27 August 1962: At 06:53:14 UTC (2:53 a.m., Eastern Daylight Time), Mariner 2 lifted off from Launch Complex 12 at Cape Canaveral Air Force Station, Florida, aboard an Atlas-Agena B launch vehicle. This was the second space probe to be sent to Venus.

Mariner 1 and 2 were identical space probes built by the Jet Propulsion Laboratory (JPL) of the California Institute of Technology (Caltech), Pasadena, California. The spacecraft were designed to obtain radiometric temperatures of Venus, and to measure the Interplanetary Magnetic Field.

The Mariner 1 mission failed when the launch vehicle veered off course and was destroyed by the Range Safety Officer, 4 minutes, 53 seconds into its flight, 22 July 1962.

The Atlas Agena B combined an Atlas LV-3A rocket with an Agena B upper stage. The Atlas was derived from the U.S. Air Force SM-65 Atlas intercontinental ballistic missile (ICBM), and was built by the Convair Division of General Dynamics at San Diego, California.

The height of the total vehicle, including the protective shroud encasing Mariner, 103 feet, 5 inches (31.70 meters). The Atlas Agena B first stage was 20.70 meters (67 feet, 11 inches) long, with a maximum diameter of 3.05 meters (10 feet). The maximum width across the booster section was 4.88 meters (16 feet).

The LV-3A is a “1-½ stage” liquid-fueled rocket with three engines. The “half-stage,” was a booster section consisting of two LR89-NA-5 rocket engines. This stage produced approximately 369,800 pounds of thrust (1,645 kilonewtons). The center, or “sustainer,” engine is a LR105-NA-5, rated at 86,800 pounds of thrust (386 kilonewtons). Both engines were built by the Rocketdyne Division of North American Aviation, Inc., at Canoga Park, California. The Atlas rocket used liquid oxygen and RP-1 (a highly-refined kerosene) propellant. The LV-3A had a total thrust of 456,587 pounds (2,031 kilonewtons).

The second stage was an Agena B, built by Lockheed Missiles and Space Systems, Sunnyvale, California. This engine was capable of being restarted in orbit. The Agena B was 7.20 meters (23 feet, 7 inches) long and had a maximum diameter of 1.50 meters (4 feet, 11 inches). It was also liquid fueled, but used a hypergolic mixture of nitric acid and UDMH. The single engine was a Bell Aerosystems Company LR81-BA-7, with 16,000 pounds of thrust (71.1 kilonewtons).

The Mariner probe was mounted atop the Agena second stage, enclosed in a protective shroud. Mariner had a gross weight of 447 pounds (202.8 kilograms). The probe was 9 feet, 11 inches long (3.02 meters) long, folded for launch, and 5 feet (1.52 meters) wide. When antennas and the solar panels were fully expanded, the spacecraft was 11 feet, 11 inches (3.63 meters) long and had a span of 16 feet, 6 inches (5.03 meters).

At liftoff, all three main engines were burning. After 2minutes, the two-engine booster assembly was jettisoned and the vehicle continued with the center LR105 sustainer. After 4 minutes, 25 seconds, this engine shut down and the Agena second stage separated. At this point, guidance was lost and the vehicle began to roll, but did not deviate significantly from the planned trajectory. About a minute later, guidance was restored and the mission continued.

The Agena B second stage placed the Mariner in a parking orbit at about 118 kilometers (73.3 miles) altitude. 16 minutes, 20 seconds later, the Agena engine was reignited and  Mariner 2 was then placed on a trajectory planned to take it to Venus.

After 3 months, 17 days, at 19:59:28 UTC, 14 December 1962, the probe passed within 34,773 kilometers (21,607 miles) of Venus and measured the planet’s surface and cloud temperatures. It continued inward across the solar system and came within 105,464,560 kilometers (65,432,640 miles) of the sun.

The last transmission was received at 07:00 UTC, 3 January 1963, 129 days into the mission. Mariner 2 remains in orbit around the sun, circling every 292 days.

© 2018, Bryan R. Swopes