A balloon satellite, sometimes referred to as a "satelloon", is a satellite inflated with gas after it has been put into

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

Echo 1 and Echo 2 balloon satellites

The first flying body of this type was Echo 1, which was launched into a high

on August 12, 1960, by the United States. It originally had a spherical shape measuring , with a thin metal-coated plastic shell 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 stability, dimensional stability, transparency reflectivity, an ...

. It served for testing as a "passive"

communication Communication is commonly defined as the transmission of information. Its precise definition is disputed and there are disagreements about whether Intention, unintentional or failed transmissions are included and whether communication not onl ...

and

geodetic Geodesy or geodetics is the science of measuring and representing the geometry, gravity, and spatial orientation of the Earth in temporally varying 3D. It is called planetary geodesy when studying other astronomical bodies, such as planets ...

satellite. One of the first radio contacts using the satellite was successful at a distance of nearly (between the east coast of the US and California). By the time Echo 1 burned up in 1968, the measurements of its orbit by several dozen earth stations had improved our knowledge of the precise shape of the planet by nearly a factor of ten. Its successor was the similarly built Echo 2 (1964 to about 1970). This satellite circled the Earth about lower, not at an angle of 47° like that of Echo 1, but in a polar orbit with an average angle of 81°. This enabled radio contact and measurements to be made at higher latitudes. Taking part in the Echo orbit checks to analyze disturbances in its orbit and in the Earth's gravitational field were thirty to fifty professional earth stations, as well as around two hundred amateur astronomers across the planet in "Moonwatch" stations; these contributed around half of all sightings.

Range of radio waves, visibility

The

Pythagorean theorem In mathematics, the Pythagorean theorem or Pythagoras' theorem is a fundamental relation in Euclidean geometry between the three sides of a right triangle. It states that the area of the square whose side is the hypotenuse (the side opposite t ...

allows us to calculate easily how far a satellite is visible at such a great height. It can be determined that a satellite in a orbit rises and sets when the horizontal distance is . However, the atmosphere causes this figure to vary slightly. Thus if two radio stations are apart and the satellite's orbit goes between them, they may be able to receive each other's reflected radio signals if the signals are strong enough. Optical visibility is, however, lower than that of radio waves, because * the satellite must be illuminated by the sun * the observer needs a dark sky (that is, they must be in the Earth's own shadow on the planet's twilight or night side) * the brightness of a sphere depends on the angle between the incident light and the observer (see

phases of the moon A lunar phase or Moon phase is the apparent shape of the Moon's directly sunlit portion as viewed from the Earth. Because the Moon is Tidal locking, tidally locked with the Earth, the same Hemisphere (geometry), hemisphere is always facing the ...

) * the brightness of a sphere is much reduced as it approaches the horizon, as atmospheric

extinction Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

swallows up as much as 90% of the light Despite this there is no problem observing a flying body such as Echo 1 for precise purposes of satellite geodesy, down to a 20° elevation, which corresponds to a distance of . In theory this means that distances of up to between measuring points can be "bridged", and in practice this can be accomplished at up to . For visual and photographic observation of bright satellites and balloons, and regarding their geodetic use, see Echo 1 and Pageos for further information.

Other balloon satellites

For special testing purposes two or three satellites of the

Explorer Exploration is the process of exploring, an activity which has some Expectation (epistemic), expectation of Discovery (observation), discovery. Organised exploration is largely a human activity, but exploratory activity is common to most organis ...

series were constructed as balloons (possibly Explorer 19 and 38). Echo 1 was an acknowledged success of radio engineering, but the passive principle of telecommunications (reflection of radio waves on the balloon's surface) was soon replaced by active systems.

Telstar 1 Telstar 1 is a defunct communications satellite launched by NASA on July 10, 1962. One of the earliest communications satellites, it was the first satellite to achieve live transmission of broadcast television images between the United States ...

(1962) and Early Bird (1965) were able to transmit several hundred audio channels simultaneously in addition to a television program exchanged between continents. Satellite geodesy with Echo 1 and 2 was able to fulfill all expectations not only for the planned 2–3 years, but for nearly 10 years. For this reason

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

soon planned the launch of the even larger balloon Pageos. The name is from "passive geodesic satellite", and sounds similar to "Geos", a successful active electronic satellite from 1965.

Pageos and the global network

Pageos was specially launched for the "global network of satellite geodesy", which occupied about 20 full-time observing teams all over the world until 1973. All together they recorded 3000 usable photographic plates from 46 tracking stations with calibrated all-electronic BC-4 cameras (1:3 / focal length ). From these images they were able to calculate the stations' position three-dimensionally with a precision of about . The coordinator of this project was Professor

Hellmut Schmid Hellmut H. Schmid (12 September 1914 – 27 April 1998) was a Swiss professor of geodesy and photogrammetry. He taught at ETH Zürich (Switzerland). In the 1950s, he worked on space exploration in the United States. Between 1968 and 1974, he promo ...

, from the

ETH Zurich ETH Zurich (; ) is a public university in Zurich, Switzerland. Founded in 1854 with the stated mission to educate engineers and scientists, the university focuses primarily on science, technology, engineering, and mathematics. ETH Zurich ran ...

