Long-term survival of bacterial spores in space.

On board of the NASA Long Duration Exposure Facility (LDEF), spores of Bacillus subtilis in monolayers (10(6)/sample) or multilayers (10(8)/sample) were exposed to the space environment for nearly six years and their survival was analyzed after retrieval. The response to space parameters, such as vacuum (10(-6) Pa), solar electromagnetic radiation up to the highly energetic vacuum-ultraviolet range (10(9) J/m2) and/or cosmic radiation (4.8 Gy), was studied and compared to the results of a simultaneously running ground control experiment. If shielded against solar ultraviolet (UV)-radiation, up to 80 % of spores in multilayers survive in space. Solar UV-radiation, being the most deleterious parameter of space, reduces survival by 4 orders of magnitude or more. However, up to 10(4) viable spores were still recovered, even in completely unprotected samples. Substances, such as glucose or buffer salts serve as chemical protectants. With this 6 year study in space, experimental data are provided to the discussion on the likelihood of "Panspermia".     

Annual solar UV exposure and biological effective dose rates on the Martian surface.

The ultraviolet (UV) environment of Mars has been investigated to gain an understanding of the variation of exposure throughout a Martian year, and link this flux to biological effects and possible survival of organisms at the Martian surface. To gain an idea of how the solar UV radiation varies between different regions, including planned landing sites of two future Mars surface missions, we modelled the total solar UV surface flux throughout one Martian year for two different dust scenarios. To understand the degree of solar UV stress on micro-organisms and/or molecules essential for life on the surface of Mars, we also calculated the biologically effective dose (BED) for T7 and Uracil in relevant wavelength regions at the Martian surface as a function of season and latitude, and discuss the biological survival rates in the presence of Martian solar UV radiation. High T7/Uracil BED ratios indicate that even at high latitudes where the UV flux is significantly reduced, the radiation environment is still hostile for life due to the persisting UV-C component of the flux.     

Dayside reconnection during IMF northward: A possible foreshock effect

The northward and southward orientation of the interplanetary magnetic field (IMF) is usually considered as providing the external boundary conditions in the solar wind interaction with the Earth's magnetopause but it is the magnetic field in the magnetosheath that interacts with the Earth's magnetic field. In this paper, we consider the possibility that the wave activity in the foreshock region may affect the magnetic field orientation in the magnetosheath with time scales that might be geomagnetically effective. If magnetosheath magnetic field becomes disturbed on plasma streamlines which are connected to the quasi-parallel bow shock and foreshock, the magnetic field orientation on the inner magnetosheath may differ significantly from the undisturbed IMF. We present a model of dayside reconnection which may occur when the IMF northward and illustrate its effects on the erosion of the magnetopause.     

Pigment composition and concentrations within the plant (Ceratophyllum demersum L.) component of the STS-89 C.E.B.A.S. Mini-Module spaceflight experiment.

The Closed Equilibrated Biological Aquatic System (C.E.B.A.S.) Mini-Module, a Space Shuttle middeck locker payload which supports a variety of aquatic inhabitants (fish, snails, plants and bacteria) in an enclosed 8.6 L chamber, was tested for its biological stability in microgravity. The aquatic plant, Ceratophyllum demersum L., was critical for the vitality and functioning of this artificial mini-ecosystem. Its photosynthetic pigment concentrations were of interest due to their light harvesting and protective functions. "Post-flight" chlorophyll and carotenoid concentrations within Ceratophyllum apical segments were directly related to the quantities of light received in the experiments, with microgravity exposure (STS-89) failing to account for any significant deviation from ground control studies.     

Solar UV irradiance variation during cycles 22 and 23

The Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) aboard the Upper Atmosphere Research Satellite (UARS) has been measuring solar UV irradiances since October 1991, a period which includes the decline of solar cycle 22 followed by the rise of cycle 23. Daily solar measurements include scans over the wavelength range 115–410 nm at 1.1 nm resolution. As expected, the measured time series of UV irradiances exhibit strong periodicities in solar cycle and solar rotation. For all wavelengths, the UV irradiance time series are similar to that of the Mg II core-to-wing ratio. During solar cycle 22, the irradiance of the strong Ly- line varied by more than a factor of two. The peak-to-peak irradiance variation declined with increasing wavelength, reaching 10% just below the Al edge at 208 nm. Between the Al edge and 250 nm the variation was 6–7%. Above 250 nm, the variation declines further until none is observed above 290 nm. Preliminary results for the first portion of cycle 23 indicate that the far UV below the Al edge is rising at about the same rate as the Mg II index while the irradiances in the Ly- emission line and for wavelengths longer than the Al edge are rising more slowly — even after accounting for the lower level of activity of cycle 23.     

The effects of microgravity on induced mutation in Escherichia coli and Saccharomyces cerevisiae.

We examined whether microgravity influences the induced-mutation frequencies through in vivo experiments during space flight aboard the space shuttle Discovery (STS-91). We prepared dried samples of repair-deficient strains and parental strains of Escherichia (E.) coli and Saccharomyces (S.) cerevisiae given DNA damage treatment. After culture in space, we measured the induced-mutation frequencies and SOS-responses under microgravity. The experimental findings indicate that almost the same induced-mutation frequencies and SOS-responses of space samples were observed in both strains compared with the ground control samples. It is suggested that microgravity might not influence induced-mutation frequencies and SOS-responses at the stages of DNA replication and/or DNA repair. In addition, we developed a new experimental apparatus for space experiments to culture and freeze stocks of E. coli and S. cerevisiae cells.     

