Temperature effects in the ATIC BGO calorimeter

The Advanced Thin Ionization Calorimeter (ATIC) Balloon Experiment had a successful test flight and a science flight in 2000–01 and 2002–03 and an unsuccessful launch in 2005–06 from McMurdo, Antarctica, returning 16 and 19 days of flight data. ATIC is designed to measure the spectra of cosmic rays (protons to iron). The instrument is composed of a Silicon matrix detector followed by a carbon target interleaved with scintillator tracking layers and a segmented BGO calorimeter composed of 320 individual crystals totaling 18 radiation lengths to determine the particle energy. BGO (Bismuth Germanate) is an inorganic scintillation crystal and its light output depends not only on the energy deposited by particles but also on the temperature of the crystal. The temperature of balloon instruments during flight is not constant due to sun angle variations as well as differences in albedo from the ground. The change in output for a given energy deposit in the crystals in response to temperature variations was determined.     

Why space science and exploration benefit everyone

As well as providing practical information on Earth-besetting problems, space science and exploration are vital tools for capturing the public imagination and encouraging young people's interest in space. The relatively small scale of some scientific instruments also allows mission participation by developing countries. Citing the work of the UN and various NGOs in promoting study and distribution of space science data, the authors recommend that it be given a higher profile and suggest a number of projects -- the Mars drill study in Egypt, refurbishment of a telescope facility in Sri Lanka -- involving developing countries that should be followed up, as well as listing ongoing successful projects. The UN is urged to continue its annual workshops on space science (apparently under threat) and to ensure its inclusion in the forthcoming UNISPACE III Conference.     

X-ray emission from isolated hot white dwarfs

Hot white dwarfs are objects that copiously emit in the Extreme Ultraviolet and soft X-ray range. They are the brightest sources seen in the Low Energy Telescope of EXOSAT, with countrates up to 25 cnts/s. in contrast to their optical and UV spectrum the total flux and spectral distribution at soft X-ray energies are highly sensitive to the effective temperature, structure and elemental composition of the dwarf's atmosphere. The imaging soft X-ray experiments onboard EXOSAT cover with large sensitivity the spectral region where the peak of emission of hot white dwarfs is expected to occur.I here review some of the (preliminary) results obtained so far with broadband X-ray photometry on a dozen or so white dwarfs, and some of the high-resolution spectra obtained for three white dwarfs with the grating spectrometers.     

Newly developed techniques for the analysis of micrometer-sized interplanetary dust particles and comet grains

Electron transparent thin sections (30–100 nm thick) of interplanetary dust particles and other fine-grained meteoritic materials are produced using an ultramicrotome equipped with a diamond knife. An analytical electron microscope (AEM) is imployed to examine indigenous physical properties (e.g. porosity), mineralogy, and petrography. Large data sets of quantitative point count analyses obtained from thin sections enable direct mineralogical comparison of IDPs and Halley.     

Initiation of spherical detonation in hydrocarbon/air mixtures

Spherical detonations have been initiated by solid explosive (Tetryl) charges in well-mixed stoicheiometric air mixtures with each of the hydrocarbons, ethane, propane, n-butane, isobutane and ethylene at atmospheric pressure. Prior to initiation, the gases were contained in plastic bags; total gas volume and available path length were up to 1.6 m³ and 2 m, respectively. The detonations were shown to be self-sustained by continuous measurement of detonation velocity using X-band microwave interferometry. Measured detonation velocities were in all cases close to calculated C-J values.In a few experiments close to the limits of detonability, velocity and blast pressure/time records indicated that the propagating wave system is sometimes irregular. The irregularity that occurs just after initiation is characterised by a reaction front velocity very much lower than the constant detonation velocity, but subsequently attaining the latter by an acceleration process. These observations indicate the existence of a dissociated phase in which shock and reaction fronts may no longer be coupled.Because similar experimental conditions were used throughout, it was possible to establish the relative susceptibilities of the various fuel gases to detonation. Comparison is made with the Zeldovich criterion and a detonation kernel theory of Lee.     

