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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Vhf/uhf stellar calibration error analysis.

Results of a statistical error analysis performed to determine the degree of uncertainty encountered when calibrating steerable vhf/uhf receiving antennas with the stellar calibration method. The analysis considers the propagation of precision error indices. It is shown that an antenna gain calibration by the stellar method has a one-sigma (1 sigma) uncertainty of plus or minus 0.65 dB at 1440 MHz (L-band), and plus or minus 0.8 dB (1 sigma) at 136 MHz (vhf). Somewhat increased precision can be achieved by monitoring the antenna gain-to-noise temperature ratio at a station; a worst-case uncertainty of plus or minus 0.4 dB (1 sigma) can be realized at both L-band and vhf. Finally, field test measurements of antenna gain, obtained at 136 MHz in the NASA space tracking and data acquisition network, demonstrate an uncertainty of plus or minus 1.0 dB or less, which effectively confirms the analytical result.

Taylor, R. E.↗
NASA NTRS1971

The effect of bandlimiting of a PCM/NRZ signal on the bit-error probability.

The explicit expressions for the intersymbol interference as a function of bandwidth-bit duration product and bit positions for PCM/NRZ systems operating in the presence of Gaussian noise and in a bandlimited channel are determined. Two types of linear bit detectors are considered, integrate and dump, and bandlimit and sample. Restriction of bandwidth results in a performance degradation. The degradation of signal-to-noise ratio is presented as a function of bandwidth-bit duration product and bit patterns. The average probability of bit errors is computed for various bandwidths. The calculations of the upper bound and lower bound on the error probability are also presented.

Tu, K.↗
NASA NTRS1972

Error correction in adders using systematic subcodes.

A generalized theory is presented for the construction of a systematic subcode for a given AN code in such a way that error control properties of the AN code are preserved in this new code. The 'systematic weight' and 'systematic distance' functions in this new code depend not only on its number representation system but also on its addition structure. Finally, to illustrate this theory, a simple error-correcting adder organization using a systematic subcode of 29 N code is sketched in some detail.

Rao, T. R. N.↗
NASA NTRS1972

Some effects of bias errors in redundant flight control systems.

The controllability and steady-state response of parallel-redundant flight control systems are examined. It is found that state components which appear in the parallel signal paths, e.g., individual actuator commands, are not controllable, although the sum of the command signals is well-behaved. If the response modes associated with these components are not stable, bias errors can cause the components to diverge, leading to the possibility of 'nuisance trips' in failure detection/isolation logic and eventual control system lockup (at saturation). Combining the inputs to the control computers assures that sensor bias will not cause divergence, while cross-strapping control strings bounds divergent response to all bias error inputs. Results of numerical solutions confirm the problem and its solutions.

Stengel, R. F.↗
NASA NTRS1973

Validity test for linear error analysis

To determine whether estimation process simulated by linear error analysis will converge, criterion has been developed based on extension of classical observability. Particular application of technique is with groups of batched navigation data where statistics of estimation errors are derived with classical minimum-variance methods.

Diamant, L. S.↗
NASA NTRS1972

Magnitude error bounds for sampled-data frequency response obtained from the truncation of an infinite series, and compensator improvement program

The frequency response method of analyzing control system performance is discussed, and the difficulty of obtaining the sampled frequency response of the continuous system is considered. An upper bound magnitude error equation is obtained which yields reasonable estimates of the actual error. Finalization of the compensator improvement program is also reported, and the program was used to design compensators for Saturn 5/S1-C dry workshop and Saturn 5/S1-C Skylab.

Mitchell, J. R.↗
NASA NTRS1972

Error analysis in the Mariner 6 and 7 occultation experiments

The Mariner 6 and 7 occultation experiments provide sets of Doppler residuals from which physical properties of the Martian atmosphere may be derived, such as the ionospheric electron density distribution and the lower atmosphere temperature profile. The Doppler residuals contain both systematic and random errors. The former are removed during the data reduction, and the latter are analyzed to yield error limits on the derived physical properties of the atmosphere.

Stewart, R. W.↗
NASA NTRS1972

The pseudonoise test set: Communication system's performance evaluation based upon RMS error testing

A pseudonoise (PN) test set was built to provide a relatively easy means of accurately determining the end-to-end rms error introduced by a communication system when subjected to wideband data. It utilizes a filtered pseudorandom sequence generator as a wideband data source, providing a convenient means for digitally delaying the input reference signal for comparison with the distorted test communication system output. In addition to providing a means to measure the end-to-end rms error and the average delay of a communication system, the PN test set also provides a means to determine the tested system's impulse response and correlation function. The theory of PN testing is discussed in detail along with the most difficult aspects of implementation, the building of matched filter pairs. Both analytical and empirical results are reported which support the contentions that this is an accurate and practical way to acquire figures of merit for complete communication systems.

