Memory seems to be everywhere in the brain and yet nowhere. During the past year, scientists at the Goddard Space Flight Center have developed a model of brain memory function which appears to overcome certain deficiencies of other models and provides a more natural and straight forward explanation of the many observed phenomena, both physiological and psychological. The model provides a unitary explanation of such phenomena as short and long term memory and motivational effects. It contains a plausible read-in read-out scheme, shows a good correspondence with brain anatomy and is sufficiently conservative of components that electronic circuits have been postulated which may provide a limited but similar capability.

The memory model is postulated upon the hypothesis that memory results from a stimulus induced modification of the junctions between nerve fibers and brain cells (synaptic junctions). While other synaptic junction models have been developed, the Goddard Space Flight Center model differs in critical detail. Unlike existing models it distinguishes between specific nerve pathways which terminate at single nerve cells and thus directly affect the cell, and nonspecific pathways which terminate upon many cells rather than a single cell and influence cell activity only when there is a coincidence of specific and nonspecific nerve impulses at the cell. Activation of a cell under such coincident impu'se conditions induces a change in the characteristics of the nonspecific synapse and thus modifies the response of the cell to subsequent stimuli. In Fiscal Year 1972, efforts will be made to refine this basic model and develop experimental circuits for testing.

OPTICAL COMPONENTS AND SYSTEMS

TELESCOPE TECHNOLOGY

During Fiscal Year 1971 effort in the telescope technology program has been concentrated on moving the equipment and personnel formerly located at the Electronics Research Center in Cambridge to the Goddard Space Flight Center and planning a renewed attack on the problems in this area. The Vertical Optical Test Tank and the large mirror grinding facility shown in Figure 12

are now being installed in an existing building at Goddard and should be ready for service during Fiscal Year 1972. The major effort during this next year will be to reexamine the error budget of the three-meter space telescope to determine where additional effort is needed. Work will continue on figure sensors which can maintain the figure of the primary mirror to an error no greater than 2 microns as required by scientists for exploring the very edge of the universe. This will include a new idea for placing such a sensor at the focal plane of the telescope rather than at the center of curvature of the primary mirror, and thus shorten the telescope by one half and at the same time detect other errors such as those caused by decentering and misalignment of the secondary mirror. This will require the development of an entirely new concept in error sensors and in the control logic needed to move the elements of the telescope into a ignment with one another as indicated by signals from the error sensor. We will also evaluate the possibility of testing a large primary telescope mirror in a weightless environment by installing it in an aircraft and "pushing over" to achieve weightlessness for the brief periods of time needed to make these vital measurements. Such tests might give sufficient results to indicate whether the use of active optics is in fact needed for the large space telescope and thus obviate the requirement for a test in space.

OPTICAL COMMUNICATIONS

Since space applications programs planned for the future, such as the earth resources satel'ite, will generate useful data in quantities which a'most outstrip our imagination at this time, it is necessary to explore all practical approaches to communications system design. Even with the most stringent processing aboard the spacecraft, the data to be transmitted back to earth either directly or through a relay satellite will exceed the capability of the microwave part of the spectrum for some missions. One logical approach to this problem is to use the laser, which operates at infrared and visible wavelengths where spectrum space is almost unlimited as indicated in Figure 13, as the basis for a communication link which can already carry data rates as high as one billion bits per second.

Much progress has been made in the development of laser communication components and systems. In the infrared at 10.6 microns, the carbon dioxide (CO,) laser as well as modulators and detectors of reasonable quality have been developed at Goddard Space Flight Center and are available for space flight tests. Solutions to the Doppler problem and bandwidth limitations inherent at this frequency will be sought in the coming year. At 1.06 microns in the near infrared, the neodymium Yttrium-Aluminum-Garnet (YAG) laser is being improved and offers promise for the highest data rates in the future. Modulators and detectors are available but would be even more efficient if the output of the laser could be doubled in frequency into the green spectrum. A technique has been developed for doing this in the laboratory using "bananas" crystals (Ba2NaNb5O15), but the equipment must be made more rugged before it can be flown in space. At 0.63 microns the red-light-emitting helium-neon laser is avai able and space qualified for early experimental purposes although it shows little promise for increased power and efficiency.

A space flight experiment is planned for commencement in Fiscal Year 1972 using these available components to demonstrate the capability of laser communications in the space environment, to evaluate the components now available, and to make critically needed measurements of the effect of the atmosphere on vertically oriented laser beams. The capability for performing such an experiment is an indication of the maturity of the development program but is a so essential to choosing the proper courses of action for future component and system development.

LASER SURVEYING POLE

The technology applicable to laser communications and tracking has also been adapted under the Technology Applications program to meet some of the special needs of the U.S. Forest Service and the Bureau of Land Management.

