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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1975

Precision Selenodesy via Differential Very-Long-Baseline Interferometry

The technique of differential very-long baseline interferometry was used to measure the relative positions of the ALSEP transmitters at the Apollo 12, 14, 15, 16, and 17 lunar landing sites with uncertainties less than 0.005 of geocentric arc. These measurements yielded improved determinations of the selenodetic coordinates of the Apollo landing sites, and of the physical libration of the moon. By means of a new device, the differential Doppler receiver (DDR), instrumental errors were reduced to less than the equivalent of 0.001. DDRs were installed in six stations of the NASA spaceflight tracking and data network and used in an extensive program of observations beginning in March 1973.

King, R. W., Jr.↗

NASA NTRS1975

Flight instrumentation specification for parameter identification: Program user's guide

A set of four digital computer programs is presented which can be used to investigate the effects of instrumentation errors on the accuracy of aircraft and helicopter stability-and-control derivatives identified from flight test data. The programs assume that the differential equations of motion are linear and consist of small perturbations about a quasi-steady flight condition. It is also assumed that a Newton-Raphson optimization technique is used for identifying the estimates of the parameters. Flow charts and printouts are included.

Mohr, R. L.↗

NASA NTRS1977

Inverse solution of the pseudoscalar transfer equation through nonlinear matrix inversion

Nonlinear matrix inversion operators have been developed which, applied to observed radiances, infer maximal information regarding atmospheric scattering parameters and vertical distribution of radiant sources and sinks. The algorithm has the attractive feature of noise discrimination, attributing instrumental errors to extra-atmospheric sources.

King, J. I. F.↗

NASA NTRS1980

Snow extent measurements from geostationary satellites using an interactive computer system

The author has identified the following significant results. A time series of GOES full resolution visible image sectors was viewed on the McIDAS video component in chronological order and registered to within plus or minus 1 image pixel to compute real time snow melting rates. Synoptic scale clouds were eliminated to create a snow covered area from a composite image. Results show good agreement with NESS products although a significant difference was noted for one two-day period when the NESS products showed an increase in the snow cover for the Verde Basin, while the GOES/McIDAS product implied no change in the snow cover for approximately the same period. A check of NWS radar reports indicated no precipitation had occurred within the Verde basin. The use of the registered image sequence eliminates instrument error since small changes in the snow cover between any two days are easily detected.

Gird, R. S.↗

NASA NTRS1980

Model development for automatic guidance of a VTOL aircraft to a small aviation ship

This paper describes a detailed mathematical model which has been assembled to study automatic approach and landing guidance concepts to bring a VTOL aircraft onto a small aviation ship. The model is used to formulate system simulations which in turn are used to evaluate different guidance concepts. Ship motion (Sea State 5), wind-over-deck turbulence, MLS-based navigation, implicit model following flight control, lift fan V/STOL aircraft, ship and aircraft instrumentation errors, various steering laws, and appropriate environmental and human factor constraints are included in the model. Results are given to demonstrate use of the model and simulation to evaluate performance of the flight system and to choose appropriate guidance techniques for further cockpit simulator study.

Goka, T.↗

NASA NTRS1980

Estimation of Kalman filter model parameters from an ensemble of tests

A methodology for estimating initial mean and covariance parameters in a Kalman filter model from an ensemble of nonidentical tests is presented. In addition, the problem of estimating time constants and process noise levels is addressed. Practical problems such as developing and validating inertial instrument error models from laboratory test data or developing error models of individual phases of a test are generally considered.

Gibbs, B. P.↗

NASA NTRS1981

Flight evaluation of a simplified gross thrust calculation technique using an F100 turbofan engine in an F-15 airplane

A simplified gross thrust calculation technique was evaluated in flight tests on an F-15 aircraft using prototype F100-PW-100 engines. The technique relies on afterburner duct pressure measurements and empirical corrections to an ideal one-dimensional analysis to determine thrust. In-flight gross thrust calculated by the simplified method is compared to gross thrust calculated by the engine manufacturer's gas generator model. The evaluation was conducted at Mach numbers from 0.6 to 1.5 and at altitudes from 6000 meters to 13,700 meters. The flight evaluation shows that the simplified gross thrust method and the gas generator method agreed within plus or minus 3 percent. The discrepancies between the data generally fell within an uncertainty band derived from instrumentation errors and recording system resolution.

