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GSAT0202 (GALILEO 6)

European Navigation Satellite (Galileo — Stranded, Used for Relativity Test) · ESA / European Commission

GSAT0202 (Galileo 6), the twin satellite stranded alongside GSAT0201 by the same August 2014 Fregat upper stage failure, became half of one of the most elegant accidental physics experiments in recent memory. Rather than write off two satellites worth hundreds of millions of euros, ESA scientists used their unplanned elliptical orbits — constantly shifting altitude between roughly 10,500 and 16,000 miles — to measure how strongly Earth's gravity affects the passage of time at different heights, testing Einstein's general relativity to a precision four times sharper than any prior satellite-based experiment. Both satellites were eventually raised into partially useful orbits and now also contribute limited navigation signal coverage.