|
Table of Contents Fig 5-4 (Orbit insertion approach - 1) Fig 5-3 (Orbit insertion geometry) Fig 5-5 (Orbit insertion approach - 2) Fig 5-6 (Orbit insertion approach - 3) Probe Anomalies: Fig 5-17 (mission phases and periapsis altitude) Pioneer Venus Orbiter Prelaunch Pioneer Venus Orbiter Cometary Observing Phase Fig 5-19 (comet Halley encounter geometry) Pioneer Venus Orbiter Phase 3 (Re-Entry) Pioneer Venus Multiprobe Launch Pioneer Venus Multiprobe Encounter Table 2-2 (Instruments, Acronyms & PI) Fig 3-13 (Communication system) Orbital Characteristics: (Table 5-6, p150, Fimmel et al, 1995) Fig 5-7 (Venus imaging geometry) Fig 5-17 (mission phases and periapsis altitude) Fig 5-15 (Prime mission periapsis evolution) Table 5-6 (Prime mission periapsis values) Fig 5-18 (Re-entry periapsis alt) Probe Entry Timing Events: (Table 5-2, p141, Fimmel et al, 1995) Probe Entry Impacts: (Table 5-3, p144, Fimmel et al, 1995) Bus Entry and Location of Sun and Earth: (Table 5-4, p144, Fimmel et al, 1995) Fig 3-19 (Large/small probe alt vs time) |
The Pioneer mission set the stage for U.S. space exploration. Pioneer 1 was the first man-made object to escape the Earth's gravitational field. Later Pioneer 4 was the first spacecraft to fly to the moon, Pioneer 10 was the first to Jupiter, Pioneer 11 was the first to Saturn and Pioneer 12 was the first U.S. spacecraft to orbit another planet, Venus. The following table summarizes the Pioneer spacecraft and scientific objectives of the Pioneer mission.
The focus of this document is on Pioneer Venus (12), the last spacecraft in a mission of firsts in space exploration. Pioneer Venus separated into two spacecraft on Aug 8, 1978: an Orbiter (PVO) and a Multiprobe. The latter was separated into five separate vehicles near Venus. These were the probe transporter (called the Bus), a large atmospheric entry probe (dubbed Sounder) and three identical smaller probes (called North, Day, and Night in accordance with their entry locations). At Venus all six spacecraft communicated directly back to the Earth-based Deep Space Network (DSN) and, in the case of the Multiprobe mission, to two special receiving sites near Guam and Santiago (Chile). p. 37 Fig 2-4 (PATH TO VENUS, FIMMEL ET AL, 1995)
The Orbiter encountered Venus on December 4, 1978, and was inserted into orbit on that same day after a Type II interplanetary cruise trajectory lasting 198 days and covering more than 500 x 10^6 km. Twelve scientific experiments were included in the instrumentation payload and a few radio science investigations were planned using the S-band telemetry signal carrier and a special X-band beacon included as part of the Orbiter hardware. Scientific observations were made both in-cruise and in-orbit. The nominal in-orbit mission was designed to extend for one Venus year (243 days) with an orbital period of approximately 24 hours. At the end of the nominal mission (Aug 14, 1979), the spacecraft periapsis was raised from its 150-200 km altitude to more then 2000 km to conserve fuel for an extended mission. As fuel began to run out and periapsis began to drop back down into the Venusian atmosphere the end of the mission could no longer be avoided. On Oct 8, 1992 the Orbiter made its final encounter with the Venus atmosphere. More then 13 years had passed the end of the nominal mission. p. 133 Fig 5-4 (ORBIT INSERTION APPROACH - 1, FIMMEL ET AL, 1995)
p. 131 Fig 5-3 (ORBIT INSERTION GEOMETRY, FIMMEL ET AL, 1995)
p. 135 Fig 5-5 (ORBIT INSERTION APPROPACH - 2, FIMMEL ET AL, 1995)
p. 136 Fig 5-6 (ORBIT INSERTION APPROACH - 3, FIMMEL ET AL, 1995)
During the nominal Orbiter mission all but two experiments operated 100% successfully. One, the Radar Mapper, produced unusable data for a 32-day period from December 18, 1978 to January 19, 1979. The radar instrument was successfully used during the extended mission until the periapsis altitude rose too high. The instrument was not used during the final re-entry phase of the mission at low periapsis due to the success of the Magellan radar mapping mission. The Infrared Radiometer was the other instrument to fail during the nominal mission. It failed to operate after February 14, 1979, but had collected and enormous quantity of valuable information prior to that date. Later