Locating the Mirrors on the Satellite
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.
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.