ber. (Fig. 4-11.) The tests are part of the technology development effort for achieving a parabolic antenna 1,500 meters in diameter capable of operating in space and receiving natural radio signals in the 1 to 10 MHz range. Current research is concentrated on the solution of difficult structural and dynamic problems related to an advanced concept of a spinning antenna constructed as a parabolic net which maintains its shape by a combination of centrifugal forces and a system of filamentary stays attached to a central mast. The entire structural system is packed on drum-like devices mounted on a storage cannister. It is deployed by spinning and unreeling the antenna net with its stays and extending the central mast.

The model tests showed that the deployment can be simulated in the laboratory and that preliminary dynamic characteristics can be demonstrated.

Space Vehicle Design Criteria

Six space vehicle design criteria documents were published in this period. The new publications, prepared by technical specialists from the aerospace community and published by NASA as guides for the design of new space vehicles and for modifications in existing vehicles, are listed in Appendix N. (SP-8013, 8017, 8020, 8021, 8023, and 8029.)

Space Shuttle Technology

Preliminary investigations have been initiated to define configurations and to investigate aerodynamics, structures, materials, dynamics, and aeroelasticity characteristics. Significant results have already been obtained particularly with regard to understanding complex flows surrounding candidate configurations.

SPACECRAFT ELECTRONICS and CONTROL

Communications and Tracking

Optical Propagation Tests.-Plans were completed for two series of flight tests to determine the effect of the atmosphere on optical communication systems for space vehicles. The tests will emphasize the collection of data on laser beams projected vertically. Goddard Space Flight Center will test equipment on high altitude balloons by pointing laser beams of various wavelengths at the balloon equipment as it rises and floats. A sensor on the balloon will record variations in amplitude and coherence width, meteoro

logical data will be taken at the same time, and the two sets of data will later be correlated.

Marshall Space Flight Center will conduct propagation tests using a U-2 or similar aircraft. These tests will determine the effect of the atmosphere on propagation of laser beams at various elevation angles and meteorological conditions, including cloud cover. Lasers and communication receivers will be installed in the aircraft and on the ground.

The flight tests are two parts of a single unified program designed to achieve results for researchers in propagation effects and for engineers designing practical communication systems.

Active Optics Technology.-A microinch actuator for use in active optics systems was developed and successfully demonstrated under an Electronics Research Center contract. The actuator, which is used to change the position of the various parts of a primary mirror for a large space telescope, can achieve controlled movements as small as one ten-thousandth the diameter of a human hair. An array of such actuators can completely control a large mirror and compensate in space for changes in the gravity field, thermal effects, and structural deformations. (Fig. 4-12.)

Pilot Warning Indicator.-The microwave pilot warning indicator (PWI) developed at Langley Research Center was flight tested in two aircraft with satisfactory results. Primary effort will now be to make the equipment light and inexpensive enough for use by general aviation aircraft.

Optical pilot warning equipment was also being developed by the Electronics Research Center. Similar equipment, developed and funded by an electronics concern as a result of the request for quotations by the Electronics Research Center, was purchased and will be flight tested early in 1970. (Fig. 4-13.)

Spacecraft Attitude Control

The Ames Research Center has developed a new and powerful attitude control concept for large-angle satellite maneuvers required to change the pointing direction of spaceborne telescopes. The new concept (derived from Euler's theorem) permits closed loop coordinated rotation that allows any change of attitude to be carried out by a single rotation. It is insensitive to unexpected force or system performance changes and is stable under any ma

neuver.

Guidance and Navigation

The radiometric calibration of infrared devices used in horizon sensors and measurement equipment is limited to an accuracy of about 5 percent. Future flights will require system calibration approximately five times more accurate. The Langley Research Center researchers demonstrated the feasibility of developing a 1-percent system. A precision blackbody source was built and tested, and a design study for the complete calibration system was completed.

General Aviation Avionics

The objective of work in this area is to provide avionic system technology, development, and criteria that will enhance the safety and utility of general aviation aircraft. Simulators and flight vehicles were used to investigate new concepts in flight control, displays, and system components. Projects completed included an investigation of the effectiveness of yaw dampers during the critical phase of a final approach under turbulent conditions and an examination of the efficiency of angle of attack as a control display. In addition, various elements of a total electronics system were being developed or studied. A digitally controlled frequency synthesizer capable of time shared operation to give two Very High Frequency Omni Range (VOR) bearing inputs to a course line computer and a Morse code VOR station identification decoder were fabricated and being evaluated, and a liquid crystal chart overlay was undergoing feasibility studies.

Instrumentation

Photodetectors.—Many experiments involving detection of very low level light signals require a sensitive detector-the photomultiplier. Langley Research Center developed a system which will display in real time a color coded sensitivity map of a photodetector on a color TV receiver. Immediate observation of changes in area sensitivity make it possible to determine optimum performance conditions and to record the effects of localized fatigue of photocathodes and the time required for their recovery. This information, in turn, makes it possible to improve such photomultiplier characteristics as stability and uniformity of area sensitivity.

Irradiated Semiconductors.-Earlier Langley studies of changes in the electrical and optical properties of semiconductors (silicon and germanium) caused by controlled radiation showed that the changes were similar to those caused by chemical doping; as a

result, radiation doping was used to obtain a substantial improvement in the temperature-critical characteristics of semiconductor strain gages. More recently, radiation-doping techniques used in making infrared photodetectors from silicon produced detectors with better uniformity and stability than commercial photodetectors. The radiation-doping technique permits better process control in the manufacture of semiconductor detectors without increase in cost.

Scanning Imaging System.-Langley Research Center conducted preliminary tests of a laboratory version of a multispectral facsimile camera (an imaging and multispectral radiometry system) and completed a first analysis of its application in a planetary lander. The system is intended to demonstrate a simple but effective and reliable way of obtaining spatially well registered multispectral images; it is light (4 lb.), low in power requirements (6 W), small (2 in. dia., 6 in. long), and provides an adjustable scanning rate which can be matched to the data transmission rate.

Data Processing

Magnetic Logic Circuits.-A materials processing technique was