ABSTRACT

With the increasing application of the Navy Navigation Satellite System (NNSS) to geophysical and oceanographic exploration and carrier ship navigation, a greater concern of equipment cost vs. performance has arisen. One area of compromise is utilizing a single channel satellite receiver rather than a dual channel receiver. Experimental data taken gives a direct comparison of the two systems detailing the effect on individual passes as well as the ensemble data. Also, the effect of altitude uncertainties on position fix accuracy can be shown by recomputing the satellite data with various assumed altitudes.

The practicality of using each system for shipboard use or for drilling rig, monument placing and platform positioning is discussed.

The basic conclusion is that for a mobile system employed in detailed surveys, the dual channel receiver should be used. For static applications where time is of no concern, the single channel receiver can be employed.

INTRODUCTION

Within the past two years, the Navy Navigation Satellite System (NNSS) has enjoyed increasing popUlarity as a navigation source among the users in the commercial offshore industry. However, the potential user can quite easily become confused by literature and verbal information given to him unless he is totally familiar with what is being communicated. This paper will describe the effects of several of the more recent items of interest. Specifically, what is relative accuracy of., the dual channel satellite receiver to the single channel receiver? Is the single channel receiver accuracy adequate for my application? Can geographic elevation be determined from the NNSS?

A simplified theoretical interpretation of the basic fundamentals will be presented. From these fundamentals and results of actual data taken on Julian days 287 through 292 of calendar year 1970 several conclusions will be drawn. Although this data does not represent an infinite set upon which to base conclusions, the conclusions drawn herein rely on this data only to illustrate a trend.

The data was gathered using a dual channel receiver to compute a position fix in real time. This data was then processed through a FORTRAN fix computation program with the refraction correction being ignored; thus, single channel receiver data was generated.

THEORY OF OPERATION

To assist in understanding the basic theory, a brief summary of the NNSS system is included below.

General

The NNSS is a world-wide, all weather system from which accurate navigational position fixes can be obtained using the data transmitted from the orbiting satellites, four tracking stations, two injection stations, the u.s. Naval Observatory, and a computing center. Any number of user navigational installations can exist with no interference between them.

The navigation satellites are placed in circular, polar orbits at an altitude of approximately 600 nautical miles. The orbital planes of the satellites have a common point along the earth';s rotational axis. Each satellite orbits the earth approximately every 108 minutes. The geometrical placement of the orbiting satellite allows an earth bound observer to cross directly under the satellite twice daily.

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