Pioneer Venus Unified Abstract Data Library And Quick Look Data Delivery System

Development of the Pioneer Venus (PV) Unified Abstract Data System (UADS) and Quick Look Data System (QLDS) was prompted by the need to provide PV investigators rapid and easy access to PV mission data. The UADS is intended to maximize the scientific benefits of the mission by facilitating the exchange of reduced scientific data. QLDS provides a method by which sampled daily mission data is rapidly transmitted to principal investigators providing them a quick look at that orbit's data.     

Pioneer Venus Orbiter Fluxgate Magnetometer

The fluxgate magnetometer on the Pioneer Venus orbiter spacecraft is described. Special features include gradiometer operation, on board despinning, a floating point processor and variable Nyquist filters. Initial operations have been entirely successful.     

Pioneer Venus Spacecraft Design And Operation

The Pioneer Venus Orbiter and Multiprobe spacecraft design and operation enabled both remote and in-situ measurements of the Venusian environment from the outermost fringes of the atmosphere all the way to the surface. Both spacecraft were spin-stabilized and solar-cell powered from launch to Venus. Since orbit insertion, the Orbiter has been transmitting measurements from a highly elliptical 24-h orbit with periapsis altitudes down to about 150 km. Data rates up to 2048 bits/s have been utilized through a despun high-gain antenna transmitting at S-band frequency. Spacecraft attitudes, orbit periods, and periapsis altitudes are being maintained as required with a hydrazine propulsion system. The Multiprobe spacecraft (Bus with all four Probes attached) perfomed the necessary Probe checkouts and deployed the Probes to achieve the desired Probe and Bus targeting. Silver-zinc batteries provided the necessary power on each of the four Probes from separation from the Bus through the entry/descent sequence. Data rates of 256 and 128 bits/s on the Large Probe were maintained with 40-W radiated power, and 64 and 16 bits/s on the Small Probes were maintained with 10-W radiated power, through omni antennas directly to Earth-based stations. Each Probe's entry/descent sequence was controlled with a hardwired entry sequence programmer to achieve the desired scientific and spacecraft operations.     

Pioneer Venus Sounder Probe Gas Chromatograph

The Pioneer Venus Sounder Probe gas chromatograph (GC) instrument's design logic, construction, function, and data processing are discussed.     

Pioneer Venus Multiprobe Entry Telemetry Recovery

The Entry Phase of the Pioneer Venus Multiprobe Mission involved data transmission over only a two-hour span. The criticality of recovery of those two hours of data, coupled with the fact that there were no radio signals from the Probes until their arrival at Venus, dictated unique telemetry recovery approaches on the ground. The result was double redundancy, use of spectrum analyzers to aid in rapid acquisition of the signals, and development of a technique for recovery of telemetry data without the use of real-time coherent detection which is normally employed by all other NASA planetary missions.     

Radiometer for the Pioneer Venus Orbiter

A review of the design and operation of a radiometer to study the upper atmosphere of Venus from the Pioneer Venus orbiter is presented.     

Pioneer Venus Orbiter Electron Temperature Probe

The Orbiter Electron Temperature Probe (OETP) instrumentation and measurement technique has been designed to perform in-situ measurements of electron temperature and electron and ion density in the ionosphere of Venus. Adaptive sweep voltage circuitry continuously tracks the changing electron temperature and spacecraft potential while auto-ranging electrometers adjust their gain in response to the changing plasma density. Control signals used in the instrument to achieve this automatic tracking provide a continuous monitor of the ionospheric parameters without telemetering each volt-ampere curve. Internal data storage permits high data rate sampling of selected raw characteristic curves for low rate transmission to Earth. These curves are used to verify or correct the inflight processed data. Sample in orbit measurements are presented to demonstrate insrument performance.     

