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At least 937 records · Page 52

Goldstone solar system radar

This task provides for the planning, experiment design, and coordination of the data acquisition and engineering activities in support of all Goldstone planetary radar astronomy. Activities related to up-grades of the receiver systems, transmitter systems, and data processing support systems are currently intense. Also, the hardware and software maintenance of the data processing facility used by many of the Goldstone Solar System Radar investigators are covered.

Jurgens, Raymond F.

Meteoroid and Debris Impact Features Documented on the Long Duration Exposure Facility: A Preliminary Report

The Long Duration Exposure Facility (LDEF) was host to several individual experiments designed to characterize aspects of the meteoroid and space-debris environment in low-Earth orbit. It was realized from the very start, however, that the most complete way to accomplish this goal was to exploit the meteoroid and debris record of the entire LDEF. The Meteoroid and Debris Special Investigation Group (M&D SIG) was organized to achieve this end. Two dominant goals of the M&D SIG are the documentation of the impact record of the entire LDEF, and the dissemination of this information to all interested workers. As a major step towards the accomplishment of these goals, we have prepared this publication describing the M&D SIG observations of impact features made during LDEF deintegration activities at KSC in the spring of 1990. It is hoped that this report will serve as a useful guide for spacecraft designers as well as for meteoroid and space-debris workers, and that it will spur further work on the LDEF impact-laden surfaces collected by the M&D SIG and now available for allocation to qualified investigators. An important aim is to present all data and descriptions of impact features in a form which, though terse, remains comprehensible to the wider community. There is a deliberate minimum of interpretations. Thus, this catalog is intended to serve as a guide to the impact features found on LDEF and is not intended to stand as a definitive interpretive work.

See, T.

Space charge enhanced plasma gradient effects on satellite electric field measurements

It has been recognized that plasma gradients can cause error in magnetospheric electric field measurements made by double probes. Space charge enhanced Plasma Gradient Induced Error (PGIE) is discussed in general terms, presenting the results of a laboratory experiment designed to demonstrate this error, and deriving a simple expression that quantifies this error. Experimental conditions were not identical to magnetospheric conditions, although efforts were made to insure the relevant physics applied to both cases. The experimental data demonstrate some of the possible errors in electric field measurements made by strongly emitting probes due to space charge effects in the presence of plasma gradients. Probe errors in space and laboratory conditions are discussed, as well as experimental error. In the final section, theoretical aspects are examined and an expression is derived for the maximum steady state space charge enhanced PGIE taken by two identical current biased probes.

Diebold, Dan

A senior manufacturing laboratory for determining injection molding process capability

The following is a laboratory experiment designed to further understanding of materials science. This subject material is directed at an upper level undergraduate/graduate student in an Engineering or Engineering Technology program. It is assumed that the student has a thorough understanding of the process and quality control. The format of this laboratory does not follow that which is normally recommended because of the nature of process capability and that of the injection molding equipment and tooling. This laboratory is instead developed to be used as a point of departure for determining process capability for any process in either a quality control laboratory or a manufacturing environment where control charts, process capability, and experimental or product design are considered important topics.

Wickman, Jerry L.

Microwave absorption by a lossy dielectric sphere in a rectangular cavity

A new theory of absorption of microwave power by a lossy dielectric sphere in a resonant rectangular chamber is developed here. In this treatment, resonant modes of the cavity are resolved into traveling plane-wave fields, and Mie's theory of scattering and absorption of a plane electromagnetic wave by a sphere is utilized. The fields in the cavity containing the sphere are found by superposition of results for the individual scattering problem for each traveling plane wave. Absorbed power is then calculated by evaluating the time-averaged Poynting vector and integrating over the surface of the sphere. Applications of microwave power absorption are discussed, with particular emphasis on processing of materials. Numerical studies based on the newly derived formulas are presented. The results exhibit the manner in which microwave absorption is influenced by a number of different experimentally controllable parameters. The examples considered were chosen with a view toward designing experiments and apparatus for containerless processing of materials in the microgravity environment of space.

Jackson, H. W.

Microgravity effects of sea urchin fertilization and development

Gravity has been a pervasive influence on all living systems and there is convincing evidence to suggest that it alters fertilization and embryogenesis in several developmental systems. Notwithstanding the global importance of gravity on development, it has only been recently possible to begin to design experiments which might directly investigate the specific effects of this vector. The goal of this research program is to explore and understand the effects of gravity on fertilization and early development using sea urchins as a model system. Sea urchin development has several advantages for this project including the feasibility of maintaining and manipulating these cells during spaceflight, the high percentage of normal fertilization and early development, and the abundant knowledge about molecular, biochemical, and cellular events during embryogenesis which permits detailed insights into the mechanism by which gravity might interfere with development. Furthermore, skeletal calcium is deposited into the embryonic spicules within a day of fertilization permitting studies of the effects of gravity on bone calcium deposition.

Steffen, S.

