In general, the geomagnetic storms and increased solar ultraviolet emission heat the Earth's upper atmosphere, causing it to expand. The heated air rises, and the density at the orbit of satellites up to about 1000 km increases significantly. This results in increased drag on satellites in space, causing them to slow and change orbit. Some satellites have experienced a drop up to 5 km during a geomagnetic storm.
Naturally the space stations need boosting, too. The first US space station, Skylab burned in the atmosphere in 1979, after having been unmanned for five years.
