be conducted when the probe was closer than over the planet. A 20 watt S-band signal (1.757 gigahertz) was sent to the surface that reflected it, with the probe analyzing the echo. Resolution at periapsis was . an infrared radiometer (OIR) to measure IR emissions from Venus' atmosphere an airglow ultraviolet spectrometer (OUVS) to measure scattered and emitted UV light a neutral mass spectrometer (ONMS) to determine the composition of the upper atmosphere a solar wind plasma analyzer (OPA) to measure properties of the solar wind a magnetometer (OMAG) to characterize the magnetic field at Venus an electric field detector (OEFD) to study the solar wind and its interactions an electron temperature (OETP) to study the thermal properties of the ionosphere an ion mass spectrometer (OIMS) to characterize the ionospheric ion population a charged particle retarding potential analyzer (ORPA) to study ionospheric particles two radio science experiments to determine the gravity field of Venus a radio occultation experiment to characterize the atmosphere an atmospheric drag experiment to study the upper atmosphere a radio science atmospheric and solar wind turbulence experiment a gamma ray burst (OGBD) detector to record gamma ray burst events The spacecraft conducted radar altimetry observations allowing the first global topographic map of the Venusian surface to be constructed. Observations of Halley's Comet From its orbit of Venus, the Pioneer Venus Orbiter was able to observe Halley's Comet when it was unobservable from Earth due to its proximity to the sun during February 1986. UV spectrometer observations monitored the loss of water from the comet's nucleus at perihelion on February 9. See also Pioneer Venus Multiprobe List of missions to Venus Timeline of artificial satellites and space probes References External links NASA: Pioneer Venus Project Information Pioneer Venus Program Page by NASA's Solar System Exploration Kasprzak, W. T – The Pioneer Venus Orbiter: 11 years of data. (May 1, 1990) – NASA Science Magazine in year 1979 issue 4401 1978 in spaceflight Missions to Venus Pioneer program Spacecraft launched by Atlas-Centaur rockets Destroyed space probes Spacecraft launched in 1978