Eight years ahead of schedule, a 1,300-pound spacecraft is falling out of orbit — and the sun is why.
Van Allen Probe A, a 600-kilogram satellite that has circled Earth for nearly 14 years, was predicted to stay aloft until 2034 when it ran out of fuel in 2019. That estimate did not account for what the sun was about to do. The current solar cycle, which began in late 2019, has been more active and peaked sooner than scientists anticipated. The resulting space weather created enough atmospheric drag on the powerless probe to pull it down years ahead of forecast.
NASA placed reentry at approximately 7:45 p.m. EDT on March 10, based on U.S. Space Force calculations, though the agency noted a 24-hour margin of error around that window. Most of the spacecraft is expected to burn up during atmospheric entry. Some components, according to the announcement, are likely to survive. The agency puts the probability of harm to any person at 1-in-4,200.
What the solar cycle did to the orbit
The sun runs on a roughly 11-year cycle, peaking at a period of intense activity called solar maximum. That peak generates stronger space weather events — bursts of plasma, elevated radiation, geomagnetic disturbances. For a satellite with no fuel to correct its path, those events translate directly into orbital decay. The atmosphere expands slightly under solar bombardment, increasing drag even at high altitudes where spacecraft typically cruise undisturbed.
Van Allen Probe A had no way to compensate. Its twin, Van Allen Probe B, remains in orbit and is expected to stay there until 2030, according to NASA.
The two probes launched together in 2012, designed for a two-year mission to study Earth’s radiation belts — the twin rings of charged particles held in place by the planet’s magnetic field, named after American physicist James Van Allen. The mission ran for roughly seven years instead of two.
What the probes found before going dark
During their operational life, the spacecraft produced a series of findings about the radiation belts. They detected that electrons within the belts can be accelerated to near light speed by riding plasma waves ejected from the sun. They also identified a third radiation belt — one that appears only during periods of intense solar activity — adding to the two permanent belts previously known.
The mission formally ended in 2019 when both probes exhausted their fuel supply. Since then, the satellites have drifted passively, subject entirely to the forces around them. For Probe A, those forces ran out of patience first.
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