![]() ![]() ![]() Direction vector could be calculated from rotary encoder reading. Early star trackers comprised of a star sensor mounted on gimbaled platform that was commanded to center an image of one star. A star tracker is a device that measures direction vector from vehicle to a star. With the advent of inertial navigation stars became a powerful source of globally available aiding information. Celestial longitude determination required in its turn more efforts and additional tools such as nautical almanac and chronometer. For example in the Northern Hemisphere mariners could determine latitude by simply measuring elevation angle of the North Star above the horizon. Stars have been used for navigation since ancient times. Groves, Principles of GNSS, inertial, and multisensor integrated navigation systems, 2nd ed. Centreville, Md: Cornell Maritime Press, 1998. Bushy, Marine radionavigation and communications. Among them are Loran, Iridium, cellphone positioning, marine radio beacons. There exist more radio navigation systems and technologies. It is based on request-response technology and allows to measure slant range from airplane to station. Distance measurement equipment (DME) is another widely spread means of radio navigation. Thus accuracy of radial determination is independent of aircraft’s orientation and wind conditions, which presents a considerable advantage. ![]() VOR onboard receiver, unlike ADF, does not need to determine direction to the station, because it is already encoded in transmitted signal. Very high frequency omnidirectional range (VOR) is a further development of short-range radio navigation systems. Air traffic controller can command pilot to follow specific magnetic track either towards or away from the station that is to say to perform QDM/QDR interceptions. Signal transmitted by NDB is received by onboard automatic direction finder (ADF) that determines direction to the beacon relative to the aircraft and displays it on radio-magnetic indicator (RMI). Nowadays a large network of ICAO standardized non-directional radio beacons (NDBs) is widely used in civil aviation. In order to get to desired destination pilot was commanded to fly from one beacon to another. First radionavigation systems appeared before World War II and presented a network of ground radio stations. Radio beacons were the earliest means of aircraft navigation and air traffic control. ![]()
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