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An analysis of the operation of OAO 3, Copernicus, the orbiting astronomical observatory, is given with particular emphasis upon the Princeton Experiment Package. Malfunctions and their impact are discussed, as are orbital observations and operations. Software is described.
Data is introduced on the iron concentrations of the lunar surface which have been refined by means of convolution corrections to restore the spatial resolution and contrast lost by the omnidirectional spectrometer. This refined iron data is synthesized with other orbital seismic, and lunar sample data to derive highland crustal density and thickness, and isostasy and lunar centers of mass models are examined in light of this new information. A model is developed by which highland crustal density is calculated for each highland region from orbital observations of Fe, Mg and Ti concentrations. The results of this model are presented numerically and graphically for 35 highland and two non-highland regions. Density and thickness results are then applied to two long-standing lunar problems: (1) the nature of highland isostasy, which is shown to be controlled by crustal thickness rather than density, and (2) the separation of the moon's mass and figure centers, which is shown to be due to the crustal thickness difference between the lunar near and far sides.
Recent ISEE 3 and Pioneer Venus Orbiter observations relevant to the altitude structure of the hard X-ray source down to 3000 km or less above the photosphere are reported. About 90 percent of the impulsive X-ray emission and about 70 percent of the gradual emission originates at altitudes 2500 km or less above the photosphere. In the 100-500 keV range, this altitude dependence is essentially independent of photon energy. Brightness of the impulsive X-ray source decreases rapidly with increase in altitude. As far as models of the impulsive phase are concerned, the thermal model with adiabatic compression and expansion of a magnetically confined plasma and the thin target model are not consistent with these observations. The thick target model and the dissipative thermal model are consistent with the observed low altitude of the hard X-ray source.
Latch fittings which kinematically mount the replaceable scientific instruments onto the Space Telescope must maintain precise alignment and thermal stability for on-orbit observations. Design features which are needed to meet stringent criteria include the use of ceramic isolators for thermal and electrical insulation, materials with different coefficients of thermal expansion for athermalization, precision manufacturing procedures, and extremely tight tolerances. A specific latch fitting to be discussed is a ball-and-socket design. In addition, testing, crew aids, and problems will be covered.
Detailed maps of wind streaks in Tharsis and Elysium have been compiled from Viking Orbiter observations spanning one complete Martian year. The streak pattern is controlled by slope winds on the central volcanoes and on the flanks of the Tharsis bulge, while the global circulation dominates in Elysium. Dust erosion by downslope winds occurs over much of Tharsis and in the vicinity of Elysium Mons; this process is effective even at the low atmospheric pressures found near the summits of the large volcanoes. Erosional streaks are largely absent in Elysium Planitia; net deposition of dust might have occurred during the period of the observations. Surface properties such as slope, thermal inertia, and roughness may influence the efficiency of slope wind production sufficiently to account for the pronounced differences in streak types and patterns present in these two regions.
Venus deflects incident solar wind by means of thermal and magnetic pressure, both of which are produced by ionospheric currents that are in turn driven by pressure gradients and electric fields induced in the ionosphere by the flowing magnetized solar wind plasma. The ionospheric currents connect across the ionopause into the ionosheath region, and close on, and behind, the bow shock. The computed ionospheric plasma velocity distribution is found to be spatially asymmetric, with the fastest flow velocities lying perpendicular to the ionospheric magnetic fields. Computations also indicate that the ionosphere is susceptible to an MHD shear instability whose extent and location is a function of external solar wind conditions. The present Venus ionosphere model compares well with in situ Pioneer Venus Orbiter observations.
