As we mentioned above, the flash angle θ′ between the satellite’s spin
axis and a line perpendicular to the mirror is very important in our
calculations. We made detailed studies of the various flash angles that
would be possible during the first 60 days after launch. We plotted the
times when the satellite would be above the horizon while our Crawford’s
Hill, New Jersey, observing station was in darkness, and we made
allowance for satellite orbits that might deviate slightly from the
planned one. These calculations told us that the best flash angle for
the mirror would be 68 degrees—which is the angle made by the first
facets above Telstar’s equatorial antenna band. So we located a flat
mirror on one of these facets. Because one of the solar aspect cells was
already installed in the center of this facet, we were forced to cut a
circular hole out of the center of the mirror.
But we knew that one mirror could not do the whole job. After Telstar I
had been in orbit more than 30 days, the 68-degree mirror would only be
in position to give infrequent flashes, and one at about 95 degrees
would be more useful. This presented two problems. First, no facet on
the satellite makes a 95-degree angle with the spin axis. However, we
could use one of the facets just below the equatorial antenna, which
makes a 112-degree angle, and groove or _facet_ the mirror so that its
reflecting faces became narrow strips slanted 17 degrees away from the
base at the angle of 95 degrees (112 - 17 = 95). Our second problem was
space—since there was not enough room left on any of the 112-degree
facets to mount a second large mirror, we substituted two smaller
mirrors and mounted them 120 degrees apart. This arrangement lets us
know from which mirror we see flashes—the plane mirror gives one flash
for each revolution of the satellite; the faceted mirrors give two
flashes for each revolution of the satellite.
[Illustration: _Sketches of three reflecting mirrors and their
locations on the Telstar satellite. The upper plane mirror is set at
68° to the spin axis; the lower ones are faceted to give reflecting
surfaces at 95°. Two of the satellite’s six solar aspect cells can
be seen within the circular cut-outs in the mirrors._]