An Overview of the Fast Auroral SnapshoT (FAST) Satellite

The FAST satellite is a highly sophisticated scientific satellite designed to carry out in situ measurements of acceleration physics and related plasma processes associated with the Earth's aurora. Initiated and conceptualized by scientists at the University of California at Berkeley, this satellite is the second of NASA's Small Explorer Satellite program designed to carry out small, highly focused, scientific investigations. FAST was launched on August 21, 1996 into a high inclination (83°) elliptical orbit with apogee and perigee altitudes of 4175 km and 350 km, respectively. The spacecraft design was tailored to take high-resolution data samples (or `snapshots') only while it crosses the auroral zones, which are latitudinally narrow sectors that encircle the polar regions of the Earth. The scientific instruments include energetic electron and ion electrostatic analyzers, an energetic ion instrument that distinguishes ion mass, and vector DC and wave electric and magnetic field instruments. A state-of-the-art flight computer (or instrument data processing unit) includes programmable processors that trigger the burst data collection when interesting physical phenomena are encountered and stores these data in a 1 Gbit solid-state memory for telemetry to the Earth at later times. The spacecraft incorporates a light, efficient, and highly innovative design, which blends proven sub-system concepts with the overall scientific instrument and mission requirements. The result is a new breed of space physics mission that gathers unprecedented fields and particles observations that are continuous and uninterrupted by spin effects. In this and other ways, the FAST mission represents a dramatic advance over previous auroral satellites. This paper describes the overall FAST mission, including a discussion of the spacecraft design parameters and philosophy, the FAST orbit, instrument and data acquisition systems, and mission operations.     

Power Generation?Some Tasks and Goals

Generating capacity additions planned for the 1970's and beyond include a high percentage of nuclear power plants. The light water reactor is the dominant type of commercial nuclear reactor being installed during the 1970's. Advancement to more efficient designs, such as the high-temperature gas-cooled reactor, is expected around 1980. Prospects for the breeder reactor and fusion energy systems dictate a major research and development effort. Attempts to control effluents from fossil-fired plants have resulted in a sharp increase in the use of low sulfur fuels. Research and development efforts are being intensified in an attempt to obtain a breakthrough in methods of stack emission control.     

A thermodynamic analysis of microbial growth experiments

The common thread of energy release suggests that diverse microbial metabolic processes can be compared through thermodynamic analyses. The resulting energy and power requirements can provide quantitative constraints on habitability. Because previous thermodynamic analyses have focused on the minimum amount of energy needed for the growth of a microorganism or community, the focus of this study is to gain a fuller understanding of the microbial response to highly habitable conditions. This communication summarizes the results of a thermodynamic analysis of the energy and power consumed by microorganisms in experiments that were designed to optimize growth. Reports of microbial growth experiments taken from the literature were combined with speciation and standard state calculations to assess the overall Gibbs energy change during the experiments. Results show that similar numbers of cells (10(9) to 10(10) ) were produced in these experiments regardless of the duration of log phase growth (from <2 to >200 hours) or the total Gibbs energy change [from 1.3-29.6 kJ (mol electrons transferred)(1)]. As a result, optimal growth conditions appear to produce between 10(10) and 10(14) cells per watt of power consumed.     

Quantitative habitability

A framework is proposed for a quantitative approach to studying habitability. Considerations of environmental supply and organismal demand of energy lead to the conclusions that power units are most appropriate and that the units for habitability become watts per organism. Extreme and plush environments are revealed to be on a habitability continuum, and extreme environments can be quantified as those where power supply only barely exceeds demand. Strategies for laboratory and field experiments are outlined that would quantify power supplies, power demands, and habitability. An example involving a comparison of various metabolisms pursued by halophiles is shown to be well on the way to a quantitative habitability analysis.     

The Whirlwind computer project

The authors describe how they led the development of the Whirlwind I (WWI) digital computer and its evolution into the SAGE (Semi-Automatic Ground Environment) air-defense system for North America. The project from 1945 through 1956, beginning at a time when no general-purpose, high-speed, electronic computer existed, was from the start dedicated to performance and reliability suitable for real-time control. After several shifts in objectives, Whirlwind became an experimental system for demonstrating that a digital computer could analyze the flow of radar data and generate control orders for fighter-plane interceptions of bombers. The resulting successor computers, the AN/FSQ-7, were installed in a network across the United States and Canada in the late 1950s. The SAGE System control centers were in operation about 25 years and demonstrated a 99.8% up-time reliability. In the Whirlwind Project, vacuum tube life was raised from 500 hours to 500000 hours, marginal checking allowed the automatic detection of aging and drifting of electronic components before they reached the point of failure, random-access magnetic-core storage was invented and developed to become the industry standard computer memory for more than two decades, synchronous parallel logic was used, computer-driven cathode-ray tube displays were used for the first time, light guns were used to permit an operator to identify displayed images to the computer for action, and multiple displays were time-shared between different operators     

