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NASA NTRS1993

Near-infrared and ultraviolet spectrophotometry of the young planetary nebula Hubble 12

The young planetary nebula Hubble 12 is observed using near-IR and UV spectrophotometry. The brightness of the O I lines, which is greater than in any other planetary nebula yet measured, indicates that fluorescent excitation by stellar continuum is the principal mechanism generating these lines. Extinction, electron density, and electron temperature are determined using infrared measurements combined with UV data and published optical observations. The range in extinction, density, and temperature implies that, within the ionized region, pockets of emission with distinctly different conditions exist. Logarithmic abundances for helium, oxygen, and sulfur are presented.

Rudy, Richard J.↗

NASA NTRS1993

Three-body effects in the PSR 1257+12 planetary system

A detailed theoretical analysis of the three-body effects in the putative planetary system of PSR 1257+12 is presented. Ways in which these effects are manifested in the pattern of pulse arrival times are discussed; the dominant perturbation is described as a modulation of the phases of the near-sinusoidal signals of the two planetary companions. Explicit formulas for the time dependence of the oscillating orbital elements that are needed for an improved timing model for this system are provided. If a timing model with fixed, independent Keplerian orbits continues to be used for the timing analysis, and if two planets are indeed orbiting this pulsar, then the three-body effects should become detectable by means of a growth in the postfit residuals as more observations are accumulated. If the typical error in the pulse arrival time measurements is about 10 microsec, the amplitude of the postfit residuals will increase beyond this level with three to five years of timing observations.

Malhotra, Renu↗

NASA NTRS1993

International Ultraviolet Explorer observations of the white dwarf nucleus of the very old, diffuse planetary nebula, IW-2

UV low-dispersion spectra of the central star of the faint planetary nebula, IW-2, were obtained with the IUE. The apparent large diameter of the very diffuse nebula, about half that of the moon, as seen on the Palomar Sky Survey plates by Ishida and Weinberger (1987), indicates this object to be potentially quite evolved, and nearby. The IUE spectra clearly reveal a hot stellar continuum extending over the entire wavelength range of the short-wavelength prime camera (1200-2000 A). This object with V = 17.7 +/- 0.4 is definitely one of the faintest stars ever successfully observed with the IUE. Comparisons of the IUE observed fluxes with those from white dwarf model atmospheres suggest extinction near E(B - V) = 0.45 for a white dwarf of T(eff) roughly 100,000 K. Constraints from estimates of the nebular emission measure and observed visual magnitude also argue for a white dwarf of T(eff) roughly 100,000 K at a distance of 300 to 350 pc. The nucleus of IW-2 is one of the most evolved stars to be identified with a planetary nebula.

Bruhweiler, F. C.↗

NASA NTRS1993

The morphology and interaction with the interstellar medium of the planetary nebula IC 4593

We present a morphological study of the planetary nebula IC 4593, based on our observations in H-alpha, forbidden O III, and forbidden S II. From the H-alpha intensity map, we calculate densities and masses for constituent structures and for the nebula as a whole. We argue that the morphology of IC 4593 suggests that it is moving supersonically through the ISM, and that the ISM shock may be thermally unstable, oscillating between adiabatic and radiative (isothermal) shock conditions. Spectroscopic observations are necessary to further explore the nature of the interaction between IC 4593 and the ISM. An improved understanding of such interactions will greatly expand the potential use of planetary nebulae to probe the ISM.

Zucker, Daniel B.↗

NASA NTRS1993

Planets around pulsars - Implications for planetary formation

Data on planets around pulsars are summarized, and different models intended to explain the formation mechanism are described. Both theoretical and observational evidence suggest that very special circumstances are required for the formation of planetary systems around pulsars, namely, the prior presence of a millisecond pulsar with a close binary companion, probably a low mass main-sequence star. It is concluded that the discovery of two planets around PSR 1257+12 is important for better understanding the problems of dynamics and stellar evolution. The process of planetary formation should be learned through intensive studies of the properties of disks near young objects and application of techniques for detection of planets around main-sequence solar-type stars.

Bodenheimer, Peter↗

NASA NTRS1993

Exploring planetary worlds

A review of the planetary system is presented from a uniform perspective, taking advantage of the data obtained during the planetary space missions. A comparative approach is used, which makes it possible to consider each planet or a satellite in context, focusing both on their common origin and on the processes that have influenced their evolution. The discussion focuses on the Jovian planets, the moon and the Mercury, Venus and Earth, and small bodies in the outer solar system. Attention is also given to comets, asteroids, and cosmic impacts.

Morrison, David↗

NASA NTRS1992

An analysis of an inflatable module for planetary surfaces

Design and construction of a structure on planetary surfaces requires addressing a host of issues not encountered on earth. A modular quilted inflatable structure consisting of thin membranes of composite material integrated with supporting columns and arches is proposed. An initial linear analysis of the structure is briefly reviewed. The actual response of an inflatable membrane is nonlinear and, hence, a nonlinear numerical analysis of the stresses and displacements was undertaken. Results based on the loadings on a lunar structure clearly indicate that an inflatable structure is a feasible concept and is ideally suited for a planetary surface structure.