The effect of gravity on surface temperature and net photosynthetic rate of plant leaves.

To clarify the effects of gravity on heat/gas exchange between plant leaves and the ambient air, the leaf temperatures and net photosynthetic rates of plant leaves were evaluated at 0.01, 1.0, 1.5 and 2.0 G of 20 seconds each during a parabolic airplane flight. Thermal images of leaves were captured using infrared thermography at an air temperature of 26 degrees C, a relative humidity of 15% and an irradiance of 260 W m-2. The net photosynthetic rates were determined by using a chamber method with an infrared gas analyzer at an air temperature of 20 degrees C, a relative humidity of 50% and a photosynthetic photon flux of 0.5 mmol m-2 s-1. The mean leaf temperature increased by 1 degree C and the net photosynthetic rate decreased by 13% with decreasing gravity levels from 1.0 to 0.01 G. The leaf temperature decreased by 0.5 degree C and the net photosynthetic rate increased by 7% with increasing gravity levels from 1.0 to 2.0 G. Heat/gas exchanges between leaves and the ambient air were more retarded at lower gravity levels. A restricted free air convection under microgravity conditions in space would limit plant growth by retarding heat and gas exchanges between leaves and the ambient air.     

A Far Infrared Photometer (FIRP) for the Infrared Telescope in Space (IRTS)

We describe the design and calibration of the Far-Infrared Photometer (FIRP), one of four focal plane instruments on the Infrared Telescope in Space (IRTS). The FIRP will provide absolute photometry in four bands centered at 150, 250, 400, and 700 μm with spectral resolution λ/Δλ ≈ 3 and spatial resolution ΔΘ = 0.5 degrees. High sensitivity is achieved by using bolometric detectors operated at 300 mK in an AC bridge circuit. The closed-cycle ³He refrigerator can be recycled in orbit. A 2 K shutter provides a zero reference for each field of view. More than 10% of the sky will be surveyed during the ≈3 week mission lifetime with a sensitivity of <10⁻¹³ W·cm⁻²·sr⁻¹ per 0.5 degree pixel.     

X-ray and gamma-ray observations of a white-light flare

HEAO-1 observed hard radiations (X- and gamma-rays) from a major solar flare on 11 July 1978. The observations showed gamma-ray line and continuum emission extending to the highest energy observed. The lines are identified with the 2.2 MeV line of deuterium formation and the 4.4 MeV line of inelastic scattering on ¹²C, both previously observed in the flares of August 1972 [1]. The 11 July flare was identified as a white-light flare by observations at Debrecen [2]. It thus provides the first opportunity for a detailed examination of white-light flare theories that depend upon proton heating of the photosphere. The line strength over a four-minute integration at 2.2 MeV was 1.00 ± 0.29 ph(cm² sec)⁻¹, and the gamma-ray emission (excluding the 2.2 MeV line which was appreciably delayed) lagged by less than 20 sec approximately after the hard X-ray and microwave fluxes. We conclude that the “second-stage” acceleration of high-energy solar particles must commence promptly after the impulsive phase.     

Life sciences flight hardware development for the International Space Station.

During the construction phase of the International Space Station (ISS), early flight opportunities have been identified (including designated Utilization Flights, UF) on which early science experiments may be performed. The focus of NASA's and other agencies' biological studies on the early flight opportunities is cell and molecular biology; with UF-1 scheduled to fly in fall 2001, followed by flights 8A and UF-3. Specific hardware is being developed to verify design concepts, e.g., the Avian Development Facility for incubation of small eggs and the Biomass Production System for plant cultivation. Other hardware concepts will utilize those early research opportunities onboard the ISS, e.g., an Incubator for sample cultivation, the European Modular Cultivation System for research with small plant systems, an Insect Habitat for support of insect species. Following the first Utilization Flights, additional equipment will be transported to the ISS to expand research opportunities and capabilities, e.g., a Cell Culture Unit, the Advanced Animal Habitat for rodents, an Aquatic Facility to support small fish and aquatic specimens, a Plant Research Unit for plant cultivation, and a specialized Egg Incubator for developmental biology studies. Host systems (Figure 1A, B: see text), e.g., a 2.5 m Centrifuge Rotor (g-levels from 0.01-g to 2-g) for direct comparisons between g and selectable g levels, the Life Sciences Glovebox for contained manipulations, and Habitat Holding Racks (Figure 1B: see text) will provide electrical power, communication links, and cooling to the habitats. Habitats will provide food, water, light, air and waste management as well as humidity and temperature control for a variety of research organisms. Operators on Earth and the crew on the ISS will be able to send commands to the laboratory equipment to monitor and control the environmental and experimental parameters inside specific habitats. Common laboratory equipment such as microscopes, cryo freezers, radiation dosimeters, and mass measurement devices are also currently in design stages by NASA and the ISS international partners.