in the mission (orbit 3601) the magnetometer data pickup failed such that data from only one of the three sensors (P sensor) was returned to Earth in the telemetry stream. The Multiprobe encountered Venus on December 9, 1978 (just five days following the Orbiter insertion) after a Type I interplanetary cruise trajectory lasting 123 days and covering 330 x 106 km. The Sounder was released from the Bus on November 15, 1978, and the three small probes were released simultaneously on November 19, 1978. All probes entered (200-km altitude) the Venus upper atmosphere within a time span of about 11 min and descended to the surface in a period from 53 to 56 min, all the time performing scientific observations. The Bus made a delayed (~90 min) entry relative to the probes into Venus' upper atmosphere and burned up at about 110-km altitude since it was not protected, as were the probes, with entry heat shields. Scientific observations were made during the one-minute interval from 700 to 110 km. Although not designed for `survival' after impact, the Day probe managed to transmit for over 67 min on the surface (it in fact continued to transmit after the Bus transmission ceased). Seven scientific experiments were included in the Sounder instrumentation payload, three identical experiments in each small probe, and two in the Bus. Again, Radio Science experiments were performed using, separately or together, the S-band telemetry signal carriers emanating from the spacecraft and received at the Earth-based tracking stations. In general, all instruments performed nominally, although certain instruments behaved anomalously on all four probes near the surface. PROBE ANOMALIES: (Table 5-5, p. 146 FIMMEL ET AL, 1995)
The long 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 (Sept 8-15, 1985), Halley (Dec 27, 1985 -Mar 9, 1986), Wilson (Mar 13 - May 2, 1987), NTT (April 8, 1987), and McNaught (Nov 19-24, 1987) were all observed in this way. The Pioneer Venus Orbiter (PVO) phases are presented followed by the Pioneer Venus Multiprobe (PVMP) phases. p. 154 Fig 5-17 (MISSION PHASES AND PERIAPSIS ALTITUDE, FIMMEL ET AL, 1995)
PIONEER VENUS ORBITER PRELAUNCH The spacecraft was delivered to the launch site at Kennedy Space Center on March 14, 1978. Spacecraft Id : PVO The spacecraft was launched atop an Atlas-Centaur from Kennedy Space Center. Spacecraft Id : PVO Two small trajectory correction maneuvers were made on June 1 and November 2, 1978. Interplanetary cruise scientific data were collected. The Pioneer Venus Orbiter completed its 300-million-mile voyage in 6+ months and was placed into Venusian orbit on December 4, 1978. Spacecraft Id : PVO The orbiter was placed into Venusian orbit on December 4, 1978, less than a week before the arrival of the Pioneer Venus Multiprobe. The planned mission ended August 4, 1979. The extended mission began August 5, 1979 and ended when the Orbiter entered the Venusian atmosphere on Oct. 8, 1992. Spacecraft Id : PVO Orbiter Phase 1 was the primary mission which began on Dec 4, 1979 at orbital insertion and ended after 1 Venusian year (243 days) on Aug. 4, 1979. During Phase 1, the orbiter periapsis was maintained between 150-200 km altitude using the main thrusters. Spacecraft Id : PVO Orbiter Phase 2 was the extended mission at high periapsis which began on Aug. 5, 1979, immediately following Phase 1. Phase 2 was the period where the project flight controllers did not control periapsis altitude. Periapsis altitude was allowed to rise and fall under the influence of solar perturbations to conserve fuel. Phase 2 ended when the periapsis altitude fell below the 1000 km level in early 1991. Spacecraft Id : PVO PIONEER VENUS ORBITER COMETARY OBSERVING PHASE The long 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 (Sept 8-15, 1985), Halley (Dec 27, 1985 - Mar 9, 1986), Wilson (Mar 13 - May 2, 1987), NTT (April 8, 1987), and McNaught (Nov 19-24, 1987) were all observed in this way. Spacecraft Id : PVO p. 165 Fig 5-19 (COMET HALLEY ENCOUNTER GEOMETRY, FIMMEL ET AL, 1995)
