Tracking Science

There were six tracking antennas at CRO. The Acquisition Aid (Acq Aid) broad-beam antenna acted as the ‘ears’ for the station providing angle pointing data to the Station’s acquisition bus so that other MSFN tracking systems with narrower beam widths lock on to the spacecraft more quickly using the angles it provided. Similarly the R&RR VHF antenna acted as an acquisition aid to the R&RR S-band antenna.

Next were the two pulse radars, the FPQ-6 and the Verlort (VERy LOng Range Tracking) radar The Q6, a 'state of the art' precision C-band radar with a maximum range of 59,000Km, was one of only two in the MSFN network. Computer feedback and control, and frequency stability featured prominently as factors in the precision of its tracking. The Verlort S-band radar, originally designed in WWII, was a veteran of the Mercury missions; it was transported from Muchea as a backup for the Q6.

STADAN’s two R&RR systems were examples of the continuous wave (CW) ranging process. Both used ranging tones; upgraded to digital coding for the S-band system in later years. A feature of CW systems is the deduction of the spacecraft’s velocity from the frequency shift between the uplink and downlink signals. We know this shift as the Doppler effect - the ‘eeeee-aaaaah’ engine sound you hear as a racing car comes towards you standing at the side of the track, and as it goes past you and off into the distance; the change from a high tone to a lower one.

The sixth system, the Unified-S Band, added for the Apollo missions, was also a CW system with many sub-carriers, combining angle and range measurement, telemetry data, biomedical data, command, television and voice communications on a single carrier frequency.