX has previously said that Starlink satellites have been engineered to “fully demise” during atmospheric re-entry, thus posing no threat to the public. But in Thursday’s statement, the company said small fragments from the burning debris can continue to fly toward Earth.
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Still, the company maintains the satellite debris poses no danger. For example, the chance of the company’s newest Starlink satellites causing human harm has been rated at “less than 1 in 100 million, significantly more conservative than the current industry standard,” it said.
Whether the risk is higher for older Starlink satellites launched five years ago was left unclear. But SpaceX says it adopted a “more conservative approach” than current US regulations, which require operators to keep the risk levels of falling space debris from causing a human casualty to under 1 in 10,000.
Although the company’s newest V2 mini Starlink satellites should disintegrate if they’re sent burning through the atmosphere, SpaceX also noted: “we predict that approximately 5% of the mass of the entire satellite could survive reentry.”
“The biggest contributor (~90% of the surviving mass) is silicon from the solar cells, which has a high melting point and a very low ballistic coefficient, which could survive reentry in extremely small fragments,” the company added. That said, if any silicon fragments survive, they would end up landing on Earth with less than one joule of energy — or about how much energy it takes to lift an apple.
(SpaceX)
While the falling silicon debris should be harmless, SpaceX noted that the magnetic ceramic materials in “the core of inductors and transformers” of a Starlink satellite can also survive re-entry. As a result, the company says its “limiting the size and the mass of each inductor core, even at the cost of reducing their efficiency and increasing the complexity of the system design.”
SpaceX’s cautious approach to safety includes ensuring that any debris fragments land with less than 3 joules of energy —well below the US regulatory threshold, which considers objects exceeding 15 joules a potential human casualty risk. “For reference, 15 Joules of energy corresponds to roughly that of a 1.7” piece of hail,” the company said.
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In the same report, SpaceX points out it’s preparing to de-orbit 329 Starlink satellites. The company also says it’s already de-orbited a total of 865. The numbers align with findings from astronomer and satellite watcher Jonathan McDowell, who’s spotted SpaceX de-orbiting about 4 to 5 Starlink sats per day.
The increasing number of disposals might spark concerns about Starlink debris landing over populated areas. But SpaceX says it always tries to retire the satellites “over the open ocean, away from populated islands and heavily trafficked airline and maritime routes.”
That didn’t occur in January when one five-year-old Starlink satellite was recorded blazing through the night skies over northern Illinois. Michael Nicolls, VP of Starlink Engineering, attributed the botched re-entry to “degraded attitude control.” Thursday’s statement from SpaceX adds this requires controlling the satellite at very low altitudes, under 125 kilometers, or “far below the design requirement of these early Starlink vehicles.”
The company has since improved the altitude control systems for its newer V2 and upcoming V3 satellites. In addition, SpaceX has been conducting experimental tests simulating the atmospheric re-entry conditions and whether the conditions will disintegrate the printed circuit boards used in the satellites. The company currently has over 7,000 satellites in orbit with plans to launch thousands more.
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About Michael Kan
Senior Reporter
