Center. Its original purpose was for unmanned planetary landers, but its predicted performance indicates it may also be useful as a radar altimeter for V/STOL aircraft. The initial tests showed promise and this concept will be further investigated during the next year. Other research will be directed toward improved aircraft antennas and the application of digital methods to subsystems and sensors currently using analog computer technology.

L-BAND EXPERIMENT

Satellite navigation and communication experiments in the L-band frequency region (390-1550 MHz) for aeronautical services were conducted in 1970 through cooperative efforts of the Department of Transportation and NASA. As shown in Figure 3, signals containing ranging modulation were transmitted from the NASA STADAN station at Mojave, California, relayed through the ATS-V satellite and received by a contractor operated ground station (Allied Information Industries, Moorestown, New Jersey) and the ice breaking tanker, S.S. Manhattan, while en route to the Northwest Passage.

This was the first use of L-band signals, relayed by synchronous satellite, for navigation and data communications. The results compared favorably with position determination measurements from ground-based systems and demonstrated that a relatively simple system can produce precise and stable range measurements for navigational use.

The L-band propagation tests using high altitude balloons begun by the Electronics Research Center are being continued by the DOT Transportation Systems Center with completion expected by the middle of Fiscal Year 1972.

VEHICLE TECHNOLOGY

Efforts in this area are directed towards developing advanced avionics technology to meet the projected requirements of specific types of aircraft. There is need for avionics equipment to improve the stability and contro' ability of light planes which normally have limited capability for hands-off operation. While single-axis wing levelers have become available at reasonable costs, low-cost

three-axis attitude and flight path control would greatly alleviate pilot workload and provide increased safety. Fluidics and advanced electronics have both shown promise in flight tests conducted by the Flight Research Center. Improvements in fluidic systems have been realized through the development of fluidic components by Langley Research Center. Continuing effort in electronic flight control by the Flight Research Center will be directed towards developing simple display formats depicting key flight condition cues and vehicle status information to the pilot.

As noted earlier, V/STOL aircraft will be particularly dependent on avionics technology to achieve their promised potential for providing fast and reliable short-haul transportation and relieving air traffic congestion in the high altitude airways used by conventional jet aircraft. The pilot workload is typically very high for V/STOL operations because of extensive operation in low level turbulence and the many takeoffs and landings performed each day. The pilot's attention should be on his primary functions of planning navigation, flight procedures, communications, collision avoidance, and approach and landing during visual and instrument flight. The aircraft should require as little attention as possible to be flown and maneuvered as desired. The effects of gusts and wind shear can be particularly hazardous during the relatively low speed final approach into restricted sites. The complementary human aspects of this problem are treated in detail in the Aeronautical Life Sciences statement.

For V/STOL aircraft, hovering and transition handling qualities and the design of appropriate stability augmentation systems is an important problem because the control requirements affect the whole aircraft design. The objective of the technology efforts in this area is to define the control and stability systems required to allow operations in a foul weather, zero visibility environment. The potential of digital flight control techniques for solving these problems is great and this effort is a major step towards an automatic flight capability. The on-going program in this area at the Ames Research Center will use a modified X-14 VTOL aircraft as a flight test bed. This effort will use an onboard digital computer and an autopilot which can be used to vary the stability characteristics of the aircraft to investigate advanced control system concepts which will give the pilot greater attitude, altitude, and translational stability and control. A new and complementary effort in digital flight control is described in the following paragraphs.

DIGITAL ELECTRONIC FLY-BY-WIRE

Digital fly-by-wire systems replace the mechanical linkages between the pilot controller and the input to the control surface actuators with electronic signals. These signals are derived by sensing vehicle and stick motions and processing the sensed information in a computer to develop appropriate control surface commands. A typical system is illustrated in Figure 4.

Digital flight control system technology, successfully developed for the Apollo Command and Lunar Modules will be applied to aircraft control systems in a new program initiated in Fiscal Year 1971 and scheduled for preliminary flight testing in Fiscal Year 1972.

The first phase of the program, directed by the Flight Research Center. will use modified Apollo equipment installed and flown in an F8C aircraft. Based upon successful results in this phase, follow-on efforts are planned to design optimum computer configurations and advanced flight hardware to more fully exploit the flexibility, adaptability and self-checking capability of digital systems. As illustrated in the figure, this effort should make possible the application of aircraft aerodynamic designs which take advantage of the increased stability potential of digital systems and provide improved ride characteristics and improved flight performance.

