A hard X-ray experiment for long-duration balloon flights

The Naval Research Lab has developed a balloon-borne hard X-ray experiment which is designed for 60- to 90-day flight durations soon to be available with around the world Sky Anchor or RACOON balloon flights. The experiment's scintillation detector is sensitive to the 15 – 250 keV X-ray energy range. The experiment includes three microcomputer systems which control the data acquisition and provide the orientation and navigation information required for global balloon flights. The data system supports global data communications utilizing the GOES satellite as well as high bit rate communications through L-band li line-of-site transmissions     

Modelling canopy photosynthesis in response to environmental conditions.

Physiological models in the plant and crop sciences provide a means of integrating different aspects of the system, in particular the interaction between plant processes and environmental factors. This paper focuses on the response of canopy photosynthesis, including adaptation, to environmental conditions. Adaptation is likely to be important when considering controlled ecological life support systems since physiological characteristics are affected by past as well as current environmental conditions. In particular, the level of photosynthetic enzymes in a plant is generally greater for plants grown in high irradiance levels than for similar plants grown in low irradiance. The models have been developed to apply to 'normal' growing conditions, although the principles will apply to closed bioregenerative systems.     

Minimizing space radiation exposure during extra-vehicular activity

Continued assembly of the International Space Station (ISS) requires numerous extra-vehicular activities (EVAs). Prudent radiological safety practices require minimizing additional exposures to crewmen during these periods. The spatial distribution of the “normal” trapped proton and electron radiation sources in low Earth orbit is strongly governed by the geomagnetic field. It is possible to use ISS trajectory information to estimate crew exposures during EVAs and to identify periods that can result in minimal EVA crew exposures through avoidance of these trapped radiation regions. Such exposure minimization planning can also accommodate the unforeseen development of a solar proton event. An EVA exposure estimation tool, EVADOSE, is described and applied to various EVA exposure scenarios. Procedures and parameters that influence EVA exposures are discussed along with techniques to minimize crew exposures.     

Fluid volumes changes induced by spaceflight

The blood volume (BV), plasma volume (PV), and extracellular fluid volume changes produced in crewmembers during spaceflights of 11-84 days were compared to changes after 14 or 28 days of bedrest. Spaceflight and bedrest produce approximately equal BV changes but the recorded PV change after spaceflight was less. However, the diurnal change in PV may explain the smaller decreases recorded after spaceflight. The cardiovascular deconditioning caused by spaceflight and bedrest was compared using the mean heart rate response to lower body negative pressure (LBNP) testing at -50 mmHg pressure. These tests show approximately equal LBNP produced heart rate changes after bedrest and spaceflight. A countermeasure which includes 4 hr of LBNP treatment at -30 mmHg and the ingestion of one l. of saline was studied and found capable of returning the heart rate response and the PV of bedrested subjects to control (prebedrest) levels suggesting that it would be useful to the crewmembers after a spaceflight.     

Observations and Models of the Long-Term Evolution of Earth’s Magnetic Field

The geomagnetic signal contains an enormous temporal range—from geomagnetic jerks on time scales of less than a year to the evolution of Earth’s dipole moment over billions of years. This review compares observations and numerical models of the long-term range of that signal, for periods much larger than the typical overturn time of Earth’s core. On time scales of 10⁵–10⁹ years, the geomagnetic field reveals the control of mantle thermodynamic conditions on core dynamics. We first briefly describe the general formalism of numerical dynamo simulations and available paleomagnetic data sets that provide insight into paleofield behavior. Models for the morphology of the time-averaged geomagnetic field over the last 5 million years are presented, with emphasis on the possible departures from the geocentric axial dipole hypothesis and interpretations in terms of core dynamics. We discuss the power spectrum of the dipole moment, as it is a well-constrained aspect of the geomagnetic field on the million year time scale. We then summarize paleosecular variation and intensity over the past 200 million years, with emphasis on the possible dynamical causes for the occurrence of superchrons. Finally, we highlight the geological evolution of the geodynamo in light of the oldest paleomagnetic records available. A summary is given in the form of a tentative classification of well-constrained observations and robust numerical modeling results.     

Growth protocols for etiolated soybeans germinated within BRIC-60 canisters under spaceflight conditions.

As part of the GENEX (Gene Expression) spaceflight experiment, protocols were developed to optimize the inflight germination and subsequent growth of 192 soybean (Glycine max cv McCall) seeds during STS-87. We describe a method which provided uniform growth and development of etiolated seedlings while eliminating root and shoot restrictions for short-term (4-7 day) experiments. Final seedling growth morphologies and the gaseous CO2 and ethylene levels present both on the last day in space and at the time of recovery within the spaceflight and ground control BRIC-60 canisters are presented.     

