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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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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Servomechanism for Doppler shift compensation in optical correlator for synthetic aperture radar

A method and apparatus for correcting Doppler shifts in synthetic aperture radar data is described. An optical correlator for synthetic aperture radar data has a means for directing a laser beam at a signal film having radar return pulse intensity information recorded on it. A resultant laser beam passes through a range telescope, an azimuth telescope, and a Fourier transform filter located between the range and azimuth telescopes, and forms an image for recording on an image film. A compensation means for Doppler shift in the radar return pulse intensity information includes a beam splitter for reflecting the modulated laser beam, after having passed through the Fourier transform filter, to a detection screen having two photodiodes mounted on it.

Constaninides, N. J.↗
NASA NTRS1983

Attitude control and drag compensation propulsion system for Gravity Probe-B spacecraft

An on board propulsion system for attitude control and drag compensation is presented which uses helium boiloff gas from an experiment package dewar as propellant. This boiloff gas would normally be vented nonpropulsively. Use of a small allowable temperature range in the dewar is exploited to store helium and accommodate incompatibilities in dewar heat leak and thruster demand flow over periods of more than one orbit. A relatively detailed thermodynamics analysis of the two phase helium dewar and simulation of pressure loss through the helium distribution system is included.

Blount, D. H.↗
NASA NTRS1983

Classification of journal surfaces using surface topography parameters and software methods to compensate for stylus geometry

Measurements made with a stylus surface tracer which provides a digitized representation of a surface profile are discussed. Parameters are defined to characterize the height (e.g., RMS roughness, skewness, and kurtosis) and length (e.g., autocorrelation) of the surface topography. These are applied to the characterization of crank shaft journals which were manufactured by different grinding and lopping procedures known to give significant differences in crank shaft bearing life. It was found that three parameters (RMS roughness, skewness, and kurtosis) are necessary to adequately distinguish the character of these surfaces. Every surface specimen has a set of values for these three parameters. They can be regarded as a set coordinate in a space constituted by three characteristics axes. The various journal surfaces can be classified along with the determination of a proper wavelength cutoff (0.25 mm) by using a method of separated subspace. The finite radius of the stylus used for profile tracing gives an inherent measurement error as it passes over the fine structure of the surface. A mathematical model is derived to compensate for this error.

Li, C. J.↗
NASA NTRS1983

Vibration isolation and pressure compensation apparatus for sensitive instrumentation

A system for attenuating the inherent vibration associated with a mechanical refrigeration unit employed to cryogenically cool sensitive instruments used in measuring chemical constituents of the atmosphere is described. A modular system including an instrument housing and a reaction bracket with a refrigerator unit floated there between comprise the instrumentation system. A pair of evacuated bellows that "float' refrigerator unit and provide pressure compensation at all levels of pressure from seal level to the vacuum of space. Vibration isolators and when needed provide additional vibration damping for the refrigerator unit. A flexible thermal strap (20 K) serves to provide essentially vibration free thermal contact between cold tip of the refrigerator unit and the instrument component mounted on the IDL mount. Another flexible strap (77 K) serves to provide vibration free thermal contact between the TDL mount thermal shroud and a thermal shroud disposed about the thermal shaft.

Averill, R. D.↗
NASA NTRS1983

Battery charge control with temperature compensated voltage limit

Battery charge control for orbiting spacecraft with mission durations from three to ten years, is a critical design feature that is discussed. Starting in 1974, the General Electric Space Systems Division designed, manufactured and tested battery systems for six different space programs. Three of these are geosynchronous missions, two are medium altitude missions and one is a near-earth mission. All six power subsystems contain nickel cadmium batteries which are charged using a temperature compensated voltage limit. This charging method was found to be successful in extending the life of nickel cadmium batteries in all three types of earth orbits. Test data and flight data are presented for each type of orbit.

Thierfelder, H. E.↗
NASA NTRS1982

A novel input filter compensation scheme for switching regulators

A novel input-filter compensation scheme is proposed which uses feedforward loops to cancel the effects of peaking of the output impedance of the input filter, such that the converter is immune from performance degradation due to loop gain reduction. The scheme makes it possible to concurrently implement a high-performance converter and an effective input filter design with minimum weight and loss. A buck regulator with continuous current conduction is used as an example, and an analysis followed by a design procedure for the feedforward loops is presented.

Kelkar, S. S.↗
NASA NTRS1983

Image motion compensation for the OSS-3/7 telescopes

The three telescope for the NASA Office of Space Science (OSS) Missions 3/7 will be clustered on the Instrument Point System (IPS). The IPS is to be mounted on a Spacelab pallet in the space shuttle orbiter. The three telescopes include the Ultraviolet Imaging Telescope (UIT), the Hopkins Ultraviolet Telescope (HUT), and the Wisconsin Ultraviolet Photopolarimetry Experiment (WUPPE). All three instruments have the ability to view from earth orbit stellar objects which are fainter than those which can be seen with ground-based telescopes. An Image Motion Compensation (IMC) system will be required for the appropriate conduct of the observations. The OSS-3/7 pointing problem is discussed, and a cost effective IMC system is proposed.

