No abstract

A controlled descent of space station Mir requires the choice of an optimal con guration (positions of solar arrays) that allows one to minimize the disturbing aerodynamic torques and maximize the drag. An approximate approach for choosing the positions based on free-molecular analysisis developed. The aerodynamiccharacteristics of the chosen con gurations are studied by engineering and statistical methods along the descent trajectory. The study showed that a decrease in the ight altitude from 200 to 130 km does not exert a noticeable effect on the magnitude of the force and moment coef cients and also revealed the reasons for the decreasing accuracy of the engineering prediction. It was shown that the gas/surface interaction model signi cantly affects the torques and, therefore, the choice of the optimal con guration. Nomenclature C A = axial force normalized by 1 2 ½ 1 V 2 1 S C m = pitching moment normalized by 1 2 ½ 1 V 2 1 S L C n = yawing moment normalized by 1 2 ½ 1 V 2 1 S L H = altitude, km Kn = Knudsen number,¸1=L LB L = reference length, 13:6 m L LB = reference length determining rarefaction effect for local bridging method, m M 1 = freestream Mach number N M = molecular weight of mixture S = reference area, 13:5 m 2 T W = wall temperature, K T 1 = freestream temperature, K V 1 = freestream velocity, m/s ® = angle of attack, deḡ = sideslip angle, deģ 1 = freestream mean free path, m ½ 1 = freestream density, kg/m 3 Á = angle of solar array position, deg

The work performed during the implementation phase of an integrated set of computer codes developed to study plume ows generated from satellite main engines and thrusters is described. The major aim of the work was to achieve the capability to cover the complete cycle of gasdynamics analyses required to assess the impact that plume impingement effects may have on the satellite and on its sensitive payload or instrumentation. A simpli ed con guration of the European Space Agency's satellite for the X-Ray Multi-Mirror Mission was considered as a test case for the purpose of implementing and testing the computer codes. In this regard, the issue of major concern consisted of the estimation of the thrust loss produced by plume impingement during the injection maneuver of the satellite into a higher perigee orbit. Results obtained by Navier-Stokes, direct simulation Monte Carlo, and test particle Monte Carlo calculations are described, and the ow patterns settling in during thruster ring in the regions of interest are discussed. The major nding of the study was the detection of a serious incompatibility between the preliminary assumed design orientation of the satellite thrusters and the ight dynamics requirements imposed by the satellite mission. In conclusion, the study fully provides evidence of the critical role and usefulness of this kind of numerical analyses in providing answers contributing to the optimization of successful satellite design. NomenclatureA = axial force per unit area, N/m 2 A = species contributions to A, N/m 2 /kg B = breakdown parameter F = nozzle thrust, N Ma = Mach number m = mass ow rate, kg/s P = pressure, N/m 2 R = equivalent gas constant, J/kg/K T = temperature, K X , Y = nozzle axial and radial coordinates, m x, y, z = satellite body axis coordinates, m Z r = rotational-relaxation collision number = equivalent speci c-heat ratio = mass density, kg/m 3 = circumferential angle, deg Subscripts c = chamber conditions calc = calculated value nom = design nominal value

In order to evaluate the behavior of the intermediate experimental vehicle (IXV) in the upper layer of the atmosphere, series of computations were carried out by means of the Direct Simulation Monte Carlo (DSMC) method, which are reported hereby. First an introduction is given about the IXV mission followed by a short explanation on DSMC and the computational methodology. A ¦rst validation case is demonstrated for computations based on the geometry of the Apollo capsule, showing good agreement with a reference in literature. Then, simulations of the IXV are presented, including §owthruster interaction. Finally, the result matrix of aerodynamic properties is shown.

No abstract