alekseysidorov

02.04.2022 01:40

Английский язык

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Выпишите предложения со следующими грамматическими явлениями: 1) Предложения с "Пассивные конструкции с модальным глаголом"
2) Предложения с инфинитивом
3) Предложения с причастием настоящего времени
4) Предложения с определительными придаточными предложениями

Artificial satellites can be equipped to transmit electromagnetic radiation at precisely controlled times and frequencies. The frequencies are chosen to avoid interference with other services, to minimize attenuation or delay as the signals penetrate the ionosphere, and to minimize the power needed by the satellite for broadcasting the signals. The practical range of frequencies corresponds to wavelengths between 10 and 200 cm.
During the early 1960s a series of satellites named Transit was launched by the U.S. Navy to provide a worldwide navigation system. These satellites circled the Earth about every 90 minutes, moving in polar orbits about 600 miles (1,000 km) above the Earth’s surface. They broadcast continuous electromagnetic signals carefully modulated to indicate departures from the nominal frequencies and orbits. A receiver on the surface or in a submarine near the surface could compare the frequency received with that known to be transmitted and identify its own location by measuring both the magnitude and the rate of change of the Doppler shift. The calculations, which were performed by a small digital computer, were accurate to about 180 yards (165 metres).
Any sudden and unexpected change in the user’s velocity during the navigation interval modifies the Doppler shift trace, which in turn introduces positioning errors. An uncertainty of two knots (one metre per second) in the user’s velocity can cause an uncertainty of one-half nautical mile (about one kilometre) in the deduced position. Such an error is inconsequential for ships at sea, but it disqualifies the Transit system for the navigation of aircraft.The global positioning system (GPS), which is suitable for aircraft and spacecraft navigation, was initiated by the U.S. Department of Defense in 1973. In 1978 the first two Navstar GPS satellites were launched into orbit.
The latest versions of these radio-navigation satellites move in circular orbits inclined 55° to the equatorial plane at an altitude of about 12,500 miles (20,000 km). Their orbital period is 12 hours. More than 24 of these satellites (the number has varied) provide continuous worldwide coverage adequate for providing simply equipped users with their longitude, latitude, and altitude within about 30 feet (10 metres). Millions of users benefit from the use of the GPS satellite signals, including airplanes, ships, tanks, backpackers, and ordinary private cars. The Navstar navigation system, consisting of 24 operational satellites, was declared fully operational by the U.S. Air Force Space Command in 1995. Click on the Navstar Block II satellite for further details. The Navstar navigation system, consisting of 24 operational satellites, was declared fully operational by the U.S. Air Force Space Command in 1995. Click on the Navstar Block II satellite for further details. Encyclopædia Britannica, Inc. The Navstar GPS does not depend on Doppler shift to fix the position of the user. It does, however, use instantaneous Doppler-shift measurements from multiple satellites to obtain accurate velocities.