PIONEER VENUS ORBITER PHASE 3 (RE-ENTRY) Orbiter Phase 3 was the extended mission at low periapsis which began in early 1991 when the project flight controllers could no longer afford to conserve fuel and allow the periapsis altitude to continue dropping under gravitational influence. Periapsis was maintained using the thrusters during Phase 3 until the fuel ran out. The Orbiter was able to map deeper into the upper atmosphere in Phase 3 than was prudent in Phase 1, typically in the 140-160 km range in the later stages of Phase 3. Spacecraft Id : PVO Pioneer Venus Multiprobe Launch The spacecraft was launched atop an Atlas-Centaur from Kennedy Space Center. Spacecraft Id : PVMP Pioneer Venus Multiprobe Encounter The Multiprobe encountered Venus on December 9, 1978 (just five days following the Orbiter insertion) after a Type I interplanetary cruise trajectory lasting 123 days and covering 330 x 106 km. The Sounder was released from the Bus on November 15, 1978, and the three small probes were released simultaneously on November 19, 1978. All probes entered (200-km altitude) the Venus upper atmosphere within a time span of about 11 min and descended to the surface in a period from 53 to 56 min, all the time performing scientific observations. The Bus made a delayed (~90 min) entry relative to the probes into Venus' upper atmosphere and burned up at about 110-km altitude since it was not protected, as were the probes, with entry heat shields. Scientific observations were made during the one-minute interval from 700 to 110 km. Although not designed for `survival' after impact, the Day probe managed to transmit for over 67 min on the surface (it in fact continued to transmit after the Bus transmission ceased). Seven scientific experiments were included in the Sounder instrumentation payload, three identical experiments in each small probe, and two in the Bus. Again, Radio Science experiments were performed using, separately or together, the S-band telemetry signal carriers emanating from the spacecraft and received at the Earth-based tracking stations. In general, all instruments performed nominally, although certain instruments behaved anomalously on all four probes near the surface. p. 38 Fig 2-5 (Probe impact sites FIMMEL ET AL, 1995)
Figure 2-5. Approaching Venus, the Multiprobe released its four probes toward different target areas of the planet. (Top) Artist's concept of the probes and the Bus shortly after their release. (Bottom) Diagram of the paths of the probes and their entry points on the planet in relation to the orbit of the Orbiter spacecraft.
Spacecraft Id : PVMP NASA established the Pioneer Venus Science Steering Group in Jan. 1972 in order to enlist widespread science community participation in designing the mission science requirements. This group concluded that a successful mission to Venus would answer the following list of scientific questions (Fimmel et al, 1995, Table 2-2, p25): 1) Cloud layers: What is their number and where are they located? Dothey vary over the planet? 2) Cloud forms: Are they layered, turbulent, or merely hazes? 3) Cloud physics: Are the clouds opaque? What are the sizes of the cloud particles? What is the density of cloud particles? 4) Cloud composition: What is the chemical composition of the clouds? Is it different in the different layers? 5) Solar heating: Where is the solar radiation deposited in the atmosphere? 6) Deep circulation: What is the nature of the wind in the lower regions of the atmosphere? Is there any measurable wind near the surface? 7) Deep driving forces: What are the horizontal differences in temperature in the deep atmosphere? 8) Driving force for the 4-day circulation: What are the horizontal temperature differences at the top of the cloud layer that could cause the high winds there? 9) Loss of water: Has water been lost from Venus? If so, how? 10) Carbon dioxide stability: Why is molecular CO2 stable in the upper atmosphere? 11) Surface composition: What is the composition of the crustal rocks? 12) Seismic activity: What is its level? 13) Earth tides: Do tidal effects from Earth exist at Venus, and if so, how strong are they? 14) Gravitational moments: What id the figure of the planet? What are the higher order gravitational moments? 15) Extent of the 4-day circulation: How does this circulation vary with latitude and depth in the Venusian atmosphere? 