Energy Deposition in Planetary Atmospheres by Charged Particles and Solar Photons

We discuss here the energy deposition of solar FUV, EUV and X-ray photons, energetic auroral particles, and pickup ions. Photons and the photoelectrons that they produce may interact with thermospheric neutral species producing dissociation, ionization, excitation, and heating. The interaction of X-rays or keV electrons with atmospheric neutrals may produce core-ionized species, which may decay by the production of characteristic X-rays or Auger electrons. Energetic particles may precipitate into the atmosphere, and their collisions with atmospheric particles also produce ionization, excitation, and heating, and auroral emissions. Auroral energetic particles, like photoelectrons, interact with the atmospheric species through discrete collisions that produce ionization, excitation, and heating of the ambient electron population. Auroral particles are, however, not restricted to the sunlit regions. They originate outside the atmosphere and are more energetic than photoelectrons, especially at magnetized planets. The spectroscopic analysis of auroral emissions is discussed here, along with its relevance to precipitating particle diagnostics. Atmospheres can also be modified by the energy deposited by the incident pickup ions with energies of eV’s to MeV’s; these particles may be of solar wind origin, or from a magnetospheric plasma. When the modeling of the energy deposition of the plasma is calculated, the subsequent modeling of the atmospheric processes, such as chemistry, emission, and the fate of hot recoil particles produced is roughly independent of the exciting radiation. However, calculating the spatial distribution of the energy deposition versus depth into the atmosphere produced by an incident plasma is much more complex than is the calculation of the solar excitation profile. Here, the nature of the energy deposition processes by the incident plasma are described as is the fate of the hot recoil particles produced by exothermic chemistry and by knock-on collisions by the incident ions.     

Cavity element for resonant micro optical gyroscope

Significant strides have been made towards a feasible resonant micro optic gyro (RMOG). Uniquely crucial components have been developed. Experimental measurements, when coupled with theoretical analysis predicts that 1 degree/hour performance can be achieved. Three critical elements required for the successful development have been demonstrated. A high quality trench waveguide has been designed, fabricated and demonstrated to have losses as little as 0.1 dB/cm. The waveguide has been demonstrated to have gain in the 4.0 dB/cm range. Finally, a waveguide laser has been fabricated and has shown nearly enough power to adequately drive an RMOG. Analysis of the measured performance predicts that a 1 degree/hour RMOG can be constructed. The small size and projected ruggedness of the RMOG will be advantageous in high G applications. Other applications, such as man portable guidance systems, where weight and size are critical, may also benefit from RMOG technology     

Surface and downhole prospecting tools for planetary exploration: tests of neutron and gamma ray probes

The ability to locate and characterize icy deposits and other hydrogenous materials on the Moon and Mars will help us understand the distribution of water and, therefore, possible habitats at Mars, and may help us locate primitive prebiotic compounds at the Moon's poles. We have developed a rover-borne neutron probe that localizes a near-surface icy deposit and provides information about its burial depth and abundance. We have also developed a borehole neutron probe to determine the stratigraphy of hydrogenous subsurface layers while operating within a drill string segment. In our field tests, we have used a neutron source to "illuminate" surrounding materials and gauge the instruments' efficacy, and we can simulate accurately the observed instrument responses using a Monte Carlo nuclear transport code (MCNPX). An active neutron source would not be needed for lunar or martian near-surface exploration: cosmic-ray interactions provide sufficient neutron flux to depths of several meters and yield better depth and abundance sensitivity than an active source. However, for deep drilling (>or=10 m depth), a source is required. We also present initial tests of a borehole gamma ray lithodensity tool and demonstrate its utility in determining soil or rock densities and composition.     

Radiation measured during ISS-Expedition 13 with different dosimeters

Radiation in low Earth orbit (LEO) is mainly composed of galactic cosmic rays (GCR), solar energetic particles and particles in SAA (South Atlantic Anomaly). The biological impact of space radiation to astronauts depends strongly on the particles’ linear energy transfer (LET) and is dominated by high LET radiation. It is important to measure the LET spectrum for the space radiation field and to investigate the influence of radiation on astronauts. At present, the preferred active dosimeters sensitive to all LET are the tissue equivalent proportional counter (TEPC) and the silicon detectors in various configurations; the preferred passive dosimeters are CR-39 plastic nuclear track detectors (PNTDs) sensitive to high LET and thermoluminescence dosimeters (TLDs) as well as optically stimulated luminescence dosimeters (OSLDs) sensitive to low LET. The TEPC, CR-39 PNTDs, TLDs and OSLDs were used to investigate the radiation field for the ISS mission Expedition 13 (ISS-12S) in LEO. LET spectra and radiation quantities (fluence, absorbed dose, dose equivalent and quality factor) were measured for the space mission with different dosimeters. This paper introduces the role of high LET radiation in radiobiology, the operational principles for the different dosimeters, the LET spectrum method using CR-39 detectors, the method to combine the results measured with TLDs/OSLDs and CR-39 PNTDs, and presents the LET spectra and the radiation quantities measured and combined.