The Pioneer Venus Orbiter Plasma Analyzer Experiment

The plasma analyzer experiment on the Pioneer Venus Orbiter was designed to determine the basic characteristics of the plasma environment of Venus and the nature of the solar wind interaction at Venus. The plasma analyzer experiment is an electrostatic energy-per-unit charge (E/Q) spectrometer which measures ions and electrons. There is a curved plate electrostatic analyzer system with multiple collectors. The experiment obtains the three dimensional plasma distribution function. Some of the scientific objectives of the instrument are briefly discussed, the general characteristics of the experiment are summarized, and some of the analyses based on the data are presented.     

The Pioneer Venus Orbiter Gamma Burst Detector

The Orbiter Gamma Burst Detector was designed to record the temporal and spectral characteristics of cosmic gamma-ray bursts. The primary mission of the experiment is the accurate determination of the directions to the sources of such bursts through a technique of triangulation, as a member of a widely spaced array of similar instruments. The system consists of a pair of scintillation spectrometers sensitive in the range 100 < E < 2000 keV, together with logics and data storage to provide a capability for recording these events. Nineteen events which have been verified as cosmic gamma-ray bursts were recorded within the first year's operation.     

Pioneer Venus Sounder Probe Solar Flux Radiometer

The Solar Flux Radiometer aboard the Pioneer Venus Sounder Probe operated successfully during its descent through the atmosphere of Venus. The instrument measured atmospheric radiance over the spectral range from 400 to 1800 nm as a function of altitude. Elevation and azimuthal measurements on the radiation field were made with five optical channels. Twelve filtered Si and Ge photovoltaic detectors were maintained near 30°C with a phase-change material. The detector output currents were processed with logarithmic transimpedance converters and digitized with an 11-bit A/D converter. Atmosphetic sampling in both elevation and azimuth was done according to a Gaussian integration scheme. The serial output data averaged 20 b/s, included housekeeping (sync, spin period, sample timing and mode). The data were used to determine the deposition of solar energy in the atmosphere of Venus between 67 km and the surface along with upward and downward fluxes and radiances with an altitude resolution of several hundred meters. The results allow for more accurate modelling of the radiation balance of the atmosphere than previously possible.     

Pioneer Venus Sounder Probe Particle Size Spectrometer

The Pioneer Venus Sounder Probe Particle Size Spectrometer measured the particle size and number density in the atmosphere of Venus from 66 km to the surface. This instrument performs particle size measurements over a 0.5 to 500-?m size range using a combination of shadowgraph imaging and light scattering techniques. Size resolution is approximately ±10 percent of size with 100-400-m vertical spacial resolution. The instrument features a laser-fed optical system incorporating a complex beam-splitting multipath imaging optical system.     

Pioneer Venus Sounder Probe Neutral Gas Mass Spectrometer

A neutral gas mass spectrometer was flown to Venus as part of the Pioneer Venus Multiprobe to measure the composition of its lower atmosphere. Encounter occurred on December 9, 1978. The instrument, mounted in the Sounder Probe, was activated after the probe entered the top of the atmosphere, and it obtained data during the descent from 62 km to the surface. Atmospheric gases were sampled through a pair of microleaks, the effluent from which was pumped by a combination of ion and getter pumping. A pneumatically operated valve, controlled by the ambient atmospheric pressure, maintained the ion source pressure at a nearly constant value during descent while the atmospheric pressure varied by 3 orders of magnitude. This action preserved the more than 6-decade dynamic range of the instrument throughout the descent. A single focusing magnetic sector field mass spectrometer with mass resolution sufficient to reasonably separate argon from C3H4 at 40 amu provided the mass analysis and relative abundance measurements. A microprocessor controlled the operation of the mass spectrometer through a highly efficient peak-top stepping routine and data compression algorithm that effected a scan of the mass spectrum from 1 to 208 amu in 64 s while requiring an information rate of only 40 b/s to return the data to earth. A subscale height altitude resolution was thus obtained. Weight, size, and power requirements were minimized to be consistent with interplanetary flight constraints.     

