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Project Echo was the first passive communications satellite experiment. Each of the two American spacecraft, launched in 1960 and 1964, was a metalized balloon satellite acting as a passive reflector of microwave signals. Communication signals were bounced off them from one point on Earth to another. ==Echo 1== NASA's Echo 1 satellite was built by Gilmore Schjeldahl's G.T. Schjeldahl Company in Northfield, Minnesota. The balloon satellite functioned as a reflector, not a transceiver, so that after it was placed in a low Earth orbit, a signal would be sent to it, reflected or bounced off its surface, and then returned to Earth. During ground inflation tests, of air was needed to fill the balloon, but while in orbit, several pounds of gas were all that was required to fill the sphere. At launch, the balloon weighed which included of sublimating powders of two types.〔 The first weighing with a very high vapor pressure, the second with a much lower vapor pressure.〔 According to NASA, "To keep the sphere inflated in spite of meteorite punctures and skin permeability, a make-up gas system using evaporating liquid or crystals of a subliming solid were incorporated inside the satellite."〔(Static Inflation Test of 135 Ft Satellite In Weeksville, NC ) NASA Langley Research Center (NASA-LaRC), 1961-06-28.〕 The first attempt to orbit an Echo satellite (also the maiden voyage of the Thor-Delta launch vehicle) miscarried when Echo 1 lifted from Cape Canaveral's LC-17A on the morning of May 13, 1960. The Thor performed properly, but during the coasting phase, the attitude control jets on the unproven Delta stage failed to ignite, sending the payload into the Atlantic Ocean instead of orbit. Echo 1A (commonly referred to as just ''Echo 1'') was put successfully into a orbit by another Thor-Delta,〔(Astronautix.com, ''Echo'' )〕〔(【引用サイトリンク】url=http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1960-009A )〕 and a microwave transmission from the Jet Propulsion Laboratory in Pasadena, California, was received at Bell Laboratories in Holmdel, New Jersey, on August 12,〔 1960. The 30.5-meter (100 ft) diameter balloon was made of metalized biaxially oriented PET film ("Mylar") material, and it was used to redirect transcontinental and intercontinental telephone, radio, and television signals.〔 The satellite also aided the calculation of atmospheric density and solar pressure due to its large area-to-mass ratio.〔 As its shiny surface was also reflective in the range of visible light, Echo 1A was easily visible to the unaided eye over most of the Earth. The spacecraft was nicknamed a 'satelloon' by those involved in the project, as a portmanteau of satellite-balloon. It also had 107.9 MHz beacon transmitters for telemetry purposes, powered by five nickel-cadmium batteries that were charged by 70 solar cells mounted on the balloon. During the latter portion of its life, the spacecraft was used to evaluate the technical feasibility of satellite triangulation. It had a total mass of . Echo 1A was originally loosely estimated to survive until soon after its fourth dip into the atmosphere in July 1963 but possibly until 1964 or beyond but it ended up living much longer than these estimates and reentered Earth's atmosphere, burning up on May 24, 1968. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Project Echo」の詳細全文を読む スポンサード リンク
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