Wallace, G. R.↗
NASA NTRS1972

Some effects of bias errors in redundant flight control systems

The controllability and steady-state response of parallel-redundant flight control systems are examined. It is found that state components which appear in the parallel signal paths, or individual actuator commands, are not controllable, although the sum of the command signals is well-behaved. If the response modes associated with these components are not stable, bias errors can cause the components to diverge, leading to the possibility of nuisance trips in failure detection/isolation logic and eventual control system lockup (at saturation). Combining the inputs to the control computers assures that sensor bias will not cause divergence, while cross-strapping control strings bounds divergent response to all bias error inputs. Results of numerical solutions confirm the problem and its solutions.

Stengel, R. F.↗
NASA NTRS1973

Error analysis for Mariner Venus/Mercury 1973 conducted at the JPL Mesa west antenna range

Theoretical analysis and experimental data are combined to yield the errors to be used with antenna gain, antenna patterns, and RF cable insertion loss measurements for the Mariner Venus-Mercury 1973 Flight Project. These errors apply to measurements conducted at the JPL Mesa, West Antenna Range, on the high gain antenna, low gain antenna, and RF coaxial cables.

Vincent, N. L.↗
NASA NTRS1973

Statistical error model for a solar electric propulsion thrust subsystem

The solar electric propulsion thrust subsystem statistical error model was developed as a tool for investigating the effects of thrust subsystem parameter uncertainties on navigation accuracy. The model is currently being used to evaluate the impact of electric engine parameter uncertainties on navigation system performance for a baseline mission to Encke's Comet in the 1980s. The data given represent the next generation in statistical error modeling for low-thrust applications. Principal improvements include the representation of thrust uncertainties and random process modeling in terms of random parametric variations in the thrust vector process for a multi-engine configuration.

Bantell, M. H.↗
NASA NTRS1972

Data smoothing and error detection based on linear interpolation

A method is presented, based on linear interpolation, for detecting and correcting bad data points in a set of data without contaminating the good data points. The method used is not concerned with the small random errors usually attributed to a noisy system. It assumes that the data points which are in error are relatively isolated from each other and that the number of such points is small compared to the total number of data points.

Guerra, V. M.↗
NASA NTRS1973

Study of an instrument for sensing errors in a telescope wavefront

Partial results are presented of theoretical and experimental investigations of different focal plane sensor configurations for determining the error in a telescope wavefront. The coarse range sensor and fine range sensors are used in the experimentation. The design of a wavefront error simulator is presented along with the Hartmann test, the shearing polarization interferometer, the Zernike test, and the Zernike polarization test.

Golden, L. J.↗
NASA NTRS1973

Reduction of truncation errors in modal analysis

A condensation method and computer program are described for large discrete parameter vibration analysis of complex structures that greatly reduces truncation errors and provides accurate definition of modes in a selected frequency range. A dynamic transformation is obtained from the partitioned equations of motion that relates modes not explicitly in the condensed solution to the retained modes at a selected system frequency. The generalized mass and stiffness matrices, obtained with existing modal synthesis methods, are reduced using this transformation and solved. Revised solutions are then obtained using new transformations at the calculated eigenvalues and are also used to assess the accuracy of the results. Computations are made tractable by simplified forms of the transformation that result with various modal synthesis methods. Three examples using the dynamic transformation in conjunction with a General Electric stiffness coupling method and the method of Craig and Bampton indicate large reductions in truncation errors and demonstrate the method for sequential groups of modes.

Kuhar, E. J.↗
NASA NTRS1972

Error-erasure decoding of product codes.

Two error-erasure decoding algorithms for product codes that correct all the error-erasure patterns guaranteed correctable by the minimum Hamming distance of the product code are given. The first algorithm works when at least one of the component codes is majority-logic decodable. The second algorithm works for any product code. Both algorithms use the decoders of the component codes.

Wainberg, S.↗
NASA NTRS1973

Error analysis for the Mariner-6 and -7 occultation experiments.

The Mariner-6 and -7 occultation experiments provide sets of Doppler residuals from which physical properties of the Martian atmosphere, such as the ionospheric electron-density distribution and the lower-atmosphere temperature profile, may be derived. The Doppler residuals contain both systematic and random errors. The former are removed during the data reduction, and the latter are analyzed to yield error limits on the derived physical properties of the atmosphere.

Stewart, R. W.↗
NASA NTRS1973

Note on the error signal of block quantizers.

Demonstration that the error signal incurred by block quantizing stationary data is nonstationary under some conditions. Examples are presented which indicate that the mean square error is largest at the block edges. When block quantizers are used to encode pictures at low bit rates, this effect tends to make the block edges visible in the reconstructed picture.

Tasto, M.↗
NASA NTRS1973

Some effects of bias errors in redundant flight control systems.

The controllability and steady-state response of parallel-redundant flight control systems are examined. It is found that state components which appear in the parallel signal paths, e.g., individual actuator-commands, are not controllable, although the sum of the command signals is well behaved. If the response modes associated with these components are not stable, bias errors can cause the components to diverge, leading to the possibility of nuisance trips in failure detection/isolation logic and eventual control system lockup (at saturation). Combining the inputs to the control computers assures that sensor bias will not cause divergence, while cross-strapping control strings bounds divergent response to all bias error inputs.

Stengel, R. F.↗