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Project Echo was the first passive
communications satellite A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. ...
experiment. Each of the two American spacecraft, launched in 1960 and 1964, were metalized
balloon satellite A balloon satellite is inflated with gas after it has been put into orbit. It is also occasionally referred to as a "satelloon", which is a trademarked name owned by Gilmore Schjeldahl's G.T. Schjeldahl Company. List of balloon satellites abb ...
s acting as passive reflectors of
microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency rang ...
signals. Communication signals were transmitted from one location on
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and bounced off the surface of the satellite to another Earth location. The first transmissions using Echo were sent from Goldstone, California to Holmdel, New Jersey on 12 August 1960. The last Echo satellite deorbited and burned up in the atmosphere on 7 June 1969.Astronautix.com, ''Echo''


Background

The concept of using orbital satellites to relay communications predated space travel, first being advanced by Arthur C. Clarke in 1945. Experiments using the moon as a passive reflecting way station for messages began as early as 1946. With the launching of
Sputnik 1 Sputnik 1 (; see § Etymology) was the first artificial Earth satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957 as part of the Soviet space program. It sent a radio signal back to Earth for ...
, Earth's first artificial satellite, in 1957, interest quickly developed in orbiting communications satellites. In July 1958, at a
US Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Signal ...
sponsored meeting on communications satellites,
Bell Telephone Laboratories Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mult ...
engineer
John R. Pierce John Robinson Pierce (March 27, 1910 – April 2, 2002), was an American engineer and author. He did extensive work concerning radio communication, microwave technology, computer music, psychoacoustics, and science fiction. Additionally to his ...
put forth a presentation on passive satellite relay, describing how a reflective orbiting body could be used to bounce transmissions from one point on the Earth to another. William H. Pickering, director of Jet Propulsion Laboratory (JPL), also attended the conference and suggested that JPL facilities, specifically a diameter polar-mounted antenna installed near Goldstone Dry Lake in the Mojave Desert, might be used as a ground facility for experiments with such a satellite. In October 1958, Pierce, along with fellow Bell engineer
Rudolf Kompfner Rudolf Kompfner (May 16, 1909 – December 3, 1977) was an Austrian-born inventor, physicist and architect, best known as the inventor of the traveling-wave tube (TWT). Life Kompfner was born in Vienna to Jewish parents. He was original ...
, designed an experiment to observe atmospheric refractive effects using reflective balloon satellites. Believing the experiment would advance research toward transoceanic communications via satellites, the two engineers presented a paper advocating for the launch of balloon satellites to be used as passive communications reflectors to the National Symposium on Extended Range and Space Communication on 6 and 7 October 1958. That same month, the
National Aeronautics and Space Administration The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding ...
(NASA) was formed, and two months later JPL was transferred from the
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to the new agency. Project Echo, NASA's first communications satellite project, was officially laid out in a 22 January 1959 meeting with representatives from NASA, JPL, and Bell Telephone Laboratories setting the initial launch for September 1959.


Objectives

Project Echo was a pathfinder mission with the objective of testing new technologies and preparing for future missions. Spaceflight engineers used Echo to prove new ideas and test limits in aerodynamics, satellite shape and size, construction materials, temperature control and satellite tracking. Echo was designed as an experiment to demonstrate the potential of satellite communications, not to function as a global communications system. Echo was designed, approved and built with the following objectives: * Observe and measure the effects of atmospheric drag * Passively reflect ground based transmissions * Demonstrate two-way communications * Demonstrate commitment to the development of an American space program * Provide precedent for the overflight of other nations by surveillance satellites All of these objectives were accomplished with Project Echo. Further experiments used the satellite to engage a two-way telephone conversation on 15 August 1960 and to relay a live television transmission in April 1962.


