通訊衛星
Communications satellite

context: zh_tw: 由於近地軌道衛星的高度很低，它們僅僅在其星下點周圍 1,000 公里（620 英里）的範圍內可見。另外，近地軌道衛星與地面的相對位置變化的很快。所以，即便是使用近地衛星進行區域通訊，也需要大量的衛星，這樣才能保證不間斷通訊。
en: A low Earth orbit (LEO) typically is a circular orbit about 160 to 2,000 kilometres (99 to 1,243 mi) above the earth's surface and, correspondingly, a period (time to revolve around the earth) of about 90 minutes.Because of their low altitude, these satellites are only visible from within a radius of roughly 1,000 kilometres (620 mi) from the sub-satellite point. In addition, satellites in low earth orbit change their position relative to the ground position quickly. So even for local applications, a large number of satellites are needed if the mission requires uninterrupted connectivity.
qas: question: zh_tw: 當衛星接近地面時，它們改變軌道的速度有多快？
en: how fast do satellites change orbit when  they are close to the ground?
answers: zh_tw: text: 很快
en: text: quickly

context: zh_tw: 一些應用需要大量的地面天線，比如 DirecTV 衛星直播，在這種情況下，地面裝置節省出來的費用會超過把一顆衛星發射到靜止軌道的代價。
en: In applications that require a large number of ground antennas, such as DirecTV distribution, the savings in ground equipment can more than outweigh the cost and complexity of placing a satellite into orbit.
qas: question: zh_tw: 什麼情況會導致複雜性，並超過地面裝置節所省出來的費用？
en: What can cause complexity and outweigh the cost of savings in ground equipment?
answers: zh_tw: text: 一些應用需要大量的地面天線
en: text: applications that require a large number of ground antennas

context: zh_tw: 世界上第一顆靜止軌道通訊衛星是 Syncom 3，該衛星於 1964 年 8 月 19 日發射，並在 1964 年東京奧運會期間開始了跨太平洋電視轉播。在 Syncom 3 發射後不久，休斯公司製造的 Intelsat I (綽號為 “Early Bird”) 於 1965 年 4 月 6 日發射升空，該衛星定點與西經 28 度，成為第一顆跨大西洋通訊的靜止軌道衛星。1972 年 11 月 9 日，加拿大的 Telesat 公司發射了 Anik A1，它是第一顆用於大洲通訊的靜止軌道衛星。美國的西聯公司於 1974 年 4 月 13 日發射了一顆類似的衛星 Westar 1。世界上第一顆三軸穩定的靜止軌道通訊衛星是 NASA 的 ATS-6，該衛星於 1974 年 5 月 30 日發射。在 Telstar 和 Westar 1 發射之後，RCA Americom 公司（後來改名為 GE Americom，現在叫做 SES）於 1975 年發射了 Satcom 1。這顆衛星促進了早期的有線電影片道的發展，如 WTBS (現在的 TBS Superstation)、HBO、CBN (現在的 ABC Family 頻道) 以及天氣頻道等，它們都使用 Satcom 1 衛星來向當地的有線電視前端播送節目。此外，這顆衛星也是美國第一顆用於廣播電視組網的衛星，為 ABC、NBC 和 CBS 提供轉發服務。Satcom 1 有 24 路轉發器，相比之下 Westar 1 只有 12 路，這不僅使得 Satcom 1 的通訊能力更為出色，而且轉發成本更低，所以 Satcom1 得到更廣泛地應用。後來幾十年發射的通訊衛星甚至安裝了更多的轉發器。到 2000 年，全球範圍的通訊網路已有了上百顆衛星，其中有近 40% 是由 ' 休斯太空通訊公司 (現在的波音衛星研發中心) 製造的。其他的一些衛星製造商主要包括 Space Systems/Loral、軌道科學公司 (該公司製造了 STAR Bus 系列衛星)、印度空間研究組織、洛克希德・馬丁、諾斯洛普・格魯門、阿爾卡特宇航公司、如今的泰雷茲・阿萊尼亞宇航公司以及阿斯特里姆公司。
en: On November 9, 1966, Canada's first geostationary satellite serving the continent, Anik A1, was launched by Telesat Canada, with the United States following suit with the launch of Westar 1 by Western Union on April 13, 1967.
qas: question: zh_tw: 韋斯特一號是誰發射的？
en: Westar 1 was launched by whom?
answers: zh_tw: text: 美國的西聯公司於 1974 年 4 月 13 日發射了一顆類似的衛星 Westar
en: text: Western Union

