Theoretical studies of shock-initiated detonations

The dynamics of shock propagation have been studied theoretically for a variety of two-dimensional lattices. The approach used is based on molecular dynamics and hinges on the exact numerical solution by computer of the equations of motion for the individual atoms or molecules in each lattice. Shocks have been launched into the lattices under study by methods designed to simulate flyer-plate impact. Two different interatomic potentials have been used, one endothermic and one net-exothermic. For both types of potential, a shock launched at one side of the lattice will spall a group of atoms off the other side. However, the subsequent behavior of the two types of lattice is very different. For endothermic potentials, after the initial atomic spall, the residual lattice is quiescent with little further activity. For net-exothermic potentials, the initial atomic spall injects additional energy into the system in such a manner that subsequently further spall occurs at both sides. Once this new spall is initiated, it leads rapidly to further bond breaking and explosive disintegration of the system.     

Towards a Global Unified Model of Europa’s Tenuous Atmosphere

Despite the numerous modeling efforts of the past, our knowledge on the radiation-induced physical and chemical processes in Europa’s tenuous atmosphere and on the exchange of material between the moon’s surface and Jupiter’s magnetosphere remains limited. In lack of an adequate number of in situ observations, the existence of a wide variety of models based on different scenarios and considerations has resulted in a fragmentary understanding of the interactions of the magnetospheric ion population with both the moon’s icy surface and neutral gas envelope. Models show large discrepancy in the source and loss rates of the different constituents as well as in the determination of the spatial distribution of the atmosphere and its variation with time. The existence of several models based on very different approaches highlights the need of a detailed comparison among them with the final goal of developing a unified model of Europa’s tenuous atmosphere. The availability to the science community of such a model could be of particular interest in view of the planning of the future mission observations (e.g., ESA’s JUpiter ICy moons Explorer (JUICE) mission, and NASA’s Europa Clipper mission). We review the existing models of Europa’s tenuous atmosphere and discuss each of their derived characteristics of the neutral environment. We also discuss discrepancies among different models and the assumptions of the plasma environment in the vicinity of Europa. A summary of the existing observations of both the neutral and the plasma environments at Europa is also presented. The characteristics of a global unified model of the tenuous atmosphere are, then, discussed. Finally, we identify needed future experimental work in laboratories and propose some suitable observation strategies for upcoming missions.     

A tour of the ISS

The Commander of the International Space Station Expedition Three describes what the space station looks like. The tour includes the American communications link, the Express rack for science experiments, the Node with its collapsible water containers, the Airlock, the FGB, and living space in the Service Module.     

A search for soot from global wildfires in central Pacific Cretaceous-Tertiary boundary and other extinction and impact horizon sediments

Hypotheses of global wildfires following the Cretaceous-Tertiary (KT) boundary impact are supported by high concentrations of elemental carbon (3.6 mg cm(-2)) and soot (1.8 mg cm(-2)) in DSDP Site 465, which was located several thousand kilometers from potential continental sources at 65 Ma. Soot is not preserved at four other central Pacific KT localities, but this is attributed to loss during oxic diagenesis. We find no evidence for wildfires related to major impacts in the late Eocene or to Ir anomalies and extinctions in the late Cenomanian.     

Columbia: what went wrong?

The results of the Gehman board's exhaustive investigation of the Columbia accident (STS-107) will have far-reaching effects on the U.S. space program.     

Novel aquatic modules for bioregenerative life-support systems based on the closed equilibrated biological aquatic system (C.E.B.A.S.)

The closed equilibrated biological aquatic system (C.E.B.A.S) is a man-made aquatic ecosystem which consists of four subcomponents: an aquatic animal habitat, an aquatic plant bioreactor, an ammonia oxidizing bacteria filter and a data acquisition/control unit. It is a precursor for different types of fish and aquatic plant production sites which are disposed for the integration into bioregenerative life-support systems. The results of two successful spaceflights of a miniaturized C.E.B.A.S version (the C.E.B.A.S. MINI MODULE) allow the optimization of aquatic food production systems which are already developed in the ground laboratory and open new aspects for their utilization as aquatic modules in space bioregenerative life support systems. The total disposition offers different stages of complexity of such aquatic modules starting with simple but efficient aquatic plant cultivators which can be implemented into water recycling systems and ending up in combined plant/fish aquaculture in connection with reproduction modules and hydroponics applications for higher land plants. In principle, aquaculture of fishes and/or other aquatic animals edible for humans offers optimal animal protein production under lowered gravity conditions without the tremendous waste management problems connected with tetrapod breeding and maintenance. The paper presents details of conducted experimental work and of future dispositions which demonstrate clearly that aquaculture is an additional possibility to combine efficient and simple food production in space with water recycling utilizing safe and performable biotechnologies. Moreover, it explains how these systems may contribute to more variable diets to fulfill the needs of multicultural crews.     

Sensitivity Discriminating Observer Design for Instrument Failure Detection

A procedure is presented for the design of a pair of sensitivity discriminating Luenberger observers for instrument failure detection (IFD). The proposed IFD scheme permits detection of instrument malfunctions with reduced sensitivity to process parameter variations. The efficiency of detecting instrument malfunctions and the influence of parameter variations are illustrated with an example.     

MLS: keeping pace with the future

It is argued that the instrument landing system (ILS) is now at its operational limit in terms of radio frequency availability, approach flexibility, and technology. The operational requirements for a microwave landing system (MLS), which will overcome key limitations of the ILS and provide growth to meet future requirements of precision landing systems, are discussed, John F. Kennedy (JFK) International Airport and LaGuardia Airport in New York City are discussed as examples to demonstrate the capabilities of MLS     

Synthetic aperture radar image formation from compressed data usinga new computation technique

A convolution technique is proposed that allows direct reconstruction of the processed synthetic-aperture radar (SAR) image from the digitally-sampled, block-encoded raw data. This computational compression technique reduces the number of arithmetic operations from that required by fast Fourier transform (FFT) convolution for SAR processing. SAR phase histories are block encoded and directly processed into an image where only arithmetic additions are required for the processing. For SAR data previously block encoded, the processing time is reduced by a factor of 100 or more. A speed-up of three times over SAR processing by FET convolution has been demonstrated when both computation of the block encoding and subsequent direct processing are included in the time. SAR image quality measurements for a method of block encoding called vector quantization at compression ration ranging from 5:1 to 50:1 show image degradation proportional to the compression ratio. For a 5:1 compression radio, image quality measurements show minimal degradation