Celestial navigation, automatic tracking of stars to determine position, is an often overlooked technology in the current age of satellite navigation systems. Nevertheless, it is one of the key alternatives immune to the vulnerabilities of GPS. Along with inertial guidance, it is employed widely in missile guidance (US’s Snark, Poseidon, Polaris, Trident, MX; China’s CSS-N-4 Mod 0, CSS-NX-4 Mod I, CSS-NX-4 Mod II), satellite attitude determination (XTE, SWAS, STEX, DS-1, WIRE), aircraft (SR-71, RC-135, B2) and spacecraft (shuttle). Star trackers, such as the Lockheed Martin AST-201 are becoming lighter, cheaper, smaller, and more precise.

China is a leader in this area and its researchers are publishing an increasing number of papers both in international and domestic journals. For example, researchers at Qinghua University’s Department of Precision Instruments and Mechanics have developed an original “4-star matching” identification algorithm for a charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS). Tests of the algorithm using an on-board database (composed of a brightness independent guide mission catalog and K-vector star pair catalog) with a CMOS active pixel sensor (APS) star tracker resulted in a 99.9% success rate in identification to acquire 3-axis attitude when the angular measurement accuracy of the tracker is at least 0.01 degrees. Researchers in the Chinese Academy of Sciences and Changchun Institute of Optics, Fine Mechanics, and Physics are looking to overcome the impracticality of CCD in small satellites and other craft, and instead are exploring the advantages of CMOS APS (no blooming, single power, low power consumption, small size, little support circuitry, simple system design, direct digital input, radiation-hard). They have developed a prototype ground-based star camera based on a STAR250 CMOS image sensor and a subpixel accuracy centroiding algorithm. The faculty of the Second Artillery Engineering College in Xian have been publishing papers on methods for determining attitude of missiles in free flight and others are examining FPGA-based submarine star tracking systems.

US GPS will continue to dominant navigation systems. However, like the personal computer’s challenge to the mainframe, ever smaller, cheaper, robust, and precise star trackers will weaken this advantage. As celestial navigation technology becomes more widely available and creatively applied in more platforms, it has the potential to become a cheap and reliable means of determining position, especially on ground systems, as the “poor man’s GPS.” This will weaken the US’s tactical advantage in both the battlefield and the marketplace. China, as a developer and manufacturer of such systems, stands to benefit greatly especially in sales to third world countries.

Advanced Materials and Devices for Sensing and Imaging II. Proceedings of the SPIE, Volume 5633, pp. 536-542 (2005).

Tsinghua Science and Technology, Vol. 11, Issue 5, October 2006, pp. 543-548 (doi:10.1016/S1007-0214(06)70232-2 )

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