Nowak, Paul S.↗

NASA NTRS1992

Composite materials for structures on planetary surfaces

The physical and mechanical properties of advanced composite materials as related to their use in structures on planetary surfaces are reviewed. Polymer matrix composites are recommended as the best materials in the first exploration stages. Achievement of mechanical properties, physical properties, improved processability, and ease of assembly required on planetary surfaces depends on the tailorability of composites.

Radford, Donald W.↗

NASA NTRS1992

A vision for planetary exploration

A vision for planetary exploration is proposed which combines historical perspective and current NASA studies with the realities of changing political climates, economic environments, and technological directions. The concepts of Strategic Implementation Architectures (SIA), Open System Infrastructure Standards (OSIS), and Minimum Service Level Infrastructure (MSLI) are presented in order to propose a structure for the SEI which allows the realization of incremental mission objectives, establishes an investment strategy that efficiently uses public resources, and encourages partnerships with the government. The SIA is a hypothetical master plan which will allow the implementation of the complete spectrum of envisioned system capabilities for planetary exploration. OSIS consists of standards for interconnection, interoperability, and administration. MSLI can be defined as the minimum level of services provided by the system that are not justified by profit or parochial motives.

Connolly, John F.↗

NASA NTRS1993

Spacecraft studies of planetary surfaces using bistatic radar

Spaceborne transmitters have been used in bistatic geometries for a number of planetary surface studies including inference of topography, Fresnel reflectivity, and rms surface slopes on the moon, Mars, and Venus. For the moon and Mars in particular, the bistatic geometry has enabled remote probing in regions and under conditions not obtainable with Earth-based radar systems, yielding information about surface characteristics and properties on scales of centimeters to hundreds of meters that complements monostatic radar observations. A new generation of planetary spacecraft now provides opportunities for further experiments, including more nearly complete definition of the surface scattering function and, possibly, imaging. Targets of interest include the polar regions of Venus (by Magellan) and Mars (by Mars Observer), the enigmatic icy Galilean satellites of Jupiter (by Galileo), and Saturn's largest moon Titan (by Cassini).

Simpson, Richard A.↗

NASA NTRS1993

The ultraviolet spectrum of the planetary nebula Vy 2-2

New ultraviolet short-wavelength (SWP) IUE observations for the proto-planetary nebula Vy 2-2 were obtained in the low-dispersion mode. An exposure of 400-min duration reveals a weak stellar continuum and several definite emission lines as well as a number of absorption features. Emission features of semiforbidden C III, semiforbidden Si III, and forbidden Ne III are clearly observed, while C IV, Si II, and possibly C II appear in absorption. Emission features of He II, semiforbidden O III, and Al III are also indicated, though less certain. The UV spectrum tends to confirm that Vy 2-2 is a young, dense planetary nebula excited by a central star with T(eff) greater than 60,000 K.

Feibelman, Walter A.↗

NASA NTRS1992

Simulations of the seasonal evolution of planetary waves in the stratosphere

Results are presented of experiments performed with the 3D primitive equation model of the middle atmosphere to elucidate the connections between the behavior of planetary waves in the stratosphere and in the upper troposphere during the seasonal cycle. In these experiments the geopotential height fields at the model's lower boundary consisted of a time-varying zonally symmetric component plus a time-independent wave 1. Experiments were also performed with the same time-varying zonally symmetric component plus a time-independent combination of wave 1 and 2. In each of the wave 1-only experiments, the wave 1 amplitude in the middle stratosphere has two maxima, one in fall and the other in spring, separated by a midwinter minimum. It is suggested that some important transient features in the seasonal evolution of stratospheric planetary waves do not depend on time variations in the amplitude or phase of the corresponding tropospheric waves.

Farrara, John D.↗

NASA NTRS1992

Virtual reality and planetary exploration

NASA-Ames is intensively developing virtual-reality (VR) capabilities that can extend and augment computer-generated and remote spatial environments. VR is envisioned not only as a basis for improving human/machine interactions involved in planetary exploration, but also as a medium for the more widespread sharing of the experience of exploration, thereby broadening the support-base for the lunar and planetary-exploration endeavors. Imagery representative of Mars are being gathered for VR presentation at such terrestrial sites as Antarctica and Death Valley.

