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 slightly. Unless low-Earth-orbit satellites are routinely boosted to higher orbits, they slowly fall, and eventually burn up in the Earth’'s atmosphere. Skylab is an example of a spacecraft re-entering the Earth’'s atmosphere prematurely as a result of higher-thanexpected solar activity. During the great geomagnetic storm of March 1989, four Navy navigational satellites had to be taken out of service for up to a week.
As technology has allowed spacecraft components to become smaller, their miniaturized systems have become increasingly vulnerable to the more energetic solar particles. These particles can cause single event upsets which often cause physical damage to microchips and change software commands in satellite-borne computers.
Another problem for satellite operators is differential charging. During geomagnetic storms, the number and energy of electrons and ions increase. When a satellite travels through this energized environment, the charged particles striking the spacecraft cause different portions of the spacecraft to be differentially charged. Eventually, electrical discharges can arc across spacecraft components, harming and possibly disabling them.
Bulk charging (also called deep charging) occurs when energetic particles, primarily electrons, penetrate the outer covering of a satellite and deposit their charge in its internal parts. If sufficient charge accumulates in any one component, it may attempt to neutralize by discharging to other components. This discharge is potentially hazardous to the electronic systems of the satellite.
Reference : NOAA Space Weather Prediction Center, "A Profile of Space Weather", pp4~6. 2001.