only one of the four probes which continued to send radio signals back after impact, for over an hour. Launch The Pioneer Venus Multiprobe was launched by an Atlas SLV-3D Centaur-D1AR rocket, which flew from Launch Complex 36A at the Cape Canaveral Air Force Station. The launch occurred at 07:33 on August 8, 1978, and deployed the Multiprobe into heliocentric orbit for its coast to Venus. Arrival at Venus Prior to the Multiprobe reaching Venus, the four probes were deployed from the main bus. The large probe was released on November 16, 1978, and the three small probes on November 20. All four probes and the bus reached Venus on December 9, 1978. The large probe was the first to enter the atmosphere, at 18:45:32 UTC, followed over the next 11 minutes by the other three probes. The bus entered the atmosphere at 20:21:52 UTC and returned its last signal at 20:22:55 from an altitude of . The four probes transmitted data until they impacted the surface of Venus. The Day Probe survived the impact, returning data from the surface for 67 minutes and 37 seconds after reaching the surface. Scientific results Below the altitude of the temperatures measured by the four probes are identical to within a few degrees. They are between on the surface. The ground pressure is between . Nephelometers identified three cloud layers with different characteristics. The most remarkable discovery was that the ratio of 36argon / 40argon isotopes was much higher than in the Earth's atmosphere, which seems to indicate that the genesis of the Venusian atmosphere is very different from that of Earth. The reconstituted trajectory of atmospheric probes was determined that the wind averaged a speed of in the middle cloud layer at at the base of these clouds and just at the ground. Overall data from airborne sensors confirmed, while specifying the data obtained by the Soviet space probe Venera program that preceded this mission. Trajectory Diagram of the PVM's path to planet Venus from Earth in 1978, and this also notes the launch of the Pioneer Venus Orbiter which took place that year also. Graphic overview See also Pioneer Venus Orbiter List of missions to Venus Timeline of artificial satellites and space probes Galileo Probe (Jupiter atmospheric probe delivered by Galileo spacecraft) List of spacecraft powered by non-rechargeable batteries References External links NASA: Pioneer Venus Project Information Pioneer Venus Program Page