UV photobiochemistry under space conditions

The response of spores of Bacillus subtilis, cells of Deinococcus radiodurans and conidia of Aspergillus ochraceus to actual and simulated space conditions (UV in combination with long-term exposure to extremely dry conditions, including vacuum) has been studied: The following effects have been analyzed: decrease of viability, occurrence of DNA double strand breaks, formation of DNA-protein cross-links and DNA-DNA cross-links. All organisms show an increased sensitivity to UV light in extreme dryness (dry argon or vacuum) compared to an irradiation in aqueous suspension. The UV irradiation leads in all cases to a variety of DNA lesions. Very conspicuous is the occurrence of double strand breaks. Most of these double strand breaks are produced by incomplete repair of other lesions, especially base damages. The increase in DNA lesions can be correlated to the loss in viability. The specific response of the chromosomal DNA to UV irradiation in extreme dryness, however, varies from species to species and depends on the state of dehydration. The formation of DNA double strand breaks and DNA-protein cross-links prevails in the case of B. subtilis spores. In cells of Deinococcus radiodurans DNA-DNA cross-links often predominate, in conidia of Aspergillus ochraceus double strand breaks. The results obtained by direct exposure to space conditions (EURECA mission and D2 mission) largely agree with the laboratory data.     

Physical properties of dust grains deduced by optical probing techniques

In-situ space observations of dust in the solar system are seldom possible. On the opposite, remote observations of solar light scattered by dust are relatively easy to perform from Earth- or satellite-based observatories; the evolution of the polarization of light scattered by dust particles as a function of the phase angle may provide information on the physical properties of these particles. Unfortunately, since remote observations are integrated along the line-of-sight of the observer, they can hardly be used to determine local physical properties. We have precisely developed Optical Probe techniques to forge the link between the numerous remote observations and the unique in-situ measurements. A short review of the remote observations of light scattered by cometary dust is first presented. Then, the Optical Probe concept is analyzed. Finally, the OPE instrument, which had been designed to optically probe the inner coma of comet Halley is described; its limitations and its achievements during Halley and Grigg-Skjellerup encounters are discussed.     

Evaluation of Cyanothece sp. ATCC 51142 as a candidate for inclusion in a CELSS.

Controlled ecological life support systems (CELSS) have been proposed to make long-duration manned space flights more cost-effective. Higher plants will presumably provide food and a breathable atmosphere for the crew. It has been suggested that imbalances between the CO2/O2 gas exchange ratios of the heterotrophic and autotrophic components of the system will inevitably lead to an unstable system, and the loss of O2 from the atmosphere. Ratio imbalances may be corrected by including a second autotroph with an appropriate CO2/O2 gas exchange ratio. Cyanothece sp. ATCC 51142 is a large unicellular N2-fixing cyanobacterium, exhibiting high growth rates under diverse physiological conditions. A rat-feeding study showed the biomass to be edible. Furthermore, it may have a CO2/O2 gas exchange ratio that theoretically can compensate for ratio imbalances. It is suggested that Cyanothece spp. could fulfill several roles in a CELSS: supplementing atmosphere recycling, generating fixed N from the air, providing a balanced protein supplement, and protecting a CELSS in case of catastrophic crop failure.     

INTERBALL statistical study of ion flow fluctuations in the plasma sheet

We use ion distribution measurements with CORALL instrument on-board the INTERBALL/Tail spacecraft to study plasma flows in the mid-tail (−9> X> −27 R_E) plasma sheet. Three velocity components computed every 2 minutes exhibit two types of velocity variations: Earthward bursty bulk flows (BBFs) and random flow fluctuations. Their properties are in a good agreement with the observations of the ISEE-2 spacecraft (Borovsky et al., 1997). The INTERBALL/Tail spacecraft configuration favors measurements of V_z component, in contrast to previous experiments in which only V_x and V_y were measured reliably. In the outer part of the plasma sheet V_y and V_z fluctuations were close to each other (variances σ(V_y) and σ(V_z) were about 160 and 110 km/s, respectively), but in the inner part at the dusk flank amplitude of V_y fluctuations increased and was 2 times higher than that of V_z component. This asymmetry of fluctuations should be taken into account during modern theoretical analysis and simulations.     