Estimation of the rate of aeolian abrasion of rocks on Mars requires knowledge of: (1) particle flux, (2) susceptibilities to abrasion of various rocks, and (3) wind frequencies on Mars. Fluxes and susceptibilities for a wide range of conditions were obtained in the laboratory and combined with wind data from the Viking meteorology experiment. Assuming an abundant supply of sand-sized particles, estimated rates range up to 2.1 x 10 to the minus 2 power cm of abrasion per year in the vicinity of Viking Lander 1. This rate is orders of magnitude too great to be in agreement with the inferred age of the surface based on models of impact crater flux. The discrepancy in the estimated rate of abrasion and the presumed old age of the surface cannot be explained easily by changes in climate or exhumation of ancient surfaces. The primary reason is thought to be related to the agents of abrasion. At least some sand-sized (approx. 100 micrometers) grains appear to be present, as inferred from both lander and orbiter observations. High rates of abrasion occur for all experimental cases involving sands of quartz, basalt, or ash. However, previous studies have shown that sand is quickly comminuted to silt- and clay-sized grains in the martian aeolian regime. Experiments also show that these fine grains are electrostatically charged and bond together as sand-sized aggregates. Laboratory simulations of wind abrasion involving aggregates show that at impact velocities capable of destroying sand, aggregates from a protective veneer on the target surface and can give rise to extremely low abrasion rates.
Schumann emulsions, having low gelatin content and no protective gelatin overcoating, are extremely sensitive to environmental conditions and handling. Experiments using this emulsion are to be flown on the space shuttle within the cargo-bay. Because the environment of the cargo-bay is unknown, a Get-Away-Special payload was designed to expose Kodak-type SO 652 Schumann emulsion to the residual atmosphere of the cargo-bay. The experiment was programmed to make exposures for various time periods to determine the maximum length of time the film could be exposed in making a measurement and what precautions would be required to preserve the film during ascent into orbit and reentry. The results of the STS-7 and STS-8 flights indicated that long exposures in the shuttle bay do not produce high fog levels in orbit. Observations of severe bleaching of the latent image makes protection of the emulsion during reentry manditory and increase of fog levels with time set a limit of four weeks (preferably less than three) between installation and recovery of the emulsion for processing.
An evaluation of mission requirements for postulated earth observation orbital payload experiments has indicated that high accuracy pointing and stabilization must be provided for adequate performance. A computer simulation has been conducted to determine the capabilities of an auxiliary pointing system which employs a combination of conventional gimbals and magnetic bearing actuators. This Annular Suspension and Pointing System (ASPS) is found to be a viable means of providing the high slew rates associated with landmark tracking from low orbit, while simultaneously achieving the high degree pointing and stabilization dictated by science payload requirements.
Mars and Earth experience quasiperiodic variations in the distribution of incident solar radiation due to secular perturbations in their orbital and axial elements. On Mars, the potential climatic effects of these perturbations are large because the mass of the Martian atmosphere may be determined by the vapor pressures of semipermanent CO2 frost deposits at the poles. The Viking Orbiter observations of the Martian polar caps suggest that the sensitivity of the Martian climate system to the variations in the polar insolation may be considerably reduced by the tendency for polar frost deposits to become brighter with increasing rates of incident solar radiation. This phenomenon can be explained by the tendency for dust particles to sink into CO2 frost at rates that depend on the magnitude of the incident solar flux.
Mariner 9 and Viking Orbiter observations of the topography and mass of layered deposits in the north polar region of Mars suggest a density of about 1 gm/cu cm. Consideration of the self-compaction of these deposits further suggests that this low density cannot be explained by a high porosity sediment. Rather, a significant component of ice is probably required to account for the low value. The density further implies that the silicate fraction, regardless of its density (i.e., its composition), represents a volumetrically almost negligible component of the deposit. The most likely values, 5 percent silicate dust and 95 percent ice, agree well with a theoretical model for the formation of the deposits through cyclic incorporation of the perennial polar ice cap. Additional tests of this model may be posed in advance of future spacecraft missions to Mars.
Over the past decade COMPLEX has published three strategy reports which, taken together, encompass the entire planetary system and recommend a coherent program of planetary exploration. The highest priority for outer planet exploration during the next decade is intensive study of Saturn (the planet, satellites, rings, and magnetosphere) as a system. The Committee additionally recommends that NASA engage in the following supporting activities: increased support of laboratory and theoretical studies; pursuit of earth-based and earth-orbital observations; commitment to continued operation of productive spacecraft; implementation of the instrument development plan as appropriate for the outer solar system; studies of deep atmospheric probes; development of penetrators or other hard landers; development of radiation-hardened spacecraft; and development of low-thrust propulsion systems. Longer-term objectives include exploration and intensive study of: the Uranus and Neptune systems; planetology of the Galilean satellites and Titan; and the inner Jovian system.
