Engineering topics
Publications and source records attributed to Knowles, G..
The tracking problem for a globally minimum phase nonlinear system is considered. It is assumed that the signal to be tracked is slowly varying and a priori bounds on its magnitude are known. It is shown that if the system has bounded derivatives and exponentially stable zero dynamics then the system admits an output feedback controller which solves the tracking problem.
Optical Components of spectrophotovoltaic system concentrate light from Sun and redirect short-wavelength portion of spectrum to solar cell having large gap in energy band (gallium arsenide cell). Longer-wavelength portion of spectrum passes through beam splitter to cell with smaller gap in energy band (silicon band). Available energy in Sunlight thus exploited more fully and, improvements in energy-conversion efficiency possible.
A subscale model of a photovoltaic power system employing spectral splitting and 1000:1 concentration was fabricated and tested. The 10-in. aperture model demonstrated 15.5% efficiency with 86% of the energy produced by a GaAs solar cell and 14% of the energy produced by an Si cell. The calculated efficiency of the system using the same solar cells, but having perfect optics, would be approximately 20%. The model design, component measurements, test results, and mathematical model are presented.
A subscale model of the spectral splitting concentrator system with 10" aperture is defined and designed. The model is basically a scaled down version of Phase 1 design with an effective concentration ratio up to 1000:1. The system performance is predicted to be 21.5% for the 2 cell GaAs/Si system, and 20% for Si/GaAs at AM2 using realistic component efficiencies. Component cost of the model is projected in the $50K range. Component and system test plans are also detailed.
A system with 1000 : 1 concentration ratio is defined, using a cassegrain telescope as the first stage concentration (270 x) and compound parabolic concentrators (CPC) for the second stage concentration of 4.7 x for each spectral band. Using reported state of the art (S.O.A.) solar cells device parameters and considering structural losses due to optics and beamsplitters, the efficiencies of one to four cell systems were calculated with efficiencies varying from approximately 22% to 30%. Taking into account cost of the optics, beamsplitter, radiator, and the cost of developing new cells the most cost effective system is the GaAs/Si system.
An experiment was conducted during October 1971 aboard a sounding rocket to observe the operation of several heat pipes in a zero gravity environment. The pipe designs which were tested included a spiral artery, a pedestal artery, and a plain groove. Two control pipes without wicking were also flown. The two artery pipes were similar to those which will be used on the OAO-C satellite, while the groove pipe was similar to that used on the ATS-F spacecraft. The results of the experiment indicate that the heat pipes operated satisfactorily during the flight which included four minutes of zero gravity.