Mariner’s injection into the Venus trajectory yielded a predicted miss of 233,000 miles in front of the planet, well within the normal miss pattern expected as a result of the launch. Because the spacecraft was designed to cross the orbit of Venus behind the planet and pass between it and the Sun, it was necessary to correct the trajectory to an approximate 8,000- to 40,000-mile “fly-by” so the scientific instruments could operate within their design ranges.
After comparison of the actual flight path with that required for a proper near-miss, the necessary roll, pitch, and motor-burn commands were generated by the JPL computers. When, on September 4, it had been established that the spacecraft was indeed oriented on the Earth and not the Moon, a set of three commands was transmitted to the spacecraft from Goldstone, to be stored in the electronic “memory unit” until the start command was sent.
At 1:30 p.m., PST, the first commands were transmitted: a 9.33-degree roll turn, a 139.83-degree pitch turn, and a motor-burn command to produce a 69.5-mile-per-hour velocity change.
At 2:39 p.m., a fourth command was sent to switch from the directional antenna to the omni-antenna. Finally, a command went out instructing the spacecraft to proceed with the now “memorized” maneuver program.
Mariner then turned off the Earth and Sun sensors, moved the directional antenna out of the path of the rocket exhaust stream, and executed a 9.33-degree roll turn in 51 seconds.
Next, the pitch turn was completed in 13¼ minutes, turning the spacecraft almost completely around so the motor nozzle would point in the correct direction when fired.
The spacecraft was stabilized and the roll and pitch turns controlled by gyroscopes, which signalled the attitude control system the rate of correction for comparison with the already computed values.
With the solar panels no longer directly oriented on the Sun, the battery began to share the power demand and finally carried the entire load until the spacecraft had again been oriented on the Sun.
At the proper time, the motor—controlled by the CC&S—ignited and burned for 27.8 seconds, while the spacecraft’s acceleration was compared with the predetermined values by the accelerometer. During this period, when the gas jets could not operate properly, the spacecraft was stabilized by movable vanes or rudders in the exhaust of the midcourse motor.
The velocity added by the midcourse motor resulted in a decrease of the relative speed of the spacecraft with respect to the Earth by 59 miles per hour (from 6,748 to 6,689 miles per hour), while the speed relative to the Sun increased by 45 miles per hour (from 60,117 to 60,162 miles per hour).