2 _The command tracker, knowing from computer data the satellite’s
approximate location, begins to search for its continuous
136-megacycle beacon. A quad-helix antenna (four long spirals) tracks
the satellite to an accuracy of one degree._
3 _When the satellite is located, the command transmitter turns on the
satellite’s transistor circuits and telemetry. The ground station then
checks on the satellite’s operating condition, as reported by
telemetry._
4 _The command transmitter then turns on the satellite’s
traveling-wave tube, which starts the transmission of a 4080-megacycle
beacon signal._
5 _The precision tracker—an eight-foot parabolic dish (known as a
Cassegrainian antenna) mounted on a pylon—locates this beacon and
tracks it to within one-fiftieth of a degree._
6 _The horn antenna’s autotrack mechanism, which is pointed by both
the precision tracker and data from magnetic tapes, locates the
satellite’s beacon signal._
7 _Now the horn antenna locks onto the satellite, with the autotrack
continuing to make fine adjustments in pointing the horn._
8 _The equipment is now ready for communications signals to be sent
from the two-kilowatt ground transmitter to the satellite._
9 _The satellite receives the signals and converts them down to a
frequency of 90 megacycles; they are amplified in transistor circuits
and converted up to a new frequency of 4170 megacycles._
10 _The signals are amplified again by the traveling-wave tube—for a
total amplification of as much as ten billion times—to get a radiated
power of 2¼ watts._
11 _The 4170-megacycle signals are now transmitted in all directions
by the satellite’s equatorial antenna._
12 _These signals can be picked up at Andover or at any other ground
station equipped with a suitable antenna that is within line of sight
of the satellite._
13 _At Andover, the received signals are amplified by means of a
solid-state maser and a frequency-modulation-with-feedback circuit._
14 _They can now be relayed via regular land lines to their
destination._
15 _Near the end of a pass, the command tracker turns off the
communications circuits and telemetry in the satellite._