Lunar Reconnaissance Orbiter Overview: The Instrument Suite and Mission

NASA’s Lunar Precursor Robotic Program (LPRP), formulated in response to the President’s Vision for Space Exploration, will execute a series of robotic missions that will pave the way for eventual permanent human presence on the Moon. The Lunar Reconnaissance Orbiter (LRO) is first in this series of LPRP missions, and plans to launch in October of 2008 for at least one year of operation. LRO will employ six individual instruments to produce accurate maps and high-resolution images of future landing sites, to assess potential lunar resources, and to characterize the radiation environment. LRO will also test the feasibility of one advanced technology demonstration package. The LRO payload includes: Lunar Orbiter Laser Altimeter (LOLA) which will determine the global topography of the lunar surface at high resolution, measure landing site slopes, surface roughness, and search for possible polar surface ice in shadowed regions, Lunar Reconnaissance Orbiter Camera (LROC) which will acquire targeted narrow angle images of the lunar surface capable of resolving meter-scale features to support landing site selection, as well as wide-angle images to characterize polar illumination conditions and to identify potential resources, Lunar Exploration Neutron Detector (LEND) which will map the flux of neutrons from the lunar surface to search for evidence of water ice, and will provide space radiation environment measurements that may be useful for future human exploration, Diviner Lunar Radiometer Experiment (DLRE) which will chart the temperature of the entire lunar surface at approximately 300 meter horizontal resolution to identify cold-traps and potential ice deposits, Lyman-Alpha Mapping Project (LAMP) which will map the entire lunar surface in the far ultraviolet. LAMP will search for surface ice and frost in the polar regions and provide images of permanently shadowed regions illuminated only by starlight. Cosmic Ray Telescope for the Effects of Radiation (CRaTER), which will investigate the effect of galactic cosmic rays on tissue-equivalent plastics as a constraint on models of biological response to background space radiation. The technology demonstration is an advanced radar (mini-RF) that will demonstrate X- and S-band radar imaging and interferometry using light weight synthetic aperture radar. This paper will give an introduction to each of these instruments and an overview of their objectives.     

Tailored analyses of 24 Galactic WN stars

The fundamental properties of 24 Galactic WN stars are determined from analyses of their optical, UV and IR spectra using sophisticated model atmosphere codes (Hillier, 1987, 1990). Terminal velocities, stellar luminosities, temperatures, mass loss rates and abundances of hydrogen, helium, carbon, nitrogen and oxygen are determined. Stellar parameters are derived using diagnostic lines and interstellar reddenings found from fitting theoretical continua to observed energy distributions.Our results confirm that the parameters of WN stars span a large range in temperature (T_*=30–90,000 K), luminosity (log L_*/L=4.8–5.9), mass loss (M=0.9–12×10^–5 M yr^–1) and terminal velocity (v =630–3300 km s^–1). Hydrogen abundances are determined, and found to be low in WNEw and WNEs stars (<15% by mass) and considerable in most WNL stars (1–50%). Metal abundances are also determined with the nitrogen content found to lie in the range N/He=1–5×10^–3 (by number) for all subtypes, and C/N 0.02 in broad agreement with the predictions of Maeder (1991). Enhanced O/N and O/C is found for HD 104994 (WN3p) suggesting a peculiar evolutionary history. Our results suggest that single WNL+abs stars may represent an evolutionary stage immediately after the Of phase. Since some WNE stars exist with non-negligible hydrogen contents (e.g. WR136) evolution may proceed directly from WNL+abs to WNE in some cases, circumventing the luminous blue variable (LBV) or red supergiant (RSG) stage.     

Toward optimizing lighting as a countermeasure to sleep and circadian disruption in space flight

Light is being used as a pre-launch countermeasure to circadian and sleep disruption in astronauts. The effect of light on the circadian system is readily monitored by measurement of plasma melatonin. Our group has established an action spectrum for human melatonin regulation and determined the region of 446-477 nm to be the most potent for suppressing plasma melatonin. The aim of this study was to compare the efficacy of 460 and 555 nm for suppressing melatonin using a within-subjects design. Subjects (N=12) were exposed to equal photon densities (7.18 x 10(12) photons/cm2/s) at 460 and 555 nm. Melatonin suppression was significantly stronger at 460 nm (p<0.02). An extension to the action spectrum showed that 420 nm light at 16 and 32 microW/cm2 significantly suppressed melatonin (p<0.04 and p<0.002). These studies will help optimize lighting countermeasures to circadian and sleep disruption during spaceflight.