ExoMars alternative escape trajectories with Soyuz/Fregat.

The objectives of ExoMars are to inject an orbiter around Mars and to land a rover on the surface to look for possible traces of life. During the first stages of the feasibility analysis, the mass margin of the orbiter was very small for a direct transfer in the Soyuz/Fregat scenario. An analysis of the combined use of lunar swing-bys and the Sun gravity gradient is performed with WESBOT in order to obtain alternative trajectories for injecting higher mass into Mars transfer. WESBOT is a GMV tool to find WSB transfers to the Moon and to design escape trajectories by performing several swing-bys with the Moon and the Earth. The weak stability boundary has been successfully used for lunar transfers (Hiten, SMART-1). For escape trajectories from the Earth, the potential mass gains depend on the escape direction and the departure date to make a series of gravity assists with the help of the Sun gravity gradient to save DeltaV. Several strategies are studied depending on the number and order of swing-bys. The departing conditions (date and orbit) are optimized but the arrival date to Mars is maintained because of mission requirements. For each type of strategy, a systematic search of initial guess trajectories is performed. The initial guess trajectory is made up of patched conics arcs and multiple shooting arcs when necessary. The optimal trajectories for the various scenarios are presented and show different morphologies. An analysis in terms of applicability to the ExoMars mission is included.

Stressors, stress and stress consequences during long-duration manned space missions: a descriptive model.

Keeping crew members in good health is a major factor in the success or failure of long-duration manned space missions. Among the many possible agents that can affect the crew's general well-being, stress is certainly one of the most critical because of its implications on human health and performance, both physical and mental. Nevertheless, very few studies have been performed on this fundamental issue and none of them has addressed it in its entirety, considering its diverse physical and psychological aspects. In this work, a descriptive model is proposed to expound the mechanism and sequence of events which mediate stress. A critical analysis of the information provided by past manned spaceflights and by dedicated research performed in analogous environments is presented, and an extrapolation of the available data on human stress in such extreme conditions is proposed. Both internal and external stressors have been identified, at physical and psychosocial levels, thus providing the basis for their early detection and preventive reduction. The possible negative consequences of stress that may lead to disease in crewmembers are described. Finally, the most effective instruments which may be of help in reducing space-related human stress and treating its negative consequences are suggested.

Fucosterol epoxide lyase of insects: synthesis of labeled substrates and development of a partition assay.

Fucosterol epoxide labeled with tritium in the C-29 methyl has been synthesized and employed in the development of a partition assay which allows the rapid determination of fucosterol epoxide lyase activity in vitro in homogenates of insect tissues. An independent synthesis of [24-14C]fucosterol epoxide provided a control substrate to evaluate nondealkylative transfer of labeled steroid to the aqueous layer during the enzyme assay. The diastereomeric 24R,28R- and 24S,28S-[29-3H]fucosterol epoxides were obtained via HPLC separation of their benzoate esters. Homogenates of the midgut tissue of larval tobacco hornworms (Manduca sexta) were examined at pH 5 to 9 in several buffer systems, and at temperatures of 7 to 67 degrees C in phosphate buffer. Optimal activity was found using pH 7.4, 76 mM phosphate buffer at 37 degrees C. The 24R,28R diastereomer of fucosterol epoxide was metabolized at a rate at least 100 times that of the 24S,28S isomer by this enzyme system.