A modification of the boundary condition describing the interaction between a gas molecule and a wall is proposed for use in the calculation of internal rarefied gas flows. The effect of the altered boundary condition on a number of flows of interest is calculated. In several cases, for which experimental data are available, comparison is made between predicted and measured transport. It is found that significant improvement in the predicted transport results from the suggested boundary condition modification.

A brief topical review of current knowledge available for predicting the characteristics of sandstorms is presented. Particular emphasis is placed on extrapolations to Mars where saltation of loose surface material appears to be a necessary condition for initiation of observed dust storms. Considerable data are now available to predict threshold winds under earth's environmental conditions, but techniques for predicting the quantity of material transported and the height and velocity to which it travels are still crude. Extrapolation of current knowledge to Mars is probably sufficient only for estimating purposes and landing craft design. The upcoming Viking landing mission on Mars will, it is hoped, shed additional light on the problem. Owen [1964] presents a solution, qualitatively valid for the 135 136 MAEGLEY: SALTATION AND MARTIAN SANDSTORMS Altitude, z Em] 0.012F

Results of precise measurements of the pressure dependence of the flow of gases through annuli of various radius ratio are presented. The data cover a range of Knudsen numbers for about 0.01 to 450. The depth of the Knudsen minimum is found to vary markedly with radius ratio and increases as the radius ratio increases. (Radius ratio is defined as the ratio of inside to outside radii). About 50% of the total change in the depth of the Kundsen minimum occurring between flat plates (radius ratio = 1.0) and capillaries (radius ratio = 0) is effected by a 13% change in radius ratio from 1.0 to 0.8711. Previously observed deviations from classical kinetic theory are verified; and, in particular, in the free-molecule and near free-molecule regimes, the flows are found to be lower than those predicted based on diffuse scattering of gas molecules from the annulus wall. The data are generally found to be in good agreement with flows predicted by the BGK and variational techniques presented by Berman and Maegley [Phys. Fluids 15, 772 (1972)].

Results of wind tunnel tests to determine aerodynamic heating patterns and general flowfield characteristics on the MX missile are discussed. 5% and l2 l /2% scale models of the missile configuration were tested at Mach 6 and 8. Infrared scanning and phase change paint thermal mapping techniques were used to determine smooth wall turbulent and laminar heating levels and localized heating effects due to protuberances. Protuberances included a scaled raceway, lateral support pad shear tabs, and stage II roll control jets. The flowfield about the missile during the stage I/stage II separation event was investigated using a cold gas simulation of the stage II motor plume. Measured smooth wall heating rates confirmed both laminar and turbulent theoretical predictions and significant heating augmentation in excess of five times the smooth wall values was found in the vicinity of the leading edge of the raceway and the shear tabs. An extensive interaction region was produced by the roll control system jets. Schlieren photography of the staging event showed plume induced flow separation extending to the nose of the missile. NomenclatureA = area A ref = missile reference area D m = missile or model cross-sectional diameter h = heat-transfer coefficient (see Eq. 1), Btu/ft 2 -s-°R hi/hu = ratio of interference heating to undisturbed heating i.r. = infrared camera view £ = model or missile length M = Mach number p = static pressure P t = tunnel total pressure q -convective heat-transfer rate q = dynamic pressure RCS = roll control system Re? = freestream Reynolds number based on missile or model length Re/ft = unit freestream Reynolds number S = stage separation distance T r = recovery temperature T t = tunnel total temperature T w = model wall (surface) temperature a = model angle of attack 7 = ratio of specific heats Subscripts e = stage II nozzle exit £ = local external flow over missile or based on model/missile length oo = undisturbed freestream

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