Mariner II was launched while Venus was far behind the Earth. During the 109-day flight, Venus overtook and passed the Earth. It rendezvoused with the spacecraft at a point about 36,000,000 miles from the Earth.
During the midcourse maneuver, the trajectory of Mariner II was corrected so that the spacecraft would approach within 21,598 miles of Venus.
ROLL MANEUVER ANTENNA UP PITCH MANEUVER MOTOR BURN SUN REAQUISITION ANTENNA REPOSITION EARTH REAQUISITION
The Sun sensors then activated the gas jets and moved the spacecraft about until the roll or long axis was pointed at the Sun. This maneuver required only 2½ minutes after the CC&S issued the command. The solar panel power output of 195 watts was somewhat higher than anticipated, as were the spacecraft temperatures, which decreased and stabilized six hours after the spacecraft oriented itself on the Sun.
On August 29, a command from Johannesburg turned on the cruise scientific experiments, including all the instruments except the two radiometers. The rate of data transmission was then observed to decrease as planned and the data conditioning system was functioning normally.
For seven days, no attempt was made to orient the spacecraft with respect to the Earth because the Earth sensors were too sensitive to operate properly at such a close range. On September 3, the CC&S initiated the Earth acquisition sequence. The gyroscopes were turned on, the cruise scientific instruments were temporarily switched off, and a search for the Earth began about the roll axis of the spacecraft.
During this maneuver, the long axis of the spacecraft was held steady in a position pointing at the Sun and the gas jets rolled the spacecraft around this axis until the sensors, mounted in the directional antenna, could “see” the Earth. Apparently, the Earth sensor was already viewing the Earth because the transmitter output immediately switched from the omni- to the directional antenna, indicating that no search was necessary.
However, the initial brightness reading from the Earth sensor was 38, an intensity that might be expected if the spacecraft were locked onto the Moon instead of the Earth. As a result, the midcourse maneuver was delayed until verification of Earth lock was obtained.