DECELERATION AND MASS CHANGE OF AN ABLATING BODY DURING HIGH-VELOCITY MOTION IN THE ATMOSPHERE

The factors affecting the dynamics and mass loss of ablating bodies during high-velocity motion were examined. The classic meteor case, where the flow is assumed to be of the free-molecule type with constant heat-transfer and drag coefficients, was reviewed and presented in terms of general dimensionless parameters which allow application to cases other than that of meteor atmospheric entry. An analytic solution is obtained for the specific variation of the heattransfer coefficient corresponding to a sphere with laminar convective heating in hypersonic flight at a constant altitude. The increase of heat-transfer coefficient due to decreasing body size (thus effectively increasing the efficiency) can result in a complete loss of mass during the deceleration process. For both cases, the velocity variation during the major part of the mass loss differs only slightly from that for a body with an unchanging ballistic coefficient. This approximation is used to formulate the analytic solution of a case which corresponds to the laminar convective heating of a sphere in hypersonic re-entry - i.e., a large slow meteor or fireball. Due to the dominant effect of the decrease in heat-transfer coefficient with increasing fluid density, the rate of mass loss is reduced and the final mass is appreciable compared to the initial mass.