16) Vertical temperature structure: Is there an isothermal region? Are there other departures from adiabaticity? What is the structure near the cloud tops? 17) Ionospheric motions: Are these motions sufficient to transport ionization from the day to night hemisphere? 18) Turbulence: How much turbulence is there deep in the atmosphere? 19) Ion chemistry: What is the chemistry of the ionosphere? 20) Exospheric temperature: What is the temperature and does it vary over the planet? 21) Topography: What features exist on the surface of the planet? How do they relate to the thermal maps? 22) Magnetic moments: Does the planet have any internal magnetism? 23) Bulk atmospheric composition: What are the major gases in the Venus atmosphere? How do they vary with altitude? 24) Anemopause: How does the solar wind interact with the planet? The wide range of science questions to be answered by the Pioneer Venus mission could not be answered by an orbiter mission alone. An orbiter could address the questions regarding the upper atmosphere, ionosphere, solar wind, and surface topography, but a probe would be needed to make in situ measurements in the lower atmosphere. Likewise, a single probe would be inadequate to address the all of the questions posed about the lower atmosphere. Multiple probes targeting different parts of the planet simultaneously were required to meet the science objectives. Thus the Pioneer Venus mission developed into an Orbiter and Multiprobe spacecraft. A large number of scientific instruments were required on both the orbiter and the various probes in order to meet the mission science objectives. The orbiter carried 4 remote sensing instruments and 8 in situ experiments. In addition, several radio science experiments were performed using the S-band telemetry signal plus a special X-band beacon that was included on the Orbiter. The first letter of the instrument acronym designates which component of the spacecraft carried the instrument: O for Orbiter, L for Large Probe, S for the Small Probes, and B for the Bus. The remote sensing instruments were: 1) Cloud Photopolarimeter (OCPP), 2) Radar mapper (ORAD), 3) Ultraviolet Spectrometer (OUVS), and 4) Infrared Radiometer (OIR). The in situ instruments included 4 plasma and gamma ray detectors: 1) Ion Mass Spectrometer (OIMS), 2) Electron Temperature Probe (OETP), 3) Retarding Potential Analyzer (ORPA), 4) Plasma Analyzer (OPA), and 5) Gamma Burst Detector (OGBD). In addition, the neutral atmosphere composition was sampled by the Neutral Mass Spectrometer (ONMS), the magnetic field was measured by MAG (OMAG) and the wave electric fields were measured by the Electric Field Detector (OEFD). The large probe, bus, and small probes each carried slightly different instrumentation. The probe instruments were: Neutral Mass Spectrometers (LNMS, SNMS, BNMS), Gas Chromatograph (LGC), Atmospheric Structure experiment (LAS, SAS), Nephelometers (LN, SN), Cloud Particle Size (LCPS), Solar Flux Radiometer (LSFR), Infrared Radiometer (LIR), Net Flux Radiometer (SNFR), Finally, the spacecraft and probe telemetry signal distortions were used to probe the Venus atmosphere and ionosphere. The radio science experiments included the Atmospheric Propagation Experiment (OGPE), Atmospheric Drag (OAD), Differential Long Baseline Interferometry (DBLI), Dopler tracking of the probes (MWIN), Atmospheric Turbulence (MTUR/OTUR), Dual Frequency Occultation (ORO), Internal Density (OIDD), and finally, Celestial Mechanics experiments (OCM)." p. 29 Table 2-2 (Instruments, Acronyms & PI, FIMMEL ET AL, 1995) Table 2-2. Science Instruments: Project Acronyms and Principal Investigators
Composition and Structure of the Atmosphere
The Pioneer Venus mission objectives dictated the requirement for two spacecraft designs designated the Orbiter and the Multiprobe. (The Multiprobe is defined as the Bus with the one Large Probe and three identical Small Probes attached in the launch/cruise configuration.) The conceptual designs of these spacecraft resulted from Phase B studies conducted from October 1972 to July 1973, and after selection of the spacecraft contractor, Hughes Aircraft Company, in February 1974, a spacecraft conceptual design review was conducted in November 1974. The Orbiter and Multiprobe utilized the same designs to the maximum extent possible to minimize costs. In addition, designs of subsystems