ABSTRACT

The portable TRANSIT satellite simulator described in this paper can test entire satellite receiver computer systems, from antenna input to the resulting computed fix, simulating any location in the world. Also described are the basic satellite signals, fix equations, and differences in receivers, as related to the design of the simulated satellite pass.

Units now in use test only individual parts of a satellite-receiver system; namely, the Doppler counters and decoding logic.

Oil-industry marine activities use a variety of satellite receivers and even more varied computer hardware-software systems. Each contractor processes the received satellite data using different Doppler-count intervals, tropospheric models, time recovery schemes, and offset frequencies. The TRANSIT satellite simulator can compare the performances of these systems.

Where useful satellite passes may come only at 6- to 8-hour intervals, days have often been lost waiting to confirm repair of a minor malfunction. The satellite simulator will minimize such lost time.

A TRANSIT SATELLITE SIMULATOR

Navigation and positioning for the oil industry's marine operations invariably use, as an integral part of subsystem, a TRANSIT satellite receiver and computer. In completing the geophysical and drilling operations in a given area, we often have to use two or three different types of satellite receiver-computer systems. These different systems use different techniques in the collection and processing of the satellite data. Currently, we have no simple way of comparing these different systems. In equatorial regions there can be periods of 6 to 8 hours between useful satellite passes. In these areas, a minor breakdown of the satellite system could cause costly delays awaiting a satellite pass to confirm correction of the malfunction.

At present there are available many different satellite test units that test parts (namely, the Doppler counters and the decoding logic) of the satellite systems, but there is no means of testing a satellite system in its entirety, from antenna input to the computed fix output.

A few years ago, Chevron Oil Co. felt the need for a TRANSIT satellite test system, one that could be used by non technical personnel to test and assure themselves that the system is working correctly.

With this in mind, Chevron approached Magnavox Co. (one of the larger manufacturers of satellite systems) with the idea of a joint feasibility study. The success of this feasibility study has resulted in a project at Chevron Oil Field Research Co. to design and build a compact TRANSIT satellite simulator.

The TRANSIT satellite simulator described in this paper is designed to test the current satellite receiver-computer systems that are used for marine surveys from antenna input to the resulting computed fix at any location in the world (Fig. 1). From inputs of local latitude, longitude, GMT time, antenna height, and receiver type, parameters are calculated that control the transmission of signals from the simulator that, to the satellite receiver's antenna, is indistinguishable from a real, live satellite pass. The satellite system's computed fix should result in the latitude and longitude that was the input to the simulator.

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