Advanced regenerative environmental control and life support systems: Air and water regeneration

Extended manned space missions will require regenerative life support techniques. Past U.S. manned missions used nonregenerative expendables, except for a molecular sieve-based carbon dioxide removal system aboard Skylab. The resupply penalties associated with expendables becomes prohibitive as crew size and mission duration increase. The U.S. Space Station, scheduled to be operational in the 1990's, is based on a crew of four to sixteen and a resupply period of 90 days or greater. It will be the first major spacecraft to employ regenerable techniques for life support. The paper uses the requirements for the Space Station to address these techniques.     

The influence of gravity on the structure and functions of plant material

Growth process generate plant form and relate to most physiological functions. The Earth's gravity force affects plant growth in both obvious and subtle ways. It is a major environmental influence on morphology and physiology of plants. Gravity is less important as an agent for plant stress than as an environmental signal to guide growth. The plant's bioaccelerometers are remarkably sensitive, especially in hypogravity. Simulation (clinostat) studies and experiments in satellite laboratories are needed to understand the sensing, transduction, and response characteristics of g related mechanisms. By examining how plants alter growth processes to accomplish developmental or physiological “objectives” we may find it pragmatically desirable to ask ourselves how we might design a plant to achieve such responses to environmental influences. Examples of this design engineering approach for gravity related effects are described as an aid to experimentation.     

New multifrequency measurements of the spectrum of the cosmic background radiation

New measurements of the Cosmic Background Radiation temperature at 12 cm, 6.3 cm, 3 cm, 0.9 cm and 0.3 cm have made in July 1982 from the White Mountain High Altitude Research Station. The results are presented and the existence of spectral distortions discussed.     

The influence of radiation quality on the formation of DNA breaks.

We have aimed to present a comprehensive review of our understanding to date of the formation of DNA strand breaks induced by high LET radiation. We have discussed data obtained from DNA in solution as well as from the formation and "repair" of strand breaks in cell DNA. There is good agreement, qualitatively, between these two systems. Results were evaluated for two parameters: (1) effectivity per particle, the cross section (sigma) in micrometers 2/particle; and (2) the strand break induction frequency as number of breaks per Gy per unit DNA (bp or dalton). A series of biological effects curves (one for each Z-number) is obtained in effectivity versus LET plots. The relationships between induction frequencies of single-strand breaks, or double-strand breaks, or the residual "irrepairable" breaks and LET-values have been evaluated and discussed for a wide spectrum of heavy ions, both for DNA in solution and for DNA in the cell. For radiation induced total breaks in cell DNA, the RBE is less than one, while the RBE for the induction of DSBs can be greater than one in the 100-200 keV/micrometers range. The level of irrepairable strand breaks is highest in this same LET range and may reach 25 percent of the initial break yield. The data presented cover results obtained for helium to uranium particles, covering a particle incident energy range of about 2 to 900 MeV/u with a corresponding LET range of near 16 to 16000 keV/micrometers.     

Biological life support for manned missions by ESA.

The anticipated evolution of life support technologies for ESA, considering both the complementary life support system requirements and the missions' characteristics, is presented. Based on these results, promising biological life support technologies for manned space missions have been selected by ESA either for their intrinsic ability and performance in effecting specific tasks for atmosphere-, water-, waste-management versus physico-chemical alternatives and/or for longer-term application to a more ecological concept (CES) focusing ultimately on food production. Actual status and plan for terrestrial and space testing of biological life support presented focusing on the "task specific" decontamination technology of the Biological Air Filter (BAF), and on food reprocessing technologies from biodegradable wastes with the MELISSA microbial ecosystem.