Shelton, H.L.↗
NASA NTRS1983

Laboratory evaluation of an airborne ozone instrument that compensates for altitude/sensitivity effects

One problem encountered in the use of air-quality instrumentation on aircraft is the variation of instrument sensitivity with pressure as the result of altitude changes of the aircraft. Many instruments experience sensitivity changes of as much as a factor of 2 at altitudes of 6 km. Discussed are recent modifications to a chemiluminescent (ethylene) ozone detector that allow the instrument to automatically compensate for pressure/sensitivity effects. The modification provides automated mass flow rate control for both the sample and ethylene gas flows. The flow control systems maintain flow rate to within 15 percent for a 100-torr instantaneous pressure change, and flow rates are returned to the desired set points within 10 s after the pressure change. During simulated altitude changes (300 m/min from mean sea level to 3-km altitude), flow rates were controlled to within 3 percent of the set point. Laboratory data are summarized verifying the operation of the instrument for a pressure range of 760 torr (sea level) to 350 torr (approximately 20,000 ft) and an ozone concentration range from 20 to approximately 700 ppb.

Gregory, G. L.↗
NASA NTRS1984

Apparatus for and method of compensating dynamic unbalance

An apparatus to stabilize a fine platform that carries a parabolic reflecting dish, utilized in connection with the large aperture, multichannel microwave radiometer, is discussed. It provides compensation for dynamic unbalance imparted to a fixed body by a shaft about which the rotating body rotates. Force components exerted on the fixed body by the rotating body in a plane at right angles to the axis are determined. In response to the determined force components, the rotational speed and effective direction of mass means mounted on the rotating body are controlled. The mass means has an effective axis of rotation in a plane at right angles to the longitudinal axis.

Hrastar, J. A.↗
NASA NTRS1983

Models of human problem solving - Detection, diagnosis, and compensation for system failures

The role of the human operator as a problem solver in man-machine systems such as vehicles, process plants, transportation networks, etc. is considered. Problem solving is discussed in terms of detection, diagnosis, and compensation. A wide variety of models of these phases of problem solving are reviewed and specifications for an overall model outlined.

Rouse, W. B.↗
NASA NTRS1983

Roundoff noise and scaling in the digital implementation of control compensators

Researchers in digital signal processing have examined at length the effects of finite wordlength in the design of digital filters. The issues that have been considered apply to any digital system. In particular, the design of digital control systems must consider these issues. The paper will use, adapt, and extend the ideas developed in digital signal processing to the issue of roundoff noise in digital linear-quadratic-Gaussian (LQG) compensators. The roundoff noise effects for a particular LQG example and several different implementation structures will be then examined.

Moroney, P.↗
NASA NTRS1985

Shaft Seal Compensates for Cold Flow

Seal components easy to install. Ring seal for rotating or reciprocating shafts spring-loaded to compensate for slow yielding (cold flow) of sealing material. New seal relatively easy to install because components preassembled, then installed in one piece.

Myers, W. N.↗
NASA NTRS1986

Compensating for Shrinkage in Machined Ceramics

Technique insures machined ceramics shrink to correct dimensions after baked in kiln. New method automatically compensates during machining for shrinkage later, when part baked. Applicable to numerically controlled machines that include provision to adjust for variations in cuttingtool size, but do not provide for automatic verification of dimensions of machined parts.

Aguilar, L.↗
NASA NTRS1984

Compensator development and examination of performance and robustness

A compensator was synthesized to minimize the mean square surface error of a wrap rib antenna. Two separate cases were considered; one in which the flexible ribs and mesh were given weight, thereby penalizing the actual error of the reflecting area; and the other in which the antenna is considered rigid, thus penalizing only the rigid body rotation. The numerical results show that the flexible modes of the antenna have to be included in the performance criterion to obtain a better performance.

Source record↗
NASA NTRS1985

Drag-compensated, precision-powered hinge system

The design of a high precision powered hinge is complicated by the unavoidable presence of parasitic drag torque resulting mainly from friction and transfer of power, signals, and fluids across the hinge. Regardless of the type of drive system selected, it is impossible to completely eliminate all parasitic drag. However, the mechanism described here comes very close to providing a drag free system. All sources of parasitic drag torque are collected on a shaft which is powered by an electric motor independent of the main hinge drive. Under control of a sensor, the electric motor applies a compensating torque equal to that of the parasitic drag torque, allowing the main hinge drive to operate in a practically drag free environment with very high positioning precision.

Jacquemin, G. G.↗
NASA NTRS1983

Dynamic isolation of a spacecraft science platform via momentum compensation

The dynamic isolation of a two degree of freedom inertially stabilized science platform from the spacecrft basebody is examined. The important implications of a momentum compensated platform for pointing performance and cost are discussed, and the concept of a new system called the Integrated Platform Pointing and Attitude Control Subsystem utilizing the above property is presented. The results established in this paper are demonstrated by a computer simulation.

Boussalis, D.↗
NASA NTRS1984

A fast time domain digital simulation technique for power converters - Application to a buck converter with feedforward compensation

Small signal analysis was performed earlier to demonstrate the marked improvement of dynamic properties and stability margins of a switching regulator employing a novel feedforward input filter compensation scheme. A large signal nonlinear recurrent time domain model is presented for the converter to analyse the transient response due to a step input change with and without the presence of the proposed feedforward loop. The results are verified with experimental data.

Kelkar, S. S.↗