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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Experimental measurements of motion cue effects on STOL approach tasks

An experimental program to investigate the effects of motion cues on STOL approach is presented. The simulator used was the Six-Degrees-of-Freedom Motion Simulator (S.01) at Ames Research Center of NASA which has ?2.7 m travel longitudinally and laterally and ?2.5 m travel vertically. Three major experiments, characterized as tracking tasks, were conducted under fixed and moving base conditions: (1) A simulated IFR approach of the Augmentor Wing Jet STOL Research Aircraft (AWJSRA), (2) a simulated VFR task with the same aircraft, and (3) a single-axis task having only linear acceleration as the motion cue. Tracking performance was measured in terms of the variances of several motion variables, pilot vehicle describing functions, and pilot commentary.

Ringland, R. F.↗
NASA NTRS1972

A single axis electrostatic beam deflection system for a 5-cm diameter ion thruster

A single-axis electrostatic beam deflection system has been tested on a 5-cm diameter mercury ion thruster at a thrust level of about 0.43 mlb (25 mA beam current at 1400 volts). The accelerator voltage was 500 volts. Beam deflection capability of plus or minus 10 deg was demonstrated. A life test of 1367 hours was run at the above conditions. Results of the test indicated that the system could possibly perform for upwards of 10,000 hours.

Lathem, W. C.↗
NASA NTRS1972

Invariant poles feedback control of flexible, highly variable spacecraft.

This paper describes a technique for single-axis control of a model of a highly flexible Space Station. Active damping of lower frequency flexibility modes is employed. In the control technique, referred to as invariant poles feedback control (IPFC), feedback gains are adjusted so that the closed-loop system's characteristic equation is matched to that of a reference model; hence, closed-loop system's poles will not move - they will be invariant (provided bending frequencies and parameters can be identified accurately). This is accomplished by obtaining the system's characteristic equation in closed form; equating respective coefficients between terms of like powers in s in the system and reference model characteristic equations; and, solving for the feedback gains. The feedback gains are explicit functions of system plant parameters and the coefficients of the reference model's characteristic equation, and are easily programmed for the digital computer.

Mendel, J. M.↗
NASA NTRS1972

Motion cue effects on pilot tracking

The results of two successive experimental investigations of the effects of motion cues on manual control tracking tasks are reported. The first of these was an IFR single-axis VTOL roll attitude control task. Describing function data show the dominant motion feedback quantity to be angular velocity. The second experimental task was multiaxis, that of precision hovering of a VTOL using separated instrument displays with reduced motion amplitude scaling. Performance data and pilot opinion show angular position to be the dominant cue when simulator linear motion is absent.

Ringland, R. F.↗
NASA NTRS1972

Attitude propulsion technology for TOPS

The thermoelectric outer planet spacecraft (TOPS) attitude propulsion subsystem (APS) effort is discussed. It includes the tradeoff rationale that went into the selection of an anhydrous hydrazine baseline system, followed by a discussion of the 0.22 N thruster and its integration into a portable, self-contained propulsion module that was designed, developed, and man rated to support the TOPS single-axis attitude control tests. The results of a cold-start feasibility demonstration with a modified thruster are presented. A description of three types of 0.44 thrusters that were procured for in-house evaluation is included along with the results of the test program. This is followed by a description of the APS feed system components, their evaluations, and a discussion of an evaluation of elastomeric material for valve seat seals. A list of new technology items which will be of value for application to future systems of this type is included.

Moynihan, P. I.↗
NASA NTRS1973

Design and analysis of a star image motion compensator

The feasibility of designing and fabricating a small optical system to compensate for motions of a stellar field image on the focal plane of a large orbiting telescope is examined for a single-axis system. An all-reflecting two-mirror star image motion compensator maintains both a flat focal plane and image focus for one or more star images. Both theoretical and experimental evaluations show that only one adjustment is needed to aline the system since the change in focus is linearly related to the misalinements of all critical components. Results of an error analysis show that the focus error resulting from fabrication tolerances is very small compared to the adjustment capability of the system.

