NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Accuracy of automatic celestial navigation
From: Paul Hirose
Date: 2002 Dec 6, 13:32 -0800
From: Paul Hirose
Date: 2002 Dec 6, 13:32 -0800
A time of two I have mentioned the B-2 bomber's astro-inertial nav system. During my years in the program its accuracy was classified, and as far as I know it still is, so I have never given any figures. However, a publicly available U.S. military document from the office of the Chairman of the Joint Chiefs of Staff, CJCSI 6130.01B, "Master Positioning, Navigation, and Timing Plan", has this to say: [quote] e. Celestial Navigation. Celestial navigation, as traditionally practiced, provides an average error in position of 2 nm. Increased flexibility, more accurate calculations, and decreased time to solution (fix) can be achieved by performing calculations electronically. Accuracies corresponding to 15 to 30 meters on the Earth's surface are attained by automated celestial systems, depending on the degree of automation. Automated star trackers on spacecraft, missile guidance systems, and aircraft provide high-accuracy, real-time calibration of position and orientation with respect to the absolute inertial reference frame provided by stellar sources. Typically a star tracker augments an inertial (or other) guidance system. The System to Estimate Latitude and Longitude Astronomically (STELLA) is a computer application that automates all of the calculations of celestial navigation, including derivation of a fix (2D). It is equally useful for determination of the gyro/compass error, and supports the necessary planning activities for both functions with numeric and graphic displays. STELLA eliminates the need for printed tables, log and manual calculations, and can be installed on fixed, portable, or lap-top computers for use when needed. STELLA has built-in capability for higher accuracy if used in conjunction with stabilized or compensated sensors vice hand-held instruments. [Apparently, STELLA is in the DoD section of the USNO's site. Sob. Further on in this document:] (4) Advanced Celestial Navigator (a) Description. Using fully-developed space-tested astro-trackers, the advanced celestial navigator (ACN) will provide day and night celestial navigation in partially obscured skies. The highly sensitive charged coupled devices, operating in the near infrared, will be able to define angles to celestial bodies to within 1 arcsecond, a sixty-fold improvement over the current hand-held visual system. Celestial fixes to within 30 meters will be common. For aircraft, altitudes to 100 feet are realizable. (b) Mission to be Enhanced Through This Technology. When closely coupled to the INS, the ACN will provide stabilization for both position and platform alignment. For high-flying aircraft, the ACN/INS combination provides a nearly all-weather, unjammable, and precise navigation system should GPS be denied. [end quote] Here is the complete document (300 k PDF file): https://www.peterson.af.mil/GPS_Support/documents/masternav_timing_plan.pdf