Ground stations

Two ground stations were used for testing Project Echo. The Goldstone facility located at Goldstone Dry Lake in the Mojave Desert, California and the Holmdel facility located at Holmdel, New Jersey. Both sites used separate antennas for transmitting and receiving. West-to-east transmissions were sent from Goldstone by a dish antenna built for Project Echo by JPL. The signals were received at Holmdel by a aperture horn-reflector antenna.
Horn antenna A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz. They are ...
s were known to have low-noise properties. A transmission frequency of 2390
megahertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
was selected, as this was the planned frequency band for future satellite experiments. East-to-west transmissions were sent from
Holmdel Holmdel Township (usually shortened to Holmdel) is a township in Monmouth County, New Jersey, United States. The township is centrally located in the Raritan Valley region, being within the regional and cultural influence of the Raritan Bays ...
using a diameter parabolic antenna and received at Goldstone using the existing
Pioneer program The Pioneer programs were two series of United States lunar and planetary space probes exploration. The first program, which ran from 1958 to 1960, unsuccessfully attempted to send spacecraft to orbit the Moon, successfully sent one spacecraft to ...
antenna. A transmission frequency of 960.05 megahertz was used for westbound communications because the JPL receiver was already tuned to this frequency from the Pioneer lunar program. Satellite acquisition and tracking were accomplished by three methods: optical, digital slave, and automatic radar. Optical tracking was the easiest method but could only be used at night when the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
illuminated the satellite. Broad and narrow field telescopes with a
television camera A professional video camera (often called a television camera even though its use has spread beyond television) is a high-end device for creating electronic moving images (as opposed to a movie camera, that earlier recorded the images on film). ...
were mounted to the structure of the antenna at each site. The camera images were displayed to a servo operator who would control the position of the antenna to track the satellite. When optical tracking could not be used, a computer system called digital slave could acquire and track Echo. Digital slave worked by receiving primary tracking data from the NASA
Minitrack The Minitrack Network was the first U.S. satellite tracking network to become operational, in 1957. It was used to track the flights of Sputnik, Vanguard, Explorer, and other early space efforts. Minitrack was the progenitor of Spacecraft Tracki ...
network of stations. The computer would then issue antenna-pointing commands to control the antenna. The third tracking method was a continuous-wave radar subsystem. Radar was not suitable for acquisition of the satellite, but once Echo was acquired by optical, or digital slave, radar signals could be used to automatically maintain tracking.


Spacecraft

The Echo spacecraft (Echo 1, Echo 1A, and Echo 2) were large thin skinned spheres that were inflated in orbit after leaving the atmosphere. These balloon satellites were approximately in diameter with a thin skin made of
Mylar BoPET (biaxially-oriented polyethylene terephthalate) is a polyester film made from stretched polyethylene terephthalate (PET) and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and ...
(a trade name for stretched polyethylene terephthalate or BoPET), and were built by Gilmore Schjeldahl's G.T. Schjeldahl Company in
Northfield, Minnesota Northfield is a city in Dakota and Rice counties in the State of Minnesota. It is mostly in Rice County, with a small portion in Dakota County. The population was 20,790 at the 2020 census. History Northfield was platted in 1856 by John W. ...
. The satellites functioned as a reflector, not a transceiver; after being placed in
low Earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never mor ...
, signals could be sent from a ground station, reflected by its surface, and returned to
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surface ...
. As its shiny surface was also reflective in the range of visible light, Echo was easily visible to the unaided eye over most of the Earth. The spacecraft was nicknamed a "satelloon" by those involved in the project (a
portmanteau A portmanteau word, or portmanteau (, ) is a blend of wordstelephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into el ...
,
radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...
, and
television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, e ...
signals. During the latter portion of its life, it was used to evaluate the technical feasibility of satellite triangulation.


Echo 1

Echo 1 was in diameter, had a non-rigid skin made of -thick Mylar, and had a total mass of , weighing at launch. During ground inflation tests, of air were needed to fill the balloon, but while in orbit, several pounds of gas were all that was required to fill the sphere. To address the problem of
meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object en ...
punctures and keep the sphere inflated, Echo 1 included a make-up gas system using two types of sublimating powders – of anthraquinone and of
benzoic acid Benzoic acid is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin, wh ...
. It also had 107.9 MHz telemetry beacons, powered by five nickel-cadmium batteries that were charged by 70
solar cell A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.
s mounted on the balloon. The spacecraft was useful to the calculation of atmospheric density and solar pressure, due to its large area-to-mass ratio.


Echo 2

Echo 2 was a -diameter balloon satellite, the last launched by Project Echo. A revised inflation system was used for the balloon, to improve its smoothness and
sphericity Sphericity is a measure of how closely the shape of an object resembles that of a perfect sphere. For example, the sphericity of the balls inside a ball bearing determines the quality of the bearing, such as the load it can bear or the speed at ...
. Echo 2's skin was rigidizable, unlike that of Echo 1. Therefore, the balloon was capable of maintaining its shape without a constant internal pressure; a long-term supply of inflation gas was not needed, and it could easily survive strikes from
micrometeoroids A micrometeoroid is a tiny meteoroid: a small particle of rock in space, usually weighing less than a gram. A micrometeorite is such a particle that survives passage through Earth's atmosphere and reaches Earth's surface. The term "micrometeoroid ...
. The balloon was constructed from a -thick mylar film sandwiched between and bonded with two layers of -thick aluminum foil. It was inflated to a pressure that caused the metal layers of the laminate to plastically deform slightly, while the polymer was still in the elastic range. This resulted in a rigid and very smooth spherical shell. A beacon telemetry system provided a tracking signal, monitored spacecraft skin temperature between , and measured the internal pressure of the spacecraft between 0.00005 mm of mercury and 0.5 mm of mercury, especially during the initial inflation stages. The system consisted of two beacon assemblies powered by solar cell panels and had a minimum power output of 45 mW at 136.02 MHz and 136.17 MHz.


