Implicit plasma simulation

Implicit time integration methods have been used extensively in numerical modelling of slowly varying phenomena in systems that also support rapid variation. Examples include diffusion, hydrodynamics and reaction kinetics. This article discusses implementation of implicit time integration in plasma codes of the “particle-in-cell” family, and the benefits to be gained.     

Petrographic criteria for recognizing certain types of impact spherules in well-preserved precambrian successions

Impact spherule layers in sedimentary successions can open a new window on large impacts to complement the better-known record of terrestrial craters. At least six spherule layers have been found in well-preserved late Archean to Paleoproterozoic strata, and a growing body of geochemical evidence indicates they are impact ejecta. The most distinctive characteristics of these impact spherules are: (1) a predominance of highly spherical grains; (2) the presence of grains with unusual shapes such as teardrops and dumbbells; (3) fibroradial aggregates of K-feldspar crystals nucleated on the edges of spherules; and (4) clear internal spots representing both cement-filled vesicles and replaced glass cores, which, in contrast to the nuclei of ooids and armored lapilli, are not always located in the centers of the spherules. These characteristics permit the reliable differentiation of these impact spherules from spheroidal particles of other origins, such as sedimentary ooids or volcanic accretionary lapilli, often with just a hand lens. However, petrographic identification becomes progressively more difficult as the spherules become smaller or more altered. Moreover, impact spherules in other layers of other ages sometimes have different textures, so the ones described here are not representative of all types of impact spherules. They are provided as a starting point for researchers interested in identifying impact spherule layers. Given the visible record of impacts on the Moon and the much greater mass of the Earth, there should be many more impact spherule layers on Earth than have been discovered to date.     

The Composition of Interstellar Molecular Clouds

We consider four aspects of interstellar chemistry for comparison with comets: molecular abundances in general, relative abundances of isomers (specifically, HCN and HNC), ortho/para ratios for molecules, and isotopic fractionation, particularly for the ratio hydrogen/deuterium. Since the environment in which the solar system formed is not well constrained, we consider both isolated dark clouds where low mass stars may form and the "hot cores" that are the sites of high mass star formation. Attention is concentrated on the gas phase, since the grains are considered elsewhere in this volume. This revised version was published online in June 2006 with corrections to the Cover Date.     

Economics of the solid rocket booster for space shuttle

Solid Rocket Boosters (SRB's) became viable contenders as the booster for the Space Transportation System (STS) early in the concept studies of Space Shuttle because of their low development cost compared with equivalent liquid propellant boosters. Program risks and costs have been held down by scaling and adapting existing technology to the 146 in. SRB selected for development. To retain this low cost edge for the operational phase, NASA has concentrated on maintaining or reducing the cost of expendables and has demonstrated the feasibility of reusing the expensive nonexpendable SRB hardware. Drop tests of Titan III motor cases and nozzles in 1973 proved that boosters could survive water impact at vertical velocities of approx. 100 ft/s. SRB components have been designed with reuse in mind. In most cases, hardware designed for ascent will withstand water impact loads with little modification.

Cost effective refurbishment is a foremost design consideration. Continuing review of each component assures that design for reusability and/or cost of refurbishment does not become so costly that a low-cost expendable approach may be more cost effective.

The cost of expendables has been minimized by selecting proven propellants, insulations, and nozzle ablatives whose costs are well known. The propellant, which is approx. 95% of the expendables, is the lowest cost composite formulation available. As lower cost ablative materials such as pitch carbon fibers become available in quantity and are reliably demonstrated, they will be introduced to reduce operations costs.

Thus, by use of proven technology, low cost expendables and reuse of more expensive non-expendables, the development and operations costs of SRB's are held to a level that make the SRB an economical booster for the Space Shuttle.     

Heat transfer of thermocapillary convection in a two-layered fluid system under the influence of magnetic field

Heat transfer of a two-layer fluid system has been of great importance in a variety of industrial applications. For example, the phenomena of immiscible fluids can be found in materials processing and heat exchangers. Typically in solidification from a melt, the convective motion is the dominant factor that affects the uniformity of material properties. In the layered flow, thermocapillary forces can come into an important play, which was first emphasized by a previous investigator in 1958. Under extraterrestrial environments without gravity, thermocapillary effects can be a more dominant factor, which alters material properties in processing. Control and optimization of heat transfer in an immiscible fluid system need complete understanding of the flow phenomena that can be induced by surface tension at a fluid interface. The present work is focused on understanding of the magnetic field effects on thermocapillary convection, in order to optimize material processing. That is, it involves the study of the complicated phenomena to alter the flow motion in crystal growth. In this effort, the Marangoni convection in a cavity with differentially heated sidewalls is investigated with and without the influence of a magnetic field. As a first step, numerical analyzes are performed, by thoroughly investigating influences of all pertinent physical parameters. Experiments are then conducted, with preliminary results, for comparison with the numerical analyzes.     

