SFR 106 Lecture Notes - Lecture 4: Ephemeris, United States Department Of Defense, Orbital Period
19 Dec 2016
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Document Summary
A us military funded system that allows us to accurately measure our position, speed, and direction on the earth"s surface. Satellite based system: 30 active satellites, unknown number of spares, 10,900 nautical miles above earth, 12 hour orbital period, provides 5-8 satellites at a given time. Provides: accurate navigation, worldwide coverage, 24 hour access. Developed & maintained by the us dod. Gps receivers trialaterate, a position by measuring distance using the travel time of radio signals between subject (gps receiver) and reference points (gps satellites) Along with distance, satellite locations are required. Gps uses an almanac and ephemeris for this information. Almanac includes orbital information (like a bus schedule) There are several types of errors contained within the signal: When on, it was the largest source of error in gps (+/- 100 meters) To prevent hostile forces from using gps to full accuracy. By introducing intentional errors of timing signals and/or satellite ephemeris.
