without auxiliary preheating. The new units will continue to operate and produce power as long as hydrogen and oxygen gases are fed into the system, whereas primary batteries produce power only until the plates have been consumed. Useful life of this system is expected to exceed present state-of-the-art devices.

Guidance, control, communications and information processing

A third major subsystem group in aircraft and space vehicles is the equipment that tracks, guides, and controls the vehicle; that senses or measures an event or phenomenon; and that stores, communicates, and reduces data to usable form. These electronic systems which deal with space information and vehicle control, are the eyes, ears, voice, and brains of the spacecraft and its link to Earth stations.

In guidance and control research, the means for navigating in space is under continuing investigation. The gyro, which provides attitude reference, is an essential element of such guidance and control systems. Research on electrostatically suspended gyros has been underway for several years. Such a gyro is illustrated schematically by figure 212. The fabrication of a second phase experimental gyro has been completed and the results of its tests have established the basic feasibility of the principle of electric suspension of gyro rotors for space use. Both research and development work on the concept is continuing. The potential advantages

of this type of gyro over the present mechanically supported gyros are as follows:

1. Very long lifetimes and high performance because there is no mechanical contact to cause wear and decrease lifetime and accuracy.

2. Provision of a truly "free rotor" gyro for flexibility of operation when mounted directly on the space vehicle, thereby eliminating the need for heavy, precision gimbaled platforms and associated precision servos.

An early application for the electrostatic gyro-the optical inertial sextant is under investigation. This device, under development by the Ames Research Center, is illustrated schematically by figure 213. It involves the use of an advanced electronically scanned optical tracker, together with two electrostatically suspended gyros as an advanced sextant for spacecraft navigation. The sextant optics applicable to distant and near-body celestial measurements will use the gyros for direct digital angle readout and angle memory. This technique will provide a single instrument which, with an onboard spacecraft digital computer, can accurately and efficiently handle navigation problems for the various phases of manned and unmanned space missions. The first phase of this effort, involving study and research on the optical portion of the sextant, is nearing completion. Further design of the optical and associated electronic circuits is in process and it is planned to start the development of an experimental model of the complete sextant.

A third example of research and technology in guidance and navigation is work underway at the Ames Research Center on advanced spacecraft guidance simulation. The simulator, shown schematically by figure 214, consists of a three-man crew compartment on an air bearing to provide freedom of motion, with an internal visual display of stars and a lunar model. Investigations are underway, of the accuracy obtainable with hand-held as well as spacecraft-mounted navigational instruments. Experienced Air Force navigators and Ames Research Center engineering personnel are participating in these studies. The results of the studies to date show that readings can be obtained with accuracy on the order of one-third minute of arc with simple manually operated instruments whether hand-held or affixed to the vehicle. This is less accurate than can be done with more sophisticated instruments but very encouraging for emergency use to backup the primary navigation system.

An illustration of the work in the area of controls is a study of the use of a pilot as a prime controller, launch monitor, and emergency and abort controller for a booster. Full use can thus be made of man's integrative and interpretive capabilities provided he is not overloaded with a flow of information and duties. Experiments at Marshall Space Flight Center and Ames Research Center have been conducted to determine a pilot's performance under simulated launch conditions. Different configurations were tried, first with the pilot controlling attitude, with and without rate of turn information displayed in the cockpit; then the pilot controlled attitude and tried to reduce the "g" loading forces on the vehicle as well. The results of

these experiments, summarized by figure 215, indicate that man can operate as a prime controller and can effectively augment the existing automatic control system. Future manned SATURN launches may use this operational mode, and close ties are being maintained with the SATURN project office in developing this area of technology.

In the stabilization or control of spacecraft orientation, an interesting technique known as gravity-gradient stabilization makes use of the small change in gravity force with height above the Earth. This gradient in gravity force can be used to provide preferred orientation of a satellite without the need for external power. The principle involved is illustrated schematically by figure 216. An object on a spring scale at sea level will register a greater weight than at a higher altitude. In the same way, the lower side of an orbiting satellite will experience a larger gravitational attraction than the upper side. If the object in orbit is sufficiently long, this difference in attraction will be large enough to establish and maintain one orientation toward the Earth. Work on gravity-gradient stabilization includes analytical and experimental studies to define the design requirements for attitude control of Earth-oriented orbital vehicles in near-circular orbits in the range of 300 nautical miles to synchronous altitudes. Analytical work at the Ames Research Center has produced an effective configuration, and industry has built a prototype of a damping mechanism, an important element for the stability of this passive control system. In addition, rods have been proposed that can provide the satellite with the necessary large dimensions that are called for by the analytical studies. Continuing work will emphasize new damping

mechanisms that will increase the stability of the system, as well as attacks on the problem of rod bending which results from the thermal gradients encountered in the rods. A flight experiment is planned by the Office of Space Sciences and Applications that will exercise a gravity-gradient satellite under controlled disturbances and varying inertias. These data will be extremely helpful in verifying the laboratory and analytical results and in providing data for the design of future satellites employing the gravity-gradient principle.

Improvement of deep space communications is presently one of the most important research objectives. Communication capability as a function of frequency is illustrated by figure 217.

As would be expected, the bulk of today's technology lies in the microwave region of the spectrum. The greatest potential for deep space communications, however, exists in the submillimeter, or pseudooptical portion, of the spectrum. In this portion of the spectrum large antenna gain can be achieved with small apertures, quantum noise is not a predominant limitation, and atmospheric losses are relatively low. Much of the current communications research effort is therefore concentrated in the submillimeter area.

In the area of optical or laser technology, an interesting application is point-to-point communications via satellites. This communications system, illustrated schematically by figure 218, is called MIROS for modulation inducing retrodirective optical system. Its objective is to consume little or no spacecraft power, the energy being derived principally from the laser beams themselves, thus increasing the overall system reliability and operational lifetime. In operation, two laser