or portions of subsystems from previous spacecraft designs (such as OSO and Intelsat) were utilized to the maximum extent possible with little or no modifications. This commonality in the two spacecraft designs also resulted in certain amounts of commonality in ground test equipment and test software as well as commonality in spacecraft flight operations and associated software. [ Extracted from: Nothwang, George J., `Pioneer Venus Spacecraft Design and Operation', IEEE Transactions on Geoscience and Remote Sensing, vol. GE-18, No. 1, January 1980]. The main body of the spacecraft is a flat cylinder 2.5 meters in diameter and 1.2 meters high. In the upper end of this cylinder there is a circular equipment shelf with an area of 4.37 square meters on which all the scientific instruments and electronic subsystems are mounted. The shelf is mounted on the forward end of a thrust tube that connects the spacecraft to the launch vehicle. Below the shelf, 15 thermal louvers control heat radiation from an equipment compartment located between the shelf and the top of the spacecraft. A cylindrical solar array attached to the shelf by 24 brackets forms the circumference of the flat cylinder of the spacecraft. The spacecraft spins about its cylindrical axis wit ha nominal spin period of 12 seconds. On top of the spacecraft, a 1.09 meter diameter, despun, high-gain, parabolic dish antenna is mounted on a mast so that its line of sight clears equipment mounted outside the spacecraft. The despun design allows the antenna to be mechanically directed to Earth from the spinning spacecraft. The antenna operates at S- and X-bands. The spacecraft also carries a solid propellant rocket motor. Including the antenna mast, the Orbiter is almost 4.5 meters high, and it weighed 553 kg when launched. The launch weight included 45 kg of scientific instruments and 179 kg of rocket propellant. p. 56 Fig 3-2 (PVO main body, FIMMEL ET AL, 1995)
p. 60 Fig 3-9 (Orbiter x-section, FIMMEL ET AL, 1995)
p. 64 Fig 3-12 (antenna, FIMMEL ET AL, 1995)
p. 65 Fig 3-13 (Communication system, FIMMEL ET AL, 1995)
p. 62 Fig 3-11 (telemetry formats, FIMMEL ET AL, 1995)
Figure 3-11. Assignment of data formats for the Orbiter appear in this figure. PER refers to the periapsis portion of the orbit, APO to apoapis. PBK is for playback. The various scientific instruments appear by their project acronyms. Orbital Characteristics: (Table 5-6, p. 150, Fimmel et al, 1995)
p. 137 Fig 5-7 (Venus imaging geometry, FIMMEL ET AL, 1995)
p. 154 Fig 5-17 (mission phases and periapsis altitude)
p. 151 Fig 5-15 (Prime mission periapsis evolution, FIMMEL ET AL, 1995)
p. 162 Fig 5-18 (Re-entry periapsis alt, FIMMEL ET AL, 1995)
p. 166 Fig 5-20 (re-entry, FIMMEL ET AL, 1995)
Platform Descriptions MAGNETOMETER BOOM An 4.8 meter long boom (188.9 inches) that was unfurled and extended automatically after launch. The magnetometer boom is located 240 degrees from the X-axis of the spacecraft coordinate system, measured in towards the Y-axis (in the spin direction) of the spin plane (XY). The total distance from the end of the boom to the orbiter spin axis is 5.94 meters (234.0 inches). Mass: 290 kg (bus), 315 kg (large probe),
90 kg (each small probe) The Pioneer Venus Multiprobe consisted of a bus which carried one large and three small atmospheric probes. The large probe was released on November 16, 1978 and the three small probes on November 20. All four probes entered the Venus atmosphere on December 9, followed by the bus. p. 67 Fig 3-14 (Multiprobe, FIMMEL ET AL, 1995)
The Pioneer Venus large probe was equipped with 7 science experiments, contained within a sealed spherical pressure vessel. This pressure vessel was encased in a nose cone and aft protective cover. After deceleration from initial atmospheric entry at about 11.5 km/s near the equator on the Venus night side, a parachute was deployed at 47 km altitude. The large probe was about 1.5 m in diameter and the pressure vessel itself was 73.2 cm in diameter. The science experiments were: * a neutral mass spectrometer to measure
the atmospheric composition p. 71 Fig 3-17 (Large probe, FIMMEL ET AL, 1995)
Figure 3-17. Detail of the Large Probe, including pressure vessel, protective nose cone, aft shield, and major components.
