Next in the operating cycles are the shock loadings that occur as the engines ignite. This is followed shortly by the shock that occurs as the vehicle is released and permitted to rise. During all this time, the vehicle structure experiences an acoustical loading that is greater in magnitude than any vehicle has had to experience in the past.

In the early phases of flight, the vehicle is subjected to flight winds and wind shear in addition to buffeting and aerodynamic noise. There is also the possibility for an instability to occur such as "flutter," "POGO," and "liquid sloshing." Further along the flight, the separation of the two vehicles can result in severe dynamic loads to both vehicles. This is a particularly serious problem if the separation occurs due to an abort at low altitudes where dynamic pressures may be significant.

The orbiter next proceeds to dock with the space station while the fuel inside moves about and may cause unwanted vehicle motions and create unanticipated dynamic stresses. When the booster and later the orbiter reenter the earth's atmosphere, they will, of course, be subjected to reentry heating. When they reach the sensible atmosphere, buffeting can once again take place only this time the structure being hot is less able to resist the buffet loads. The mission ends with the landing of the vehicle where once again both booster and orbiter are subjected to dynamic loading conditions.

A potential flutter problem is depicted in the center panel of the figure. When the orbiter is mounted on top of the booster, the wing of one vehicle may be in close proximity to the wing or tail of the other, thus resulting in a "biplane" type configuration. The figure shows the effect of one wing being placed directly above the other. The solid curve on the plot of flutter speed versus Mach number shows the flutter speed when the wings are well separated and no interference occurs. The dashed curve shows the flutter speed when the wings are brought together to a separation distance of about a quarter of the chord. The result is a significant drop in the flutter speed in the Mach range below the transonic region. This condition will be examined closely as the shuttle configuration develops so there is no severe weight penalty required for increasing the stiffness to prevent flutter.

While much of the activity in the structures and dynamic program has, within the past year, been concentrated on the space shuttle, activities having to do with deep space probes in satellites have not been neglected. Figure 18 (RW 71-3806) is illustrative of one such program. In this program, we are seeking to apply optimum structural design principles and exploit the zero gravity of space in this case to achieve a space antenna with dimensions and weight which would not be practical for use on earth. The antenna known as a conicalgregorian configuration will allow for small volume spacecraft storage during launch and later unfurling to full size. The main reflector surface is developed as a conical shape, thereby allowing fabrication from flat inextensible sheet materials. This design also provides for easy assembly, inspection and dimensional control. In preliminary laboratory tests, the concept was checked out and the design was found to be insensitive to axial misalignment. This latter feature is particularly useful to avoid problems caused by maneuvering loads and temperature excursions. In the coming fiscal year, we anticipate constructing and testing a scale model of such an antenna to assess the state of technology and feasibility of such antenna structures.

Another advanced structural concept under investigation has been reported previously as a method of deploying in orbit a large radio telescope. It consists of a large parabolic network which is rotated to maintain its shape. During the coming fiscal year, an actual scale model flight test is planned which will determine the feasibility of this concept.

One of the major problems faced by the structural designer is that the systems with which he is concerned are becoming more complex. In addition, the vehicle, component, or stage that he is designing, more often than not, is mated or coupled with another vehicle, component, or stage designed by a different company. Unfortunately, the technique that the other company uses to analyze its component is specifically designed to run on the particular computer equipment that the other company uses. Therefore, in the past, to analyze the coupled vehicle usually required a complete new analysis of the two components in the mated configuration. To improve this communication deficiency, NASA developed the NASTRAN (NAsa STRuctural ANalysis) Computer Program that is designed to operate on most of the large computers being used in industry. This permits a transfer of structural data between the NASA Centers and their contractors.

