The Pioneer Venus Orbiter, also known as Pioneer Venus 1 or Pioneer 12, was a mission to Venus conducted by NASA as part of the Pioneer Venus project. Launched in May 1978 atop an Atlas-Centaur rocket, the spacecraft was inserted into an elliptical orbit around Venus on December 4, 1978. It returned data from Venus until October 1992.[2][4]
Launch and arrival at Venus
Orbit attitude of Pioneer Venus 1 between 1978–1980 and 1992
Manufactured by Hughes Aircraft Company, the Pioneer Venus Orbiter was based on the HS-507 bus.[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 the magnetometer, which was at the end of a 4.7 meters (15 ft) boom. A solar array extended around the circumference of the cylinder. A 1.09 metres (3 ft 7 in) despun dish antenna provided S and X band communication with Earth. A Star-24 solid rocket motor was integrated into the spacecraft to provide the thrust to enter orbit around Venus.[5]
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 an apoapsis 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 arrived Magellan spacecraft. In May 1992, Pioneer Venus 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 orbit decayed naturally. The spacecraft continued to return data until 8 October 1992, with the last signals being received at 19:22 UTC.[4] The Pioneer Venus Orbiter disintegrated upon entering the atmosphere of Venus on October 22, 1992.[2]
Instruments
A map of Venus produced from Pioneer data
The Pioneer Venus Orbiter carried 17 experiments with a total mass of 45 kilograms (99 lb):[6]
An image of Venus in ultraviolet light by the Pioneer Venus Orbiter
a cloud photo-polarimeter (OCPP) to measure the vertical distribution of the clouds, similar to Pioneer 10 and Pioneer 11 imaging photo-polarimeter (IPP)
a surface radar mapper (ORAD) to determine topography and surface characteristics. Observations could only be conducted when the probe was closer than 4,700 kilometres (2,900 mi) 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 23 by 7 kilometres (14.3 mi × 4.3 mi).
Orbiter Internal Density Distribution Experiments (OIDD)
Orbiter Celestial Mechanics Experiments (OCM)
High-energy astronomy
Orbiter Gamma Burst Detector (OGBD)
Observations of Comets
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.[8]
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. Comets Encke (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.[7]
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, Harry A.; Brinton, Henry C.; Bauer, Siegfried J.; Hartle, Richard E.; Cloutier, Paul A.; Daniell, Robert E.; Donahue, Thomas M. (6 July 1979). "Ionosphere of Venus: First Observations of Day-Night Variations of the Ion Composition". Science. 205 (4401): 96–99. Bibcode:1979Sci...205...96T. doi:10.1126/science.205.4401.96. JSTOR1748528. PMID17778915. S2CID11269827.
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, Harry A.; Brinton, Henry C.; Bauer, Siegfried J.; Hartle, Richard E.; Cloutier, Paul A.; Daniell, Robert E.; Donahue, Thomas M. (6 July 1979). "Ionosphere of Venus: First Observations of Day-Night Variations of the Ion Composition". Science. 205 (4401): 96–99. Bibcode:1979Sci...205...96T. doi:10.1126/science.205.4401.96. JSTOR1748528. PMID17778915. S2CID11269827.
Payloads are separated by bullets ( · ), launches by pipes ( | ). Crewed flights are indicated in underline. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in (brackets).