Kurtenbach, F. J.↗

NASA NTRS1976

Ultraviolet spectroscopy of comets

The advantages of the space shuttle being used as an observing platform with advanced instrumentation for the study of comets are discussed. The ground-based observations of the comet West (1976) were used to illustrate the many problems caused by the Earth's atmosphere. The spectrum of comet Bennett (1970 II) was compared to that the of comet West in order to correct instrument errors.

Lillie, C. F.↗

NASA NTRS1981

Thrust imbalance of the Space Shuttle solid rocket motors

The Monte Carlo statistical analysis of thrust imbalance is applied to both the Titan IIIC and the Space Shuttle solid rocket motors (SRMs) firing in parallel, and results are compared with those obtained from the Space Shuttle program. The test results are examined in three phases: (1) pairs of SRMs selected from static tests of the four developmental motors (DMs 1 through 4); (2) pairs of SRMs selected from static tests of the three quality assurance motors (QMs 1 through 3); (3) SRMs on the first flight test vehicle (STS-1A and STS-1B). The simplified internal ballistic model utilized for computing thrust from head-end pressure measurements on flight tests is shown to agree closely with measured thrust data. Inaccuracies in thrust imbalance evaluation are explained by possible flight test instrumentation errors.

Foster, W. A., Jr.↗

NASA NTRS1982

Methods of editing cloud and atmospheric layer affected pixels from satellite data

Subvisible cirrus clouds (SCi) were easily distinguished in mid-infrared (MIR) TIROS-N daytime data from south Texas and northeast Mexico. The MIR (3.55-3.93 micrometer) pixel digital count means of the SCi affected areas were more than 3.5 standard deviations on the cold side of the scene means. (These standard deviations were made free of the effects of unusual instrument error by factoring out the Ch 3 MIR noise on the basis of detailed examination of noisy and noise-free pixels). SCi affected areas in the IR Ch 4 (10.5-11.5 micrometer) appeared cooler than the general scene, but were not as prominent as in Ch 3, being less than 2 standard deviations from the scene mean. Ch 3 and 4 standard deviations and coefficients of variation are not reliable indicators, by themselves, of the presence of SCi because land features can have similar statistical properties.

Nixon, P. R.↗

NASA NTRS1983

Accuracy and resolution of Earth Radiation Budget Estimates

A numerical filter inversion technique that reduces wide-angle satellite measurements to top-of-the-atmosphere radiant exitances has been proposed for the Earth Radiation Budget Experiment (ERBE). The matrix formulation of this technique is presented, and the design of the numerical filter is discussed. The filter is smoothed with a singular value decomposition. The inversion process is simulated by generating synthetic measurements from a 24 degree spherical harmonic radiation field derived from Nimbus 6 ERB data. The numerical filter is applied to these measurements after they are corrupted with instrument error. The results are curves of expected error versus resolution area.

Green, R. N.↗

NASA NTRS1982

Development of a new, completely implantable intraventricular pressure meter and preliminary report of its clinical experience

A completely implantable intracranial pressure sensor designed for long-term measurement of intraventricular pressure in hydrocephalic patients is described. The measurement principal of the device is discussed along with the electronic and component structure and sources of instrument error. Clinical tests of this implanted pressure device involving both humans and animals showed it to be comparable to other methods of intracranial pressure measurement.

Osaka, K.↗

NASA NTRS1983

Application of in-flight thrust determination uncertainty

A numerical example is given of a previously proposed methodology for the evaluation of in-flight thrust measurement uncertainty, using data extracted from a performance report comparing two different missile prototypes under a variety of flight conditions. Attention is given to the data for the AGM-68B Air Launched Cruise Missile, which is powered by the F107 dual-spool, mixed flow turbofan engine. Assessments are made of the definition of the measurement process, instrumentation error estimation, the propagation of errors to thrust calculation, mathematical model errors, the in-flight thrust error component, and correction to standard conditions. It is concluded that in-flight thrust measurement uncertainty limits can be evaluated from measurement system error analysis results and test data for the missile evaluation process presently described.

