Station Director Bob Leslie was taking no chances for the Mariner IV encounter with Mars.

All possible sources of radio interference were to be turned off. There would be no hot meal in the canteen on Thursday 15th July 1965.

Preserved and scanned by Gary Peach.

This image, adapted from a slide shown at the Pre-encounter Press Conference at JPL, shows which stations will be tracking during the encounter.

DSIF-11 (Goldstone) and DSIF-42 (Tidbinbilla) will both see the radio occultation and re-emergence.

Preserved by Les Whaley. Modified by Colin Makkellar.

This JPL diagram shows the expected occultation geometry.

Preserved by Les Whaley. Scan: Colin Mackellar.

Station Director Bob Leslie (left) and Les Whaley examine the output from the chart recorder showing the Mariner IV radio occultation as it went behind Mars. Scan: Mike Dinn.

Bruce Window explains:

“This is a record from DSS42 Analog Instrumentation System’s large chart recorder (CLC 5-123 Oscillograph) which was visible in near-real-time.

It shows, amongst other things, Receiver-1 AGC voltage which represents the received signal level of the spacecraft.

At the time of occultation, this signal dropped from a steady figure (say -160dBm) to receiver threshold, (say -170dBm). The diagonal line on the chart is Receiver-1 ACG voltage.

The first “O” of the word ‘occultation’ cuts this trace of ACG voltage. The magnitude of the signal increases towards the left of the chart. Thus, when Receiver-1 lost lock because the spacecraft was obscured by the planet Mars, the chart shows the AGC going to the right.”

“This is a continuation of the same CLC Oscillograph record, and shows amongst other things, Receiver-1 AGC voltage when Receiver 1 became locked onto the one-way downlink signal after the spacecraft emerged from behind Mars.

Receiver-1 AGC is the trace that intersects the letter “L” from the word “occultation” and shows that when it locked onto the spacecraft initially, it was a false lock on a sideband of the carrier.

The trace shows that false lock was intentionally broken, and then a true, downlink lock on the signal was achieved. The strength of the signal increases towards the left of the chart.”

“This is a record from a Sanborn 8 channel thermal chart recorder which was a backup to the AIS CLC Oscillograph. It is of Mariner IV occultation. It was generally run in parallel with the CLC for special events because it was instantly visible.

The configuration of this recorder was more under station control than the CLC which was dictated by the Mission documentation.”

Large, Larger.