When I first discovered satelloons a few months ago, I admit, I was a little disappointed to have fallen so hard for the first generation satelloons of Project Echo. This disappointment kicked in when I saw this photo of the PAGEOS satelloon being tested before its June 1966 launch. It wasn't much bigger than Echo I [31m vs 30m; Echo II was 40m]; what set it apart was PAGEOS' incredible mirror-like skin.
Which, I find out, was by design. PAGEOS, short for PAssive GEOdetic Satellite, was used in the impressive-sounding Worldwide Satellite Triangulation Network, an international collaboration to create a single global characterization of the earth's surface, shape, and measurements.
Geodesy, the science of measuring and representing the earth, helped identify things like plate tectonics and the equatorial bulge. From what I can tell, the WSTN involved taking pictures of the PAGEOS against identical star fields from different points on the earth's surface, then backing out precise values for latitude, longitude, and elevation from the photos' variations.
Stellar geodesy was obsoleted during PAGEOS' lifetime by lasers [more on that later], but not before the WSTN, under the direction of the Swiss scientist Dr. Hellmut Schmid, was able to calculate the accuracy of locations on the earth's surface to within 4m. According to Wikipedia, between 1966 and 1974, Schmid's project, using "all-electronic BC-4 cameras" installed in 46 stations around the free world [the USSR and China were not participating for some reason], produced "some 3000 stellar plates." Photographs of the stars with a 100-foot-wide metallic sphere--designed to capture and reflect the sun's light, and placed in an orbit that provided maximum visibility--moving in front of them.
I'd love to see some of these plates, or find any useful reference sources beyond the kind of scattershot, autotranslated Wikipedia articles.