Visualization showing first how early spacecraft like NIMBUS-7 had to communicate with ground stations, second how a typical modern spacecraft communicates with the TDRS fleet, and finally how the fleet of users communicate with TDRS fleet.
The Tracking Data Relay Satellite (TDRS) fleet has provided spacecraft communications and tracking since the 1980's. Designed to replace most ground stations and provide longer periods of coverage, TDRS spacecraft have become an indispensable component of both manned and unmanned Earth orbiting space missions.
This visualization begins by showing how a typical spacecract (NIMBUS-7) communicated with the ground before TDRS. The spacecraft occassionally communicated with ground stations as its orbit briefly took it within range. This required ground stations to be spread all over the world and only allowed for sporatic communications between spacecraft and the ground.
As the animation continues, the TDRS fleet of spacecraft are introduced and a typical modern-day spacecraft, the Tropical Rainfall Measuring Mission (TRMM), is also introduced. As TRMM orbits the Earth, various TDRS spacrecraft are able to track and communicate with TRMM. This contact could be continuous, but for most spacecraft, continuous coverage is unnecessary. Constant communications between TDRS spacecraft and ground stations at White Sands and Guam are shown.
The visualization then adds many of the other TDRS users and shows how they communicate.
An additional ("extra") visualizaiton of the TDRS fleet communicating with user spacecraft is provided from a slightly different angle. These animations were created for a video supporting the launch of TDRS-12 (also called TDRS-L).