Flights

Five suborbital ballistic tests to determine whether the launch, deploy, and expansion mechanisms would work were flown using the Shotput test vehicle. The first Shotput flew at 5:40 pm on 27 October 1959. Shotput 1 successfully delivered the Echo prototype to the desired altitude, but a small amount of residual gas in the folds of the balloon violently expanded, bursting the test article. People up and down the Atlantic coast witnessed what looked like distant fireworks as thousands of pieces of shredded Mylar reflected sunlight in a display that lasted for about 10 minutes. Four more Shotput tests were flown on 16 January, 27 February, 1 April, and 31 May 1960. On 13 May 1960, the first attempt to orbit an Echo satellite was made. The mission, which was also the maiden voyage of the
Thor-Delta The Thor-Delta, also known as Delta DM-19 or just Delta was an early American expendable launch system used for 12 orbital launches in the early 1960s. A derivative of the Thor-Able, it was a member of the Thor family of rockets, and the first ...
launch vehicle A launch vehicle or carrier rocket is a rocket designed to carry a payload (spacecraft or satellites) from the Earth's surface to outer space. Most launch vehicles operate from a launch pads, supported by a launch control center and system ...
, failed before deployment of the payload. Echo 1 lifted off from Cape Canaveral's
LC-17A Space Launch Complex 17 (SLC-17), previously designated Launch Complex 17 (LC-17), was a launch site at Cape Canaveral Air Force Station (CCAFS), Florida used for Thor and Delta launch vehicles launches between 1958 and 2011. It was built in ...
, and the Thor stage performed properly, but during the coasting phase, the attitude control jets on the unproven
Delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D ( NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also ...
stage failed to ignite, sending the payload into the
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instead of into orbit. On 12 August 1960, Echo 1A (commonly referred to as ''Echo 1'') was successfully put into an orbit of by another Thor-Delta. A microwave transmission from the JPL Goldstone facility in California, was relayed by the satellite to
Bell Laboratories Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mult ...
in Holmdel, New Jersey, that same day. It was originally expected that Echo 1A would not survive long after its fourth dip into the atmosphere in July 1963, although estimates allowed the possibility that it would continue to orbit until 1964 or beyond. It ended up surviving much longer than expected, and finally reentered Earth's atmosphere and burned up on 24 May 1968. On 25 January 1964, Echo 2 was launched on a Thor Agena launch vehicle. In addition to passive communications experiments, it was used to investigate the dynamics of large spacecraft and for global geometric
geodesy Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), Earth rotation, orientation in space, and Earth's gravity, gravity. The field also incorporates studies of how these properti ...
. Since it was larger than Echo 1A and orbiting in a near-polar orbit, Echo 2 was conspicuously visible to the unaided eye over all of the Earth. It reentered Earth's atmosphere and burned up on 7 June 1969. Both Echo 1A and Echo 2 experienced a
solar sail Solar sails (also known as light sails and photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large mirrors. A number of spaceflight missions to test solar propulsion and navigation have been p ...
effect due to their large size and low mass. Later passive communications satellites, such as OV1-08 PasComSat, solved the problems associated with this by using a grid-sphere design instead of a covered surface. Later yet, NASA abandoned passive communications systems altogether, in favor of active satellites.