Romanczyk, K. C.↗
NASA NTRS1973

Evaluation of the electro-optic direction sensor

Evaluation of a no-moving-parts single-axis star tracker called an electro-optic direction sensor (EODS) concept is described and the results are given in detail. The work involved experimental evaluation of a breadboard sensor yielding results which would permit design of a prototype sensor for a specific application. The laboratory work included evaluation of the noise equivalent input angle of the sensor, demonstration of a technique for producing an acquisition signal, constraints on the useful field-of-view, and a qualitative evaluation of the effects of stray light. In addition, the potential of the silicon avalanche-type photodiode for this application was investigated. No benefit in noise figure was found, but the easily adjustable gain of the avalanche device was useful. The use of mechanical tuning of the modulating element to reduce voltage requirements was also explored. The predicted performance of EODS in both photomultiplier and solid state detector configurations was compared to an existing state-of-the-art star tracker.

Johnson, A. R.↗
NASA NTRS1973

Estimation and identification study for flexible vehicles

Techniques are studied for the estimation of rigid body and bending states and the identification of model parameters associated with the single-axis attitude dynamics of a flexible vehicle. This problem is highly nonlinear but completely observable provided sufficient attitude and attitude rate data is available and provided all system bending modes are excited in the observation interval. A sequential estimator tracks the system states in the presence of model parameter errors. A batch estimator identifies all model parameters with high accuracy.

Jazwinski, A. H.↗
NASA NTRS1973

The development and demonstration of hybrid programmable attitude control electronics

In the course of extended life attitude control system (ELACS) research sponsored by NASA a hybrid programable attitude control electronics (HYPACE) concept was developed and demonstrated. The wide variety of future planetary missions demanded a new control approach to accommodate the automatic fault tolerance and long the life requirements of such missions. HYPACE provides an adaptable, analog/digital design approach that permits preflight and in-flight accommodation of mission changes, component performance variations, and spacecraft changes, through programing. This enabled broad multimission flexibility of application in a cost effective manner. Previously, flight control computers have not been not flown on planetary missions because of weight and power problems. These problems were resolved in the design of HYPACE. The HYPACE design, which was demonstrated in breadboard form on a single-axis gas-bearing spacecraft simulation, uses a single control channel to perform the attitude control functions sequentially, thus significantly reducing the number of component parts over hard-wired designs.

Smith, L. S.↗
NASA NTRS1972

Invariant poles feedback control of flexible highly variable spacecraft.

Description of a technique for single-axis control of a model of a highly flexible space station. Active damping of lower frequency flexibility modes is employed. In the control technique, referred to as invariant poles feedback control, feedback gains are adjusted so that the closed-loop system characteristic equation is matched to that of a reference model. Hence closed-loop system poles will not move; they will be invariant (provided that bending frequencies and parameters can be identified accurately). This is accomplished by obtaining the system characteristic equation in closed form; equating respective coefficients between terms of like powers in s in the system and reference model characteristic equations; and solving for the feedback gains. The feedback gains are explicit functions of system plant parameters and the coefficients of the reference model characteristic equation, and are easily programmed for the digital computer.

Mendel, J. M.↗
NASA NTRS1974

Research study on stabilization and control modern sampled-data control theory

The methods of continuous and discrete describing function analysis were applied to predicting the existence of self-sustained oscillations in the single-axis model of the large space telescope system with nonlinear control moment gyroscope friction characteristics. It is shown that the stability equations may be solved by a numerical-iterative technique using the describing function analysis, instead of the usual graphical methods. The numerical method is found to be effective in leading to a convergent solution rapidly, with an appropriate guess of the initial condition.

Kuo, B. C.↗
NASA NTRS1973

A unique control system simulator for the evaluation of pulsed plasma thrusters

Because of the low thrust characteristics of solid-propellant pulsed plasma thrusters and their operational requirement to operate in a vacuum environment, unique and sensitive test techniques are required. A technique evolved for testing and evaluating pulsed plasma thrusters in an open- or closed-loop system mode employs a unique air bearing platform as a single-axis simulator on which the thruster is mounted. The simulator described was developed to evaluate pulsed plasma thrusters in the low micropound range; however, the simulator can be extended to cover the operational range of currently developed millipound thrusters.

