Instrument Boom Mechanisms on the THEMIS Satellites; Magnetometer, Radial Wire, and Axial Booms

The five “Time History of Events and Macroscale Interactions during Substorms” (THEMIS) micro-satellites launched on a common carrier by a Delta II, 7925 heavy, on February 17, 2007. This is the fifth launch in the NASA MeDIum class EXplorer (MIDEX) program. In the mission proposal the decision was made to have the University of California Berkeley Space Sciences Laboratory (UCB-SSL) mechanical engineering staff provide all of the spacecraft appendages, in order to meet the short development schedule, and to insure compatibility. This paper describes the systems engineering, design, development, testing, and on-orbit deployment of these boom systems that include: the 1 and 2 meter carbon fiber composite magnetometer booms, the 40 and 50 m tip to tip orthogonal spin-plane wire boom pairs, and the 6.3 m dipole stiff axial booms.     

Clathrate hydrates of oxidants in the ice shell of Europa

Europa's icy surface is radiolytically modified by high-energy electrons and ions, and photolytically modified by solar ultraviolet photons. Observations from the Galileo Near Infrared Mapping Spectrometer, ground-based telescopes, the International Ultraviolet Explorer, and the Hubble Space Telescope, along with laboratory experiment results, indicate that the production of oxidants, such as H2O2, O2, CO2, and SO2, is a consequence of the surface radiolytic chemistry. Once created, some of the products may be entrained deeper into the ice shell through impact gardening or other resurfacing processes. The temperature and pressure environments of regions within the europan hydrosphere are expected to permit the formation of mixed clathrate compounds. The formation of carbon dioxide and sulfur dioxide clathrates has been examined in some detail. Here we add to this analysis by considering oxidants produced radiolytically on the surface of Europa. Our results indicate that the bulk ice shell could have a approximately 1.7-7.6% by number contamination of oxidants resulting from radiolysis at the surface. Oxidant-hosting clathrates would consequently make up approximately 12-53% of the ice shell by number relative to ice, if oxidants were entrained throughout. We examine, in brief, the consequences of such contamination on bulk ice shell thickness and find that clathrate formation could lead to substantially thinner ice shells on Europa than otherwise expected. Finally, we propose that double occupancy of clathrate cages by O2 molecules could serve as an explanation for the observation of condensed-phase O2 on Europa. Clathrate-sealed, gas-filled bubbles in the near surface ice could also provide an effective trapping mechanism, though they cannot explain the 5771 A (O2)2 absorption.     

Exposure of Arabidopsis thaliana to hypobaric environments: implications for low-pressure bioregenerative life support systems for human exploration missions and terraforming on Mars

Understanding how hypobaria can affect net photosynthetic (P (net)) and net evapotranspiration rates of plants is important for the Mars Exploration Program because low-pressured environments may be used to reduce the equivalent system mass of near-term plant biology experiments on landers or future bioregenerative advanced life support systems. Furthermore, introductions of plants to the surface of a partially terraformed Mars will be constrained by the limits of sustainable growth and reproduction of plants to hypobaric conditions. To explore the effects of hypobaria on plant physiology, a low-pressure growth chamber (LPGC) was constructed that maintained hypobaric environments capable of supporting short-term plant physiological studies. Experiments were conducted on Arabidopsis thaliana maintained in the LPGC with total atmospheric pressures set at 101 (Earth sea-level control), 75, 50, 25 or 10 kPa. Plants were grown in a separate incubator at 101 kPa for 6 weeks, transferred to the LPGC, and acclimated to low-pressure atmospheres for either 1 or 16 h. After 1 or 16 h of acclimation, CO(2) levels were allowed to drawdown from 0.1 kPa to CO(2) compensation points to assess P (net) rates under different hypobaric conditions. Results showed that P (net) increased as the pressures decreased from 101 to 10 kPa when CO(2) partial pressure (pp) values were below 0.04 kPa (i.e., when ppCO2 was considered limiting). In contrast, when ppCO(2) was in the nonlimiting range from 0.10 to 0.07 kPa, the P (net) rates were insensitive to decreasing pressures. Thus, if CO(2 )concentrations can be kept elevated in hypobaric plant growth modules or on the surface of a partially terraformed Mars, P (net) rates may be relatively unaffected by hypobaria. Results support the conclusions that (i) hypobaric plant growth modules might be operated around 10 kPa without undue inhibition of photosynthesis and (ii) terraforming efforts on Mars might require a surface pressure of at least 10 kPa (100 mb) for normal growth of deployed plant species.     

Investigating behavioural and computational approaches for defining imprecise regions

People often communicate with reference to informally agreed places, such as “the city centre”. However, views of the spatial extent of such areas may vary, resulting in imprecise regions. We compare perceptions of Sheffield’s City Centre from a street survey to extents derived from various web-based sources. Such automated approaches have advantages of speed, cost and repeatability. We show that footprints from web sources are often in concordance with models derived from more labour-intensive methods. Notable exceptions however were found with sources advertising or selling residential property. Agreement between sources was measured by aggregating them to identify locations of consensus.     

