Editing Communications satellite (section)

=== Early active and passive satellite experiments ===
There are two major classes of communications satellites, ''[[Balloon satellite|passive]]'' and ''active''. Passive satellites only [[Reflector (antenna)|reflect]] the signal coming from the source, toward the direction of the receiver. With passive satellites, the reflected signal is not amplified at the satellite, and only a small amount of the transmitted energy actually reaches the receiver.  Since the satellite is so far above Earth, the radio signal is attenuated due to [[free-space path loss]], so the signal received on Earth is very weak. Active satellites, on the other hand, amplify the received signal before retransmitting it to the receiver on the ground.<ref name="aerospace.org">{{cite web |url=http://www.aerospace.org/2013/12/12/military-satellite-communications-fundamentals/ |title=Military Satellite Communications Fundamentals |website=[[The Aerospace Corporation]] |date=2010-04-01 |access-date=2016-02-10 |archive-url=https://web.archive.org/web/20150905170449/http://www.aerospace.org/2013/12/12/military-satellite-communications-fundamentals/ |archive-date=2015-09-05 |url-status=dead }}</ref> Passive satellites were the first communications satellites, but are little used now.

Work that was begun in the field of electrical intelligence gathering at the [[United States Naval Research Laboratory]] in 1951 led to a project named [[Communication Moon Relay]]. Military planners had long shown considerable interest in secure and reliable communications lines as a tactical necessity, and the ultimate goal of this project was the creation of the longest communications circuit in human history, with the Moon, Earth's natural satellite, acting as a passive relay. After achieving the first transoceanic communication between [[Washington, D.C.]], and Hawaii on 23 January 1956, this system was publicly inaugurated and put into formal production in January 1960.<ref name="nasa-sp-4217">{{Cite book |last=van Keuren |first=David K. |url=https://history.nasa.gov/SP-4217/ch2.htm |title=Beyond The Ionosphere: Fifty Years of Satellite Communication |publisher=[[NASA]] History Office |year=1997 |editor-last=Butrica |editor-first=Andrew J |chapter=Chapter 2: Moon in Their Eyes: Moon Communication Relay at the Naval Research Laboratory, 1951-1962 |bibcode=1997bify.book.....B |id=SP-4217 |archive-url=https://web.archive.org/web/20231029142748/https://history.nasa.gov/SP-4217/ch2.htm |archive-date=29 October 2023 |url-status=live }}</ref>

[[File:Atlas-B with Score payload.jpg|The Atlas-B with SCORE on the launch pad; the rocket (without booster engines) constituted the satellite.|thumb]]
The first satellite purpose-built to actively relay communications was [[SCORE (satellite)|Project SCORE]],  led by [[Advanced Research Projects Agency]] (ARPA) and launched on 18 December 1958, which used a tape recorder to carry a stored voice message, as well as to receive, store, and retransmit messages. It was used to send a Christmas greeting to the world from U.S. President [[Dwight D. Eisenhower]]. The satellite also executed several realtime transmissions before the non-rechargeable batteries failed on 30 December 1958 after eight hours of actual operation.<ref>{{cite book|title=Communications Satellites: Project SCORE|url=http://www.satmagazine.com/story.php?number=768488682|publisher=AIAA|edition=5th|date = March 16, 2007|isbn=978-1884989193|last1=Martin|first1=Donald|last2=Anderson|first2=Paul|last3=Bartamian|first3=Lucy}}</ref><ref>{{cite web|url= https://www.nasa.gov/wp-content/uploads/2024/01/presrep1958.pdf |title= United States Aeronautics and Space Activities - first Annual Report to Congress |date=2 February 1959|work= Published as House Document Number 71, 86th Congress, first Session|publisher=The White House|pages=13–14|access-date=2 January 2021}}</ref>

The direct successor to SCORE was another ARPA-led project called Courier. [[Courier 1B]] was launched on 4 October 1960 to explore whether it would be possible to establish a global military communications network by using "delayed repeater" satellites, which receive and store information until commanded to rebroadcast them. After 17 days, a command system failure ended communications from the satellite.<ref>{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1960-013A|title=Courier 1B|year=2020|publisher=NASA|access-date=3 January 2021}}</ref><ref name=PR1960>{{cite web|url=https://www.nasa.gov/wp-content/uploads/2024/01/presrep1960.pdf |title= United States Aeronautics and Space Activities 1960 |date=18 January 1961|publisher=The White House|pages=12–13, 26|access-date=3 January 2021}}</ref>

[[NASA]]'s satellite applications program launched the first artificial satellite used for passive relay communications in [[Echo 1]] on 12 August 1960. Echo 1 was an aluminized [[balloon satellite]] acting as a passive [[reflection (physics)|reflector]] of [[microwave]] signals. Communication signals were bounced off the satellite from one point on Earth to another. This experiment sought to establish the feasibility of worldwide broadcasts of telephone, radio, and television signals.<ref name=PR1960/><ref>{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1960-009A|title=Echo 1|year=2020|publisher=NASA|access-date=3 January 2021}}</ref>