Balloon satellite

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.

Optical visibility is, however, lower than that of radio waves, because 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 2,900 kilometers (1,800 mi).

Telstar 1 (1962) and Early Bird (1965) were able to transmit several hundred audio channels simultaneously in addition to a television program exchanged between continents.

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 30 and 45 cm (12 and 18 in)).

Three stations of the global network were situated in Europe: Catania in Sicily, Hohenpeißenberg in Bavaria and Tromsø in northern Norway.

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.

Only newly developed methods of observation using CCD and the highly precise star positions of the astrometry satellite Hipparcos made further improvement possible in the measurement of distance.