Spacecraft ground instrumentation

(engineering) Instrumentation located on the earth for monitoring, tracking, and communicating with manned spacecraft, satellites, and space probes. Also known as ground instrumentation.

Instrumentation located on the Earth for monitoring, tracking, and communicating with satellites, space probes, and crewed spacecraft. Radars, communication antennas, and optical instruments are classified as ground instrumentation. They are deployed in networks and, to a lesser extent, in ranges. Ranges are relatively narrow chains of ground instruments used to follow the flights of missiles, sounding rockets, and spacecraft ascending to orbit. Some ranges are a few miles long; others, such as the U.S. Air Force's Eastern Test Range, stretch for thousands of miles. Networks, in contrast, are dispersed over wide geographical areas so that their instruments can follow satellites in orbit as the Earth rotates under them at 15° per hour, or space probes on their flights through deep space.

Networks are of two basic kinds: networks supporting satellites in Earth orbit, and networks supporting spacecraft in deep space far from Earth. A third concept was added in the 1980s with the Tracking and Data Relay Satellite System (TDRSS), also called the Space Network (SN). TDRSS replaced most of the ground stations used for Earth orbital support. The Tracking and Data Relay Satellites (TDRS) are placed in geosynchronous orbits to relay signals to and from other orbiting spacecraft during more than 85% of each orbit, to and from a single ground station.

Ranges and networks have various technical functions:

1. Tracking: determination of the positions and velocities of space probes and satellites through radio and optical means.

2. Telemetry: reception of telemetered signals from scientific instruments and spacecraft housekeeping functions.

3. Voice reception and transmission: provision for communication with the crew of a spacecraft, such as the space shuttle.

4. Command: transmission of coded commands to spacecraft equipment, including scientific instruments.

5. Television reception and transmission: provision for observation of the crew, spacecraft environment, and so on.

6. Ground communications: telemetry, voice, television, command, tracking data, and spacecraft acquisition data transmission between network sites and the central mission control center, and payload information to user facilities.

7. Computing: calculation of orbital elements and radar acquisition data prior to transmission to users; also, computation of the signals that drive visual displays at a mission control center.

NASA operates two ground-based networks and the TDRSS. The ground-based networks are the Spaceflight Tracking and Data Network (STDN), which tracks, commands, and receives telemetry from United States and foreign satellites in Earth orbit; and the Deep Space Network (DSN), which performs the same functions for all types of spacecraft sent to explore deep space, the Moon, and solar system planets. The TDRSS provides the same support to Earth orbital spacecraft as the STDN. The U.S. Department of Defense operates two classified networks: the Satellite Control Facility (SCF); and the National Range Division Stations, which include those of all United States military ranges. Russia and the European Space Agency (ESA) also maintain similar networks.

The Laser Tracking Network consists of a series of both fixed and mobile laser systems used for ranging to retroreflector-equipped satellites in highly stable orbits. Laser stations obtain ranging data for these satellites by bouncing a highly concentrated pulse of laser light off the retroreflector corner cube installed on the spacecraft exterior. The exact position of the spacecraft in orbit can then be mathematically determined for a given point in time. By comparing several ranging operations, orbital predictions can be interpolated and extrapolated. The resultant data have a variety of applications, such as precise prediction of satellite orbit and measurement of the Earth's gravitational field, polar motion, earth tides, Earth rotation, tectonic plate motion, and crustal motion to accuracies within the centimeter range. The Laser Tracking Network is a multinational cooperative effort with over 30 laser sites located in North and South America, Europe, China, Japan, and Australia.