The NASA Deep Space Network, a precision telecommunications and radio navigation facility, is described in detail. The first spacecraft relativity test with Mariner 6 and Mariner 7 at solar conjunction is discussed as well as more accurate tests using the Mariner 9 anchored to Mars. Consideration is also given to solar system tests of relativistic celestial mechanics and future prospects. It is noted that the NASA Mars Observer orbital mission is under development and is expected to reach Mars in 1991.
New geodetic data obtained during the years of 1983-1986 on terrestrial planets are presented. New or improved data on rotation, topography, and gravity are reported for Venus (from Pioneer Venus Orbiter observations), Jupiter (Pioneer 10 and 11 and Voyager 1 and 2 data) and its satellites, Saturn (from Voyager data) and its satellites, Uranus (from Voyager 2) and its satellites, and Neptune and Pluto (from various indirect observations). There was relatively little new to report on moon and Mars. The physical significance of the information is discussed.
Many of the scientifically interesting phenomena that occur in the Jovian system are strongly time variable. Some are episodic (e.g., Io volcanism); some are periodic (wave transport in Jupiters atmosphere); and some are exceedingly complex (magnetosphere - Io - Torus-Auroral interactions) and possibly unstable. To investigate this class of phenomena utilizing Voyager data and, in the future, Galileo results, a coherent program of ground based and earth-orbital observations, and of theory that spans the time between the missions, is required. To stimulate and help define the basis of such a scientific program researchers organized an International Workshop on the subject with the intent of publishing the proceedings which would represent the state of knowledge in 1987.
As a result of the Viking orbiter observations, the entire surface of Mars has been imaged at a resolution of 200 meters, and fractions of the surface down to resolutions of 10 meters, the thermal inertia of the entire surface is known to a resolution of 30 km, and the water content of the atmosphere has been monitored over two Martian years. In addition, at two sites, the Viking landers analyzed the atmosphere, imaged the surface, performed organic and inorganic analyses on the soil, and monitored meteorological conditions for almost three Martian years. The results show that Mars is a highly variegated planet with a long and complex history of volcanic and tectonic activity, a surface that has been modified by wind, water and ice, and an atmosphere that has experienced substantial changes, both periodic and secular. The variety of processes that have operated on the surface, and the long history of their action, result in a much broader range of sampling problems and opportunities than was experienced in the case of the Moon.
NASA's Office of Aeronautics and Space Technology has undertaken a series of manned space presence-development efforts under the aegis of the Civil Space Technology Initiative (CSTI) and Project Pathfinder. Typical of these CSTI efforts is the Aeroassist Flight Experiment, which will demonstrate techniques suitable in aerobrake design for slow trajectories to Mars and for lunar mission return. Long-duration human operations in space are a major element of Pathfinder, giving attention to such problems as space radiation exposure effects that could be several orders of magnitude greater on interplanetary exploration missions than on typical Space Shuttle flights. Mars Observer and Lunar Observer orbital missions are planned as a steppingstone to manned planetary exploration.
Space Shuttle astronauts have used handheld cameras to take about 30,000 photographs of the earth as seen from orbit. These pictures provide valuable, true-color depictions of many geologically significant areas. While the photographs have areal coverages and resolutions similar to the more familiar Landsat MSS and TM images, they differ from the latter in having a wide variety of solar illumination angles and look angles. Astronaut photographs can be used as very small scale aerial photographs for geologic mapping and planning logistical support for field work. Astronaut photography offers unique opportunities, because of the intelligence and training of the on-orbit observer, for documenting dynamic geologic activity such as volcanic eruptions, dust storms, etc. Astronauts have photographed more than 3 dozen volcanic eruption plumes, some of which were not reported otherwise. The stereographic capability of astronaut photography also permits three-dimensional interpretation of geologic landforms which is commonly useful in analysis of structural geology. Astronauts have also photographed about 20 known impact craters as part of project to discover presently unknown examples in Africa, South America, and Australia.