question: zh_tw: Satcom 1 最終是在什麼時候發射的？
en: When was Satcom 1 eventually launched?
answers: zh_tw: text: 1975 年

question: zh_tw: 哪些電視臺早期使用了 Satcom 1？
en: Which networks used Satcom 1 in their early days?
answers: zh_tw: text: ABC、NBC 和 CBS

context: zh_tw: 在這種情況下，莫尼亞軌道是一個很有吸引力的選項。莫尼亞軌道的傾斜度很大，這保證了地面上一些特定的點對北半部分軌道的有合適的仰角（仰角是衛星的視線與當地水平面的夾角。因此，位於水平面上的衛星仰角為 0 度，位於頭頂的衛星仰角為 90 度）。
en: Molniya orbits can be an appealing alternative in such cases. The Molniya orbit is highly inclined, guaranteeing good elevation over selected positions during the northern portion of the orbit. (Elevation is the extent of the satellite's position above the horizon. Thus, a satellite at the horizon has zero elevation and a satellite directly overhead has elevation of 90 degrees.)
qas: question: zh_tw: 在某些情況下，哪個軌道可能是一個很好的選擇？
en: Which type of orbit can be a good alternative in some cases?
answers: zh_tw: text: 莫尼亞
en: text: Molniya

question: zh_tw: 莫尼亞軌道的傾斜度多少？
en: What degree the Molniya orbit?
answers: zh_tw: text: 90 度
en: text: 90

context: zh_tw: 莫尼亞軌道的設計使得衛星大部分時間都執行在高緯度地區，在此期間其星下點的移動很緩慢。莫尼亞軌道的週期是半天，因此衛星每繞地球兩圈，其在目標區域上空工作的時間會達到 6 到 9 小時。在這種情況下，三顆莫尼亞衛星組成的星座 (加上在軌備份) 就可以提供不間斷的訊號覆蓋。
en: The Molniya orbit is designed so that the satellite spends the great majority of its time over the far northern latitudes, during which its ground footprint moves only slightly. Its period is one half day, so that the satellite is available for operation over the targeted region for six to nine hours every second revolution. In this way a constellation of three Molniya satellites (plus in-orbit spares) can provide uninterrupted coverage.
qas: question: zh_tw: 莫尼亞軌道的週期是多久？
en: How long is its period?
answers: zh_tw: text: 半天
en: text: one half day

context: zh_tw: 對於通訊衛星來說，最重要也最有歷史意義的應用是遠距離洲際電話服務。來自陸地的電話訊號透過固定的公共電話交換網傳遞到通訊地面站，再從這傳送到地球靜止軌道衛星上去。同樣，下行訊號的傳播路徑也是如此。20 世紀後期，隨著海底電纜的改進，人們越來越多地使用光纖通訊，這也在一定程度上減少了使用固定地面站進行衛星通訊的使用者。
en: The first and historically most important application for communication satellites was in intercontinental long distance telephony. The fixed Public Switched Telephone Network relays telephone calls from land line telephones to an earth station, where they are then transmitted to a geostationary satellite.  The downlink follows an analogous path.  Improvements in submarine communications cables through the use of fiber-optics caused some decline in the use of satellites for fixed telephony in the late 20th century.
qas: question: zh_tw: 通訊衛星首先用於那種型別的電話系統？
en: Communication satellites were first used for what type of telephone systems?
answers: zh_tw: text: 遠距離洲際電話
en: text: intercontinental long distance telephony

context: zh_tw: 在美國之外，直播衛星 (DBS) 和地面站轉發衛星 (FSS) 的區別就不是那麼明顯了，尤其是在歐洲。在歐洲，大部分直播衛星的功率和北美的 DBS 衛星相同，但是其極化方式卻和北美的 FSS 衛星相同。這種型別的衛星有 Astra、Eutelsat 和 Hotbird 衛星，它們執行在歐洲大陸的上空。由於這個原因，FSS 和 DBS 這兩個術語在北美使用得更頻繁，但是在歐洲就很少使用了。
en: The definitions of FSS and DBS satellites outside of North America, especially in Europe, are a bit more ambiguous. Most satellites used for direct-to-home television in Europe have the same high power output as DBS-class satellites in North America, but use the same linear polarization as FSS-class satellites. Examples of these are the Astra, Eutelsat, and Hotbird spacecraft in orbit over the European continent. Because of this, the terms FSS and DBS are more so used throughout the North American continent, and are uncommon in Europe.
qas: question: zh_tw: 在歐洲，哪些區別不太明顯了？
en: What definitions are more open to interpretation in Europe?
answers: zh_tw: text: 直播衛星 (DBS) 和地面站轉發衛星 (FSS)
en: text: FSS and DBS satellites

