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The trend of commercial aircraft today is toward larger size and more electric service power. As the aircraft becomes larger and environmental conditions become more severe, stringent design requirements such as a high degree of reliability, minimum operating cost, and minimum weight are imposed on the aircraft electrical power system. In reviewing the electrical power systems installed in present day aircraft, it is found that despite many improvements, the basic approach of these systems is virtually the same as about 20 years ago. In the light of recent technological advances in various related fields and the change of aircraft electrical power system requirements, a reevaluation of the conventional approach is in order. In recognition of this, a study program was initiated in 1968 by NASA Electronics Research Center to investigate possible improvements to present aircraft electrical power systems for use in future advanced types of aircraft. Study results indicate that many avenues are available for improving the present system, such as variable-speed, constant-frequency generation, optimization of system voltage and frequency, solid-state power switching and control, automatic load management, signal multiplexing, failure prediction, detection, and compensation, to name a few. A detailed discussion of these improvements is beyond the scope of this presentation. This paper specifically presents a projected development trend and depicts an example of a hybrid electrical power system offering reduced weight and improved reliability and maintainability.

The IDCSP/A satellites are communication satellites built by Philco-Ford Corporation under contract to the United States Air Force for United Kingdom applications, tailored for compatibility with the near synchronous IDCSP communication satellite network. These satellites utilize a mechanically despun antenna system and a hydrazine reaction control system for attitude control and station keeping. The design of these satellites utilizes advanced concepts reflecting current state-of-the-art. Design, integration, and test concepts of the IDCSP/A electrical power subsystem is discussed in this paper. This subsystem utilizes solar cells for primary power conversion and hermetically sealed nickel-cadmium batteries for enery storage. The power subsystem used in the IDCSP/A satellites has been designed to provide continuously regulated primary power to each satellite subsystem. This fully automatic power subsystem has been optimized to take full advantage of earth synchronous equatorial orbit characteristics. Flight data from the satellites demonstrates that the power subsystem is meeting or exceeding performance requirements.

Past, present, and future nuclear power sources for Navy underwater applications are discussed. Actual undersea nuclear power installations are illustrated. Data describing the availability, power characteristics, and cost effectiveness of underwater power sources are presented.

Spacecraft electrical power subsystems require continuous monitoring, ground supported analysis of performance, and ground intervention to provide power management and fault correction. An interplanetary fly-by mission to the outer planets necessitates long periods of relatively low activity between encounters. It would be desirable to minimize ground access and support during these times if it can be shown that power management and fault removal functions can be implemented economically and reliably within the power subsystem flight equipment. This paper describes the interim results of a study to develop the techniques and implementation methods to provide a power subsystem capable of autonomous fault correction and power management. Each subsystem element is analyzed to define failure modes and failure characteristics which permit identification of fault correction methods. Fault protection concepts for each classification of loads are formulated to provide a high probability of delivering power to the load yet protect the power subsystem in the event of a load fault. The Mariner Jupiter/Saturn power subsystem elements formed the baseline for this study.

The Pioneer F/G spacecraft is the first to use radioisotope thermoelectric generators (RTG's) for a long duration interplanetary mission. This paper describes the design of the spacecraft power subsystem which meets the unique requirements of such a mission. The primary power source consists of four SNAP 19 RTG's. The 4. 2 volt dc outputs of the RTG's are inverted to higher voltage ac by four inverters which are connected in parallel at their outputs. A power control unit (PCU) regulates the ac output of the inverters such that the RTG's are operated at near maximum power voltage throughout the mission. The PCU also contains charge and discharge controls for a silver cadmium battery which supplements the RTG's if load requirements temporarily exceed RTG power output. Battery reliability is enhanced by overcharge and cell reversal protection electronics which are provided for each cell. Multiple, low voltage, regulated dc outputs which supply power to the spacecraft subsystems are provided by a central transformer-rectifier-filter unit (CTRF). The CTRF operates directly from the regulated ac bus.

This paper presents a new concept in electrical power distribution systems for air craft and compares the conventional approach to this concept. The historical development of this concept is presented and system application as developed by the Air Force and Navy laboratories is discussed. Some of the capabilities of an electrical system using this concept are presented. Electrical distribution systems perform four basic functions. These are: (a) to gather control data information, (b) to determine from this data the proper control action, (c) to transmit this control information to the location of the control action, and (d) to perform the necessary control action. The electrical distribution system must do the above four items in a safe and orderly manner which will not result in fire or other unsafe conditions if a short circuit or any other malfunction occurs. Thus, i t must also provide circuit protection and failsafe operation.