Legacy

Project Echo facilitated the first successful satellite transmission and first two way communications between the JPL Goldstone facility and Bell Telephone Laboratories facility in
Holmdel, New Jersey Holmdel Township (usually shortened to Holmdel) is a township in Monmouth County, New Jersey, United States. The township is centrally located in the Raritan Valley region, being within the regional and cultural influence of the Raritan Bays ...
. Other groups participated in experiments including the
Collins Radio Company Rockwell Collins was a multinational corporation headquartered in Cedar Rapids, Iowa, providing avionics and information technology systems and services to government agencies and aircraft manufacturers. It was formed when the Collins Radio Compa ...
and the
Naval Research laboratory The United States Naval Research Laboratory (NRL) is the corporate research laboratory for the United States Navy and the United States Marine Corps. It was founded in 1923 and conducts basic scientific research, applied research, technological ...
. Because Echo was only a passive system, it was primarily useful in demonstrating the future potential of satellite communications and became obsolete before it deorbited in 1968. Echo was most known to the general public for its visibility as it could be seen at night with the naked eye. The Echo satellite program also provided the astronomical reference points required to accurately locate
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. This improved accuracy was sought by the U.S. military for the purpose of targeting intercontinental ballistic missiles. The large horn antenna at Holmdel constructed by Bell Labs for the Echo project was later used by
Arno Penzias Arno Allan Penzias (; born April 26, 1933) is an American physicist, radio astronomer and Nobel laureate in physics. Along with Robert Woodrow Wilson, he discovered the cosmic microwave background radiation, which helped establish the Big Bang ...
and
Robert Woodrow Wilson Robert Woodrow Wilson (born January 10, 1936) is an American astronomer who, along with Arno Allan Penzias, discovered cosmic microwave background radiation (CMB) in 1964. The pair won the 1978 Nobel Prize in Physics for their discovery. Whi ...
for their
Nobel Prize The Nobel Prizes ( ; sv, Nobelpriset ; no, Nobelprisen ) are five separate prizes that, according to Alfred Nobel's will of 1895, are awarded to "those who, during the preceding year, have conferred the greatest benefit to humankind." Alfr ...
-winning discovery of the cosmic microwave background radiation. On 15 December 1960, the U.S. Post Office issued a postage stamp depicting Echo 1.


Gallery

File:Echo Prototype.jpeg, Scale prototype of the Echo satellites undergoing a skin stress test on 1 May 1960. File:The Big Bounce.ogv, AT&T Bell Labs video about the first voice transmission via satellite and the engineers who conducted the effort.


See also

* AO-51, AMSAT-
OSCAR Oscar, OSCAR, or The Oscar may refer to: People * Oscar (given name), an Irish- and English-language name also used in other languages; the article includes the names Oskar, Oskari, Oszkár, Óscar, and other forms. * Oscar (Irish mythology), ...
51 (also known as Phase 2E, or ECHO) – an amateur radio communications satellite launched in 2004 *
Courier 1B Courier 1B, the world's first active repeater communications satellite, was successfully launched October 4, 1960 at 17:45:00 GMT from Cape Canaveral, Florida. The first Courier satellite in Project Courier, Courier 1A, was lost 2.5 minutes aft ...
– world's first active repeater satellite, launched in 1960 *
List of communications satellite firsts Milestones in the history of communications satellites. See also * Timeline of first artificial satellites by country *First images of Earth from space This is a timeline of first images of Earth from space. The initial photographs and digit ...
*
PAGEOS PAGEOS (PAssive Geodetic Earth Orbiting Satellite) was a balloon satellite which was launched by NASA in June 1966. Design PAGEOS had a diameter of exactly , consisted of a thick mylar plastic film coated with vapour deposited aluminium en ...
– a similar balloon satellite project *
Project SCORE SCORE (Signal Communications by Orbiting Relay Equipment) was the world's first purpose-built communications satellite. Launched aboard an American Atlas rocket on December 18, 1958, SCORE provided the second test of a communications relay sys ...
– world's first communications satellite, launched in 1958 *
Telstar Telstar is the name of various communications satellites. The first two Telstar satellites were experimental and nearly identical. Telstar 1 launched on top of a Thor-Delta rocket on July 10, 1962. It successfully relayed through space the fi ...
– first active, direct relay communications satellite, launched in 1962 *
TransHab TransHab was a concept pursued by NASA in the 1990s to develop the technology for expandable habitats inflated by air in space. Specifically, TransHab was intended as a replacement for the already existing rigid International Space Station crew ...
, a subsequent expandable spacecraft technology project pursued by NASA *
U.S. space exploration history on U.S. stamps With the advent of robotic and human spaceflight a new era of American history had presented itself. Keeping with the tradition of honoring the country's history on U.S. postage stamps, the U.S. Post Office began commemorating the various events ...
* Norman L. Crabill


References


Further reading

* * Nick D'Alto "The Inflatable Satellite", ''Invention and Technology'' Summer 2007, Volume 23, Number 1, pp. 38–43


External links

* * {{Orbital launches in 1964 1960 in spaceflight 1964 in spaceflight Communications satellites in low Earth orbit Passive satellites Spacecraft launched in 1960 Spacecraft launched in 1964 Articles containing video clips Balloon satellites