Engineering topics
Publications and source records attributed to Dyer, J. W..
Data for corrections of attitude derived on Earth from secondary measurements. Paper describes how attitude of Pioneer 10 spacecraft controlled since spacecraft lost signal from Sun-sensor signal. Roll calculations in paper yields insight into environment of solar system at great distances.
This paper describes the attitude control of the Pioneer 10 spacecraft since the loss of the sun-sensor signal in late 1983. It is necessary to control the attitude of the spin-stablized spacecraft so as to maintain communications with earth. Roll phase is calculated on earth using data from a science instrument on-board Pioneer 10, the imaging-photopolarimeter, which, along with its other functions, was designed to collect images of Jupiter during encounter in 1973. With calculation of instantaneous roll phase performed only once per week, the spacecraft roll angle can be predicted more than a week ahead for timing reorientation impulses. Attitude reorientation maneuvers based on roll phase predictions have been successfully executed for several years on Pioneer 10. Of 10 maneuvers analyzed in this paper, predictions were made for as many as 10 days in the future based on a roll-phase measurements spanning only 12 days of data. The average maneuver was planned by projecting the roll phase for 3 days (22,000 spacecraft revolutions) and resulted in a maneuver execution phase error of only 11 deg.
Pioneer spacecraft will continue as mankind's farthest explorer from the Sun and America's only operating planetary orbiter for many years in the future. The eleven-year old Pioneer 10 describes strong solar domination of the environment at its 29 astronomic units (AU) distance, and its sensitivity as a unique sensor of suspected gravitational phenomena is improving with distance. The four-year-old Pioneer Venus Orbiter increasingly defines the solar wind interaction with the nonmagnetic planet as its orbital axis precesses through the affected volume. Pioneer 10 promises data from 50 AU distance by 1991. The Venus Orbiter could operate until atmospheric entry in 1992.
Electrical signals attributed to lightning events on Venus have been observed by instruments aboard Veneras 11 and 12 and aboard the Pioneer Venus Orbiter. This paper reports the results of a search for optical pulses from the dark side of Venus made with the star sensor aboard the Pioneer Venus Orbiter. A comparison of both the frequency and amplitude distributions of received pulses with those of control experiments in which the star sensor observed deep space showed no statistically significant differences. Based on observations made during orbits 300 through 345, an upper limit of 30 flashes/sq km/yr has been derived for the average lightning frequency on the dark side of Venus. This value assumes that the amplitude distribution of lightning and the attenuation of the optical pulse by clouds on Venus are not substantially different from that occurring on earth.
The Pioneer Saturn spacecraft, designated Pioneer 11 until its encounter with Jupiter, is presented, and its trajectory is reported. The 550-pound spin-stabilized spacecraft carries 12 scientific instruments, 11 of which were operational during its encounters with Jupiter and Saturn. After the successful completion of the Pioneer 10 Jupiter fly-by, for which Pioneer 11 was intended as a back-up, the Pioneer 11 spacecraft was committed to a Saturn-bound trajectory, and was sent on a spiral trajectory around Jupiter to approach Saturn. After mid-course maneuvers, the spacecraft arrived at Saturn on September 1, 1979, where it penetrated the ring plane outside of the visible rings, descending from above the ecliptic plane late in the morning quadrant, and making measurements of the planetary magnetosphere and its interaction with the solar wind, infrared radiation and gravitational and atmospheric effects on the radio signal. Pioneer Saturn departed from Saturn slightly above the ring plane, crossing the orbit of Titan 25 hr after Saturn flyby, and became the second spacecraft to escape the solar system.
Plans for Pioneer 11's approach to Saturn are described. A flyby somewhat parallel to the ring plane is being proposed as an interim target, with a future option held for a possible high risk (or suicide) plunge through the nearly transparent space between Saturn and its rings.
Results of Pioneer 11's encounter with Jupiter are reviewed, and present plans for its approach to Saturn are discussed. The spacecraft is described together with its instrumentation, Jupiter-encounter operations, and scientific investigations. Scientific objectives at Saturn are outlined, including imaging of the planet, magnetospheric studies, measurements of Titan's mass and ephemeris, estimates of the mass of Saturn's rings, and penetration of the ring plane, particularly the D ring.
The mission concept is described for a spin-stabilized spacecraft being designed to deliver an array of aerodynamic probes over the surface of Venus, and, on a second flight mission, to inject the spacecraft into a Venusian orbit. Large and Small Probes and the instrumented 'Bus' structure will enter the Venusian atmosphere and directly measure its characteristics. An orbiting configuration of the same basic Bus spacecraft will serve as a platform from which to examine the planetary environment, the outer atmosphere and its interaction with the solar wind, as well as surface topography. The orbital mission will extend over a complete revolution of the planet around the sun and around its own axis. Requirements for cost effectiveness and firm adherence within early cost projections are emphatic program guidelines which affect every major element of the mission plan and conceptual design.
Biosatellite 2 operations, discussing orbiting by two stage delta launch vehicle, battery powering and STADAN planned communications
Launch window, flight performance, and recovery procedures for biosatellite