difficult. Research has been undertaken to measure the Earth's radiation to space and determine if the horizon can be accurately established by a radiation profile. Last year, laboratory research was extended to flight experiments. The Langley Research Center launched two ballistic rocket flights (Project SCANNER) to obtain radiometric data. Figure 320 shows the payload portion of the spacecraft and an oscillographic record of the resulting measurements with an Earth background for reference. As the radiometer scans from outer space across the Earth and out into space in both the 20-40 and 14-16 micron bands, a sharp change in the radiance profile is observed. The water vapor band, however, appears to be sensitive to cold cloud effects as evidenced by the wide fluctuations in the recorded data, whereas the carbon dioxide band is relatively constant. The decaying nature of the curve over the Earth's surface is a result of the system mechanization and not a change in radiance. Results obtained thus far, combined with new data to be obtained, will provide a base for improving the accuracy of spacecraft horizon sensors by an order of magnitude thereby providing comparable improvements in the accuracy of near-Earth navigation and attitude control systems.

Integrated Circuits.-A major advance in electronics has been achieved with the development of integrated circuit technology. As an example, the Apollo guidance computer would require approximately 50,000 components if built with discrete parts. Through the use of integrated circuits, in which multiple components are contained in a single silicon chip, this total was reduced to approximately 5400. Figure 321 illustrates the technique by which these circuits are constructed. A silicon wafer, sliced from a crystal, is subjected to a series of etching, cleaning, and deposition steps to obtain the multichip wafer shown in the upper left of the figure. The result of this operation is a multiplicity of individual circuits all produced on a single wafer about the size of a half dollar. The wafer is then sliced into individual circuits, as illustrated by the magnified view in the upper right of the figure. Each chip is subsequently mounted in a package and connecting wires are attached. A "flat-pack" unit, complete except for its cover, is shown in the lower right of the figure.

A prime advantage of integrated circuits is the great potential for increased reliability. Formerly, each of the 50,000 components required in the Apollo computer would have required at least two connections, a total of 100,000 connections, each hand soldered, and each an opportunity for human error, the single greatest cause of failures in electronics. Figure 322 is an enlarged view of a typical silicon monolithic integrated circuit. As can be seen in the figure, handmade connections between components have been eliminated. All components are both formed and inter-connected in the manufacturing process. The only handmade connections required are those from the circuit to external leads.

Thin-Film Microelectronics.-Because of their thickness, today's silicon monolithic devices and thick-film devices are deficient in radiation resistance, speed of response, and stability and endurance at high temperatures. A promising approach for improving these characteristics is in the "thin-film" technology, in which the conductors, resistors, and capacitors, only a few molecules thick, are vapor-deposited, in a vacuum, onto a sapphire substrate, after which the active elements (silicon flakes) are attached by hand. Recently, however, the Hughes Aircraft Company, under sponsorship of the Electronics Research Center, has shown the feasibility of a method for vapor-depositing thin-film active elements of slicon. The unit is shown in the sketch on the right of figure 323. The active elements are much thinner than the flakes, and hence less susceptible to damage of space radiation; they also have the advantage that the complete device can be made by automated processes. Further work is needed to refine this device and develop processing techniques with improved yields and greater reliability.

Strapdown Inertial Sensors and Systems.-Strapdown or gimballess inertial systems for launch vehicle and spacecraft use are major elements in this subprogram. Figure 324 illustrates on the left, a Saturn I gimballed platform and. on the right, a mockup of a strapdown platform using the same gyros and accelerometers. The simplicity of the strapdown unit packaging is apparent. Advantages of the strapdown or body mounted system are: reduced mechanical complexity, easier sensor replacement, flexibility in vehicle installation and avoidance of gimbal lock which, in a gimballed platform requires a fourth gimbal or

A study performed in FY 1966 by Thompson-Ramo-Wooldridge Systems for Marshall Space Flight Center indicated a strapdown platform using current gyros could demonstrate an early operational capability, with acceptable accuracy, when assembled in a single-axis platform configuration. This configuration would reduce the mechanical complexity without requiring the development of new gyros. A "breadboard" single-axis platform built in the laboratory at the Marshall Space Flight Center is shown in figure 325. It combines a Saturn

platform gyro in a cradle assembly with a precision encoder along with slip rings and other ancillary equipment; it has been tested recently with good results. It is planned to continue the effort in FY 1968 to develop a flight packaged configuration for flight evaluation.

The electrostatic or electrically suspended gyro has been described previously as an ideal sensor for advanced strapdown systems. This device can be used in a fully strapdown mode and does not require torquing of the output axis as is necessary with conventional gyros when used in this mode. The first packaged gyro designed by Honeywell under Jet Propulsion Laboratory sponsorship for strapdown space applications has been completed and is illustrated in figure 326. The gyro case is mounted directly on the spacecraft and the position of the rotor with respect to the gyro case is obtained by the use of three optical pickoffs which read lines inscribed on the rotor. The device will undergo exhaustive laboratory and environmental testing during CY 1967.

A joint effort by the Jet Propulsion Laboratory and the Air Force Avionics Laboratory to demonstrate the feasibility of using the electrostatic gyro for strapdown inertial navigation is well under way. The system will include a high speed digital computer capable of real-time processing of the gyro data and computations for navigation.

Inertial Navigation Data Correction.-Automatic and continuous display of position data are features characteristic of aircraft inertial navigation systems. Unfortunately, persistent error sources such as gyroscope drift have limited the