SYSTEMS TECHNOLOGY

This area of avionics is directed towards improving the vehicle/pilot combination and its interaction with the operating environment, i.e., the air traffic control system and airport. Typical requirements in this area include achieving a reliable "all-weather" landing capability and providing a low-cost pilot warning system for general aviation aircraft operating in or near high-density air carrier airlanes. An additional important area planned for study by the Langley Research Center is the application of advanced avionics system technology to terminal area navigation and the optimal sequencing and flow management of aircraft

merging into the landing pattern from multiple airlanes. The clear air turbulence detector effort using a dual frequency airborne microwave radiometer which was discussed in last year's testimony is continuing. Flight testing will begin early in Calendar Year 1971 at the Flight Research Center, using a B-57 aircraft. In contrast to this passive radiometer technique, an active system empioying a laser is described in the Aeronautical Operating Systems statement. These programs represent complementary approaches to an unsolved problem.

INDEPENDENT LANDING MONITOR

Ames Research Center is exploring techniques for an independent landing monitor to give the pilot a check on his orientation with relationship to the landing area and runway under low visibility conditions. The source data and signal processing will be independent to those used for primary control of the aircraft under standard landing procedures. One technique uses a microwave radiometer as illustrated in Figure 5, and includes a TV type out-the-window cockpit display to convey the flight status to the pilot.

The use of 8 millimeter wavelength radiometry should provide weather penetration and sufficient resolution for furnishing the pilot with adequate "seeing" of the landing area details without the use of an onboard transmitter. It may be necessary, however, to augment the passive view for approach by outlining the runway with landing "lights" radiating at the radiometer wavelength.

System trade-off studies have been completed and work is proceeding towards development and testing of a system for flight evaluation.

Further efforts on the Zero/Zero landing program discussed in previous years have been deferred. The personnel and Convair 340 aircraft are supporting a joint NASA/FAA STOL flight program under the Aeronautical Operating Systems program.

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The Electronics Research Center optical pilot warning indicator (PWI) program has been continued at the Transportation Systems Center. Two models were subjected to laboratory and flight tests in the spring of 1970. One of these is shown in Figure 6. Detection ranges of 4.5 to 8 kilometers were obtained over a range of weather conditions. The tests demonstrated that the PWI would be of considerable assistance to the pilot in avoiding collisions. The tests also uncovered a susceptibility to false alarms and electromagnetic interference.

The current program is addressed to the solution of these problems and is being conducted in cooperation with the Federal Aviation Administration. Further flight tests will be conducted in the spring of 1971 and results will be made available to industry upon completion of analysis.

Langley Research Center has tested another PWI approach based on the use of cooperative microwave devices on all participating aircraft. The interrogating aircraft emits signals which are received, suitably transformed, and retransmitted by the intruding aircraft. Upon receipt by the original sender, and after suitable processing, the pilot is provided with information on potentially dangerous situations. The feasibility of the system concept has been demonstrated in flight tests. This system, however, requires more complex electronics than the optical system. Further studies will be made in Fiscal Year 1972 to determine practical manufacturing costs of the microwave system and examine methods for reducing its complexity.

SPACE TECHNOLOGY PROGRAM

Space exploration and its application for mankind's benefit depends heavily on successful development of the Space Shuttle, Space Station, Applications, Astronomy and Planetary programs. These programs, in turn, require substantial advances in technology for efficient and effective operations. The objective of the Guidance, Control and Information Systems program is to insure that the

necessary technology base in electronic systems and components is available to meet the needs of these and other future space activities. In the following pages, examples of research and development activities in Information Systems, Optical Components and Systems, and Guidance and Control are described in terms of both technical objectives and/or achievements and their relation to the Agency's flight programs. Underlying all of the research and development activities in electronics is the fundamental work in Sensors and Components which provides the basic technology and devices used to develop functional systems and subsystems. Examples of work in this latter area are included in the last pages of this section.

INFORMATION SYSTEMS

Advances in instrumentation technology and spacecraft performance have made scientific or applications missions possible which can produce data at rates far beyond our present capability to process and transmit. Figure 7 displays in simplified graphic form the basic need for a continuing research and technology program directed toward development of information handling systems and techniques capable of exploiting the full potential of such missions.

In the figure, curve #1 is representative of the on-board experiment data collection rates postulated for future missions ranging from an advanced earth resources satellite to outer planet exploration. Curve #2 is an estimate of current communications capability at the various mission distances. Curve #3 shows the relative difficulty in communicating with the spacecraft at maximum range compared to communication with a satellite in earth orbit. For example: From curve #1 we see that the instruments of a Viking mission to Mars at planetary encounter may produce data at a maximum rate of over 4 million data bits/sec while our current capability to transmit to earth at this rate falls short by a factor of about 400 (difference between curves #1 and #2) and the relative difficulty of achieving the required transmission rate at Mars distance compared to achieving a similar rate from earth orbit is a factor of approximately 10 billion (curve #3). Thus, the area between curves #1 and #2 defines the general scope of needs for advancement of information systems technology, applicable to