Pioneer Venus Orbiter Neutral Gas Mass Spectrometer Experiment

The Pioneer Venus Orbiter Neutral Mass Spectrometer (ONMS) is designed to measure the vertical and horizontal density variations of the major neutral constituents in the upper atmosphere of Venus. The mass spectrometer sensor includes a retarding potential ion source, hyperbolic quadrupole rod analyzer, and electron multiplier detector. The supporting electronic system consists of hybrid integrated circuits to reduce weight and power. The ONMS instrument was launched aboard the Pioneer Venus Orbiter on May 20, 1978, and turned on in orbit around Venus on December 4, 1978. It has operated flawlessly for over a Venus year (243 earth days) and has returned data of the composition of the major constituents in the Venus atmosphere between the altitudes of 150 and 350 km.     

Pioneer Venus Orbiter Planar Retarding Potential Analyzer Plasma Experiment

The retarding potential analyzer (RPA) on the Pioneer Venus Orbiter Mission measures most of the thermal plasma parameters within and near the Venusian ionosphere. Parameters include total ion concentration, concentrations of the more abundant ions, ion temperatures, ion drift velocity, electron temperature, and low-energy (0-50 eV) electron distribution function. Several functions not previously used in RPA's were developed and incorporated into this instrument to accomplish these measurements on a spinning spacecraft with a small bit rate. The more significant functions include automatic electrometer ranging with background current compensation; digital, quadratic retarding potential step generation for the ion and low-energy electron scans; a current sampling interval of 2 ms throughout all scans; digital logic inflection point detection and data selection; and automatic ram direction detection.     

High-gain backup antenna design for Pioneer Venus Orbiter spacecraft

The development and performance is described of a high-gain antenna designed to serve on the Pioneer Venus Orbiter spacecraft as a backup to the principal high-gain antenna unit in the unlikely event the mechanically despun antenna mechanism malfunctioned. The final design, a center-fed standing wave array of six sleeve dipoles enclosed in a fiber glass radome, performed successfully, as did all the antennas, on the Pioneer Orbiter spacecraft which was launched on May 20, 1978, as part of the Pioneer Venus mission. Photographs of experimental models giving details of design and construction are included, as well as graphs showing measured pattern and impedance matching characteristics of the subject antenna.     

Pioneer Venus Orbiter Radar Mapper: Design And Operation

The Radar Mapper Experiment, carried abroad the Pioneer Venus Orbiter spacecraft, is designed to obtain a near-global picture of the topography, meter-scale surface slopes and reflectivity of Venus. Constraints imposed by the choice of orbit limit radar coverage to a latitude band lying between 74°N and 61°S completely around the planet. In addition to the altimetry objectives, the experiment seeks an image of the radar scattering properties of the surface at oblique incidence. Sensitivity limits the imaged region to a band around the planet lying between 45°N and 10°S. Altimetric error is less than 200 m; altimetric surface ?footprint? size varies from about 10 km in diameter at a spacecraft altitude of 200 km, to 50 km at a maximum altitude of 4700 km. Imaging resolution varies from 20 to 40 km, depending on spacecraft altitude.     

Bennett Ion Mass Spectrometers on the Pioneer Venus Bus And Orbiter

Identical Bennett radio frequency ion mass spectrometer instruments on the Pioneer Venus Bus and Orbiter have provided the first in-situ measurements of the detailed composition of the planet's ionosphere. The sensitivity, resolution, and dynamic range are sufficient to provide measurements of the solar-wind-induced bow-shock, the ionopause, and highly structured distributions of up to 16 thermal ion species within the ionosphere. The use of adaptive scan and detection circuits and servo-controlled logic for ion mass and energy analysis permits detection of ion concentrations as low as 5 ions/cm3 and ion flow velocities as large as 9 km/s for O+. A variety of commandable modes provides ion sampling rates ranging from 0.1 to 1.6 s between measurements of a single constituent. A lightweight sensor and electronics housing are features of a compact instrument package.