Engineering topics
Publications and source records attributed to Lesh, J. R..
A procedure is described which partitions the recurring costs of the Deep Space Network (DSN) over the individual DSN subsystems. The procedure results in a table showing the maintenance, operations, sustaining engineering and supportive costs for each subsystems.
Communication system processes subcarrier that is modulated with sequential range codes and with command data. Loop locks in on range codes as they occur in sequence. When range code modulated with data-frequency arrives, loop switches to DEMOD to receive data.
The combination of a bandpass limiter and an n-th power tracking loop is considered. Performance of the combination does not depend on the form of the nonlinear function used to create the n-th harmonic signal as long as some energy in that zone is produced. The order in which the limiter and n-th power nonlinearity occur is unimportant so that the results apply equally well to the n-phase Costas type of implementations of the n-th power loops. Closed form expressions for the signal suppression factors are obtained. Coherent and noncoherent SNR's out of the n-th power-limiter combination can be expressed in terms of two of these suppression factors. The loop SNR of an n-th power-limited phase locked loop is estimated by simply calculating the suppression factors for n-th and 2n-th power loops. Finally, n-th power phase locked loops without limiters are compared with similar loops with limiters; the limiter can actually enhance output SNR at moderate to large input SNR.
A multi-rate digital command system is disclosed which uses the composite signal of a mu-type ranging system as a subcarrier to transmit range codes and data from a station to a receiver where the range codes are sequentially phase modulated on a subcarrier of frequency by one of its own subharmonics and data is phase modulated on a selected ranging component. A range cleanup loop in a spacecraft locks the phase of a locally generated reference component to a received ranging component and retransmits the component to a ground station. When the inverse phase of a ranging component is received and detected, the cleanup loop is modified to demodulate phase modulated command symbols while continuing tracking the same ranging component. The command symbol rate is coherently related to the ranging signal component bit rate.
A pessimistic statistical model was developed for predicting the extent of radio frequency interference (RF1). Based on the assumptions underlying the model, DSN S-band operations can expect one RF1 interruption every 4.1 days, with the average incident lasting 24 s. This implies that 52 or more such satellites, with uncorrelated orbital trajectories, will cause in excess of 5 min of RF1 per day at a DSN station.
The combination of a bandpass limiter and an n(th) power tracking loop is considered. It is shown that the performance of the combination does not depend on the form of the nonlinear function used to create the n(th) harmonic signal so long as some energy in that zone is produced. Furthermore, the order in which the limiter and n(th) power nonlinearity occur is unimportant so that the results apply equally well to the n-phase Costas type of implementation of the n(th) power loops. Closed form expressions for the signal suppression factors are obtained and it is shown that the coherent and noncoherent SNR's out of the n(th) power-limiter combination can be expressed in terms of two of these suppression factors. This later point enables one to estimate the loop SNR of an n(th) power-limiter phase locked loop by simply calculating the suppression factors for n(th) and 2n(th) power loops. Finally, n(th) power phase locked loops without limiters are compared with similar loops with limiters where it is shown that the presence of the limiter can actually enhance the output SNR at moderate to large values of input SNR.
Preliminary results of an infrared survey of the equatorial sky zone (declinations 10 S to 10 N) with U.S. Air Force satellite sensors show that positions of previously unknown infrared sources are measured with an rms accuracy of 4 arc seconds, which is six times better than the best previous infrared survey. The search area per source for further study is thus 36 times smaller, so that identification of the infrared sources with optical objects in catalogs and sky photographs is facilitated, as is reacquisition of the sources with ground-based infrared telescopes. The survey extends the content of near-infrared source catalogs to lower flux densities and adds information at a wavelength not observable from the ground. Objects found in the survey include cool giants and supergiants, long-period and semi-regular variable stars, and sources identified with faint red stars visible on the Palomar Observatory Sky Survey.
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A new model for predicting the computational performance of a sequential decoder operating in a noisy carrier reference environment is described. The major difference between this model and previous models is that the new model characterizes the number of computations per frame as the sum of the computations resulting from a number of independent searches. This number of independent searches can then be considered as an effective frame length. When this computational model is averaged over noisy reference phase errors using a medium-rate interpolation scheme, the results are found to agree quite favorably with experimental measurements.
Ultraviolet spectra of three beta Cep variables and a nonvariable star of similar spectral type were observed by the ultraviolet spectrometer on Mariner 9. A significant light variation at 1400 A may have been detected for beta Cep. The variable stars have mean ultraviolet spectra similar to that of the nonvariable star and do not show any significant short-period spectral variations.
Photometric data from the Wisconsin Experiment package on OAO-2 were obtained for six Beta Cephei variable stars. The data were reduced in accordance with the OAO 2/Wisconsin Experiment Package Photometer Users Guide. For delta Cet and gamma Peg, there were enough data points to form reliable composite light curves at seven or eight ultraviolet wavelengths. The light curves are well represented by sine waves in phase with the blue light curve for each star. The amplitude of the light variation increases with shorter wavelengths. For theta Oph, epsilon Cen, eta Sco, and Lambda Sco, mean magnitudes and light ranges were obtained at several ultraviolet wavelengths. No significant differences were found between the mean, de-reddened ultraviolet colors of the observed stars, and the mean values for standard stars computed by Bottemiller. An attempt to derive a temperature scale from a comparison of the observed ultraviolet colors with Kurucz models was unsuccessful.
A new model for predicting the computational performance of a sequential decoder operating in a noisy carrier reference environment is described. The major difference between this model and previous models is that the new model characterizes the number of computations per frame as the sum of the computations resulting from a number of independent searches. This number of independent searches can then be considered as an effective frame length. When this computational model is averaged over noisy reference phase errors using a medium-rate interpolation scheme, the results are found to agree quite favorably with experimental measurements.
Expressions for the output signal-to-noise power ratio of a bandpass soft limiter followed by a coherent detection device are presented and discussed. It is found that a significant improvement in the output signal-to-noise ratio (SNR) at low input SNR's can be achieved by such soft limiters as compared to hard limiters. This indicates that the soft limiter may be of some use in the area of threshold extension. Approximation methods for determining output signal-to-noise spectral densities are also presented.
Expressions for the output signal-to-noise power ratio of a bandpass soft limiter followed by a coherent detection device are presented and discussed. It is found that a significant improvement in the output signal-to-noise ratio at low input SNRs can be achieved by such soft limiters as compared to hard limiters. This indicates that the soft limiter may be of some use in the area of threshold extension. Approximation methods for determining output signal-to-noise spectral densities are also presented.