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In order to evaluate the effects of gravity on growing plants, we conducted ground-based long-term experiments with dwarf wheat (cultivar "Apogee USU") and Chinese cabbage (cultivar "Khibinskaja"). The test crop had been grown in overhead position with HPS lamp below the root module so that gravity and light gradients were in opposite direction. Plants of the control crop grew in normal position under the same lamp. Both crops were grown on porous metallic membranes with stable--1 kPa water potential on the surface. Results from these studies allowed us to examine the significant differences in growth and development of the plants as well as the root systems in relation to the gravity force. Nevertheless, the experiments in greenhouse Svet aboard the Mir space station proved that it is possible to compensate the effects of weightlessness on higher plants by manipulating gradients of environmental parameters (i.e. photon flux, water potential in the root zone, etc.). Even in ground studies Svet productivity averaged no more than 14 gm of fresh salad biomass per a day. This does not provide a sufficient supplement nutrients to the ISS crew. A cylindrical design of a space plant growth facility (SPGF) allows for maximal productivity under very tight energy and volume limitations onboard the ISS and a number of operational advantages.

Based on the multiyear experience of hygienic control of the orbital stations, there are three causes of contingent air pollution: leakage of service system pipeline with chemical working bodies, spills of reagents used in biochemical and technological experiments, and air pollution by products of thermal oxidative degradation of nonmetallic materials. The authors describe their experience in successful elimination and prevention of hazardous consequences of fire aboard the space stations. Analysis of air pollution dynamics after actual fire events in the space station modules showed that it approximates a two-chamber air flow model with two phases of pollutant equilibration: first a rapid fall of concentration in the module on fire till air in the modules gets completely mixed, and then slow elimination of harmful pollutant from air. Identified were markers,--propylene and methylmetacrilate,--reacting to first signs of fire. Carbonic acid nitriles were recognized as toxic products of destruction. The positive effect of intermodular ventilation on dilution of toxic products of thermal oxidative destruction of materials was demonstrated. Satisfactory agreement of calculated and factual pollutant concentrations on board Mir permitted conclusion on applicability of the theoretical model to prediction of levels of air pollution due to contingency.

The problem of environmental compatibility of the ISS Russian and U.S. segments arises from chemical and biological inequality of their atmospheres and is attested by the data of observations during operation of Russian orbital stations Salyut and Mir. Efforts must be made to develop unified limits, and common procedures and requirements for evaluation of ISS materials and equipment by experts of the international partners.