I've been searching for historical and primary source material for Project Echo, one of NASA's earliest missions, which kicked into high gear in 1958. The giant, inflatable satelloons were functional--passive reflection communication satellites. That they were shaped just like Sputnik, only a hundred thousand times bigger, and were visible to the entire world with the naked eye, were, I'm sure, just a happy Space Race coincidence.
Echo I [above, right] was 100 feet in diameter and launched in 1960. Echo II was 135 feet, and launched in 1964. By then engineers at NASA's Langley Research Center figured out that over-stressing the aluminized Mylar would help the giant sphere keep its shape, even if it deflated a little bit. [Echo I was found to have partially caved in a few months after launch.]
Film and TV cameras were included in the Echo II rocket--the film canisters were recovered in the ocean, but I haven't found images from the footage. Video of the Echo II Inflation, however, is right here. Retired Goddard engineer Ron Muller screened it as part of a history of The Echo Project at a 2004 NASA conference on solar sails. It's pretty awesome, right down to the end. [The avi is available for download at the conference page.]
I put a little film strip together after the jump, too: