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  • Descent from satellite orbits using aerodynamic braking

    Paper ID



    • T Nonweiler


    British interplanetary society


    United Kingdom




    This paper describes the application of some of the author’s theoretical work (mostly as yet unpublished) to the problem of the descent of an aircraft from a circular orbit ; when the aircraft reaches the denser regions of the atmosphere, it is assumed that the remainder of the descent is a shallow dive during which the aircraft, supported by the lift of its wings, gradually slows down. The theoretical work is intended to provide an estimate of the temperature reached by the aircraft in this glide. The calculation of the rate of heat transfer, caused by air friction, to a body moving at very high speeds presents a problem which cannot, in general, be accurately solved. However, an approximate general solution has been obtained which compares fairly well with an accurate particular solution. In fact, it appears that the heat transfer may be satisfactorily assessed in flight at Mach Xumbers of 10 or more if the Reynolds Number is between about 10» and 108. This, as it transpires, is the condition in which we are most interested. The effects of the “slipping” of the air at the surface—a phenomenon caused by the molecular structure of the air—have also been examined, and lead to an estimate of the maximum rate of heat transfer to the surface. A limit to the skin temperature is also imposed b}r the conduction of heat along the surface; this has been calculated as well. It is then shown that the wing surface temperature will be least if a thin, double-wedge wing-section is used, with a position of the maximum thickness well aft, and with both its inner and outer surfaces acting as good radiators of heat. The temperature will be highest near the leading-edge of the wing undersurface, and its value there depends on the wing-loading—varying roughly as the fourth root of the loading. A maximum temperature of 1300° C. is reached during the descent, assuming a wing-loading of 30 Kg.s./m., occurring when the speed has dropped to 4-6 Km./sec. The mean temperature of the wing surface would be much lower—about 500° C. Although existing data are inadequate to deal with the question, there is a possibility that, as an alternative to a gradual descent, a more rapid one involving a dive, in which dive-brakes are used to provide a retardation of 4 or 5 g. might be a better means of descent. Alternatively, as slow a descent as possible seems best, in general, because any unnecessary manoeuvre such as a dive, requires extra weight of structure in the wing to provide adequate stiffness at the higher air speeds. To reduce the structure weight it is necessary, in fact, to limit the indicated air speed during the glide; if an indicated speed of GO m./sec. is not exceeded, it should be possible, for example, to accommodate a payload of 5 tonnes within an aircraft of 20 tonnes all-up weight, some two-thirds of this weight being due to the structure of the reinforced steel wing. This figure is derived assuming an all-wing design using a delta planform of high sweepback. The transport of a much heavier payload than this would be impossible, unless a more suitable material than steel could be found economically to provide strength at high temperatures. Smaller payloads could be carried without such a severe penalty in structure weight. Having in mind the low wing-loading required, an all-wing design is a natural choice. Apart from a lack of depth, there would appear to be no reason why the payload could not be housed within the wing. Moreover, given suitable insulation from radiation, there would appear to be no need to cool the crew’s accommodation, which, however, would need to be as far away from the wing leading-edge as possible. Assuming that the aircraft is initiall}7 circling the Earth at a height of some 1,200 Km., a retardation—by rocket—of about 400 m./sec. would be necessary to change the orbit into an ellipse and bring it to a height of about 80 Km., where the wings could be brought into use. The complete descent would take over three hours, during which time the aircraft could at least twice encompass the earth.