_Since the first Telstar satellite went into orbit, we have tried to
trace its path through space precisely. But we also have had to keep a
constant check on the position, or attitude, that the satellite takes as
it travels. We are particularly interested in the direction of the spin
axis about which it revolves, and we also want to know its spin rate,
which is the number revolutions the satellite makes each minute.
Although these might seem relatively simple jobs, they actually turned
out to be rather complicated. And only at virtually the last minute,
just before the satellite’s design was finally set, did we think of a
new way of using reflected flashes of sunlight to report on its spin
axis and spin rate._