urn:nasa:pds:context:instrument:pvo.oims 2.0 1.20.0.0 Product_Context 2020-08-26 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model 2024-04-02 2.0 Updated to IM 1.20.0.0 urn:nasa:pds:context:instrument_host:spacecraft.pvo instrument_to_instrument_host Brinton, H.C., L.R. Scott, M.W. Pharo, III, and J.T.C. Coulson, The Bennett ion-mass spectrometer on Atmosphere Explorer-C and -E, Radio Sci., vol. 8, 323, 1973. reference.BRINTONETAL1973 Taylor, H.A., Jr., H.C. Brinton, S.J. Bauer, R.E. Hartle, T.M. Donahue, P.A. Cloutier, F.C. Michel, R.E. Daniell, Jr., B.H. Blackwell, Ionosphere of Venus: First observations of the dayside ion composition near dawn and dusk, Science, vol. 203, 752, 1979. reference.TAYLORETAL1979C Taylor, H.A., Jr., H.C. Brinton, S.J. Bauer, R.E. Hartle, P.A. Cloutier, F.C. Michel, R.E. Daniell, Jr., T.M. Donahue, R.C. Maehl, Ionosphere of Venus: First observations of the effects of dynamics on the dayside ion composition, Science, vol. 203, 755, 1979. reference.TAYLORETAL1979D ION MASS SPECTROMETER (OIMS) for PIONEER VENUS Mass Spectrometer not applicable not applicable INSTRUMENT OVERVIEW =================== Using the Pioneer Venus Orbiter Ion Mass Spectrometer (OIMS), composition and concentration of thermal positive ions in the ionosphere of Venus were determined and interpreted in terms of vertical and horizontal components. These provided information on provided information on the solar wind interaction with Venus, upper atmosphere photochemistry, and the mass and heat transport characteristics of the atmosphere. The instrument used was a Bennett radio-frequency mass spectrometer based on the design of those flown on OGO and Atmospheric Explorer satellites. A mass range of 1-56 amu was covered with a variety of automatic scan-search modes available. Identical Ion Mass Spectrometers were mounted on the Pioneer Venus Orbiter and the Probe Bus. Each spectrometer, with a mass of 3.0 kg, consisted of two parts, an analyzer tube and an electronics package. The electronics package held printed circuit boards inside a machined magnesium housing mounted inside the spacecraft. The package contained low- and high-gain pre-amplifiers, amplifiers, a log A/D converter, an RF generator, voltage regulator, command and control, and data handling. It uses 1.5 W of power, and functions to supply RF and DC potentials to the ion analyzer tube; detect and amplify ion current flowing to the collectors; digitize, process, and format data for telemetry; configure the sensor for subsequent measurements; and decode and implement commands. The analyzer tube is a hollow cylinder of aluminum containing a series of knitted tungsten mesh grids and gold-plated aluminum spacers. These are backed by a supressor, a low-gain collector and a high-gain collector. At the head of the tube is a guard ring and an accelerating voltage. The analyzer can be set to measure any of 16 common ion masses from 1 to 56 amu (1, 2, 4, 8, 12, 14, 16, 17, 18, 24, 28, 30, 32, 40, 44, and 56 amu). It also has the ability to produce simulated ion currents for calibration. The instrument operated with repeated explore/adapt cycles, each 6.3 seconds in duration. The first 1.8 seconds of the cycle is the explore portion, which consists of measuring each of the 16 pre-selected masses for approximately 0.1 second each. In the 4.5 second adapt portion of the cycle, up to 8 ions that are found to be present in the explore portion are measured repeatedly. The ion current values from each measurement are sampled, held for A/D conversion, and transfered to telemetry storage registers.