Engineering topics
Publications and source records attributed to Bridgeforth, A. O..
Noise lower than with sliprings. Rotary transformer transfers electric power across rotary joint. No wearing contacts, no contact noise, and no contamination from lubricants or wear debris. Because additional inductor not required, size and complexity of circuit reduced considerably.
Report surveys state of art in fiber optics and explores use of microprocessors communicating over optical fibers to control complicated power system with many producing and consuming units. Power system of study is of planetary spacecraft, and fiber-optic technology extension of that now under development or used in military aircraft and ships.
Discussed in this paper are some of the problems associated with implementing microcomputer-based power system autonomy on spacecraft flight projects, as well as limitations derived from prior development programs. A new approach is given for developing the autonomy architecture, and an architecture concept, based on that approach, is described.
Many future satellites and spacecraft with spun and despun configurations will require the transfer of power across rotating interfaces in lieu of slip-rings and/or flexures. This is particularly true of spacecraft that have to demonstrate a long life expectancy. The rotary transformer has the desirable characteristics of high reliability and low noise, which qualify it as a potential replacement for slip rings. Development of a rotary power transformer follows the successful completion of a task to develop rotary signal-level transformers for the Galileo Spacecraft Project. The physical configuration of a rotary power transformer has a significant effect on its magnetic and electrical characteristics and therefore impacts the design of the dc/ac inverter driver. Important characteristics addressed during this development effort include: operating frequency, efficiency, transformer gap size, leakage inductance, and leakage flux. A breadboard inverter and rotary transformer were designed, fabricated and tested.
Two algorithms were developed to demonstrate the implementation of autonomous functions in an existing spacecraft power system. The functions selected for autonomous operation include a typical performance monitoring function, battery state of charge, and a fault detection and response function represented by a battery state of charge below a preselected limit. The constraints imposed by the existing power system configuration are the available data in the telemetry stream and the existing commands and command structure. The areas requiring future development are the degree of battery characterization, the effects of hardware/software faults, and the verification of faults.
The APSM program was initiated in 1975. The purpose of this program was to develop and demonstrate the technology and benefits of autonomous operation of planetary spacecraft power systems to meet the projected requirements of future missions. Development of the APSM program was based on implementing a selected set of autonomous functions in a state-of-the-art breadboard power system. A distributed microcomputer system was developed to implement the functions. Several critical programmatic elements were identified as necessary to implement autonomous functions. These elements, including proper skill combination, well defined autonomous functions, and management of the software design and development task, were found to be more significant than hardware management. The incorporation of APSM technology in future space programs is also discussed.
A breadboard power system incorporating autonomous functions of monitoring, fault detection and recovery, command and control was developed, tested and evaluated to demonstrate technology feasibility. Autonomous functions including switching of redundant power processing elements, individual load fault removal, and battery charge/discharge control were implemented by means of a distributed microcomputer system within the power subsystem. Three local microcomputers provide the monitoring, control and command function interfaces between the central power subsystem microcomputer and the power sources, power processing and power distribution elements. The central microcomputer is the interface between the local microcomputers and the spacecraft central computer or ground test equipment.
Automated Power Systems Management is a technology being developed at JPL to provide the capability for onboard monitoring, computation, and control of planetary-spacecraft electrical power systems without the need for ground intervention. The technology uses microcomputers to provide the control and flexibility necessary to achieve rapid and decisive control of power system functions in the event of electrical power failures or unplanned events requiring power system responses. The current program at JPL includes the design, fabrication, test, and evaluation of a breadboard spacecraft power system, modified to incorporate automated power system functions which are implemented by means of a distributed microcomputer system.