Adams, G. R.↗

NASA NTRS1984

On the remote sensing of cloud properties from satellite infrared sounder data

A method for remote sensing of cloud parameters by using infrared sounder data has been developed on the basis of the parameterized infrared transfer equation applicable to cloudy atmospheres. The method is utilized for the retrieval of the cloud height, amount, and emissivity in 11 micro m region. Numerical analyses and retrieval experiments have been carried out by utilizing the synthetic sounder data for the theoretical study. The sensitivity of the numerical procedures to the measurement and instrument errors are also examined. The retrieved results are physically discussed and numerically compared with the model atmospheres. Comparisons reveal that the recovered cloud parameters agree reasonably well with the pre-assumed values. However, for cases when relatively thin clouds and/or small cloud fractional cover within a field of view are present, the recovered cloud parameters show considerable fluctuations. Experiments on the proposed algorithm are carried out utilizing High Resolution Infrared Sounder (HIRS/2) data of NOAA 6 and TIROS-N. Results of experiments show reasonably good comparisons with the surface reports and GOES satellite images.

Yeh, H. Y. M.↗

NASA NTRS1987

Phase closure with a rotational shear interferometer

A simple and efficient way is proposed for achieving phase closure in an optical telescope (to enable recovering Fourier transform phases that would otherwise be corrupted by atmospheric and instrumental errors), by means of rotational shear interferometry. In a rotational shear interferometer, one images the telescope aperture onto the interferometer and then interferes the aperture with itself in a rotated orientation. To achieve the maximum frequency content permitted by the telescope, the shear has to be 180 deg, but better dynamic range and SNR are possible for lower frequencies. Drawbacks of the proposed method compared to radio astronomy are noted, and different approaches are indicated as to how to collect and use the phase closure data. Phase closure can be realized on existing telescopes and existing interferometers with special modifications. Although not all base lines are possible, the extra constraints provided by the closure phases greatly reduce the ambiguity now existing in phaseless image reconstruction.

Ribak, Erez↗

NASA NTRS1989

Chip Advancer For GPS Receiver

Instrument errors made negligible. For each integration interval, both delay and rate of change of delay initialized to small fraction of chip - for example, to order of 10 to the negative 7th power - thereby making feedback control and extraction of delay highly accurate and flexible. With appropriate selection of sampling rate relative to chip rate, commensurability errors reduced to extremely small levels. In Global Positioning System (GPS) receiver, pseudorandom code sequence generated by simple digital logic incorporating effects of time, delay, and rate of change of delay. Flexibility in starting time and sum interval very useful in aligning correlation interval with beginnings and endings of data bits.

Meehan, Thomas K.↗

NASA NTRS1988

Monitoring solar-type stars for luminosity variations

Since 1984, researchers have made more than 1500 differential photometric b (471 nm) and y (551 nm) measurements of three dozen solar-like lower main sequence stars whose chromospheric activity was previosly studied by O. C. Wilson. Here, researchers describe their methodology and the statistical tests used to distinguish intrinsic stellar variability from observational and instrument errors. The incidence of detected variability among the program and comparison stars is summarized. Among the 100 plus pairs of stars measured differentially, only a dozen were found that were unusually constant, with peak-to-peak amplitudes of seasonal mean brightness smaller than 0.3 percent (0.003 mag) over a two-to-three-year interval.

Lockwood, G. W.↗

NASA NTRS1990

Autonomous integrated GPS/INS navigation experiment for OMV. Phase 1: Feasibility study

The phase 1 research focused on the experiment definition. A tightly integrated Global Positioning System/Inertial Navigation System (GPS/INS) navigation filter design was analyzed and was shown, via detailed computer simulation, to provide precise position, velocity, and attitude (alignment) data to support navigation and attitude control requirements of future NASA missions. The application of the integrated filter was also shown to provide the opportunity to calibrate inertial instrument errors which is particularly useful in reducing INS error growth during times of GPS outages. While the Orbital Maneuvering Vehicle (OMV) provides a good target platform for demonstration and for possible flight implementation to provide improved capability, a successful proof-of-concept ground demonstration can be obtained using any simulated mission scenario data, such as Space Transfer Vehicle, Shuttle-C, Space Station.

Upadhyay, Triveni N.↗