Vegetation health: Nature's climate monitor

Observational data to effectively evaluate weather effects, which accumulate into current climate status, are available for affluent nations but often are inadequate elsewhere. Data acquired by satellite sensors in the visible-near infrared portion of the reflected solar energy spectrum have been accumulated daily since 1965 and for the earth's emitted radiance in the 11000 nm window since 1972. With the advent of the TIROS-N satellite in 1978, the solar reflected energy has been sensed in two separate channels and beginning with NOAA-6, the second vehicle of the TIROS-N family, these two channels became complementary rather than overlapping. This feature makes vegetative monitoring possible and now is being exploited to provide daily experimental products. These global vegetative index (GVI) arrays have been used to observe and map the effects of droughts, floods, adverse winds and thermal stresses on the global arable lands. These data and the related sea surface temperatures, both derived from satellite data, provide realistic measures of the global climate and can assist climatic forecasting.     

A Survey of Software Quality Assurance

This summarizes the authors' research into the state-of-the-practice of software quality assurance (SQA) in software organizations throughout the Department of Defense (DoD). Information was obtained through personal visits to a limited number of software facilities and by utilizing a SQA questionnaire that was mailed to 27 DoD software organizations. Twenty questionnaires were returned from Army, Navy, Marine Corps, and Air Force organizations involved in the Life Cycle Software Support (LCSS) process. The survey developed information regarding such topics as: staffing; personnel qualifications; quality standards used; SQA responsibilities; error data collection; adequacy of existing documentation; staff composition; distribution of SQA effort; and workforce mix. In addition, a list of SQA ``Lessons Learned' was developed from comments made by DoD quality managers. The results of this study indicate a wide variance in the application of SQA within the DoD.     

Virus protein assembly in microgravity.

The coat of polyomavirus is composed of three proteins that can self-assemble to form an icosahedral capsid. VP1 represents 75% of the virus capsid protein and the VP1 capsomere subunits are capable of self assembly to form a capsid-like structure. Ground-based and orbiter studies were conducted with VP1 protein cloned in an expression vector and purified to provide ample quantities for capsomere-capsid assembly. Flight studies were conducted on STS-37 on April 5-9, 1991. Assembly initiated when a VP1 protein solution was interfaced with a Ca+2 buffer solution (pH 5.0). After four days a second alignment terminated the assembly process and allowed for glutaraldehyde fixation. Flight and ground-based samples were analyzed by electron microscopy. Ground-based experiments revealed the assembly of VP1 into capsid-like structures and a heterogenous size array of capsomere subunits. Samples reacted in microgravity, however, showed capsomeres of a homogenous size, but lack of capsid-like assembly.     

Space education policy — a global imperative

The discoveries and knowledge gained from space exploration and technology development are valuable scientific education tools which are not being adequately used in the classroom. Moreover, the increasing application of space technology to everyday life and industry requires a work force educated to be able to work productively in this field and to take advantage of all it has to offer. This article provides a survey of what is presently being done in the field of space education in Europe and the USA. Although encouraging, it is not nearly enough to meet the needs of 21st century society, principally because current efforts lack government or industry support. The author argues that this state of affairs must change, and proposed an international symposium as a first step towards this goal.     

Plasma-induced sputtering of an atmosphere

Magnetospheric ions, solar wind ions, and locally produced pick-up ions can impact the atmospheres of objects in the solar system, transferring energy by collisions with atmospheric atoms and molecules. This can result in an expansion of the atmospheric corona with a fraction of the energetic atoms or molecules being lost (sputtered) from the atmosphere. The expanded corona presents a larger target to the incident plasma, which in turn enhances pick-up ion formation and collisional ejection. In this manner a significant flux of atoms or molecules can be lost from an atmosphere, affecting its long-term evolution. This has been shown to be an important process for the dynamics and evolution of the atmosphere of lo, which is bombarded by the Jovian magnetospheric plasma, and for loss of atmosphere from Titan. Sputtering by pick-up ion bombardment has been shown to remove material from the atmosphere of Mars affecting the observed isotope ratios, and energetic O⁺ precipitation affects the Earth's thermosphere. The physics of ion bombardment of a gas which leads to atmospheric sputtering is described here. Analytic expressions derived from transport equations are shown to be useful for estimating the sputtering rate. These are compared to results from transport and Monte-Carlo calculations.     

The characterization of atmospheric spread functions affecting satellite remote sensing of the earth's surface

A Monte Carlo simulation program has been used to compute the signal contribution of surface elements outside the field of view of a satellite borne sensor in both the visible and infrared spectra for realistic atmospheric models. For azimuthally symmetric reflection the effect of an arbitrary surface albedo pattern can be represented by two spread functions, namely, 1) the ground-satellite spread function, and 2) the ground-ground spread function. Examples of computed spread functions are shown together with their Fourier correspondents, the modulation transfer functions. It has been shown that the central portions of the line spread functions behave as the inverse distance while the point spread functions always possess a region behaving as the inverse square of the radial distance. The median distance is shown to relate to the weighted molecular and aerosol scale height, and for large distances the spread functions become independent of the aerosol loading.     

