Physical simulation for low-energy astrobiology environmental scenarios

Speculations about the extent of life of independent origin and the potential for sustaining Earth-based life in subsurface environments on both Europa and Mars are of current and relevant interest. Theoretical modeling based on chemical energetics has demonstrated potential options for viable biochemical metabolism (metabolic pathways) in these types of environments. Also, similar environments on Earth show microbial activity. However, actual physical simulation testing of specific environments is required to confidently determine the interplay of various physical and chemical parameters on the viability of relevant metabolic pathways. This testing is required to determine the potential to sustain life in these environments on a specific scenario by scenario basis. This study examines the justification, design, and fabrication of, as well as the culture selection and screening for, a psychrophilic/halophilic/anaerobic digester. This digester is specifically designed to conform to physical testing needs of research relating to potential extent physical environments on Europa and other planetary bodies in the Solar System. The study is a long-term effort and is currently in an early phase, with only screening-level data at this time. Full study results will likely take an additional 2 years. However, researchers in electromagnetic biosignature and in situ instrument development should be aware of the study at this time, as they are invited to participate in planning for future applications of the digester facility.     

Electrification of Polymer Films in Laboratory and under Space Conditions

A simplified theory of the electrification of polymer films, which permits estimation of the internal electric fields of films irradiated by monoenergetic electrons simulating real streams of plasma electrons during magnetic substorms at a geosynchronous orbit, is suggested. To determine the depth behavior of the forward current and the dosage rate in the irradiated polymer, numerical calculations are made by the Monte Carlo technique. The appearance of electrostatic discharges in thin (5 m) mylar films is shown to be very probable in the orbit's shadow sector under magnetic substorm conditions.     

Ceramic photocell implants could restore sight

Researchers are perfecting the use of ceramic photocells for retinal implantation. The work is being done at the Space Vacuum Epitaxy Center in Houston, TX. The photocells are the results of experiments with oxide detectors conducted in space using the Wake Shield Facility. Artificial retinas are constructed of 100,000 microscopic ceramic detectors attached to a polymer film, which disintegrates after implantation. Initially, four arrays will be implanted, totalling 400,000 detectors per eye. If successful, two additional arrays would be implanted. Human trials are expected to begin in 2002.     

Certain approaches to the development of on-board automated training system

Perspectives of long-term space programs make it necessary to develop autonomous computer expert system for crew-members physical state control. The purpose of the work--to develop a set of objective formalizable physiological indices of working capacity suitable for reliable algorithmization of physical state control. Investigations were performed in on-earth microgravity simulation (3- and 7-day dry immersion, 6 subjects; 4-month antiorthostatic hypokinesy, 10 subjects) with volunteers' participation as well with 34 members of MIR-station expeditions during flights. Model exercise investigations were made also with 20 young male volunteers to evaluate the validity of different physical state indices. A set of indices was found which, being simple enough for measuring, performs to get satisfactory adequate evaluations of current organism physical state in long-term real or simulated microgravity. It was proved that some ergometric indices along with heart rate derivatives could reflect real working ability even better than traditional characteristics of organism energy systems state.     

Solar particle event dose distributions: parameterization of dose-time profiles

Calculations of total dose and dose equivalent as a function of time since the start of the event are presented for four of the major solar particle events that occurred during the period from August to December 1989. Results are presented for exposures to the skin, ocular lens and bone marrow shielded by a nominal thickness of aluminum shielding, comparable to that provided by a spacesuit. The calculated curves of organ dose and dose equivalent versus time are parameterized using a Weibull functional form for the fitting equation. The fitting parameters are determined using least squares regression techniques. These results provide a useful starting point for the development of methods to predict the cumulative doses and times to reach various dose limits from a limited number of dose measurements early in a solar particle event.     

The NASA Performance Assessment Workstation: cognitive performance during head-down bed rest

The NASA Performance Assessment Workstation was used to assess cognitive performance changes in eight males subjected to seventeen days of 6 degrees head-down bed rest. PAWS uses six performance tasks to assess directed and divided attention, spatial, mathematical, and memory skills, and tracking ability. Subjective scales assess overall fatigue and mood state. Subjects completed training trials, practice trials, bed rest trials, and recovery trials. The last eight practice trials and all bed rest trials were performed with subjects lying face-down on a gurney. In general, there was no apparent cumulative effect of bed rest. Following a short period of performance stabilization, a slight but steady trend of performance improvement was observed across all trials. For most tasks, this trend of performance improvement was enhanced during recovery. No statistically significant differences in performance were observed when comparing bed rest with the control period. Additionally, fatigue scores showed little change across all periods.     

The Huygens Doppler Wind Experiment ' Titan Winds Derived from Probe Radio Frequency Measurements

A Doppler Wind Experiment (DWE) will be performed during the Titan atmospheric descent of the ESA Huygens Probe. The direction and strength of Titan's zonal winds will be determined with an accuracy better than 1 m s⁻¹ from the start of mission at an altitude of ∼160 km down to the surface. The Probe's wind-induced horizontal motion will be derived from the residual Doppler shift of its S-band radio link to the Cassini Orbiter, corrected for all known orbit and propagation effects. It is also planned to record the frequency of the Probe signal using large ground-based antennas, thereby providing an additional component of the horizontal drift. In addition to the winds, DWE will obtain valuable information on the rotation, parachute swing and atmospheric buffeting of the Huygens Probe, as well as its position and attitude after Titan touchdown. The DWE measurement strategy relies on experimenter-supplied Ultra-Stable Oscillators to generate the transmitted signal from the Probe and to extract the frequency of the received signal on the Orbiter. Results of the first in-flight checkout, as well as the DWE Doppler calibrations conducted with simulated Huygens signals uplinked from ground (Probe Relay Tests), are described. Ongoing efforts to measure and model Titan's winds using various Earth-based techniques are briefly reviewed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Geometric accuracy in airborne SAR images

Uncorrected across-track motions of a synthetic aperture radar (SAR) platform can cause both a severe loss of azimuthal positioning accuracy in, and defocusing of, the resultant SAR image. It is shown how the results of an autofocus procedure can be incorporated in the azimuth processing to produce a fully focused image that is geometrically accurate in azimuth. Range positioning accuracy is also discussed, leading to a comprehensive treatment of all aspects of geometric accuracy. The system considered is an X-band SAR     

Performance analysis of linearly combined order statistic CFARdetectors

Linearly combined order statistic (LCOS) constant false-alarm rate (CFAR) detectors are examined for efficient and robust threshold estimation applied to exponentially distributed background observations for improved detection. Two optimization philosophies have been employed to determine the weighting coefficients of the order statistics. The first method optimizes the coefficients to obtain efficient estimates of clutter referred to the censored maximum likelihood (CML) and best linear unbiased (BLU) CFAR detectors. The second optimization involves maximizing the probability of detection under Swerling II targets and is referred to as the most powerful linear (MPL) CFAR detector. The BLU-CFAR detector assumes no knowledge of the target distribution in contrast to the MPL-CFAR detector which requires partial knowledge of the target distribution. The design of these CFAR detectors and the probability of detection performance are mathematically analyzed for background observations having homogeneous and heterogeneous distributions wherein the trade-offs between robustness and detection performance are illustrated