ThePioneer Venus Orbiter, also known asPioneer Venus 1 orPioneer 12, was a mission toVenus conducted byNASA as part of thePioneer Venus project. Launched in May 1978 atop anAtlas-Centaur rocket, the spacecraft was inserted into anelliptical orbit around Venus on December 4, 1978. It returned data from Venus until October 1992.[2][4]
The spacecraft conductedradar altimetry observations allowing the first global topographic map of the Venusian surface to be constructed.
Manufactured byHughes Aircraft Company, thePioneer Venus Orbiter was based on the HS-507bus.[5] The spacecraft was a flat cylinder, 2.5 meters (8.2 ft) in diameter and 1.2 meters (3.9 ft) long. All instruments and spacecraft subsystems were mounted on the forward end of the cylinder, except themagnetometer, which was at the end of a 4.7 meters (15 ft) boom. Asolar array extended around the circumference of the cylinder. A 1.09 metres (3 ft 7 in) despun dishantenna providedS andX band communication withEarth. AStar 24solid rocket motor was integrated into the spacecraft to provide the thrust to enter orbit around Venus.[5]
The Orbiter Cloud Photopolarimeter was used to measure the vertical distribution ofclouds on Venus. It was a photo-polarimeter built by theGoddard Institute for Space Studies (GISS), similar toPioneer 10 andPioneer 11 imaging photopolarimeter (IPP). The principal investigator was J. Hansen, later succeeded by L. Travis. The instrument had a mass of 5 kilograms and consumed 5.4 watts of power.
The Orbiter Radar Mapper Instrument was designed to determine the topography and surface characteristics of Venus. It was a radar system developed by theMassachusetts Institute of Technology (MIT), with G. Pettengill serving as the principal investigator. Weighing 9 kilograms and consuming 18 watts, the instrument operated when the spacecraft was within 4,700 kilometres (2,900 mi) of the planet. It transmitted a 20-wattS-band signal at 1.757Gigahertz and achieved a surface mapping resolution of 23 by 7 kilometres (14.3 mi × 4.3 mi) atperiapsis.
The Orbiter Infrared Radiometer was used to measureinfrared emissions fromVenus's atmosphere. It was constructed by theJet Propulsion Laboratory (JPL), and the principal investigator was F. Taylor. The instrument had a mass of 5.9 kilograms and required 5.2 watts of power.
The Orbiter Ultraviolet Spectrometer measured scattered and emittedultraviolet light from Venus. Built by theLaboratory for Atmospheric and Space Physics (LASP), its principal investigator was A.I.F. Stewart. The spectrometer weighed 3.1 kilograms and consumed 1.7 watts of power.
The Orbiter NeutralMass Spectrometer was used to determine the composition of Venus's upper atmosphere. Manufactured by theGoddard Space Flight Center (GSFC), it was managed by principal investigator H. Neimann. The instrument had a mass of 3.8 kilograms and consumed 12 watts.
The OrbiterPlasma Analyzer measured properties of thesolar wind. Developed at theAmes Research Center (ARC), the instrument was led by principal investigator J. Wolfe, who was later succeeded by A. Barnes. It had a mass of 3.9 kilograms and required 5 watts of power.
The Orbiter Magnetometer was designed to characterize Venus’smagnetic field. It was built by theUniversity of California, Los Angeles (UCLA), with C. Russell as the principal investigator. The 2-kilogram instrument consumed 2.2 watts of power and was mounted on a 4.7-meter boom to reduce spacecraft interference.
The Orbiter Electric Field Detector studied electric fields in the Venusian environment. Built byTRW and led by principal investigator F. Scarf, it had a mass of 0.8 kilograms and used only 0.7 watts of power.
The OrbiterElectron Temperature Probe investigated the thermal properties of Venus’sionosphere. It was developed by theGoddard Space Flight Center (GSFC) under the direction of principal investigator L. Brace. The probe had a mass of 2.2 kilograms and consumed 4.8 watts.
The Orbiter Ion Mass Spectrometer was used to characterize the ion population in the ionosphere of Venus. Built by theGoddard Space Flight Center (GSFC), it was managed by principal investigator H. Taylor. The instrument had a mass of 3 kilograms and required 1.5 watts of power.
The Orbiter Retarding Potential Analyzer studied ionospheric particles. It was developed at the Lockheed Palo Alto Research Laboratory (LPARL), with W. Knudsen as the principal investigator. This instrument weighed 2.8 kilograms and consumed 2.4 watts of power.
The Orbiter Gamma-Ray Burst Detector recordedgamma-ray burst events. It was constructed by theLos Alamos Scientific Laboratory (LASL), and W. Evans served as the principal investigator. The instrument had a mass of 2.8 kilograms.
The OGPE utilized dual-frequency radio signals to investigate how Venus's atmosphere affects radio wave propagation. By analyzing signal attenuation and phase shifts, the experiment aimed to deduce atmospheric properties such as electron density and refractive index. This information is crucial for understanding the structure and composition of Venus's ionosphere.[7][8] T. Croft fromSRI was the principal investigator.
The OAD measured the deceleration of the spacecraft due to atmospheric drag at the fringes of Venus's atmosphere. By tracking changes in the spacecraft's velocity, the experiment provided data on atmospheric density and its variations with altitude and solar activity. G. Keating fromLRC was the principal investigator.
DLBI, also known as delta-VLBI, involved simultaneous observations of the spacecraft's radio signals by widely separated Earth-based antennas. By measuring the time difference in signal arrival, the experiment achieved precise spacecraft positioning, enhancing orbit determination and navigation accuracy.