A liquid propulsion panorama

Liquid-propellant rocket engines are widely used all over the world, thanks to their high performances, in particular high thrust-to-weight ratio. The present paper presents a general panorama of liquid propulsion as a contribution of the IAF Advanced Propulsion Prospective Group.After a brief history of its past development in the different parts of the world, the current status of liquid propulsion, the currently observed trends, the possible areas of future improvement and a summarized road map of future developments are presented. The road map includes a summary of the liquid propulsion status presented in the “Year in review 2007” of Aerospace America.Although liquid propulsion is often seen as a mature technology with few areas of potential improvement, the requirements of an active commercial market and a renewed interest for space exploration has led to the development of a family of new engines, with more design margins, simpler to use and to produce associated with a wide variety of thrust and life requirements.     

Finite-Difference Modeling of Acoustic and Gravity Wave Propagation in Mars Atmosphere: Application to Infrasounds Emitted by Meteor Impacts

The Jovian Auroral Distributions Experiment (JADE) on Juno provides the critical in situ measurements of electrons and ions needed to understand the plasma energy particles and processes that fill the Jovian magnetosphere and ultimately produce its strong aurora. JADE is an instrument suite that includes three essentially identical electron sensors (JADE-Es), a single ion sensor (JADE-I), and a highly capable Electronics Box (EBox) that resides in the Juno Radiation Vault and provides all necessary control, low and high voltages, and computing support for the four sensors. The three JADE-Es are arrayed 120^° apart around the Juno spacecraft to measure complete electron distributions from ～0.1 to 100 keV and provide detailed electron pitch-angle distributions at a 1 s cadence, independent of spacecraft spin phase. JADE-I measures ions from ～5 eV to ～50 keV over an instantaneous field of view of 270^°×90^° in 4 s and makes observations over all directions in space each 30 s rotation of the Juno spacecraft. JADE-I also provides ion composition measurements from 1 to 50 amu with m/Δm～2.5, which is sufficient to separate the heavy and light ions, as well as O+ vs S+, in the Jovian magnetosphere. All four sensors were extensively tested and calibrated in specialized facilities, ensuring excellent on-orbit observations at Jupiter. This paper documents the JADE design, construction, calibration, and planned science operations, data processing, and data products. Finally, the Appendix describes the Southwest Research Institute [SwRI] electron calibration facility, which was developed and used for all JADE-E calibrations. Collectively, JADE provides remarkably broad and detailed measurements of the Jovian auroral region and magnetospheric plasmas, which will surely revolutionize our understanding of these important and complex regions.     

An Investigation of the Mechanical Properties of Some Martian Regolith Simulants with Respect to the Surface Properties at the InSight Mission Landing Site

In support of the InSight mission in which two instruments (the SEIS seismometer and the \(\mbox{HP}^{3}\) heat flow probe) will interact directly with the regolith on the surface of Mars, a series of mechanical tests were conducted on three different regolith simulants to better understand the observations of the physical and mechanical parameters that will be derived from InSight. The mechanical data obtained were also compared to data on terrestrial sands. The density of the regolith strongly influences its mechanical properties, as determined from the data on terrestrial sands. The elastoplastic compression volume changes were investigated through oedometer tests that also provided estimates of possible changes in density with depth. The results of direct shear tests provided values of friction angles that were compared with that of a terrestrial sand, and an extrapolation to lower density provided a friction angle compatible with that estimated from previous observations on the surface of Mars. The importance of the contracting/dilating shear volume changes of sands on the dynamic penetration of the mole was determined, with penetration facilitated by the \(\sim1.3~\mbox{Mg/m}^{3}\) density estimated at the landing site. Seismic velocities, measured by means of piezoelectric bender elements in triaxial specimens submitted to various isotropic confining stresses, show the importance of the confining stress, with lesser influence of density changes under compression. A power law relation of velocity as a function of confining stress with an exponent of 0.3 was identified from the tests, allowing an estimate of the surface seismic velocity of 150 m/s. The effect on the seismic velocity of a 10% proportion of rock in the regolith was also studied. These data will be compared with in situ data measured by InSight after landing.