GPS Satellites

A satellite is a telecommunication device that is placed in space. A satellite vehicle (SV) is an object that contains communication electronics that revolves around another object of greater mass (such as the Earth). The satellite ‘s motion is determined by the force of attraction (gravity) of the larger object. Satellites contain power systems, attitude (position) control systems, and communication equipment. 

GPS satellites are a combination of receivers and transmitters (transponders) that receive signals from Earth stations (uplink) and retransmit them to GPS receiving stations (downlink). They are located at 17,700 km (approximately 11,000 miles) above the surface of the Earth and travel at approximately 7,000 kilometers per hour.

Each GPS satellite transmits two frequencies with 20 to 50 Watts of RF power. GPS satellites are assigned space vehicle numbers by which they are uniquely identified. The satellites transmit unique reference codes.

The design life (life span) is the operational time a device or system is expected to operate within. For satellite systems, a key design life limitation is by the amount of propulsion fuel that is used to keep the satellite in its desired orbital plane. Most of the satellite attitude propulsion fuel is used to initially position the satellite into its desired orbit. 

The life span of GPS satellites has increased from 4.5 years [1] on the original Block I satellites to more than 11 years on the new Block IIR satellites.

The weight of GPS satellites ranges from approximately 1,800 pounds (900 kilograms) to over 4,400 pounds (2,200 kilograms). Their wingspan ranges from approximately 17 feet (5.3 meters) to 116 feet (35.5 meters) [ ].

GPS satellites contain computer processors, programs and memory areas. The processor is responsible for creating the navigational messages that are transmitted to GPS receivers. The first GPS satellites had limited memory and processing capability so they could only hold approximately 3.5 days of navigation message information. Newer versions of the GPS satellites (Block II) can hold 180 days of navigation information.

   Global Positioning System - GPS Books

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Global Positioning System - GPS Book This book covers satellite position location technology and the GPS system has evolved. You will learn the functional parts of GPS systems, how they work and work together to provide position measurements that are accurate to within centimeters. $19.99 Printed, $16.99 eBook

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