Mcgreevy, Michael W.↗

NASA NTRS1993

Evolving directions in NASA's planetary rover requirements and technology

This paper reviews the evolution of NASA's planning for planetary rovers (i.e. robotic vehicles which may be deployed on planetary bodies for exploration, science analysis, and construction) and some of the technology that has been developed to achieve the desired capabilities. The program is comprised of a variety of vehicle sizes and types in order to accommodate a range of potential user needs. This includes vehicles whose weight spans a few kilograms to several thousand kilograms; whose locomotion is implemented using wheels, tracks, and legs; and whose payloads vary from microinstruments to large scale assemblies for construction. We first describe robotic vehicles, and their associated control systems, developed by NASA in the late 1980's as part of a proposed Mars Rover Sample Return (MRSR) mission. Suggested goals at that time for such an MRSR mission included navigating for one to two years across hundreds of kilometers of Martian surface; traversing a diversity of rugged, unknown terrain; collecting and analyzing a variety of samples; and bringing back selected samples to the lander for return to Earth. Subsequently, we present the current plans (considerably more modest) which have evolved both from technological 'lessons learned' in the previous period, and modified aspirations of NASA missions. This paper describes some of the demonstrated capabilities of the developed machines and the technologies which made these capabilities possible.

Weisbin, C. R.↗

NASA NTRS1993

Impact melting and vaporization in planetary regoliths

The thermal phenomena attending high-velocity impact have profound effects on virtually every aspect of the physical, chemical, and optical evolution of planetary regoliths. Not only do impacts pulverize, redistribute, and mix the various components of a regolith, but they also fuse and vaporize them - changing crystalline material to glass, releasing trapped or implanted gases, and spreading vaporized products across the planet's surface, among many other things. Those wishing to understand the details of regolith evolution must incorporate the effects of impact into their approach to the problem. Derived from a more extensive contribution, a short summary of the thermal processes accompanying impact into planetary regoliths, with the immediate acknowledgment that it is neither exhaustive in its consideration of the existing literature nor exact in any of its treatments, is presented. The reader desiring more information is directed to the relevant papers cited at the end; should they fail to provide satisfaction, he or she is then heartily encouraged to attack the problem immediately.

Cintala, Mark J.↗

NASA NTRS1993

Qualification test of the Ross Double Planetary Mixer

This test report describes the qualification test of the Ross Double Planetary Mixer used to mix room temperature vulcanized (RTV) silicone (Dow Corning 90-006-2) for the redesigned solid rocket motor (RSRM) nozzle joints. Testing was completed 18 June 1993 in the M-113A Nozzle Fabrication Facility at Thiokol Corporation, Space Operations, Brigham City, Utah. The Ross mixer provides better mixing and better control on temperature and humidity, resulting in better quality RTV and a longer usable pot life. The test began on 3 May 1993 and was stopped due to operator error during the tensile strength and elongation testing. Specimens were ruined without gathering any useful data. A 'no test' was declared, the problem was remedied, and the test was re-run with MSFC approval. The test was run and all pass/fail criteria were met, most with a considerable margin. The Ross Double Planetary Mixer met all certification objectives and is recommended for immediate use for mixing RTV silicone for RSRM nozzle joints.

Lueders, Kurt F.↗

NASA NTRS1993

The planetary data system educational CD-ROM

The Planetary Data System (PDS) is producing a special educational CD-ROM that contains samples of PDS datasets and is expected to be released in 1993. The CD-ROM will provide university-level instructors with PDS-compatible materials and information that can be used to construct student problem sets using real datasets. The main purposes of the CD-ROM are to facilitate wide use of planetary data and to introduce a large community to the PDS. To meet these objectives the Educational CD-ROM will also contain software to manipulate the data, background discussions about scientific questions that can be addressed with the data, and a suite of exercises that illustrate analysis techniques. Students will also be introduced to the SPICE concept, which is a new way of maintaining geometry and instrument information. The exercises will be presented at the freshman through graduate student levels. With simplification, some of the material should also be of use at the high school level.

Guinness, E. A.↗

NASA NTRS1993

Teaching planetary sciences to elementary school teachers: Programs that work

Planetary sciences can be used to introduce students to the natural world which is a part of their lives. Even children in an urban environment are aware of such phenomena as day and night, shadows, and the seasons. It is a science that transcends cultures, has been prominent in the news in recent years, and can generate excitement in young minds as no other science can. Planetary sciences also provides a useful tool for understanding other sciences and mathematics, and for developing problem solving skills which are important in our technological world. However, only 15 percent of elementary school teachers feel very well qualified to teach earth/space science, while better than 80 percent feel well qualified to teach reading; many teachers avoid teaching science; very little time is actually spent teaching science in the elementary school: 19 minutes per day in K-3 and 38 minutes per day in 4-6. While very little science is taught in elementary and middle school, earth/space science is taught at the elementary level in less than half of the states. It was pointed out that science is not generally given high priority by either teachers or school districts, and is certainly not considered on a par with language arts and mathematics. Therefore, in order to teach science to our youth, we must empower our teachers, making them familiar and comfortable with existing materials. In our earlier workshops, several of our teachers taught in classrooms where the majority of the students were Hispanic (over 90 percent). However, few space sciences materials existed in Spanish. Therefore, most of our materials could not be used effectively in the classroom. To address this issue, NASA materials were translated into Spanish and a series of workshops for bilingual classroom teachers from Tucson and surrounding cities was conducted. Our space sciences workshops and our bilingual classroom workshops and how they address the needs of elementary school teachers in Arizona are addressed in detail.

Lebofsky, Larry A.↗