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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Commutated automatic gain control system

A commutated automatic gain control (AGC) system was designed and built for a prototype Loran C receiver. The receiver uses a microcomputer to control a memory aided phase-locked loop (MAPLL). The microcomputer also controls the input/output, latitude/longitude conversion, and the recently added AGC system. The circuit designed for the AGC is described, and bench and flight test results are presented. The AGC circuit described actually samples starting at a point 40 microseconds after a zero crossing determined by the software lock pulse ultimately generated by a 30 microsecond delay and add network in the receiver front end envelope detector.

Yost, S. R.↗
NASA NTRS1997

MAP Attitude Control System Design and Analysis

The Microwave Anisotropy Probe (MAP) is a follow-on to the Differential Microwave Radiometer (DMR) instrument on the Cosmic Background Explorer (COBE) spacecraft. The MAP spacecraft will perform its mission in a Lissajous orbit around the Earth-Sun L(sub 2) Lagrange point to suppress potential instrument disturbances. To make a full-sky map of cosmic microwave background fluctuations, a combination fast spin and slow precession motion will be used. MAP requires a propulsion system to reach L(sub 2), to unload system momentum, and to perform stationkeeping maneuvers once at L(sub 2). A minimum hardware, power and thermal safe control mode must also be provided. Sufficient attitude knowledge must be provided to yield instrument pointing to a standard deviation of 1.8 arc-minutes. The short development time and tight budgets require a new way of designing, simulating, and analyzing the Attitude Control System (ACS). This paper presents the design and analysis of the control system to meet these requirements.

Andrews, S. F.↗
NASA NTRS1991

Initial performance improvements due to design modifications for the Pointing Control System on the Hubble Space Telescope

Shortly after Hubble Space Telescope was deployed on orbit it became apparent that the Pointing Control System was experiencing unexpectedly large disturbances during certain portions of the orbit. While these disturbances were most pronounced during transitions of the Earth's shadow, significant disruptions to the pointing occurred at other times in the orbit. Careful analysis of the flight data has lead to the conclusion that the disturbances are caused by a combination of rapid thermal deformations of the Solar Arrays together with striction-friction mechanisms within the array that randomly release stored thermal/mechanical energy. This paper describes the baseline pointing control system design and the flight data that characterized the effects of the extraneous disturbances. The paper goes on to describe the procedure for modifying the onboard controller to attenuate the disturbances to levels consistent with the science operations. Flight data demonstrating the improved performance are shown and are tabulated to compare performance prior to and after phase I of the redesign.

Nurre, G. S.↗
NASA NTRS1990

Flexibility effects on the control system performance of large scale robotic manipulators

Structural flexibility of robotic manipulators becomes significant and limits the performance of a control system when manipulators are large structures, manipulating on large payloads, and/or operating at high speeds. The question of when a manipulator can be considered rigid or must be considered flexible is studied as a function of manipulator dynamics and task characteristics. Results are interpreted in simple quantitative forms which can be used as design and analysis tools to decide whether or not the manipulator flexibility will be a significant factor for a given task condition. The limitations imposed by the manipulator flexibility on the joint variable feedback control system performance is determined using linear and nonlinear methods. The closed loop eigenstructure behavior of finite dimensional models under joint variable feedback is studied and results are compared with the previously reported results.

Cetinkunt, Sabri↗
NASA NTRS1990

Monitoring the health of control system components

One characteristic of intelligent behavior is recognition of impaired capability. So an intelligent system should be able to monitor its own performance and determine when one of its components has failed - causing it to lose some degree of capability. This is especially important in autonomous operation which is one of the primary motivations for intelligent systems. This paper briefly reviews the principal approaches that have been suggested for monitoring control systems for failures of its sensors and actuators. The important characteristics of these methods are noted and two are selected for further consideration. These two methods, the failure detection filter and generalized parity relations, are described. Results of experiments are then given of detection and isolation of sensor failures using data taken on the Mini-Mast facility at the NASA Langley Research Center. The effects of certain design options are illustrated. The paper concludes with some observations about the general problem of monitoring the health of control systems.

Vander Velde, W. E.↗
NASA NTRS2007

Living Together in Space: The International Space Station Internal Active Thermal Control System Issues and Solutions-Sustaining Engineering Activities at the Marshall Space Flight Center From 1998 to 2005

On board the International Space Station, heat generated by the crew and equipment is removed by the internal active thermal control system to maintain a comfortable working environment and prevent equipment overheating. Test facilities simulating the internal active thermal control system (IATCS) were constructed at the Marshall Space Flight Center as part of the sustaining engineering activities to address concerns related to operational issues, equipment capability, and reliability. A full-scale functional simulator of the Destiny lab module IATCS was constructed and activated prior to launch of Destiny in 2001. This facility simulates the flow and thermal characteristics of the flight system and has a similar control interface. A subscale simulator was built, and activated in 2000, with special attention to materials and proportions of wetted surfaces to address issues related to changes in fluid chemistry, material corrosion, and microbial activity. The flight issues that have arisen and the tests performed using the simulator facilities are discussed in detail. In addition, other test facilities at the MSFC have been used to perform specific tests related to IATCS issues. Future testing is discussed as well as potential modifications to the simulators to enhance their utility.

