They were sent into orbit to measure the Earth’s invisible magnetic field.
But a cluster of scientific satellites have been suffering mysterious blackouts as they circle the planet.
Scientists were left puzzled about why the three satellites launched by the European Space Agency have regularly lost their navigation signal when passing over the equator above the Atlantic Ocean.
Now they believe they may have uncovered the underlying cause of the strange loss in the GPS signal that helps control the satellites – thunderstorms high in the ionosphere.
Professor Claudia Stolle, from the German Research Centre for Geosciences in Postdam, Germany, said the storms can cause the signal to the Swarm satellites to vanish for several minutes at a time.
She said: ‘These ionospheric thunderstorms are well known, but it’s only now we have been able to show a direct link between them and the loss of the GPS.
‘This is possible because the Swarm satellites provide high resolution observations of both phenomena at one spacecraft.’
The Swarm constellation was designed to monitor the magnetic field that envelopes the Earth and to look for electric currents in the planet’s atmosphere.
They were launched in November 2013 with two of the satellites being sent to orbit side-by-side at an altitude of 285 miles and a third orbiting at 329 miles.
The satellites use GPS signals to help determine their precise position and timing as they orbit.
Yet as the satellites passed over the equator between Africa and South America they seemed to lose the GPS signal for several minutes.
GPS is provided by a suite of 24 satellites orbiting some 12,550 miles above the surface. They provide the signal that is used by satellite navigation systems, mobile phones, aircraft and many other devices here on Earth.
Researchers, whose work is published in the journal Space Weather, found that ionospheric thunderstorms appear to be able to disrupt these signals.