当前位置:英美者>>专门英语>>科技英语>>浏览文章    

科技英语阅读:地球同步卫星

2011年12月01日  所属:科技英语  来源:外语教育网  作者:佚名

科技英语阅读材料:地球同步卫星。

地球同步卫星:Geosynchronous Satellite

    A geosynchronous satellite is a satellite whose orbital track on the Earth repeats regularly over points on the Earth over time. If such a satellite's orbit lies over the equator, it is called a geostationary satellite. The orbits of the satellites are known as the geosynchronous orbit and geostationary orbit. Other well-known geosynchronous orbits include the well-known Molnya and Tundra elliptical orbits.

    Definition

    According to Kepler's Third Law, the orbital period of a satellite in a circular orbit increases with increasing altitude. Space stations and shuttles in Low Earth orbit (LEO), typically two or four hundred miles above the Earth's surface make between fifteen and sixteen revolutions per day. The Moon, at an altitude of about 240,000 miles (385,000km), takes thirty days to make a complete rotation. Between those extremes lies the "magic" altitude of 22,300 miles (35,786km) at which a satellite's orbital period matches, or is an integral part of, the period at which the Earth rotates: once every sidereal day (23 hours 56 minutes). In that case, the satellite is said to be geosynchronous.

    If a geosynchronous satellite's orbit is not exactly aligned with the equator, known as an inclined orbit, it will appear (when viewed by someone on the ground) to oscillate daily around a fixed point in the sky. As the angle between the orbit and the equator decreases, the magnitude of this oscillation becomes smaller; when the orbit lies entirely over the equator, the satellite remains stationary relative to the Earth's surface ¨C it is said to be geostationary.

    Application

    There are approximately 300 operational geosynchronous satellites.

    Geostationary satellites appear to be fixed over one spot above the equator. Receiving and transmitting antennae on the earth do not need to track such a satellite. These antennae can be fixed in place and are much less expensive than tracking antennae. These satellites have revolutionized global communications, television broadcasting and weather forecasting, and have a number of important defense and intelligence applications.

    One disadvantage of geostationary satellites is a result of their high altitude: radio signals take approximately 1/4 of a second to reach and return from the satellite, resulting in a small but significant signal delay. This delay increases the difficulty of telephone conversation and reduces the performance of common network protocols such as TCP/IP, but does not present a problem with non-interactive systems such as television broadcasts. There are a number of proprietary satellite data protocols that are designed to proxy TCP/IP connections over long-delay satellite links ¡ª¡ª these are marketed as being a partial solution to the poor performance of native TCP over satellite links. TCP presumes that all loss is due to congestion, not errors, and probes link capacity with its "slow start" algorithm, which only sends packets once it is known that earlier packets have been received. Slow start is very slow over a path using a geostationary satellite.

    Another disadvantage of geostationary satellites is the incomplete geographical coverage, since ground stations at higher than roughly 60 degrees latitude have difficulty reliably receiving signals at low elevations. Satellite dishes in the Northern Hemisphere would need to be pointed almost directly towards the south, the general direction where the centre of our galaxy is also located, whose intense cosmic radiation bombards the receivers with strong radio noise and suppresses most signals. The signals would have to pass through the largest amount of atmosphere, and could even be blocked by land features In the USSR, a practical solution has been developed for this problem with the creation of special Molnya / Orbita inclined path satellite networks with elliptical orbits. Similar elliptical orbits are used for the Sirius Radio satellites.

下一页
本文共 2 页,第  [1]  [2]  页


科技英语 最新资讯
· 科技英语阅读文章:火星漫游
· 科技英语阅读:地球同步卫星
· 科技英语阅读文章:星系旅行
· 国际空间站简介:科技英语阅读文章
· 航空科技英语:起飞前常用的一些短句
· 与航空航天有关的一些科技英语词汇
· 航海英语通信用语标准例句
· 航海英语:船舶驾驶室为什么叫bridge?
· 航海英语:主甲板的几种英语叫法
· 海事检查常用英语口语21句

英美者 最新资讯
· 科技英语阅读文章:火星漫游
· 科技英语阅读:地球同步卫星
· 科技英语阅读文章:星系旅行
· 国际空间站简介:科技英语阅读文章
· 航空科技英语:起飞前常用的一些短句
· 与航空航天有关的一些科技英语词汇
· 买火车票时需要用到的英语句子
· 千万别误解了这些英语词汇!
· 来看看各种咖啡的英语说法!
· 生活中女朋友的英语表达
· 各种钱的英语翻译说法和表达
Death of thank you(双语)
安妮•海瑟薇宣布订婚
维也纳再获全球最宜居城市
力荐:BEC商务英语参考书目