Determination of epsomite-hexahydrite equilibria by the humidity-buffer technique at 0.1 MPa with implications for phase equilibria in the system MgSO4-H2O

Epsomite (MgSO(4).7H(2)O) and hexahydrite (MgSO(4).6H(2)O) are common minerals found in marine evaporite deposits, in saline lakes as precipitates, in weathering zones of coal and metallic deposits, in some soils and their efflorescences, and possibly on the surface of Europa as evaporite deposits. Thermodynamic properties of these two minerals reported in the literature are in poor agreement. In this study, epsomite-hexahydrite equilibria were determined along four humidity-buffer curves at 0.1 MPa and between 25 and 45 degrees C. Results obtained for the reaction epsomite = hexahydrite + H(2)O, as demonstrated by very tight reversals along each humidity buffer, can be represented by ln K(+/- 0.012) = 20.001 - 7182.07/T, where K is the equilibrium constant, and T is temperature in Kelvin. The derived standard Gibbs free energy of reaction is 10.13 +/- 0.07 kJ/mol, which is essentially the same value as that calculated from vapor pressure measurements reported in the literature. However, this value is at least 0.8 kJ/mol lower than those calculated from the data derived mostly from calorimetric measurements.     

Learning ‘smaller, faster, cheaper’ from the Applied Physics laboratory

By demonstrating the ability to build ‘smaller, faster, and cheaper’ space devices, the Johns Hopkins University Applied Physics Laboratory (APL) has played a key role in influencing NASA's current Discovery program. The APL Space Department was founded by Richard B. Kershner. This article examines the key elements of Kershner's leadership and management philosophy through the Transit satellite program and the Delta series spacecraft.     

Key science questions from the second conference on early Mars: geologic, hydrologic, and climatic evolution and the implications for life

In October 2004, more than 130 terrestrial and planetary scientists met in Jackson Hole, WY, to discuss early Mars. The first billion years of martian geologic history is of particular interest because it is a period during which the planet was most active, after which a less dynamic period ensued that extends to the present day. The early activity left a fascinating geological record, which we are only beginning to unravel through direct observation and modeling. In considering this time period, questions outnumber answers, and one of the purposes of the meeting was to gather some of the best experts in the field to consider the current state of knowledge, ascertain which questions remain to be addressed, and identify the most promising approaches to addressing those questions. The purpose of this report is to document that discussion. Throughout the planet's first billion years, planetary-scale processes-including differentiation, hydrodynamic escape, volcanism, large impacts, erosion, and sedimentation-rapidly modified the atmosphere and crust. How did these processes operate, and what were their rates and interdependencies? The early environment was also characterized by both abundant liquid water and plentiful sources of energy, two of the most important conditions considered necessary for the origin of life. Where and when did the most habitable environments occur? Did life actually occupy them, and if so, has life persisted on Mars to the present? Our understanding of early Mars is critical to understanding how the planet we see today came to be.     

Atmosphere behavior in gas-closed mouse-algal systems: An experimental and modelling study

Concepts of biologically-based regenerative life support systems anticipate the use of photosynthetic organisms for air revitalization. However, mismatches in the rates of production and uptake of oxygen or carbon dioxide between the crew and the plants will lead to an accumulation or depletion of these gases beyond tolerable limits. One method for correcting these atmospheric changes is to use physicochemical devices. This would conflict with the constraint of minimal size and weight imposed upon the successful development of a competitive bioregenerative system. An alternate control strategy is based upon reducing the gas exchange mismatch by manipulation of those environmental parameters known to affect plant or algae gas exchange ratios. We have initiated a research program using a dual approach of mathematical modelling and laboratory experimentation aimed at examining the gas exchange characteristics of artificial animal/plant systems closed to the ambient atmosphere. Our goal is to develop control techniques and management strategies for maintaining the atmospheric levels of carbon dioxide and oxygen at physiological levels. A mathematical model simulating the atmospheric behavior in these systems has been developed and an experimental gas-closed system has been constructed. These will be described and preliminary results will be presented.     

Einstein observations of cool stars

Observations of cool stars with the $\text{Einstein}$ Observatory (HEAO-2) have brought about a fundamental change in our knowledge and understanding of stellar coronae. The existence of X-ray emission from stars throughout the H-R diagram, the wide range of X-ray luminosity within a given spectral and luminosity class, and the strong correlation of X-ray luminosity with stellar age and rotation are among the more significant $\text{Einstein}$ results. These results are strong evidence for the influence of stellar dynamo action on the formation and heating of stellar coronae. A discussion of relevant consortium and guest observations will be given. The Hyades cluster, in particular, will serve as an example to demonstrate the usefulness of X-ray observations in the study of stellar activity and coronal evolution.     

Automobile Navigation: Where is it Going?

Automobile navigation systems based on dead reckoning, map matching, satellite positioning and other navigation technologies are under active development. ``Map intelligent' systems achieve high relative accuracy by matching dead-reckoned paths with road geometry encoded in a digital map data base that may also serve other functions such as vehicle routing and geocoding. Satellite-based navigation systems achieve high absolute accuracy but require dead reckoning augmentation because of signal aberrations in the automotive environment. Future systems will probably include multiple navigation technologies. Issues influencing the design of future systems include safety concerns regarding the driver interface, and the future availability of comprehensive map data bases, real-time traffic data, and mobile data communication links necessary for on-board generation of optimum routes.