. Three stations of the global network were situated in Europe: Catania in

Sicily Sicily (Italian language, Italian and ), officially the Sicilian Region (), is an island in the central Mediterranean Sea, south of the Italian Peninsula in continental Europe and is one of the 20 regions of Italy, regions of Italy. With 4. ...

, Hohenpeißenberg in

Bavaria Bavaria, officially the Free State of Bavaria, is a States of Germany, state in the southeast of Germany. With an area of , it is the list of German states by area, largest German state by land area, comprising approximately 1/5 of the total l ...

and

Tromsø Tromsø is a List of towns and cities in Norway, city in Tromsø Municipality in Troms county, Norway. The city is the administrative centre of the municipality as well as the administrative centre of Troms county. The city is located on the is ...

in northern Norway. For the completion of the navigational network exact distance measurements were needed; these were taken on four continents and across Europe with a precision of per kilometer. The global network enabled the calculation of a "geodetic date" (the geocentric position of the measurement system) on different continents, within a few meters. By the early 1970s reliable values for nearly 100 coefficients of the Earth's gravity field could be calculated.

1965–1975: Success with flashing light beacons

Bright balloon satellites are well visible and were measurable on fine-grained (less sensitive) photographic plates, even at the beginning of space travel, but there were problems with the exact chronometry of a satellite's track. In those days it could only be determined within a few milliseconds. Since satellites circle the earth at about , a time error of 0.002 second translates into a deviation of about . In order to meet a new goal of measuring the tracking stations precisely within a couple of years, a method of flashing light beacons was adopted around 1960. To build a three-dimensional measuring network, geodesy needs exactly defined target points, more so than a precise time. This precision is easily reached by having two tracking stations record the same series of flashes from one satellite. Flash beacon technology was already mature in 1965 when the small electronic satellite Geos 1 was launched in November 1965. With its companion, Geos 2, that was launched in January 1968, the GEOS system brought about a remarkable increase in measurement precision. From about 1975 on, almost all optical measurement methods lost their importance, as they were overtaken by speedy progress in electronic distance measurement. Only newly developed methods of observation using CCD and the highly precise star positions of the

astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other Astronomical object, celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, th ...

satellite

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions and distances of ...

made further improvement possible in the measurement of distance.

List of balloon satellites

{, class="wikitable" , + List of balloon satellites (sorted by launch date) !Satellite !Launch date (UTC) !Decay !Mass(kg) !Diameter(m) !NSSDC ID !Nation !Usage , - , Beacon 1 , 1958-10-24 03:21 , N/A (launch failure) , 4.2 , 3.66
1958-F18
, US , ado , - , Beacon 2 , 1959-08-15 00:31:00 , N/A (launch failure) , 4.2 , 3.66
1959-F07
, US , ado , - , Echo 1 , 1960-08-12 09:36:00 , 1968-05-24 , 180 , 30.48
1960-009A
, US , pcr, ado, spc, tri , - , Explorer 9 , 1961-02-16 13:12:00 , 1964-04-09 , 36 , 3.66
1961-004A
, US , ado , - , Explorer 19 (AD-A) , 1963-12-19 18:43:00 , 1981-10-05 , 7.7 , 3.66
1963-053A
, US , ado , - , Echo 2 , 1964-01-25 13:55:00 , 1969-06-07 , 256 , 41
1964-004A
, US , pcr, tri , - , Explorer 24 (AD-B) , 1964-11-21 17:17:00 , 1968-10-18 , 8.6 , 3.6
1964-076A
, US , ado , - , PAGEOS 1 , 1966-06-24 00:14:00 , 1975-07-12 , 56.7 , 30.48
1966-056A
, US , tri , - , PasComSat (OV1-8) , 1966-07-14 02:10:02 , 1978-01-04 , 3.2 , 9.1
1966-063A
, US , pcr , - , Explorer 39 (AD-C) , 1968-08-08 20:12:00 , 1981-06-22 , 9.4 , 3.6
1968-066A
, US , ado , - , Mylar Balloon , 1971-08-07 00:11:00 , 1981-09-01 , 0.8 , 2.13
1971-067F
, US , ado , - , Qi Qiu Weixing 1 , 1990-09-03 00:53:00 , 1991-03-11 , 4 , 3
1990-081B
,

PRC China, officially the People's Republic of China (PRC), is a country in East Asia. With a population exceeding 1.4 billion, it is the second-most populous country after India, representing 17.4% of the world population. China spans the e ...

, ado , - , Qi Qiu Weixing 2 , 1990-09-03 00:53:00 , 1991-07-24 , 4 , 2.5
1990-081C
,

, ado , - , Naduvaniy gazovoy balloon , 1991-03-30 (?) , , , , 1986-017FJ , RU , , - , Orbital Reflector , 2018-12-03 , , , , , US , sculpture , - abbreviations: * ado = atmospheric density observations * pcr = passive communications reflector, satellite reflects

microwave Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...

signals. * spc = solar pressure calculations, estimate impact of

solar wind The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...

. * tri = satellite triangulation, measuring the Earth's surface.

Sources

NSSDC Master Catalog

Heavens-Above

Jonathan's Space Report (HUGE: 5MB!)