Inflight demonstrations were conducted to evaluate the behavior of physical processes of interest under the nearweightless conditions of space. Four categories of processes were demonstrated, and segments of the demonstrations were televised over a 30-minute period during transearth flight beginning at approximately 172 hours. Final results of all four demonstrations will be published in a supplemental report after analysis of data has been completed. (See appendix E.)
5.1 ELECTROPHORETIC SEPARATION
Most organic molecules, when placed in slightly acid or alkaline water solutions, will move through them if an electric field is applied. This effect is known as elect rophoresis . Molecules of different substances move at different speeds ; thus , some molecules will outrun others as they move from one end of a tube of solution toward the other. This process might be exploited to prepare pure samples of organic materials for applications in medicine and biological research if problem due to sample sedimentation and sample mixing by convection can be overcome.
A small fluid electrophoresis demonstration apparatus (fig. 5-1) was used to demonstrate the quality of the separations obtained with three sample mixtures having widely different molecular weights. They were: (1) a mixture of red and blue organic dyes, (2) human hemoglobin, and (3) DNA (the molecules that carry genetic codes) from salmon sperm.
Postmission review of the filmed data reveals that the red and blue organic dyes separated as expected; however, separation of the hemoglobin and DNA cannot be detected. Postflight examination of the apparatus indicates that the samples were not released effectively to permit good separation, causing the dyes to streak. However, the fact that the dyes separated supports the principle of electrophoretic separation and shows that sedimentation and convection effects are effectively suppressed in the space environment. The hemoglobin and DNA samples did not separate because they contained bacteria that consumed the organic molecules prior to activation of the apparatus.
The liquid transfer demonstration (fig. 5-2) was designed to evaluate the use of tank baffles in transferring a liquid from one tank to another under near-zero-gravity conditions. The demonstration was conducted using two sets of tanks, one set containing baffles and the other without baffles. Transfer of liquid between the unbaffled tanks was unsuccessful, as expected. Transfer between the baffled tanks demonstrated the effectiveness of two different baffle designs. Photographic data indicate that both designs were successful in permitting liquid transfer.
The purpose of the heat flow and convection demonstration (fig. 5-3) was to obtain data on the types and amounts of convection that can occur in the near-weightless environment of space. Normal convective flow is almost suppressed under these conditions; however, convective fluid flow can occur in space by means of mechanisms other than gravity. For instance, surface tension gradients and, in some cases, residual accelerations cause low-level fluid flow. -Four independent cells of special design were used to detect convection directly, or detect convective effects by measurement of heat flow rates in fluids. The heat flow rates were visually displayed by color-sensitive, liquid crystal thermal strips and the color changes filmed with a 16-mm data camera. Review of the film has shown that the expected data were obtained.
This demonstration was designed to evaluate the effect of near-zerogravity on the preparation of cast metals, fiberstrengthened materials, and single crystals. Specimens were processed in a small heating chamber (fig. 5-4) and returned for examination and testing. A total of 11 specimens was processed. No problems with the procedures or equipment were noted. An xray of the samples verified that good mixing occurred.
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