Ground Infrastructure

The ground-based infrastructure for a satellite is responsible for a number of support functions, such as commanding the spacecraft, monitoring its health, tracking the spacecraft to determine its present and future positions, collecting the satellite's mission data, and distributing these data to users. A key component of the infrastructure is the ground station, which is an Earth-based point of contact with a satellite and a distributor of user data.

Spacecraft and payload support consists of maintaining a communications link with the satellite to provide satellite and payload control. The ground station collects satellite telemetry (transmitted signals) to evaluate its health, processes state of health information, determines satellite orbit and attitude, and issues satellite commands when required.

Mission data receipt and relay is a vital function of the ground station. This includes receiving mission data and payload telemetry. The ground station computers process these data into a usable format and distribute them to the users by way of electronic communication lines such as satellite or ground-line data link or even the Internet.

A generic ground station consists of an antenna to receive satellite signals; radio frequency receiving equipment to process incoming raw electronic signals; and mission data recovery equipment, computers, and data interface equipment to send data to users. Additionally, telemetry, tracking, and control equipment monitors the spacecraft's health status, and radio frequency transmitting equipment sends commands to the satellite via the station antenna.

Station Personnel

A large satellite control station has several types of centers staffed by a diverse range of qualified personnel. The Control Center (CC) accomplishes overall control of the ground station, and all other station centers are responsible to the CC. A senior individual who has several years' experience working with the satellite systems and the station leads this center. The Satellite Operations Control Center (SOCC) is responsible for satellite health. A senior engineer leads this team, which tracks the satellite and its telemetry. The Payload Operations Control Center (POCC) is responsible for the payload's status and health. A senior engineer also leads this team, which monitors the spacecraft's payload and the quality of data it is collecting. The SOCC and POCC must also determine causes for spacecraft malfunctions and corrections that might be required. The Mission Control Center is responsible for reviewing mission data to ensure their quality for the users. Because it is the last link before the users obtain their data, this center is led by an expert such as a scientist. The Station Control Center is responsible for the ground station upkeep, such as distributing power, providing cooling for the computers, and taking care of general maintenance on all other station equipment. This team is usually led by a civil engineer with a number of years of maintenance experience.

For a smaller satellite operation many of these jobs are combined. One computer might run the CC and the Mission Control Center functions while another accomplishes the SOCC and POCC jobs. If the operation is small, three people and two computers can run the entire ground station.

Commercial Satellite Ground Stations

Depending upon the size, commercial satellite ground stations are available from several corporations with different price structures. This section examines two large processing facility manufacturers: Raytheon and Honeywell; one transportable ground station company, Datron; and one foreign company, RDC ScanEx.

Raytheon Corporation of Denver, Colorado, offers large ground stations including antennas, satellite command and control, mission planning, management, front-end processing, and terminal equipment. One example of their extensive capability for satellite ground station operations is their software, which uses over three million lines of code in operations activities. With their 1800 Denver-based employees, Raytheon has built and supplied more than 40 international ground stations. The large ground stations are prohibitively expensive for any organizations other than governments or very large universities.

Another example of commercial ground stations is Honeywell's Data Lynx series of ground stations. Honeywell offers antennas, tracking, data acquisition, commanding, satellite management, and data processing. The U.S. Navy has taken advantage of Honeywell's expertise by employing their ground stations for the Naval Earth Map Observer satellite system that employs hyperspectral sensors. Lockheed Martin has also used Honeywell's ground stations in the Poker Flats Satellite Tracking facility located near Fairbanks, Alaska. Similar to the Raytheon system, the Data Lynx is very expensive to operate and maintain.

There are several examples of companies that build small satellite tracking ground stations that require few people. Datron from Simi Valley, California, has built a transportable satellite station that can be used for military tactical intelligence gathering, disaster area assessment, and remote area coverage. The Datron portable ground station is compatible with the Landsat, SPOT, RADARSAT, IKONOS, and Quickbird satellites. Although not as expensive as the Raytheon and Honeywell ground stations, Datron requires a substantial sum for its transportable ground station.

An example of a foreign commercial company that uses minimum equipment to create a ground station is the Russian private company known as RDC ScanEx. This company focuses on personal computers to acquire, track, and download data from several different weather satellites such as the National Oceanic & Atmospheric Administration polar satellites and the Russian Earth remote sensing satellites. The Liana system uses a small, omnidirectional antenna to acquire satellite signals that are sent direct to a personal computer (PC) for processing and distribution. This system requires one person with no special training to run the system as all components are within a small PC area. This company has sold more than 80 of these systems, at very competitive prices of less than $5,000 per station.

see also Communications for Human Spaceflight (volume 3); Communications Satellite Industry (volume 1); Satellite Industry (volume 1); Tracking of Spacecraft (volume 3); Tracking Stations (volume 3).

John F. Graham

Bibliography

Fleeter, Rick. The Logic of Microspace. El Segundo, CA: Microcosm Press, 2000.

Larson, Wiley J., and James R. Wertz, eds. Space Mission Analysis and Design, 3rd ed.Torrance, CA: Microcosm Press, 1999.

Sellers, Jerry Jon. Understanding Space. New York: McGraw-Hill, Inc., 1994.