Celestial Navigation - Correcting the Folklore

摘要

Celestial navigation has been guiding the mariner for hundreds of years; more recently, the GPS (GNSS, in general) has made 3-D positioning and precise time a commodity for everyday use. With an increased awareness of the vulnerabilities associated with any satellite-based system, there is a renewed interest in non-satellite PNT systems. We have been reexamining celestial navigation from the vantage point of those conversant in GNSS language. Two aspects of these parallel approaches have attracted our attention: how to choose which stars to process (similar to the GNSS satellite selection problem) and if (and at what accuracy) precise time can be estimated from celestial measurements. This paper clarifies two common misconceptions about celestial navigation: (1) that the stars selected for celestial navigation do not need to be “evenly” distributed across 360 degrees of azimuth, that multiple stars from nearly similar directions (i.e. Polaris and stars in the Big Dipper) can be very useful together in forming a good celestial fix; and (2) that while “star clocks” are advertised, their result is not precise time, and that celestial techniques can only provide a low quality source of time information.