TDRSS Satellites

Today, NASA has a fleet of satellites for communicating with Earth-orbiting satellites and manned spacecraft. This network of satellites is called the

Tracking and Data Relay Satellite System (TDRSS). When a ground station wants to send a signal to a spacecraft, it sends the signal up to the nearest TDRSS. The signal is then passed on from satel­lite to satellite around the world until it reaches a satellite in contact with the spacecraft. The TDRSS provides communication with many spacecraft, including the Space Shuttle, the International Space Station, and the Hubble Space Telescope.

TDRSS satellites orbit Earth 22,250 miles (35,800 kilometers) above the equator. This is a special orbit called geostationary orbit. A satellite in this orbit goes around the world once every 24 hours. As the Earth also spins once every 24 hours, this means that the satellite always stays above the same spot on Earth. As well as the TDRSS,

there are many other communications satel­lites using this orbit.

The radio signals sent to and from space­craft carry all sorts of information, including the voices of astronauts and mission con­trollers, video images from the Space Shuttle and International Space Station, command signals for controlling the movements of satellites, and science data from weather satellites and space tele­scopes. Engineering data also are sent automatically from rockets and spacecraft during missions so that mission controllers can monitor them. This form of com­munication is called telemetry.