These two groups survey large areas of land in rugged terrain where line of sight to the next fix or marker is obscured by hills or trees. Several trial lines of position usually must be run over the hi ì or through the trees before the degree of error can be determined by sighting the next marker. Technicians at Goddard Space Flight Center proposed the use of a vertically pointed laser placed over the distant marker to give the surveyor an accurate azimuth indicator for laying his line of position. To locate the laser beam, which is not visible to the eye, a special detector was developed which performs in the overall system as shown in Figure 14. Limited field tests have so far indicated that the system performs satisfactorily. The two prospective users identified above have estimated that such a device wi'l permit the saving of approximately 25 million dollars annually in routine surveys.

GUIDANCE AND CONTROL

DIGITAL ADAPTIVE CONTROL TECHNIQUES

Orbital and deep space missions of the future will require spacecraft to be increasingly large and often flexible. In the case of the space station, the station itself may be made up of several large components which are launched separately and assembled in space. When docked scientific modules and a logistics shuttle are added, as shown in Figure 15, the overall body is both large and flexible creating a stabilization problem much like that of stabilizing a garden hose in space. In the case of deep space missions such as the Grand Tour, it is necessary to have large flexible solar arrays or to mount radioisotope thermal generators on long booms to isolate them from scientific instruments. In such cases new and more definitive control laws must be developed and dynamic response characteristics determined. Since the inertia' and temporal characteristics of the spacecraft are continually and sometimes suddenly changing, it is also necessary to develop a technology in which the stabilization system recognizes these changes by the response to its previous commands and adjusts its own mode of operation to prevent overshoot, achieve reasonably tight control, and prevent instability. This is called an adaptive control system and is the technique which will be the subject of next year's research at Langley Research Center for developing control technology broadly applicable to several space missions.

SHUTTLE APPROACH AND LANDING

One of the most difficult phases of operation of the shuttle is the one immediately after it has completed reentry. The shuttle is at that point a large essentially unpowered vehicle which must find its designated landing field, maneuver in an optimum fashion toward it, pick up navigational aids on the ground and complete a one-opportunity landing. It is possible that there may be a go-around capability, but this wiil severely penalize the vehicle and should be avoided if possible. It is desirab.e, if practicable, to plan for the use of navigational aids already installed at the commercial and military airports to achieve flexibility in landing options. On the other hand, because of the unpowered condition of the shuttle, it may be necessary to increase the range at which it picks up, or is picked up by, such navigational aids. Even with a suitable navigational environment there are problems of vehicle control, pilot workload, and cockpit arrangement which must be solved in a quasi-operational environment. To make this possible early enough to assimilate the results into the shuttle program, Ames Research Center has configured the shuttle concept into one of their six degree of freedom simulators with a large simulated out-the-window scene as shown in Figure 16. Using this simulator and appropriate aircraft for flight tests in Fiscal Year 1972, the approach and landing problems of the shuttle will be exercised and pilot workload and vehicle approach limitations determined. This effort is described more fully in the testimony of the Shuttle Technologies Office.

SENSORS AND COMPONENTS

During the past two decades, electronics technology has been revolutionized by the development of solid state theory, materiais and processes. Figure 17 depicts the chronological change from the conventional vacuum tube and discrete components of 1950 to today's emphasis on medium and large scale integrated circuit arrays and the future potential of bulk devices in which complete electronic functions will be performed in a single, solid semiconductor device. The figure also indicates the amalgamation of technical disciplines necessary to achieve these advances in technology. As these devices increase in complexity, continuing research is needed to develop new design procedures, fabrication techniques and test methods. Current efforts are centered on the development of automated test methods in which computers are utilized to test large circuit arrays with up to 200 input and output functions in a single device. A test stand is being fabricated and appropriate software programs developed at Marshall Space Flight Center. In Fiscal Year 1972, the automated test system should be completed and test operations will be initiated. A follow-on program is planned to evaluate simplified test procedures and techniques for reducing the time and cost of testing.

COMPONENT TECHNOLOGY

A key factor in the development of improved e'ectronic devices is the processing or fabrication techniques used in making solid state devices. Figure 18 il'ustrates the evolution of processing technologies and performance characteristics. Using currently available technology such as bipolar or complementary metal-oxidesemiconductor (C-MOS) processes, trade-offs must be made in terms of operating speed, power consumption and cost depending on the desired device application. Research efforts are aimed at achieving a composite technology which maximizes the device performance. The most promising, semiconductors-on-substrates (SOS), is illustrated in the figure. A prototype 256 bit silicon-on-sapphire memory is being developed by RCA under a Marshall Space Flight Center contract. This work will continue in Fiscal Year 1972 with emphasis on characterizing the SOS processes to achieve repeatable and reliable production of electronic devices.

Research on new materials and characterization of their electronic properties are carefully followed with the objective of developing new or improved electronic devices. An example is the magnetic "bubble" phenomena which is being developed by Langley Research Center as a potentially high density, low power mass memory system for computers. Figure 19 illustrates the fundamentals of "bubble" formation in a magnetic material and shows actual bubbles observed in a thin layer of garnet material. These bubbles can be controlled by electromagnetic fields and caused to move in ordered patterns similar to the movement of a bit of information in a shift register or memory. Other material work at Langley is concentrated on the development of liquid crystals and solid state light emitting diodes for use in space and aircraft vehicle displays.