A numerical investigation of East Coast cyclogenesis during the cold-air damming event of 27-28 February 1982. II - Importance of physical mechanisms

This study presents a series of numerical experiments designed to examine the role of several physical processes on the evolution of and interaction between atmospheric phenomena having different scales, each of which contributed to the development of the storm of February 27-28, 1982 along a Carolina coastal front. The physical processes include: the role of diabatic heating associated with convective and grid-scale precipitation, the role of a thermally direct transverse circulation about the entrance region of a strong polar jet streak, and modification of the marine planetary boundary layer by fluxes of heat and moisture over the Gulf Stream. The diabatic heating associated with precipitation is found to have the most significant impact on storm development. Without latent heating, cyclogenesis does not occur along the Carolina coastal front despite the presence of strong low-level baroclinicity and cyclonic vorticity. A less dramatic but still important relationship is found between storm formation and the other two physical mechanisms.

Lapenta, William M.

Viscoplastic analysis of an experimental cylindrical thrust chamber liner

A viscoplastic stress-strain analysis of an experimental cylindrical thrust chamber is presented. A viscoelastic constitutive model incorporating a single internal state variable that represents kinematic hardening was employed to investigate whether such a viscoplastic model could predict the experimentally observed behavior of the thrust chamber. Two types of loading cycles were considered: a short cycle of 3.5-s duration that corresponded to the experiments, and an extended loading cycle of 485.1 s duration that is typical of the Space Shuttle Main Engine (SSME) operating cycle. The analysis qualitatively replicated the deformation behavior of the component as observed in experiments designed to simulate SSME operating conditions. The analysis also showed that the mode and location of failure in the component may depend on the loading cycle. The results indicate that using viscoplastic models for structural analysis can lead to a more realistic life assessment of thrust chambers.

Arya, Vinod K.

Mars Observer magnetic fields investigation

The magnetic fields experiment designed for the Mars Observer mission will provide definitive measurements of the Martian magnetic field from the transition and mapping orbits planned for the Mars Observer. The paper describes the instruments (which include a classical magnetometer and an electron reflection magnetometer) and techniques designed to investigate the nature of the Martian magnetic field and the Mars-solar wind interaction, the mapping of crustal magnetic fields, and studies of the Martian ionosphere, which are activities included in the Mars Observer mission objectives. Attention is also given to the flight software incorporated in the on-board data processor, and the procedures of data processing and analysis.

Acuna, M. H.

VLBI phase-referencing for observations of weak radio sources

Phase-referencing is a technique used in VLBI to extend the signal coherence time from a few minutes to a few hours in order to enhance significantly its sensitivity. With this technique, VLBI observations of milliJansky radio sources can be conducted for high-accuracy differential astrometry as well as imaging. We describe the technique in some details and present, as an example, a submilliarcsecond differential astrometric experiment design to identify the star responsible for the weak radio emission in the binary system Algol.

Lestrade, J.-F.

Test-Matrix Sequencer

Repetitive tasks in laboratory tests automated to increase productivity. Test-matrix sequencer is digital/analog electronic system providing for automatic implementation of multiple interrelated sequences of test conditions in laboratory experiment. Designed for use in testing aeronautical propulsion systems in wind tunnels, has potential for use in automated testing laboratories in general, sequencing of servo-controlled actuators, and programming of robotic manipulators.

Mccartney, Timothy P.

Jet Engine hot parts IR Analysis Procedure (J-EIRP)

A thermal radiation analysis method called Jet Engine IR Analysis Procedure (J-EIRP) was developed to evaluate jet engine cavity hot parts source radiation. The objectives behind J-EIRP were to achieve the greatest accuracy in model representation and solution, while minimizing computer resources and computational time. The computer programs that comprise J-EIRP were selected on the basis of their performance, accuracy, and flexibility to solve both simple and complex problems. These programs were intended for use on a personal computer, but include the ability to solve large problems on a mainframe or supercomputer. J-EIRP also provides the user with a tool for developing thermal design experience and engineering judgment through analysis experimentation, while using minimal computer resources. A sample jet engine cavity analysis demonstrates the procedure and capabilities within J-EIRP, and is compared to a simplified method for approximating cavity radiation. The goal is to introduce the terminology and solution process used in J-EIRP and to provide insight into the radiation heat transfer principles used in this procedure.

Baumeister, Joseph F.

