Venera 1 and 2 in the
Memorial Museum of Cosmonautics The first Soviet attempt at a flyby probe to Venus was launched on 4 February 1961, but failed to leave Earth orbit. In keeping with the Soviet policy at that time of not announcing details of failed missions, the launch was announced under the name
Tyazhely Sputnik ("Heavy Satellite"). It is also known as Venera 1VA. As with some of the Soviet Union's other planetary probes, the later versions were launched in pairs, with a second vehicle launched soon after the first.
Venera 1 and
Venera 2 were intended to fly past Venus without entering orbit. Venera 1 was launched on 12 February 1961. Telemetry on the probe failed seven days after launch. It is believed to have passed within of Venus and remains in heliocentric orbit. Venera 2 launched on 12 November 1965, but also suffered a telemetry failure after leaving Earth orbit. Several other failed attempts at Venus flyby probes were launched by the Soviet Union in the early 1960s, but were not announced as planetary missions at the time, and hence did not officially receive the "Venera" designation.
Venera 3 to 6 The Venera 3 to 6 probes were similar in construction. Weighing approximately one ton, and launched by the
Molniya-type booster rocket, they included a cruise "bus" and a spherical atmospheric entry probe. The probes were optimised for atmospheric measurements, but not equipped with any special landing apparatus. Although it was hoped they would reach the surface still functioning, the first probes failed almost immediately, thereby disabling data transmission to Earth.
Venera 3 became the first human-made object to impact another planet's surface as it crash-landed on 1 March 1966. However, as the spacecraft's data probes had failed upon atmospheric penetration, no data from within the Venusian atmosphere were retrieved from the mission. On 18 October 1967,
Venera 4 became the first spacecraft to measure the atmosphere of another planet. This spacecraft first showed the major gas of Venus's atmosphere to be CO2. While the
Soviet Union initially claimed the craft reached the surface intact, re-analysis, including atmospheric
occultation data from the American
Mariner 5 spacecraft that flew by Venus the day after its arrival, demonstrated that Venus's surface pressure was 75–100 atmospheres, much higher than Venera 4's 25 atm hull strength, and the claim was retracted. Realizing the ships would be crushed before reaching the surface, the Soviets launched
Venera 5 and
Venera 6 as atmospheric probes. Designed to jettison nearly half their payload prior to entering the planet's atmosphere, these craft recorded 53 and 51 minutes of data, respectively, while slowly descending by parachute before their batteries failed. This represented a significant scientific accomplishment. It had become increasingly clear that Venus was unlikely to have liquid bodies of water but designs for the Soviet
Venera probes still considered the possibility of a water landing as late as 1964.
Venera 7 The
Venera 7 probe, launched in August 1970, was the first one designed to survive Venus's surface conditions and to make a
soft landing. Massively overbuilt to ensure survival, it had few experiments on board, and scientific output from the mission was further limited due to an internal switchboard failure that stuck in the "transmit temperature" position. Still, the control scientists succeeded in extrapolating the pressure (90 atm) from the temperature data with , which resulted from the first direct surface measurements. The Doppler measurements of the Venera 4 to 7 probes were the first evidence of the existence of zonal winds with high speeds of up to 100 metres per second (330 ft/s, 362 km/h, 225 mph) in the Venusian atmosphere (
super rotation). Along with the pressure and temperature data acquired Venera 7 also measured atmospheric composition. When the system was switched to radio altimeter mode the antenna operated at an 8-centimeter wavelength band to send and receive signals off of the Venusian surface over a period of 0.67 milliseconds. The results were a detailed map of the reflectivity distribution over the surface of the Venusian Northern Hemisphere. The linear distance measurements that were taken ranged from 91 to 182 kilometers. The twin Soviet spacecraft flew in near-polar elliptical orbits and succeeded in mapping the top half of the northern atmosphere (from the north pole to 30 degrees N latitude, about 115 million square kilometers or 71 million square miles) by the end of the main mission. An altimeter provided topographical data with a height resolution of 50 m (164 feet), and an East German instrument mapped surface temperature variations.
VeGa probes The
VeGa (Cyrillic: ВеГа) probes to Venus and
comet 1/P Halley launched in 1984 also used this basic Venera design, including landers but also atmospheric balloons which relayed data for about two days. "VeGa" is a
portmanteau of the words "Venera" (
Venus in Russian) and "Gallei" (
Halley in Russian). ==Future==