Wieland, P. O.↗
NASA NTRSDate not supplied

Design of a Thrust Vector Servoelastic Filter for SLS Block 2 Booster Thrust Vector Control System

This paper presents a method to improve the thrust vector servoelastic (TVSE) response of a launch vehicle. TVSE is the coupling between the Thrust Vector Control (TVC) system nozzle dynamics and the vehicle flexible modes. A poorly phased TVC response, i.e. in phase with the structural velocity, can lead to instability of the flexible modes due to the energy injection from the thrust. For large boosters with heavy nozzles, TVSE is more likely to cause instability. This instability is part of the plant dynamics and may not be readily detected by the flight control system. In this paper, TVSE is treated as a disturbance rejection problem with the inertial force of the flexible motion viewed as an external disturbance to the TVC actuator control system. By effectively rejecting this disturbance, the engine can be decoupled from the flexible dynamics thus improving TVSE stability. The actuator disturbance transfer function is modified by inserting a filter into the servo-loop control system. The filter aims to reduce the magnitude and introduce phase lead of the disturbance transfer function over the TVSE sensitive frequency range while maintaining adequate stability margins of the actuator control system. A prefilter is also designed to improve command tracking performance. The filter and prefilter resulting from this method are usually of low order and can be included to an existing actuator controller if the controller is programmable. This method was demonstrated for a hydraulic Simplex actuator model. Its applications to the Space Launch System (SLS) Block 1 and Block 2 TVC actuator are also described. The Block 2 actuator controller was modified based on the results of this method. The tradeoff between TVSE stability and the servo-loop stability can be balanced by adjusting the amount of phase lead introduced by the TVSE filter. This method provides a useful way to solve the TVSE instability issue without costly and time-consuming hardware solutions. This method is based on the basic control principles of loop shaping and disturbance rejection and has been proven to be effective under proper circumstances.

Thrust vector control↗
NASA NTRS1983

Integrated flight/propulsion control system architectures for a high speed aircraft

The present investigation is concerned with the impact of integrated flight, inlet, and engine control system architectures on system effectiveness and life cycle cost (LCC). The aircraft employed in the investigation is a modified YF-12 with a cruise Mach number of 2.5. The aircraft has two advanced technology aircraft JT-69 afterburning, low-bypass turbofan engines. Advanced technologies suitable for use in future flight/propulsion control systems are related to distributed computer networks, fault tolerant computers and software, analytical redundancy, self-checking microprocessor pairs, advanced direct drive actuators, fiber optic data buses, VLSI microcircuits, and skewed sensors. The integrated architectures were found to have fewer sensors, actuators, and power sources than the nonintegrated architectures.

Bangert, L. H.↗
NASA NTRS1972

Nonlinear and Digital Man-machine Control Systems Modeling

An adaptive modeling technique is examined by which controllers can be synthesized to provide corrective dynamics to a human operator's mathematical model in closed loop control systems. The technique utilizes a class of Liapunov functions formulated for this purpose, Liapunov's stability criterion and a model-reference system configuration. The Liapunov function is formulated to posses variable characteristics to take into consideration the identification dynamics. The time derivative of the Liapunov function generate the identification and control laws for the mathematical model system. These laws permit the realization of a controller which updates the human operator's mathematical model parameters so that model and human operator produce the same response when subjected to the same stimulus. A very useful feature is the development of a digital computer program which is easily implemented and modified concurrent with experimentation. The program permits the modeling process to interact with the experimentation process in a mutually beneficial way.

Mekel, R.↗
NASA NTRS2011

Self-Contained Avionics Sensing and Flight Control System for Small Unmanned Aerial Vehicle

A self-contained avionics sensing and flight control system is provided for an unmanned aerial vehicle (UAV). The system includes sensors for sensing flight control parameters and surveillance parameters, and a Global Positioning System (GPS) receiver. Flight control parameters and location signals are processed to generate flight control signals. A Field Programmable Gate Array (FPGA) is configured to provide a look-up table storing sets of values with each set being associated with a servo mechanism mounted on the UAV and with each value in each set indicating a unique duty cycle for the servo mechanism associated therewith. Each value in each set is further indexed to a bit position indicative of a unique percentage of a maximum duty cycle for the servo mechanism associated therewith. The FPGA is further configured to provide a plurality of pulse width modulation (PWM) generators coupled to the look-up table. Each PWM generator is associated with and adapted to be coupled to one of the servo mechanisms.

Shams, Qamar A.↗
NASA NTRS1971

Study of automatic and manual terminal guidance and control systems for space shuttle vehicles. Volume 1: Sections 1 through 3

The results of a study to analyze, design, and evaluate guidance and control systems are presented that start at an altitude of about 100,000 feet and bring the unpowered space shuttle orbiters to a precision horizontal landing. The systems under consideration included fully automatic versions which involve no pilot participation as well as various manual configurations that provide combinations of displays and control augmentation which permit the pilot to control the vehicle to a successful landing. Two classes of vehicles were studied: the low cross range or straight-wing orbiter and the high cross range or delta-wing (delta body) orbiter. The recommended navigation, guidance and control system is shown to be compatible with realistic physical constraints that would exist in space shuttlecraft and to be consistent with the 1971 avionics equipment state of the art. Aircraft capable of aerodynamically simulating the various candidate space shuttlecraft in their unpowered, terminal area descent were investigated, and flight test recommendations, including system mechanizations, are made.

Osder, S.↗
NASA NTRS1987

Space station structural dynamics/reaction control system interaction study

The performance of the Reaction Control System is impacted by the extreme flexibility of the space station structure. The method used to analyze the periodic thrust profile of a simple form of phase plane logic is presented. The results illustrate the effect on flexible body response of the type of phase plane logic utilized and the choice of control parameters: cycle period and attitude deadband.

Pinnamaneni, M.↗