Balloon satellite

A balloon satellite is a man-made satellite, which is brought after reaching its orbit by a gas filling on its intended size. For sufficient small amounts of gas that are already at takeoff from the balloon envelope and expand through the vacuum of space to a large volume.

The great age of the balloon satellite was 1960-1975. You were the one hand, the passive radio traffic, on the other hand, because of their great brightness as a favorable destination for high geodetic purposes ( large-scale Stellartriangulation ).

• 2.1 Air Density Explorer
• 2.2 PAGEOS
• 2.3 PASCOMSAT and Gridsphere

Balloon satellite Echo 1 and Echo 2

The first such missile was Echo 1, launched on 12 August 1960 by the United States on a 1600 km high orbit. He initially had a spherical shape of 30 meters with a metal-coated thin plastic bag made ​​of Mylar and served the testing of "passive" news and as geodetic satellite. His international COSPAR number was 6000901 ( 9 starting in 1960, first component). Already one of the first radio communications managed almost 4000 km distance ( between the east coast of the United States and California). By echo 1 in 1968 burned up, improved his running web survey with satellite cameras of several dozen ground stations, the knowledge of the exact figure of the earth by nearly a factor of 10 ( a few meters ).

His successor was the similarly constructed Echo 2 with 41 meters in diameter ( approx. 1964 to 1970). He circled about 400km deep and not with an inclination of 47 ° as Echo 1, but on an approximate polar train with an average of 81 ° inclination. This was radio links and surveys also possible in higher latitudes. On the echo - path rules for the analysis of perturbations of the Earth's gravity and also about 200 amateur astronomers involved next 30-50 professional ground stations distributed worldwide so-called Moonwatch stations, which contributed about half of the weighted observations.

The harmful success of Echo -1 was indeed given, but was soon replaced for the Communications " passive principle " ( reflection of the radio waves to the balloon skin) by active systems. In particular, Telstar 1 (1962) and Intelsat I ( 1965) are worth mentioning here. They were next to a intercontinental exchanged TV audio channels simultaneously emit several hundred already.

Range of the radio waves, visible

How far a satellite is visible at such high altitudes, can be easily calculated with the Pythagorean theorem. It turns out that he just up or goes down at a 1500 km high orbit if it has 4600 km horizontal distance. The Earth's atmosphere makes this value, however, vary slightly.

If two radio stations ie 9000 km apart and go through the satellite orbit between them, they can receive their mutual reflection at a sufficiently strong radio waves.

The optical visibility, however, less than that of radio waves, because

However, it is not a problem for precise purposes of satellite geodesy, a missile like Echo 1 down to observe elevation angles of 20 ° - which corresponds to a distance of 2900 km. Therefore, in theory, distances between survey points to more than 5000 km of " bridge ", and in practice, at least 3-4000 km.

For visual or photographic observation of bright satellites and balloons and their geodetic use the article on Echo 1, PAGEOS and world networks provide more information.

More balloon satellite

Air Density Explorer

To study the density of the upper atmosphere also five satellites of the Explorer series were performed as balloons (Explorer 9, 19, 24 and 39 and DAD -B). While the air resistance of the balloon for use as a satellite communications satellite has been a problem, it was even desirable here. The low mass and high air resistance, the density of the high- atmosphere could be easily measured by the change in path of the satellite is measured over a longer period.

PAGEOS

PAGEOS was specifically designed for the so-called " World Network of Satellite Geodesy " launched worldwide were for until 1973 about 20 fully professional observation teams on the go. With the proven, fully electronic BC- 4 cameras ( 1:3 / focal length 30 or 45 cm), they recorded 46 ground stations to a total of 3000 usable photographic plates, from which the stations could be three-dimensionally calculated on an average of 4 m exactly. The coordinator of these campaigns was Univ. Prof. Hellmut Schmid of the ETH Zurich.

Satellite geodesy with Echo 1 and 2 fulfilled, however, not only during the scheduled two to three years all expectations, but for almost 10 years. Therefore, NASA launched the 30 -meter balloon called PAGEOS. He stands on German as English for " passive geodetic satellite" - in appeal also to GEOS, a successful active (electronic) satellite from 1965.

In Europe, three stations of the world network were: Catania, Sicily, the Hohenpeißenberg in Bavaria and Tromsø in northern Norway. For augmenting the network towards accurate distance measurements were necessary, on four continents - were measured with an accuracy of 0.5 mm per km - and also across Europe.

The world power now permitted for the first time, on different continents to calculate the " geodetic datum " ( geocentric position of the measurement systems ) to a few meters and mutually transform. The early 1970s were also reliable values ​​for almost 100 coefficients of the Earth's gravity field ( spherical harmonic expansion up to degree and order 12-15) are calculated.

PASCOMSAT and Gridsphere

To solve the problem of high air resistance of the passive balloon communications satellite, the United States Air Force launched a series of experimental satellites which consisted of a radio wave reflecting wire mesh, which was taken from a balloon in a spherical shape. The material of the balloon was so selected that under the influence of the sublimated solar UV radiation. Thus, the balloon broke in a short time in orbit, leaving a spherical wire mesh that the radio waves reflected as well, like a real balloon satellite, but had only a fraction of the air resistance. Although this technique worked, there was no operational use, as active communication satellites had been found to be significantly more powerful, so that no other passive models more were built.