p. 72 Fig 3-18 (Large probe, FIMMEL ET AL, 1995)
The three small probes were identical to each other, 0.8 m in diameter. These probes also consisted of spherical pressure vessels surrounded by an aeroshell, but unlike the large probe, they had no parachutes and the aeroshells did not separate from the probe. Each small probe carried a nephelometer and temperature, pressure, and acceleration sensors, as well as a net flux radiometer experiment to map the distribution of sources and sinks of radiative energy in the atmosphere. The radio signals from all four probes were also used to characterize the winds, turbulence, and propagation in the atmosphere. The small probes were each targeted at different parts of the planet and were named accordingly. The North probe entered the atmosphere at about 60 degrees north latitude on the day side. The night probe entered on the night side. The day probe entered well into the day side, and was the only one of the four probes which continued to send radio signals back after impact, for over an hour. More detailed information on the probes is available. p. 76 Fig 3-21 (Small probe, FIMMEL ET AL, 1995)
p. 77 Fig 3-22 (Small probe, FIMMEL ET AL, 1995)
The Pioneer Venus bus also carried two experiments, a neutral mass spectrometer and an ion mass spectrometer to study the composition of the atmosphere. With no heat shield or parachute, the bus survived and made measurements only to about 110 km altitude before burning up. The bus was a 2.5 m diameter cylinder weighing 290 kg, and afforded us our only direct view of the upper Venus atmosphere, as the probes did not begin making direct measurements until they had decelerated lower in the atmosphere. Probe Entry Timing Events: (Table 5-2, p. 141, Fimmel et al, 1995)
Probe Entry Impacts: (Table 5-3, p. 144, Fimmel et al, 1995)
Bus Entry and Location of Sun and Earth: (Table 5-4, p. 144, Fimmel et al, 1995)
p. 73 Fig 3-19 (Large/small probe alt vs time)
Probe Anomalies: (Table 5-5, p. 146 Fimmel et al, 1995)
========================== p. 4,5 Table 1-1, 1-2 (Venus physical const., Fimmel et al, 1995)
p. 145 Fig 5-12 (Venus Atm cartoon - probe results, Fimmel et al, 1995)
p. 209 Table 6-3 (Venus/Earth Atm comparision, Fimmel et al, 1995)
p. 220 Fig 6-42 (Venus - solar wind interaction, Fimmel et al, 1995)
p. 221 Fig 6-43 (Venus - solar wind interaction, Fimmel et al, 1995)
============================= p. 203 Fig 6-36 (Atm profile vs alt, Fimmel et al, 1995)
p. 189 Fig 6-28 (temp vs alt, Fimmel et al, 1995)
p. 191 Fig 6-29 (temp,density vs local time, Fimmel et al, 1995)
p. 194 Fig 6-30 (scattering x-section vs alt, Fimmel et al, 1995)
p. 195 Table 6-1 (Cloud characteristics, Fimmel et al, 1995)
p. 196 Fig 6-31 (Cloud features, Fimmel et al, 1995)
p. 198 Fig 6-33 (Polar temp, Fimmel et al, 1995)
p. 199 Fig 6-34 (Cloud size dist, Fimmel et al, 1995)
p. 201 Fig 6-35 (SO2 vs time, Fimmel et al, 1995)
p. 202 Table 6-2 (Cloud radiative properties, Fimmel et al, 1995)
Science Results - Magnetosphere and Ionosphere p. 222 Fig 6-44 (Bowshock height vs time, Fimmel et al, 1995)
p. 216 Fig 6-40 (diurnal variation in temp, Fimmel et al, 1995)
p. 218 Fig 6-41 (CO2 and O2 variation vs local time at 170 km, Fimmel et al, 1995)
p. 206 Fig 6-38 (lightning, Fimmel et al, 1995)
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
