On its 109th day of travel, Mariner had approached Venus in a precarious condition. Seven of the over-heated temperature sensors had reached their upper telemetry limits. The Earth-sensor brightness reading stood at 3 (0 was the nominal threshold) and was dropping. Some 149 watts of power were being consumed out of the 165 watts still available from the crippled solar panels. At JPL’s Space Flight Operations Center, there was reason to believe that the ailing CC&S might not command the spacecraft into its encounter sequence at the proper time. Twelve hours before encounter, these fears were verified. Quickly, the emergency Earth-originated command was prepared for transmission. At 5:35 a.m., PST, a radio signal went out from Goldstone’s Echo Station. Thirty-six million miles away, Mariner II responded to the tiny pulse of energy from the Earth and began its encounter sequence. After Mariner had “acknowledged” receipt of the command from the Earth, the spacecraft switched into the encounter sequence as engineering data were turned off and the radiometers began their scanning motion, taking up-and-down readings across the face of the planet. As throughout the long cruise, the four experiments monitoring the magnetic fields, cosmic dust, charged particles, and solar plasma experiments continued to operate. [Illustration: _Mariner II approached Venus from the dark side, crossed between the planet and the Sun while making three radiometer scans of the disk._] As Mariner approached Venus on its night side, it was travelling about 88,400 miles per hour with respect to the Sun. At the point of closest approach, at 11:59.28 a.m., PST, the distance from the planet was 21,598 miles. During encounter with Venus, three scans were made: one on the dark side, one across the terminator dividing dark and sunlit sides, and one on the sunlit side. Although the scan went slightly beyond the edge of the planet, the operation proceeded smoothly and good data were received on the Earth. With encounter completed, the cruise condition was reestablished by radio command from the Earth and the spacecraft returned to transmitting engineering data, together with the continuing readings of the four cruise scientific experiments. After approaching closer to a planet and making more meaningful scientific measurements than any man-made space probe, Mariner II continued on into an orbit around the Sun. December 27, 13 days after Venus encounter, marked the perihelion, or point of Mariner’s closest approach to the Sun: 65,505,935 miles. The Sun-related speed was 89,442 miles per hour. As Mariner began to pull away from the Sun in the following months, its Sun-referenced speed would decrease.