Six of the satellite’s flat facets are used for special measuring devices. Two different radiation studies are made: finding out how much damage will be done to solar cells and transistors, and determining how many actual energetic particles—protons and electrons—are present in the part of space that Telstar passes through. These different jobs are done by special devices on various facets. One, for example, consists of seven identical silicon transistors, six having different thicknesses of shielding and one being left unshielded—the amount of damage done to each is recorded and reported back to earth. Devices on another facet measure the radiation damage to solar cells protected by various thicknesses of sapphire. For the second radiation experiment—particle counting—four different types of silicon diodes are used as particle detectors. These measure the energy deposited both by protons of three energy levels and by electrons as the satellite passes through belts of natural and man-produced radiation in space. [Illustration: _The Telstar I satellite—outside_] telemetry, command and beacon antenna solar cells for power supply solar cells to measure radiation damage receiving antenna transmitting antenna transistors used to measure radiation damage solar aspect cells mirror [Illustration: _The Telstar I satellite—inside (looking at the electronics canister from the top down)_] beacon transmitter traveling-wave tube amplifier radiation measurement equipment nickel-cadmium cells (foamed) Measuring devices mounted on the surface of the Telstar I satellite [Illustration: particle detectors used to count protons] [Illustration: transistors used to measure radiation damage] [Illustration: solar cells used to measure radiation damage and as solar aspect indicators] [Illustration: particle detector used to count electrons] There are two other special devices: Six single solar cells are spaced at regular intervals around the satellite; these “solar aspect” indicators report the quantity of sunlight hitting them—and thus tell the direction in which the satellite is pointing. Three highly polished metal mirrors are also placed on Telstar; flashes of sunlight reflected from them can be seen in a telescope. To give a precise indication of the satellite’s position, the data obtained from both the solar aspect cells and from the flashes off the mirrors are combined. The Telstar I Satellite—Inside