Dahlgren, J. B.↗
NASA NTRS1974

Stability study of the Large Space Telescope /LST/ system with nonlinear CMG gimbal friction

The purpose of the investigation reported upon is to study the existence and characteristics of self-sustained oscillations in the dynamic behavior of the Large Space Telescope (LST) system due to the presence of nonlinear gimbal friction in the control moment gyroscopes (CMGs). A continuous-data single-axis model of the LST is considered. A solid friction model is used to represent CMG gimbal friction. A rigorous mathematical model is derived for use in a continuous describing function analysis. Conditions for self-sustained oscillations are then determined.

Kuo, B. C.↗
NASA NTRS1974

Interactions between SAS-C spacecraft nutations and spin control system

The SAS-C spacecraft is stabilized by a momentum biased reaction wheel and passive nutation damper. A closed-loop low-speed spacecraft spin rate control system is included which uses a single-axis gyro and a variable speed range on the reaction wheel. Dynamic instability can result from interactions among the gyro, damper, and spacecraft dynamic unbalance. This instability may be aggravated by gyro angular misalignment, gyro error signals, and spacecraft nutations. Analytic eigenvector, and digital computer analyses of the coupled systems are presented. Mechanisms for instability are described as well as the effects that gyro error signal, tilt, and spacecraft dynamic unbalance produce on control system performance.

Tossman, B. E.↗
NASA NTRS1975

Wide-angle sun sensors

Two sensors have been developed: one, single-axis device, is cylindrical; the other, two-axis device, is spherical. Multiple surface deposits of photosensitive material, such as cadmium sulfide, serve as redundancy, ensuring high reliability.

Schumacher, L. L.↗
NASA NTRS1974

The development and demonstration of hybrid programmable attitude control electronics

HYPACE provides an adaptable, analog/digital design approach that permits preflight and in-flight accommodation of mission changes, component performance variations, spacecraft changes, etc., through programing. This enabled broad multimission flexibility of application in a cost-effective manner. The HYPACE design, which was demonstrated in breadboard form on a single-axis gas-bearing spacecraft simulation, uses a single control channel to perform the attitude control functions sequentially, thus significantly reducing the number of component parts over hard-wired designs. The success of this effort resulted in the concept being selected for the Mariner/Jupiter/Saturn 1977 spacecraft application.

Smith, L. S.↗
NASA NTRS1975

Wide angle sun sensor

A single-axis sun sensor consists of a cylinder of an insulating material on which at least one pair of detectors is deposited on a circumference of the cylinder, was disclosed. At any time only one-half of the cylinder is illuminated so that the total resistance of the two detectors is a constant. Due to the round surface on which the detectors are deposited, the sensor exhibits a linear wide angle of + or - 50 deg to within an accuracy of about 2%. By depositing several pairs of detectors on adjacent circumferences, sufficient redundancy is realized to provide high reliability. A two-axis sensor is provided by depositing detectors on the surface of a sphere along at least two orthogonal great circles.

Schumacher, L. L.↗
NASA NTRS1975

Research study on stabilization and control. Modern sampled-data control theory: Stability analysis of the low cost large space telescope system

The pointing stability of the low-cost large space telescope (LST) system was investigated. The low-cost LST is characterized by the use of reaction wheels for the generation of control torques. Because of the critical requirement on the pointing accuracy of the LST, the nonlinear frictional characteristics of the bearings of the reaction wheels were studied which can cause limit cycles in a closed-loop system. Another possible source of pointing error in the LST is due to the effect of quantization and sensor noise. Since the LST is a digital system, digital to analog and analog to digital converters and sensors for positional and rate feedbacks were used. Sensor noise and amplitude quantization causes pointing error in the LST and, in addition, quantization is a nonlinear phenomenon which can cause self-sustained oscillations in the closed-loop system. The dynamic modeling of the single-axis LST is described, and several methods of evaluating the attitude error of the digital LST due to quantization and noise inputs are given.

Kuo, B. C.↗