page_title: Mariner 2
section_title: Launch
hierarchical_section_title: Mariner 2 / Mission profile / Launch
caption_attribution_description: English: Launch of an Atlas Agena B with Mariner 2, at Cape Canaveral. Français&#160;: Lancement de Mariner 2 par une Atlas Agena B, à Cape Canaveral. Nederlands: Lancering van een Atlas Agena B met Mariner 2 vanaf Cape Canaveral.
context_page_description: Mariner 2, an American space probe to Venus, was the first robotic space probe to conduct a successful planetary encounter. The first successful spacecraft in the NASA Mariner program, it was a simplified version of the Block I spacecraft of the Ranger program and an exact copy of Mariner 1. The missions of the Mariner 1 and 2 spacecraft are sometimes known as the Mariner R missions. Original plans called for the probes to be launched on the Atlas-Centaur, but serious developmental problems with that vehicle forced a switch to the much smaller Agena B second stage. As such, the design of the Mariner R vehicles was greatly simplified. Far less instrumentation was carried than on the Soviet Venera probes of this period—for example, forgoing a TV camera—as the Atlas-Agena B had only half as much lift capacity as the Soviet 8K78 booster. The Mariner 2 spacecraft was launched from Cape Canaveral on August 27, 1962, and passed as close as 34,773 kilometers to Venus on December 14, 1962.
  The Mariner probe consisted of a 100 cm diameter hexagonal bus, to which solar panels, instrument booms, and antennas were attached.
context_section_description: Mariner 2 was launched from Cape Canaveral Air Force Station Launch Complex 12 at 06:53:14 UTC on August 27, 1962 by a two-stage Atlas-Agena rocket.
  The two-stage Atlas-Agena rocket carrying Mariner 1 had veered off-course during its launch on July 22, 1962 due to a defective signal from the Atlas and a bug in the program equations of the ground-based guidance computer, and so the spacecraft was destroyed by the Range Safety Officer.
  Two days after that launch, the backup probe and booster (Atlas vehicle 179D) were rolled out to LC-12. The Atlas proved troublesome to prepare for launch, and multiple serious problems with the autopilot occurred, including a complete replacement of the servoamplifier after it had suffered component damage due to shorted transistors. At 1:53 AM EST on August 27, Mariner 2 was launched.
  The flight proceeded normally up to the point of booster engine cutoff, at which point the V-2 vernier engine lost pitch and yaw control. The vernier started oscillating and banging against its stops, resulting in a rapid roll of the launch vehicle that came close to threatening the integrity of the stack. At T+189 seconds, the rolling stopped and the launch continued without incident. The rolling motion of the Atlas resulted in ground guidance losing its lock on the booster and preventing any backup commands from being sent to counteract the roll. The incident was traced to a loose electrical connection in the vernier feedback transducer, which was pushed back into place by the centrifugal force of the roll, which also by fortunate coincidence left the Atlas only a few degrees off from where it started and within the range of the Agena's horizontal sensor. As a consequence of this episode, GD/A implemented improved fabrication of wiring harnesses and checkout procedures.
  Five minutes after liftoff, the Atlas and Agena-Mariner separated, followed by the first Agena burn and second Agena burn. The Agena-Mariner separation injected the Mariner 2 spacecraft into a geocentric escape hyperbola at 26 minutes 3 seconds after liftoff. The NASA NDIF tracking station at Johannesburg, South Africa, acquired the spacecraft about 31 minutes after launch. Solar panel extension was completed approximately 44 minutes after launch. The Sun lock acquired the Sun about 18 minutes later. The high-gain antenna was extended to its acquisition angle of 72°. The output of the solar panels was slightly above the predicted value.
  As all subsystems were performing normally, with the battery fully charged and the solar panels providing adequate power, the decision was made on August 29 to turn on cruise science experiments. On September 3, the Earth acquisition sequence was initiated, and Earth lock was established 29 minutes later.
caption: Photo of launch of Mariner 2, on August 27, 1962.
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