Starfix is a privately owned and operated positioning system which became operational In early 1986 after three years of development effort. Starfix is a 24- hour-a-day positioning system encompassing the continental US and up to 500 miles offshore with a 5 metre 2 DRMS accuracy At the present time.

Starfix has worked for every major oil company and seismic contractor, primarily in the Gulf of Mexico This chapter will describe the operation of the Starfix system and compare Starfix with Syledis.

STARFIX SYSTEM DESCRIPTION

The major components of the Starfix system are a constellation of at least three satellites; uplink facilities for transmitting signals to each satellite; a nationwide tracking network for determining the position of each satellite, a central computing station known as the Master Site (Master Computing Facility), and passive user systems that provide the navigation function.

The Starfix positioning system makes use of geostationary communication satellites that are nearly motionless m relation to the earth 22 300 miles above the equator (Fig 1).

Additional satellites may be used in the future to strengthen the geometry of the solution and provide redundancy The purpose of the uplink facilities is to send data generated from the Master Site to the Starfix satellites for broadcast to the user The data are being upllnked to the satellites at a frequency of 6 GHz The Starfix tracking network is comprised of ten sites located throughout the United States. Each Remote Site (Tracking Station) has been precisely surveyed using state-of-the-art techniques to provide consistency of the network to the level of a few centimeters The purpose of the network is to provide tracking data which allow the precise determination of the Starfix satellites in real time. The tracking stations also provide differential information that is necessary in the user position calculation.

The equipment at each tracking station consists of four Starfix receivers with antennas, a signal processing unit (SPU), a leased phone line modem to communicate with the Master Site, a back-up dial up modem to communicate with the Master Site, and a rubidium frequency standard.

Fig. 1 Starfix geostationary satellite configuration The user equipment necessary in the Starfix positioning system consists of a 5200A receiver and antenna system (Fig 2; Tables I and 11)(available in full paper)

TABLE I Starfix receiver unit (model 5200A) (available in full paper)

TABLE II Starfix antennae(available in full paper)

The purpose of the Master Site is to collect and format data for transmittal to the satellites, to calculate orbit coordinates of the satellites from all the tracking station data, and to provide a central facility for communication to the satellite uplink facilities The Master Site is located in Austin, Texas and has leased phone lines to all the Remote Sites as well as the uplinks A back-up Master Site is located in Houston, Texas with duplicate leased phone lines between all Remote Sites and the uplinks The Master Site also monitors the Starfix system to identify problems, and to alert users if a potential problem exists.

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