Van Allen Probe A, a 1,323-pound (600-kilogram) satellite that has orbited Earth since 2012, is expected to reenter the atmosphere this week — and the risk it poses to people on the ground exceeds the US government’s own safety threshold.
The probability of the reentry causing a casualty is approximately 1 in 4,200. The US government’s standard requires that probability to be no greater than 1 in 10,000.
NASA acknowledged the breach and granted itself a waiver. “Due to late-stage design changes, the potential risk of uncontrolled reentry increased,” a NASA spokesperson said, according to the report. “After taking into account the mission’s scientific benefits and the low risk of harm to anyone on Earth, NASA granted a waiver to address the non-compliance with the US Government Orbital Debris Mitigation Standard Practices.”
The agency notified the US Department of State about the exception, consistent with national policy.
Earlier Than Expected
The mission was shut down in 2019 when both satellites ran out of fuel. At that point, engineers projected Van Allen Probe A would reenter around 2034. Higher-than-anticipated solar activity caused the upper atmosphere to expand, increasing drag on the satellite and pulling it down faster than modeled.
The US Space Force placed the reentry window between late Monday and late Wednesday of this week. Atmospheric density variations make precise prediction difficult.
The satellite’s orbit is inclined 10 degrees to the equator, which confines reentry risk to a band across the tropics. Most of the spacecraft will burn up during descent. A fraction of the material is expected to survive and reach the surface.
A Pattern of Waivers
This is not the first time NASA has exceeded its own reentry risk standards. The Rossi X-ray Timing Explorer fell out of orbit in 2018 carrying a 1-in-1,000 casualty probability — far beyond the threshold. No one was hurt. That satellite launched in 1995, just four months before NASA issued its first orbital debris mitigation standard.
The companion spacecraft, Van Allen Probe B, is expected to reenter no earlier than 2030, carrying a similar risk level.
Both probes were built by the Johns Hopkins University Applied Physics Laboratory. The mission’s findings included the first observational data confirming the existence of a transient third radiation belt, which forms during intense solar activity.
For context, the US is not the most notable actor in uncontrolled high-mass reentries. China launched four Long March 5B rockets between 2020 and 2022 and left each core stage — nearly 24 tons each — to fall back uncontrolled. Two dropped wreckage on land, in the Ivory Coast and Borneo. No injuries were reported in either case.
No person on the ground has ever been confirmed injured by falling space debris.
Photo by Pixabay
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