Trends in high-speed atmospheric flight

Some of the current problems and future trends for three types of flight within the Earth's atmosphere are considered. The three areas examined are atmosphere entry at very high speeds, atmosphere exit of launch vehicles, and sustained cruise within the atmosphere. The high-speed entry problems described are those encountered by vehicles returning to Earth after a manned mission to Mars. Such vehicles will experience atmosphere entry speeds up to 50,000 and perhaps as high as 70,000 feet per second. For these vehicles to execute a successful entry, accurate guidance at Earth approach must be provided and very precise control during the flight within the atmosphere will be a necessity. At the high entry speeds radiative heating-is greater than convective and thus it tends to exert a dominant influence on entry-vehicle configuration. The study and development of relatively slender vehicles is indicated in order to minimize the large radiative heating loads and associated heat-shield weights. Manned interplanetary missions in the future may also involve a need for very large launch vehicles. These large vehicles will have aerodynamic problems which differ somewhat from current problems. For example, drag losses decrease with increasing size and large vehicles may thus be of lower fineness ratio than present-day vehicles. With lower fineness ratio some of the difficult current problems produced by ground-wind loads and by buffet of hammerhead payload mountings will be avoided. In the case of high-speed cruise within the Earth's atmosphere, the use of hydrogen-fueled, airbreathing engines may permit attractive payload capabilities for long-range high-speed transports. For such vehicles aerodynamic problems arise because of the numerous constraints placed upon their flight paths as well as from the large volumes required for the hydrogen fuel. From payload considerations alone, attractive cruise speeds for such vehicles currently appear to be about twice that of the conventionally fueled supersonic transports now being intensively studied.