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.
How We Record Flashes from the Mirrors
Now we had finally found a satisfactory way to reflect a train of tiny flashes—much too faint to be seen by the naked eye—from Telstar as it passed across the sky during the night. But our main aim was to record the exact times when these flash bursts occurred. With this information, we could, using the method we described above, tell very accurately both the satellite’s spin axis and its rate of spin. We do not have space to describe the many problems that had to be solved in setting up the equipment to record the flashes. Let us merely outline the procedure that we finally devised:
1. To pick up the satellite’s flashes we use a 12-inch-aperture photoelectric telescope mounted on a radar trailer (shown in [illustration below]). It is pointed by means of prediction drive tapes produced by an electronic computer; these are based on data from previous passes.
2. On clear, dark nights when the satellite is at relatively short range, we can see it with an auxiliary finder telescope, and then adjust the large telescope precisely. Or, if the satellite’s high-frequency beacon has been turned on, the Holmdel microwave antenna can automatically point our large telescope.
3. When flashes of light are picked up by the telescope, they fall directly onto the cathode of a photomultiplier tube. They are then filtered out from the random light in the night sky and amplified.
Twelve-inch telescope and electronics box mounted on a radar antenna pedestal at Crawford’s Hill. Three-inch sighting telescope mounted on top has since been replaced by six-inch telescope.
4. Rather than make a continuous recording of the output—one night this would have produced a record twelve miles long for us to pore over—we use an electronic trigger. This is the time base of an oscilloscope, whose sawtooth output is set in operation only if a signal of four volts or more is received ([photo below]).