Orbiter Atmospheric and Solar Wind Turbulence Experiment (OTUR)
OTUR focused on detecting and analyzing turbulence in Venus's upper atmosphere and the solar wind. By examining fluctuations in radio signal properties, the experiment aimed to understand the dynamic interactions between the solar wind and Venus's ionosphere. T. Croft from SRI was the principal investigator.
The ORO experiment employed radio occultation techniques, where the spacecraft's radio signals passed through Venus's atmosphere to Earth. By analyzing changes in signal frequency and amplitude, the experiment derived vertical profiles of atmospheric temperature, pressure, and electron density. A. Kliore from JPL was the principal investigator.
Orbiter Internal Density Distribution Experiment (OIDD)
OIDD aimed to map Venus's gravitational field by tracking the spacecraft's orbit perturbations. Variations in gravity indicated differences in mass distribution within the planet, providing insights into its internal structure and composition.[9] R. Phillips from JPL was the principal investigator.
The OCM focused on precise measurements of the spacecraft's trajectory to study Venus's gravitational field and test aspects of celestial mechanics. Data from this experiment contributed to refining models of planetary motion and gravitational interactions. I. Shapiro from MIT was the principal investigator
From Venus orbit insertion to July 1980,periapsis was held between 142 and 253 kilometres (88 and 157 mi) (at 17 degrees north latitude) to facilitate radar and ionospheric measurements. The spacecraft was in a 24-hour orbit with anapoapsis of 66,900 kilometers (41,600 mi). Thereafter, the periapsis was allowed to rise to a maximum of 2,290 kilometres (1,420 mi) and then fall, to conserve fuel.
In 1991, the Radar Mapper was reactivated to investigate previously inaccessible southern portions of the planet, in conjunction with the recently arrivedMagellan spacecraft. In May 1992, the probe began the final phase of its mission, in which the periapsis was held between 150 and 250 kilometres (93 and 155 mi), until the spacecraft's propellant was exhausted, after which the orbitdecayed naturally. The spacecraft continued to return data until 8 October 1992, with the last signals being received at 19:22 UTC.[4] ThePioneer Venus Orbiter disintegrated uponentering theatmosphere of Venus on October 22, 1992.[2]
Venus byPioneer Venus Orbiter (13 December 1978)
Venus in ultraviolet light byPioneer Venus Orbiter (5 February 1979)
Venus in ultraviolet light byPioneer Venus Orbiter (February 26, 1979)
Map of Venus produced fromPioneer Venus Orbiter radar data
Perspective view of Ishtar Terra was derived from data obtained by thePioneer Venus Orbiter's altimetry radar instrument
From its orbit of Venus, thePioneer Venus Orbiter was able to observeHalley'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.[11]
The extended mission allowed the spacecraft controllers to make several comet observations that were never part of the original mission objectives. The tilt of the spacecraft was altered during these comet observations so that the Ultraviolet Spectrometer (OUVS) could view the comets rather than Venus. CometsEncke (April 13–16, 1984),Giacobini-Zinner (September 8–15, 1985), Halley (December 27, 1985 - March 9, 1986),Wilson (March 13 - May 2, 1987), NTT (April 8, 1987), and McNaught (November 19–24, 1987) were all observed in this way.[10]
Orbit attitude ofPioneer Venus Orbiter between 1978–1980 and 1992
Taylor, F. W.; Diner, D. J.; Elson, L. S.; McCleese, D. J.; Martonchik, J. V.; Delderfield, J.; Bradley, S. P.; Schofield, J. T.; Gille, J. C.; Coffey, M. T. (6 July 1979). "Temperature, Cloud Structure, and Dynamics of Venus Middle Atmosphere by Infrared Remote Sensing from Pioneer Orbiter".Science.205 (4401):65–67.Bibcode:1979Sci...205...65T.doi:10.1126/science.205.4401.65.JSTOR1748517.PMID17778904.S2CID2023608.
Pollack, James B.; Ragent, Boris; Boese, Robert; Tomasko, Martin G.; Blamont, Jacques; Knollenberg, Robert G.; Esposito, Larry W.; Stewart, A. Ian; Travis, Lawrence (6 July 1979). "Nature of the Ultraviolet Absorber in the Venus Clouds: Inferences Based on Pioneer Venus Data".Science.205 (4401):76–79.Bibcode:1979Sci...205...76P.doi:10.1126/science.205.4401.76.JSTOR1748521.PMID17778908.S2CID28250903.
Taylor, F. W.; Diner, D. J.; Elson, L. S.; McCleese, D. J.; Martonchik, J. V.; Delderfield, J.; Bradley, S. P.; Schofield, J. T.; Gille, J. C.; Coffey, M. T. (6 July 1979). "Temperature, Cloud Structure, and Dynamics of Venus Middle Atmosphere by Infrared Remote Sensing from Pioneer Orbiter".Science.205 (4401):65–67.Bibcode:1979Sci...205...65T.doi:10.1126/science.205.4401.65.JSTOR1748517.PMID17778904.S2CID2023608.
Pollack, James B.; Ragent, Boris; Boese, Robert; Tomasko, Martin G.; Blamont, Jacques; Knollenberg, Robert G.; Esposito, Larry W.; Stewart, A. Ian; Travis, Lawrence (6 July 1979). "Nature of the Ultraviolet Absorber in the Venus Clouds: Inferences Based on Pioneer Venus Data".Science.205 (4401):76–79.Bibcode:1979Sci...205...76P.doi:10.1126/science.205.4401.76.JSTOR1748521.PMID17778908.S2CID28250903.
Missions are ordered by launch date.† indicates failure en route or before any data returned.‡ indicates use of the planet as agravity assist en route to another destination.
Payloads are separated by bullets ( · ), launches by pipes ( | ). Crewed flights are indicated inunderline. Uncatalogued launch failures are listed initalics. Payloads deployed from other spacecraft are denoted in (brackets).
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