Engineering topics
Publications and source records attributed to Taylor, A. H..
The objective of the CONTOUR mission was to conduct scientific fly-by studies of comets, Encke and Schwassmann-Wachmann 3, with the option of changing targets in-flight or visiting anadditional target after the SW3 encounter. The paper will describe the mission's planned trajectory, the navigation challenges, as well as the navigation tasks that were involved in achieving mission objectives.
The successful navigation of the Comet Nucleus Tour spacecraft was performed at JPL and was conducted with the use of the new noncoherent transceiver technique developed by the Applied Physics Laboratory. Discussions include the conditioning performed on the 2-way noncoherent Doppler data, the orbit determination process, and the post SRM trajectory reconstruction.
This paper presents analysis of when and how well, on the approach to previously unvisited small bodies, the trajectory-design relevant physical parameters are determined.
This paper describes the Casini orbit determination effort from injection through the first Venus flyby. Emphasis is placed on orbit determination modeling and the resulting orbit solutions.
This is the second of two papers which summarize orbit determination analysis accoumpliched to date as part of navigation studies for the Cassini mission. The thrust of the analysis has been to characterize orbit determination accuracy to first order for selected phases of the mission.
This paper summarizes the first round of orbit determination analysis accomplished as part of navigation studies for the Cassini mission.
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Improved values for the masses of the Uranian system and the satellites Ariel, Umbriel, Titania, Oberon, and Miranda are obtained on the basis of an analysis of the Doppler-tracking data and star-satellite imaging from the Voyager 2 spacecraft combined with earth-based astrometric satellite observations. Masses are expressed as the product, the universal gravitational constant times the mass of the body, in units of (cu km/sq s). The satellite masses are (4.4 +/- 0.5) for Miranda, (90.3 +/- 8.0) for Ariel, (78.2 +/- 9.0) for Umbriel, (235.3 +/- 6.0) for Titania, and (201.1 +/- 5.0) for Oberon. Quoted errors are standard errors and are the present assessment of the true rather than the formal errors. The Uranus rotational pole orientation angles and gravity harmonic coefficients were fixed at the values determined by French et al. (1988) from stellar occultations of the Uranian rings observed from both the earth and Voyager 2 and from the occultation of the spacecraft radio signal.
The determination of improved orbits for the Neptunian satellites Triton and Nereid is discussed. The primary results are the final set of model parameters which generate orbits that best fit both the earth-based satellite observations and data acquired by the Voyager spacecraft during the Neptune encounter. The accuracy of the improved orbits is assessed and they are compared with the orbits generated prior to the encounter. Mean elements are also provided as a geometrical representation for the orbits.
In August 1989 the Voyager 2 spacecraft encountered Neptune and Triton. Precise knowledge of the trajectory of the spacecraft relative to the Neptunian system was essential to ensure successful observations during the flyby, and to perform trajectory control. Determination of the orbit of Voyager 2 with respect to the Neptunian system was accomplished by the use of radiometric Doppler, range, and VLBI observations of the spacecraft in combination with spacecraft-based optical observations of Neptune, Triton, Nereid, and the Voyager-discovered satellite 1989N1. These data types were used in a new version of the JPL Orbit Determination Program to determine the orbit of the spacecraft as well as Neptunian system ephemerides and dynamical parameters, resulting in accurate delivery of the spacecraft to targeted conditions at Neptune and Triton.
The Voyager project used Neptunian satellite ephemerides to support both navigation and acquisition of scientific data. The development of postencounter ephemerides for the satellites Triton, Nereid, and 1989N1 is discussed. Primary results are the final set of model parameters which generate orbits that best fit both the earth-based satellite observations and data acquired by Voyager. The ephemerides are compared with those generated preencounter, and the accuracy of the final ephemerides is assessed. Mean orbital elements are also provided as a geometrical representation for the satellite orbits.
Phase-coherent Doppler data generated by the Deep Space Network with the radio communication system during the Voyager 2 encounter with Uranus in January 1986, optical navigation data generated by the Voyager Navigation Team with the Voyager 2 imaging system, and ground-based astrometric data obtained over an 8-yr period are compiled and analyzed to determine the masses and densities of Uranus and its principal satellites. The data-analysis procedures are explained in detail, and the results are presented in tables and graphs. The mean density of Uranus is found to be 1.285 + or - 0.001 g/cu cm, whereas the mean uncompressed mass of all five satellites is 1.48 + or - 0.06 g/cu cm, or 0.10 g/cu cm above the density expected for a homogeneous solar mix of rock, H2O and NH3 ice, and CH4 as clathrate hydrate. This difference is tentatively attributed to the presence of 15 mass percent of pure graphite, which would provide the thermal conductivity required to keep the satellites cold and undifferentiated.
Attention is given to a light weight foam insulation system applicable to reusable cryogenic propellant tankage for hypersonic aircraft and space launch vehicles. The insulation system consists of nominally sized blocks of a high temperature-resistant polymethacrylimide foam that is wrapped with a vapor-impermeable membrane of Kapton-aluminum-Kapton laminate, which is adhesively bonded to the outer propellant tank wall. Test results are presented which indicate that this insulation system is capable of enduring a Mach 5 service environment without structural cracking, deterioration, or loss of performance.
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Carbon/carbon piston performs same function as aluminum pistons in reciprocating internal combustion engines while reducing weight and increasing mechanical and thermal efficiencies of engine. Carbon/carbon piston concept features low piston-to-cylinder wall clearance - so low piston rings and skirts unnecessary. Advantages possible by negligible coefficient of thermal expansion of carbon/carbon.
Navigating the upcoming Voyager 2 encounter with Uranus presents unique challenges and opportunities. Uranus will be the most distant planetary encounter carried out to date, with a 2.75 hour delay each way for communication. Furthermore, Voyager 2 is the most sophisticated spacecraft ever used for first encounter with a planetary system. In this paper the special features of the encounter are analyzed from a navigation point of view. First, the most relevant science opportunities are introduced. Then the challenges posed by the Uranian distance and geometry are outlined. The result of a detailed navigation accuracy study is presented. Finally, the unique features of optical navigation at Uranus are shown.
A dual structure aerospace vehicle is described which has an aeroshell structure and an internally disposed separable and reusable integral tank/thrust structure. The tank/thrust structure is inuslated for cryogenic fuels and the cavity within aeroshell is insulated from the tank/thrust structure. An internal support ring within the cavity serves as an attachment for lugs on the tank/thrust structure via double hinges. The aft end of tank/thrust structure is provided with rocket engines and exit nozzles with a trunnion supporting the tank/thrust structure within the aeroshell.
A hybrid spar of titanium with an integrally brazed composite, consisting of an aluminum matrix reinforced with boron-carbide-coated fibers, was heated in an oven and the resulting thermal stresses were measured. Uniform heating of the spar in an oven resulted in thermal stresses arising from the effects of dissimilar materials and anisotropy of the metal matrix composite. Thermal stresses were calculated from a finite element structural model using anisotropic material properties deduced from constituent properties and rules of mixtures. Comparisons of calculated thermal stresses with measured thermal stresses on the spar are presented. It was shown that failure to account for anisotropy in the metal matrix composite elements would result in large errors in correlating measured and calculated thermal stresses. It was concluded that very strong material characterization efforts are required to predict accurate thermal stresses in anisotropic composite structures.