Hypersonic aircraft Included in NASA's program of aeronautical research are activities relating to flight at hypersonic speeds. The X-15 airplane, operating from the Flight Research Center, has been flying in the lower bounds of the hypersonic regime for several years. One of the three aircraft has been modified to increase its speed potential to mach numbers approaching 8. Its flights will provide knowledge of flight characteristics farther into the hypersonic speed range. It is a research airplane, however, and does not have the capability of satisfying either commercial or military operational requirements. It is primarily an instrument for establishing the broad technical basis for feasible and practical hypersonic aircraft. Some of the configurations of more advanced hypersonic aircraft being studied are shown by figure 176. The models shown represent a wide range of designs whose aerodynamic characteristics and performance are being pursued in supersonic and hypersonic wind tunnels at the Ames and Langley Research Centers. Related research is underway on the development of advanced, efficient structural concepts using refractory materials capable of withstanding the searing temperatures of hypersonic flight. Small civilian aircraft Not all the research problems are associated with supersonic and hypersonic aircraft. Statistics indicate a relatively high rate of accidents for small aircraft used by private individuals and executives. A large portion of these accidents occur under adverse weather conditions. There is considerable evidence that the underlying cause is a combination of marginally adequate airplane flying qualities and too heavy a pilot workload. A flight program has been initiated at the NASA Flight Research Center to investigate thoroughly the problem of flying and piloting characteristics of personal and executive-type aircraft, as shown by figure 177, with the aim of suggesting means for reducing the number of accidents in this type of aircraft. VTOL/STOL aircraft Other work on flying and piloting characteristics, figure 177, relates to vertical takeoff and landing (VTOL) and short takeoff and landing (STOL) vehicles. Vertical takeoff and landing capability for highspeed aircraft is now practical because of the development of lightweight jet engines. The helicopter, of course, has this capability but for fundamental reasons is inherently a relatively low-speed, short-range vehicle. Although it is planned to continue research at the Langley Research Center aimed at improving the handling qualities and operational characteristics of the helicopter which will undoubtedly remain a uniquely useful vehicle for certain tasks requiring lengthy periods of hovering-basic conceptual work at the Langley and Ames Research Centers is shifting in emphasis to studies of the low-speed characteristics of the higher speed type of V/STOL aircraft. At Langley, particular attention is being given to problems of jet interference effects near the ground, and to transition from hovering to forward flight for representative VTOL configurations, such as that indicated in the figure. These effects can be favorable or un favorable, depending on the airframe configuration and location of the exhaust nozzles, and thereby have an important influence on the lowspeed flight characteristics. An associated problem also receiving study in alleviation of the erosive effects of the high-velocity, hightemperature jet exhausts on the ground itself that may limit operation to sites having specially prepared surfaces. Continued emphasis is also being placed on obtaining an understanding of the factors influencing the flying and piloting characteristics of all the promising types of VTOL/STOL aircraft during hovering and transition flight, using flying "test-bed" vehicles, prototype aircraft provided by the military services, and ground-based simulators; particular attention is being given to developing the all-weather capability of these aircraft. SPACE VEHICLES The term "space vehicle" is employed to represent either the aggregate booster-spacecraft system or the booster and spacecraft as separate entities. Boosters in use or in development vary from simple sounding rockets to the large SATURN V. Similarly, spacecraft range from satellites incorporating simple experiments to the complex APOLLO service module and the excursion module for manned lunar landing. Figure 178 illustrates examples of typical space vehicles. Whereas the Offices of Manned Space Flight and Space Sciences and Applications are the users of the present generation of space vehicles, the principal concern of the Office of Advanced Research and Technology is the creation of new technology required for future space vehicles. This objective is reached largly by research conducted in laboratories on the ground, although a limited number of flight experiments are required to provide information that can be obtained only in the space environment. With deeper penetration into space, increasingly difficult problems are encountered. Among these are problems relating to the space environment, space vehicle structures and atomspheric entry from space and landing. Space environment Research is continuing to learn how to operate vehicles in the hostile space environment. Consider, for example, failure of structural members through repeated stress or fatigue. One can make rational designs for earthbound, fatigue-critical vehicles because the fatigue strength of our engineering alloys in the Earth's atmosphere is known. It is interesting to observe how the fatigue properties of metals are altered by a reduction of atmospheric pressure. Figure 179 shows how the fatigue life of a common engineering aluminum alloy increases as air pressure decreases or, as shown in the figure, as altitude increases. Some space vehicles, e.g., communication satellites, will be designed for lifetimes of many years; others, such as some scientific payloads, will complete their tasks in a few hours. Certain vehicles, such as weather satellites, will orbit fairly close to Earth; others will be as far away as the Moon or beyond, where pressure decreases to the vanishing point. To design these many different kinds of space vehicles for maximum efficiency and reliability, a better understanding of the effects of the space environment on the fatigue life of all applicable structural materials is needed. This task has an important place in the NASA materials research program. Another environmental problem is the meteoroid hazard. The severity of the meteoroid hazard to space vehicles can be ascertained by flight experiments which record the actual penetrations of strucEXPLORER XVI, launched from Wallops Station by a SCOUT vehicle in December 1962, operated successfully for 7%1⁄2 months. A summary of the results transmitted from the EXPLORER XVI experiment is shown by figure 180. Here is plotted the ac EXPLORER XVI ACCUMULATED PENETRATIONS cumulated number of penetrations experienced by two thicknesses of metal versus time expressed as days in orbit. The total number of penetrations of one one-thousandth-inch-thick beryllium-copper material is 44 and the number of penetrations of two one-thousandthsinch-thick beryllium-copper material is 12. In order to acquire penetration data on thicknesses more nearly representative of practical spacecraft structures, a larger area of exposure or longer time in orbit, or both, are required. A large-area experiment to be launched by a SATURN booster is planned and should provide the much needed penetration data for thicker materials. Radiation encountered in space is a hazard to man and to some types of equipment. Manned flights into space will avoid, when possible, periods of intense solar flare activity, but studies of this radiation hazard and protection from it are vital aspects of the research program. Much of the radiation research is directed toward establishing design criteria for protection of man. Data are being collected and studied |