Nearly Circular Transfer Trajectories for Descending Satellites

Simplified expressions describing the transfer from a satellite bit to the point of atmospheric entry are derived. The expressions are limited to altitude changes that are small compared with the earth's radius, and velocity changes small compared with satellite velocity. They are further restricted to motion about a spherical, nonrotating earth. The transfer orbit resulting from the application of thrust in any direction at any point in an elliptic orbit is considered. Expressions for the errors in distance (miss distance) and entry angle due to an initial misalignment and magnitude error of the deflecting thrust are presented. The largest potential contributing factor towards a miss distance stems from the misalignment of the retrovelocity increment. If this velocity increment is pointed in direct opposition to the path, a 1 deg misalignment leads to a miss distance of 3.45 miles. However, it is shown that this error can be avoided by applying the velocity increment at an angle between 120 deg and 150 deg below the flight-path, direction. The guidance and accuracy requirements to establish a circular orbit, in addition to the corrections applied to to transform elliptic orbits into circular ones, are also discussed

The Compressible Laminar Boundary Layer with Fluid Injection

A solution of the equations of the compressible laminar boundary layer including the effects of transpiration cooling is presented. The analysis applies to the flow over an isothermal porous plate with a velocity of fluid injection proportional to the reciprocal of the square root of the distance from the leading edge. The effect of several flow parameters on coolant-flow rates is discussed with the aid of representative examples. A stability analysis indicates that, although transpiration cooling requires a lower surface temperature for stable flow than does internal wall cooling, this lower temperature can be obtained with a smaller expenditure of coolant

Boundary-layer Transition at Supersonic Speeds

Recent results of the effects of Mach number, stream turbulence, leading-edge geometry, leading-edge sweep, surface temperature, surface finish, pressure gradient, and angle of attack on boundary-layer transition are summarized. Factors that delay transition are nose blunting, surface cooling, and favorable pressure gradient. Leading-edge sweep and excessive surface roughness tend to promote early transition. The effects of leading-edge blunting on two-dimensional surfaces and surface cooling can be predicted adequately by existing theories, at least in the moderate Mach number range

Factors Affecting Laminar Boundary Layer Measurements in a Supersonic Stream

The observed discrepancy at supersonic speeds between theoretical and apparent experimental average flat plate friction-drag coefficients calculated from boundary layer total-pressure surveys was investigated. Effects of the total-pressure probe, heat transfer through the leading edge region, change in leading-edge radius and strength of the leading-edge wave, possible early transition to turbulent flow or bursts of turbulence, and the slight stream-wise pressure gradient inherent in flat plate flow were investigated for plates with very sharp leading edges. Only one of these factors, the effect of the total-pressure probe, was found to be significant. Total-pressure probes of different tip heights, when placed in laminar boundary layers developing under identical conditions, were found to yield different values of friction drag coefficient. Extrapolation of these measurements indicates that a probe of vanishing size would yield the theoretical predicted values of average flat plate friction-drag coefficients. A correlation describing the relation between the friction-drag discrepancy and the probe tip height is presented

Apollo Lunar Exploration Missions (ALEM) program plan

This program plan supports the requirements of Apollo Program Directive 4K and is based on the most current information available at the time of publication. This directive defines the ALEM schedule and hardware planning guidelines and requirements to be used as a baseline for detailed Apollo spacecraft programming. Also, this directive reflects the requirements of Apollo Program Directive 4 (APD-4).[George M. Low]

Temperature distribution in internally heated walls of heat exchangers composed of nonnuclear flow passages

In the walls of heat exchangers composed of noncircular passages, the temperature varies in the circumferential direction because of local variations of the heat-transfer coefficients. A prediction of the magnitude of this variation is necessary in order to determine the region of highest temperature and in order to determine the admissible operating temperatures. A method for the determination of these temperature distributions and of the heat-transfer characteristics of a special type of heat exchanger is developed. The heat exchanger is composed of polygonal flow passages and the passage walls are uniformly heated by internal heat sources. The coolant flow within the passages is assumed to be turbulent. The circumferential variation of the local heat-transfer coefficients is estimated from flow measurements made by Nikuradse, postulating similarity between velocity and temperature fields. Calculations of temperature distributions based on these heat-transfer coefficients are carried out and results for heat exchangers with triangular and rectangular passages are presented