An ultra stable optical bench for the magnetic survey satellite

An optical bench has been designed and built that must hold the alignment of five optical elements to deflections of 1–2 arc s during orbital operation. In addition, it must suffer no alignment changes during the launch and prestabilization phase of the mission. Severe weight constraints, in conjunction with the thermal and structural requirements, led to the choice of graphite fiber reinforced epoxy egg crate core and face sheets for the bench construction. Active temperature control was necessary to meet thermal deflection objectives, and novel kinematic mountings were required to prevent spacecraft bending from deflecting the bench. The structural and thermal analyses both show that the mission objectives can be met with margin by the present design. No adverse effects from launch are expected, and the maximum thermal bending is expected to be less than 2 arc s.     

Dynamics of Wind Generators on Electric Utility Networks

Dynamic interaction of wind-turbine-driven generators on electric utility networks was studied by computer simulation. Nonlinear representations of wind-turbine and various drive train elements and Park equation representations of synchronous and induction generators were implemented. An infinite capacity network was assumed. Time history responses for various system configurations were computed using as the input function severe wind gust data added to cyclical torque variations occurring at turbine blade frequency. Results indicated that severe transient mechanical and electrical stresses can be induced for certain system configurations. Best results were obtained by interposing rate or damped compliant couplings between the wind turbine and a synchronous generator. The induction generator did not appear to require such means. Blade pitch control (or equivalent) was required to limit output above rated wind velocities for wind turbines configured to produce maximum mum specific power. The blade pitch control loop must exhibit high performance to limit transient overshoots. An aerodynamically limited turbine driving an induction generator exhibited good response without the need for blade pitch control, but at the cost of increased turbine rotor diameter. Further work is indicated, taking into account wind-turbine aeroelastic effects, finite capacity networks, and other factors.     

Magnetospheric and Plasma Science with Cassini-Huygens

Magnetospheric and plasma science studies at Saturn offer a unique opportunity to explore in-depth two types of magnetospheres. These are an ‘induced’ magnetosphere generated by the interaction of Titan with the surrounding plasma flow and Saturn's ‘intrinsic’ magnetosphere, the magnetic cavity Saturn's planetary magnetic field creates inside the solar wind flow. These two objects will be explored using the most advanced and diverse package of instruments for the analysis of plasmas, energetic particles and fields ever flown to a planet. These instruments will make it possible to address and solve a series of key scientific questions concerning the interaction of these two magnetospheres with their environment. The flow of magnetospheric plasma around the obstacle, caused by Titan's atmosphere/ionosphere, produces an elongated cavity and wake, which we call an ‘induced magnetosphere’. The Mach number characteristics of this interaction make it unique in the solar system. We first describe Titan's ionosphere, which is the obstacle to the external plasma flow. We then study Titan's induced magnetosphere, its structure, dynamics and variability, and discuss the possible existence of a small intrinsic magnetic field of Titan. Saturn's magnetosphere, which is dynamically and chemically coupled to all other components of Saturn's environment in addition to Titan, is then described. We start with a summary of the morphology of magnetospheric plasma and fields. Then we discuss what we know of the magnetospheric interactions in each region. Beginning with the innermost regions and moving outwards, we first describe the region of the main rings and their connection to the low-latitude ionosphere. Next the icy satellites, which develop specific magnetospheric interactions, are imbedded in a relatively dense neutral gas cloud which also overlaps the spatial extent of the diffuse E ring. This region constitutes a very interesting case of direct and mutual coupling between dust, neutral gas and plasma populations. Beyond about twelve Saturn radii is the outer magnetosphere, where the dynamics is dominated by its coupling with the solar wind and a large hydrogen torus. It is a region of intense coupling between the magnetosphere and Saturn's upper atmosphere, and the source of Saturn's auroral emissions, including the kilometric radiation. For each of these regions we identify the key scientific questions and propose an investigation strategy to address them. Finally, we show how the unique characteristics of the CASSINI spacecraft, instruments and mission profile make it possible to address, and hopefully solve, many of these questions. While the CASSINI orbital tour gives access to most, if not all, of the regions that need to be explored, the unique capabilities of the MAPS instrument suite make it possible to define an efficient strategy in which in situ measurements and remote sensing observations complement each other. Saturn's magnetosphere will be extensively studied from the microphysical to the global scale over the four years of the mission. All phases present in this unique environment — extended solid surfaces, dust and gas clouds, plasma and energetic particles — are coupled in an intricate way, very much as they are in planetary formation environments. This is one of the most interesting aspects of Magnetospheric and Plasma Science studies at Saturn. It provides us with a unique opportunity to conduct an in situ investigation of a dynamical system that is in some ways analogous to the dusty plasma environments in which planetary systems form. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heliospheric Physics: Linking the Sun to the Magnetosphere

Research into the heliospheric structure and its relation to the solar boundary is at an impasse. After successful predictions by Parker about the zeroth-order behavior of the heliospheric magnetic field and the solar wind, the heliospheric community struggles to make substantive progress toward a predictive model describing the connections between the Sun and its space environment, between the closed corona and the open corona extending to the planets. This is caused by our lack of understanding of the basic processes heating the corona and transporting open magnetic field. We detail the models used to describe this connectivity, from potential field source surface models to full MHD techniques. We discuss the current limitations of both approaches. Finally, we address a recent attempt to advance our understanding beyond these limitations. At this point in time the proposed theory remains controversial in the community, but it addresses important shortcomings of current approaches outlined above.