question: zh_tw: 由於歐洲的衛星使用光譜，哪些術語沒有在歐洲使用？
en: Because the satelites of europe utilize certain spectrums, which terms are not utilized in europe?
answers: zh_tw: text: FSS 和 DBS
en: text: FSS and DBS

question: zh_tw: 兩種衛星，除了直播衛星級，還有哪級？
en: The two types of satellites are DBS-class and what?
answers: zh_tw: text: 地面站轉發衛星
en: text: FSS-class

context: zh_tw: 一些免費的衛星電影片道通常也使用 FSS 衛星的 Ku 波段來發送訊號。北美洲上空的衛星 Intelsat Americas 5、Galaxy 10R 和 AMC 3 就是使用 Ku 波段來播送大量的 FTA 頻道節目。
en: Free-to-air satellite TV channels are also usually distributed on FSS satellites in the Ku band. The Intelsat Americas 5, Galaxy 10R and AMC 3 satellites over North America provide a quite large amount of FTA channels on their Ku band transponders.
qas: question: zh_tw: 哪些衛星帶有可供人們觀看的免費電影片道？
en: What satellites carry the tv channels that are free for people to watch?
answers: zh_tw: text: FSS 衛星
en: text: FSS satellites

context: zh_tw: 業餘無線電衛星是被設計用來傳輸業餘無線電訊號的，業餘無線電愛好者可以透過這種衛星進行無線電通訊。大多數業餘無線電衛星透過星載轉發器來工作，操作者需要使用特高頻 (UHF) 和甚高頻 (VHF) 裝置以及高定向天線，如八木天線或蝶形天線。由於發射成本的限制，現在大多數的業餘無線電衛星被髮射到較低的軌道，它們大多數只能進行短時間的通訊。一些衛星還提供使用 X.25 協議或類似協議的資料轉發服務。
en: Amateur radio operators have access to amateur satellites, which have been designed specifically to carry amateur radio traffic. Most such satellites operate as spaceborne repeaters, and are generally accessed by amateurs equipped with UHF or VHF radio equipment and highly directional antennas such as Yagis or dish antennas. Due to launch costs, most current amateur satellites are launched into fairly low Earth orbits, and are designed to deal with only a limited number of brief contacts at any given time. Some satellites also provide data-forwarding services using the X.25 or similar protocols.
qas: question: zh_tw: 誰可以訪問衛星？
en: Who can access satellites?
answers: zh_tw: text: 業餘無線電愛好者
en: text: amateurs

question: zh_tw: 衛星提供了什麼？
en: what do the satellites provide?
answers: zh_tw: text: 資料轉發服務
en: text: data-forwarding services

context: en: After the launches of the Telstar through Westar 1 satellites, RCA Americom (later GE Americom, now SES) launched Satcom 1 in 1975.  It was Satcom 1 that was instrumental in helping early cable TV channels such as WTBS (now TBS), HBO, CBN (now Freeform) and The Weather Channel become successful, because these channels distributed their programming to all of the local cable TV headends using the satellite.  Additionally, it was the first satellite used by broadcast television networks in the United States, like ABC, NBC, and CBS, to distribute programming to their local affiliate stations.  Satcom 1 was widely used because it had twice the communications capacity of the competing Westar 1 in America (24 transponders as opposed to the 12 of Westar 1), resulting in lower transponder-usage costs. Satellites in later decades tended to have even higher transponder numbers.By 2000, Hughes Space and Communications (now Boeing Satellite Development Center) had built nearly 40 percent of the more than one hundred satellites in service worldwide. Other major satellite manufacturers include Space Systems/Loral, Orbital Sciences Corporation with the Star Bus series, Indian Space Research Organisation, Lockheed Martin (owns the former RCA Astro Electronics/GE Astro Space business), Northrop Grumman, Alcatel Space, now Thales Alenia Space, with the Spacebus series, and Astrium.
qas: question: zh_tw: Satcom 1 最終是在什麼時候發射的？
answers: en: text: 1975

question: zh_tw: 哪些電視臺早期使用了 Satcom 1？
answers: en: text: ABC, NBC, and CBS