The Interstellar Boundary Explorer High Energy (IBEX-Hi) Neutral Atom Imager

The IBEX-Hi Neutral Atom Imager of the Interstellar Boundary Explorer (IBEX) mission is designed to measure energetic neutral atoms (ENAs) originating from the interaction region between the heliosphere and the local interstellar medium (LISM). These ENAs are plasma ions that have been heated in the interaction region and neutralized by charge exchange with the cold neutral atoms of the LISM that freely flow through the interaction region. IBEX-Hi is a single pixel ENA imager that covers the ENA spectral range from 0.38 to 6 keV and shares significant energy overlap and overall design philosophy with the IBEX-Lo sensor. Because of the anticipated low flux of these ENAs at 1 AU, the sensor has a large geometric factor and incorporates numerous techniques to minimize noise and backgrounds. The IBEX-Hi sensor has a field-of-view (FOV) of 6.5°×6.5° FWHM, and a 6.5°×360° swath of the sky is imaged over each spacecraft spin. IBEX-Hi utilizes an ultrathin carbon foil to ionize ENAs in order to measure their energy by subsequent electrostatic analysis. A multiple coincidence detection scheme using channel electron multiplier (CEM) detectors enables reliable detection of ENAs in the presence of substantial noise. During normal operation, the sensor steps through six energy steps every 12 spacecraft spins. Over a single IBEX orbit of about 8 days, a single 6.5°×360° swath of the sky is viewed, and re-pointing of the spin axis toward the Sun near perigee of each IBEX orbit moves the ecliptic longitude by about 8° every orbit such that a full sky map is acquired every six months. These global maps, covering the spectral range of IBEX-Hi and coupled to the IBEX-Lo maps at lower and overlapping energies, will answer fundamental questions about the structure and dynamics of the interaction region between the heliosphere and the LISM.     

The Plasma Ion and Electron Instruments for the Genesis Mission

The Genesis Ion Monitor (GIM) and the Genesis Electron Monitor (GEM) provide 3-dimensional plasma measurements of the solar wind for the Genesis mission. These measurements are used onboard to determine the type of plasma that is flowing past the spacecraft and to configure the solar wind sample collection subsystems in real-time. Both GIM and GEM employ spherical-section electrostatic analyzers followed by channel electron multiplier (CEM) arrays for detection and angle and energy/charge analysis of incident ions and electrons. GIM is of a new design specific to Genesis mission requirements whereas the GEM sensor is an almost exact copy of the plasma electron sensors currently flying on the ACE and Ulysses spacecraft, albeit with new electronics and programming. Ions are detected at forty log-spaced energy levels between ∼ 1 eV and 14 keV by eight CEM detectors, while electrons with energies between ∼ 1 eV and 1.4 keV are measured at twenty log-spaced energy levels using seven CEMs. The spin of the spacecraft is used to sweep the fan-shaped fields-of-view of both instruments across all areas of the sky of interest, with ion measurements being taken forty times per spin and samples of the electron population being taken twenty four times per spin. Complete ion and electron energy spectra are measured every ∼ 2.5 min (four spins of the spacecraft) with adequate energy and angular resolution to determine fully 3-dimensional ion and electron distribution functions. The GIM and GEM plasma measurements are principally used to enable the operational solar wind sample collection goals of the Genesis mission but they also provide a potentially very useful data set for studies of solar wind phenomena, especially if combined with other solar wind data sets from ACE, WIND, SOHO and Ulysses for multi-spacecraft investigations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Formate as an energy source for microbial metabolism in chemosynthetic zones of hydrothermal ecosystems

Formate, a simple organic acid known to support chemotrophic hyperthermophiles, is found in hot springs of varying temperature and pH. However, it is not yet known how metabolic strategies that use formate could contribute to primary productivity in hydrothermal ecosystems. In an effort to provide a quantitative framework for assessing the role of formate metabolism, concentration data for dissolved formate and many other solutes in samples from Yellowstone hot springs were used, together with data for coexisting gas compositions, to evaluate the overall Gibbs energy for many reactions involving formate oxidation or reduction. The result is the first rigorous thermodynamic assessment of reactions involving formate oxidation to bicarbonate and reduction to methane coupled with various forms of iron, nitrogen, sulfur, hydrogen, and oxygen for hydrothermal ecosystems. We conclude that there are a limited number of reactions that can yield energy through formate reduction, in contrast to numerous formate oxidation reactions that can yield abundant energy for chemosynthetic microorganisms. Because the energy yields are so high, these results challenge the notion that hydrogen is the primary energy source of chemosynthetic microbes in hydrothermal ecosystems.