NASTRAN provides the user community with the best state-of-the-art capability for detailed analysis of complete aerospace structural systems. This system, which to date has cost three million dollars, can incorporate, without dependence on special purpose programs, a complete design study that ranges from static loading and buckling through computation of vibrational modes and determination of responses to transient and random loadings. The Langley Research Center, which has been designated to maintain and further develop the NASTRAN system, is currently applying its capability to a typical shuttle type vehicle. This vehicle in its undeflected state is shown by the solid lines in Figure 19 (RW 71-3807). Superimposed on this (with dashed lines) is the deflected shape. This result is representative of that which can be obtained from a NASTRAN analysis where the structure is divided into finite elements, two types of which are shown on the right hand side of the figure. This program, through such finite element representation, permits the analysis of stress, deflections and dynamic response characteristics of such complex vehicle as the shuttle with high speed and accuracy.

The NASTRAN program will continue to be applied as the shuttle configurations become more firm and should be of benefit both to verify contractor's predictions and to insure the safety of the device.

SUMMARY

The newly formed Materia's and Structures Division has brought together studies in the areas of solid state physics, materials research, structures, and dynamics for both spacecraft and aeronautical vehicles. The studies range from very basic investigations into the nature of the solid state to the flight testing of advanced structures made with new materials. The integration of these closely related disciplines should result in an increased productivity in each and should accelerate the rate at which the research results are incorporated into the lighter, more reliable, and more socially acceptable devices that NASA, DOD, and the civil aviation community desires.

PREPARED STATEMENT OF FRANCIS J. SULLIVAN, DIRECTOR OF GUIDANCE, CONTROL AND INFORMATION SYSTEMS, OFFICE OF ADVANCED RESEARCH AND TECHNOLOGY, NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

INTRODUCTION

The role of electronics in the aerospace program has grown ever more important as we progressed from exploratory probes of an unknown environment to scientific investigations and applications of new knowledge and capabilities for the benefit of mankind. Electronic systems and devices provide the sensors for detecting the characteristics of the aerospace environment and for guiding and controlling aeronautical and space vehicles; they provide the link which enables us to communicate with manned and unmanned vehicles operating in the aerospace environment; and they provide the tools which permit us to accumulate vast quantities of data and convert it into usable information. The complexity of current and future aerospace vehicles and operating objectives require that continued emphasis be placed on the development of technology which will reduce the size, weight and cost of electronic systems while providing increased accuracy, reliability and operating life. In the following paragraphs we will describe by example, some recent accomplishments, current activities, and proposed areas of increased emphasis in the Fiscal Year 1972 Guidance, Control and Information Systems program.

AVIONICS TECHNOLOGY

Complex modern aircraft, operating in the increasingly dense air traffic environment, place more and more dependence on avionics to obtain required performance and maintain flight safety. Future generation aircraft, particularly the Short Take Off and Landing (STOL) and the Vertical Take Off and Landing (VTOL) types, will require more extensive application of avionics to: (1) augment their inherently lower stability, (2) provide the flight path flexibility to permit complementary operations with conventional aircraft in high density terminal areas, and (3) achieve safe and dependable all-weather operations. Continued progress in integrated electronic technology provides the basis for achieving significant improvements in avionics technology applied to aircraft systems. Digital avionics systems offer distinct advantages in flexibility and reliability along with a reduction in size, weight, and power consumption. As illustrated in Figure 1, this program will emphasize the application of digital data processing techniques to guidance, control, communication and identification systems and their associated sensors. Specific examples of past results and future plans in this area as well as other facets of the program are presented later in this statement.

AVIONICS RESEARCH

Avionics research is directed towards applying new theoretical concepts and advanced sensor and subsystem technology to the increasingly complex needs of aviation. The research is accomplished through in-house efforts, industry contracts and university research grants emphasizing the development of new theory and concepts. In the development of new theory, emphasis is placed on guidance and flight control system requirements and the important interface between the pilot and the avionic system. On-going work in this area includes the development of accurate mathematical models of aircraft and avionic systems to better predict the system performance analytically before committing the design to hardware. Sensor and subsystem research is aimed at exploring the potential of advanced technology to solve or alleviate problems such as altimeter inaccuracy, clear air turbulence detection and collision avoidance.

One example of systems research is shown in Figure 2. An experimental landing radar that determines vehicle velocity and measures altitude with a single system has been evaluated in helicopter flight tests for the Langley Research