October 30 was the 65th day of the mission and at 5 a.m., PST, Mariner overtook and passed the Earth at a distance of 11,500,000 miles. Since the spacecraft’s direction of travel had, in effect, been reversed by the midcourse maneuver, it had been gaining on the Earth in the direction of its orbit, although constantly falling away from the Earth in the direction of the Sun. The point of equal distance between the Earth and Venus was passed on November 6, when Mariner was 13,900,000 miles from both planets and travelling at 13,843 miles per hour relative to the Earth. As November wore on, hope for a successful mission began to mount. Using tracking data rather than assumptions of standard midcourse performance, the Venus miss distance had now been revised to about 21,000 miles and encounter was predicted for December 14. But the DSIF tracking crews, the space flight and computer operators, and the management staff could not yet relax. The elation following the successful trajectory correction maneuver on September 4 had given way alternately to discouragement and guarded optimism. Four telemetry measurements were lost on December 9 and never returned to normal. They measured the angle of the antenna hinge, the fuel tank pressure, and the nitrogen pressure in the midcourse and attitude control systems. A blown fuse, designed to protect the data encoder from short circuits in the sensors, was suspected. However, these channels could not affect spacecraft operation and Mariner continued to perform normally. The rising temperatures recorded on the spacecraft were more serious. Only the solar panels were displaying expected temperature readings; some of the others were as much as 75 degrees above the values predicted for Venus encounter. The heat increase became more rapid after November 20. By December 12, six of the temperature sensors had reached their upper limits. It was feared that the failure point of the equipment might be exceeded. The CC&S performed without incident until just before encounter, when, for the first time, it failed to yield certain pulses. JPL engineers were worried about the starting of the encounter sequence, due the next day, although they knew that Earth-based radio could send these commands, if necessary. On December 12, with the climax of the mission near, the spacecraft was 34,218,000 miles from the Earth, with a speed away from the Earth of 35,790 miles per hour, a Sun-relative speed of 83,900 miles per hour. Only 635,525 miles from Venus at this point, Mariner II was closing fast on the cloud-shrouded planet. But it was a hot spacecraft that was carrying its load of inquisitive instruments to the historic encounter. ENCOUNTER AND BEYOND