LEO to GEO Downlink
LEO satellites are not always visible to a ground station. Due to high orbital speed and near proximity to Earth (around 1,200 miles above the surface), a typical LEO satellite may be visible to a ground station for less than 20 minutes in a typical 85 to 125 minute orbit. This small window severely limits the amount of data that can be sent via downlink. By adding a GEO satellite to the data link, the data transmission window can be significantly increased.
Since the percentage of a LEO satellite’s visibility to a ground station is very low, the time to download data in a satcom system is limited. To increase the imaging capacity of a remote-sensing satellite, the data can be stored on the LEO satellite, beamed up to its network GEO satellite and downloaded at a higher data rate during a limited visibility period. In theory, two widely spaced GEO satellites can provide continuous visibility/coverage for a LEO satellite.