| 单词 | Iridium |
| 释义 | Iridium The first mobile satellite system (MSS) operating in low-Earth orbit (LEO). According to leg- end, the wife of a Motorola executive was vacationing in the Bahamas during 1987 and was irritated by her inability to place a cellular telephone call. As the story goes, she complained to her husband, and captured his imagination, so to speak. Motorola engineers subsequently determined that a constellation of 77 communications satellites in non-geosynchronous low-altitude orbits would be sufficient to provide cellular-like service to essentially all dry land on the Earth’s surface. Motorola named its proposed 77-satellite constellation Iridium, after the element iridium (Ir), which has 77 electrons whizzing around its nucleus. Subsequently, the proposal was pared down to 66 operational satellites, although the name Iridium stuck. After all, Iridium seems to roll off the tongue better than dysprosium (Dy), the rare earth element with an atomic weight of 66. Dysprosium, by the way is from the Greek dysprositos, meaning hard to get at, which is hardly a good name for a communications technology.The Iridium constellation is now fully launched and is fully operational, with 11 operational satellites, and 1 spare, placed in each of the 6 orbital planes, at altitudes of 421.5 nautical miles. Connectivity between each satellite and the Earth is established 74570c09.qxd 9/11/07 12:22 PM Page 259 |
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