Atmosphere of Earth they penetrate more deeply. The various layers of Earth's ionosphere, important to HF radio propagation, begin below 100 km and extend beyond 500 km. By comparison, the International Space Station and Space Shuttle typically orbit at 350–400 km, within the F-layer of the ionosphere where they encounter enough atmospheric drag to require reboosts every few months. Depending on solar activity, satellites can experience noticeable atmospheric drag at altitudes as high as 700–800 km. The division of the atmosphere into layers mostly by reference to temperature is discussed above. Temperature decreases with altitude starting at sea level, but variations in this
Coast earth station Earth station (article 1.63) Coast earth station Coast earth station, also called the coast earth radio station is – according to "article 1.76" of the International Telecommunication Union´s (ITU) ITU Radio Regulations (RR) – defined as «"An earth station in the fixed-satellite service or, in some cases, in the maritime mobile-satellite service, located at a specified fixed point on land to provide a feeder link for the maritime mobile-satellite service".» Each "radio station" shall be classified by the "service" in which it operates permanently or temporarily. In accordance with "ITU Radio Regulations" (article 1) this type of "radio station" might