Opportunities for research on Space Station Freedom

NASA has allocated research accommodations on Freedom (equipment, utilities, etc.) to the program offices that sponsor space-based research and development as follows: Space Science and Applications (OSSA)--52 percent, Commercial Programs (OCP)--28 percent, Aeronautics and Space Technology (OAST)--12 percent, and Space Flight (OSF)--8 percent. Most of OSSA's allocation will be used for microgravity and life science experiments; although OSSA's space physics, astrophysics, earth science and applications, and solar system exploration divisions also will use some of this allocation. Other Federal agencies have expressed an interest in using Space Station Freedom. They include the National Institutes of Health (NIH), U.S. Geological Survey, National Science Foundation, National Oceanic and Atmospheric Administration, and U.S. Departments of Agriculture and Energy. Payload interfaces with space station lab support equipment must be simple, and experiment packages must be highly contained. Freedom's research facilities will feature International Standard Payload Racks (ISPR's), experiment racks that are about twice the size of a Spacelab rack. ESA's Columbus lab will feature 20 racks, the U.S. lab will have 12 racks, and the Japanese lab will have 10. Thus, Freedom will have a total of 42 racks versus 8 for Space lab. NASA is considering outfitting some rack space to accommodate small, self-contained payloads similar to the Get-Away-Special canisters and middeck-locker experiment packages flown on Space Shuttle missions. Crew time allotted to experiments on Freedom at permanently occupied capability will average 25 minutes per rack per day, compared to six hours per rack per day on Spacelab missions. Hence, telescience--the remote operation of space-based experiments by researchers on the ground--will play a very important role in space station research. Plans for supporting life sciences research on Freedom focus on the two basic goals of NASA 's space life sciences program: to ensure the health, safety, and productivity of humans in space and to acquire fundamental knowledge of biological processes. Space-based research has already shown that people and plants respond the same way to the microgravity environment: they lose structure. However, the mechanisms by which they respond are different, and researchers do not yet know much about these mechanisms. Life science research accommodations on Freedom will include facilities for experiments designed to address this and other questions, in fields such as gravitational biology, space physiology, and biomedical monitoring and countermeasures research.

Phillips, Robert W.

PROBE (Precision Reflector Orbital Build Experiment): A proposed flight experiment to study EVA assembly of precision segmented reflectors

PROBE (Precision Reflector Orbital Build Experiment) is a Shuttle flight demonstration experiment designed to study extravehicular activity (EVA) assembly of precision segmented reflectors. PROBE will support missions being considered for NASA's Global Change Technology Initiative as well as other missions in astrophysics and spacecraft optical communications requiring large precision reflectors. Such reflectors are envisioned to consist of a low-mass backup truss to which the optical surface is attached. Because of their large size, these reflectors will be constructed on-orbit from smaller pieces which can be packaged in the launch vehicle. The technology to be developed with PROBE also has application for construction of solar dynamic collectors which are planned for the enhanced configuration of Space Station Freedom. Viewgraphs of PROBE are presented.

Heard, Walter

In-step Two-phase Flow (TPF) Thermal Control Experiment

The Two-Phase Flow Thermal Control Experiment is part of the NASA/OAST In-Space Technology Experiments (In-STEP) Program. The experiment is configured for the Hitchhiker Shuttle payload system and consists of a capillary pumped loop, heatpipe radiator, and two-phase flow heat exchanger. The flight experiment design approach, test plan, payload design, and test components are described in outline and graphic form.

Source record

NPB Cesium Space Experiment

Neutral Particle Beam (NPB) weapons systems are planned to perform the ballistic missile defense functions of nuclear weapon/decoy discrimination and warhead kill at appropriate energy levels and ion currents. Negatively charged ions are produced in a specialized ion source and focused into a high quality particle beam. NPB linear accelerators accelerate and steer the negatively charged ions using electric and magnetic fields. After acceleration and steering the neutralizer system strips away extra electrons from ions to form the electrically neutral particle beam. The neutral beam then travels through space to the target unaffected by the Earth's magnetic fields. Continuing technological advances have greatly reduced the size and weight of NPB accelerator systems. Ion current production has been enhanced by over 100 percent with the intermittent addition of cesium at the NPB ion source device. This increase in current is essential to attain the most light weight, compact NPB platforms and minimize expensive launch costs. Addition of cesium into the ion source has been identified by the NPB community as the highest priority risk reduction space experiment necessary prior to planned NPB accelerator experiments and later weapons systems. The NPB Cesium Space Experiment is planned to successfully demonstrate controlled cesium introduction and vaporization into a simulated ion source chamber. Microgravity effects on the cesium deposition will be studied as will the effects of small amounts of cesium on high voltage accelerator components that might be susceptible to electrical insulator break downs. The experiment design will simulate as closely as possible the environment, physical and operational characteristics of the actual NPB ion source.

Parsons, George M., III

Lightning-induced effects on VLF/LF radio propagation

In recent years, at least two different ways in which energy from lightning discharges couples into the lower ionosphere and the radiation belts have come to the fore. In this paper, we briefly review these recent results especially from the point of view of their effects on VLF/LF radio propagation in the earth-ionosphere wave guide. We separately discuss two different mechanisms of coupling, namely lightning-induced electron precipitation, and lightning-induced heating and ionization of the lower ionosphere. We also discuss a planned active VLF wave-injection experiment designed to investigate ionospheric heating by VLF waves under controlled conditions and to generate ELF waves by modulated VLF heating.

Inan, U. S.

The power spectrum of IRAS galaxies

A technique is presented for removing the power spectrum in flux-limited galaxy catalogs is presented and tested using Monte Carlo simulations of the IRAS survey based on N-body realizations of a standard CDM universe. The technique is applied to the 1.2 Jy IRAS catalog, comparing the resulting IRAS power spectrum with previous results in the literature. A qualitative comparison of the IRAS power spectrum with various theoretical models is shown. An extensive set of Monte Carlo experiments designed to test quantitatively the validity of standard CDM on large scales is described.

Fisher, Karl B.