Within the white aluminum-oxide outer shell of the satellite is crammed a complicated array of electronic equipment. Surprisingly, most of this gear has to do not with Telstar’s prime function—communications—but with its command and telemetry systems. The reason is that the satellite is an experimental device, not just a spectacular way to relay television programs. Altogether, the satellite’s various electronic circuits contain more than a thousand transistors and almost 1500 semiconductor diodes, plus a single electron tube—a traveling-wave tube used in the communications amplifier. The satellite itself has a magnesium frame that is covered with aluminum panels. All its electronic components are inside a aluminum canister, 20 inches in diameter, attached to the interior frame by special nylon lacings that reduced vibration inside the canister during launch. When all the components and subassemblies had been carefully put in place and thoroughly tested, the canister was filled with a liquid foam called polyurethane. This material hardens into a very light and rigid solid, completely enveloping the equipment and protecting it from damage and vibration. After the canister was solidly foamed, metal domes were welded onto the ends, and it was enclosed in a many-layered blanket of aluminum-coated Mylar (the same material used in the Echo balloon). To keep its temperature properly controlled, shutters on the canister’s two ends are operated by bellows. The satellite power system includes more than just solar cells. When operating at full capacity, the satellite’s equipment needs more energy than the 3600 solar cells can provide at one time. So Telstar also uses a storage battery made up of 19 rechargeable nickel-cadmium cells designed for this special purpose. These ensure that the satellite has a continuous and sufficient supply of power, even when all equipment is in operation or when the satellite is passing through the earth’s shadow. [Illustration: _After all electrical tests had been made on the satellite’s components, the electronics canister was filled with liquid polyurethane foam, using this specially developed foam machine_] [Illustration: _The giant horn antenna at Andover, Maine_] Ground Stations for Satellite Communications Project Telstar is actually an extension into space of microwave communications methods that have been thoroughly proved on the ground. For Project Echo and other early experiments in satellite communications, Bell Laboratories built a large antenna of the type known as a _horn-reflector_ in Holmdel, New Jersey. For Project Telstar, a similar but much larger antenna was designed. It was located in a relatively isolated spot at Andover, in the western part of Maine, where it would be close to Europe. The site is nicely protected by a surrounding ring of low hills—high enough to keep out interfering radio signals, but low enough not to block the satellite when it is near the horizon.