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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Ikhana: A NASA UAS Supporting Long Duration Earth Science Missions

The NASA Ikhana unmanned aerial vehicle (UAV) is a General Atomics Aeronautical Systems Inc. (San Diego, California) MQ-9 Predator-B modified to support the conduct of Earth science missions for the NASA Science Mission Directorate and, through partnerships, other government agencies and universities. It can carry over 2000 lb of experiment payloads in the avionics bay and external pods and is capable of mission durations in excess of 24 hours at altitudes above 40,000 ft. The aircraft is remotely piloted from a mobile ground control station (GCS) that is designed to be deployable by air, land, or sea. On-board support capabilities include an instrumentation system and an Airborne Research Test System (ARTS). The Ikhana project will complete GCS development, science support systems integration, external pod integration and flight clearance, and operations crew training in early 2007. A large-area remote sensing mission is currently scheduled for Summer 2007.

Cobleigh, Brent R.↗
NASA NTRS1990

Thermal control of a lidar laser system using a non-conventional ram air heat exchanger

This paper describes the analysis and performance testing of a uniquely designed external heat exchanger. The heat exchanger is attached externally to an aircraft and is used to cool a laser system within the fuselage. Estimates showed insufficient cooling capacity with a conventional staggered tube array in the limited space available. Thus, a non-conventional design wes developed with larger tube and fin area exposed to the ram air to increase the heat transfer performance. The basic design consists of 28 circular finned aluminum tubes arranged in two parallel banks. Wind tunnel tests were performed to simulate air and liquid flight conditions for the non-conventional parallel bank arrangement and the conventional staggered tube arrangement. Performance comparisons of each of the two designs are presented. Test results are used in a computer model of the heat exchanger to predict the operating performance for the entire flight profile. These analyses predict significantly improved performance over the conventional design and show adequate thermal control margins.

Killough, Brian D.↗
NASA NTRS1980

Residual Silicone Detection

Both photoelectron emission and ellipsometry proved successful in detecting silicone contamination on unpainted and epoxy painted metal surfaces such as those of the external tank and the solid rocket booster. Great success was achieved using photoelectron emission (PEE). Panels were deliberately contaminated to controlled levels and then mapped with PEE to reveal the areas and levels that were contaminated. The panels were then tested with regard to adhesive properties. Tapes were bonded over the contaminated and uncontaminated regions and the peel force was measured, or the contaminated panels were bonded (with CPR 483 foam) to uncontaminated panels and made into lap shear specimens. Other panels were bonded and made into wedge specimens for hydrothermal stress endurance tests. Strong adhesion resulted if the PEE signal fell within an acceptance window, but was poor outside the acceptance window. A prototype instrument is being prepared which can automatically be scanned over the external liquid hydrogen tank and identify those regions that are contaminated and will cause bond degradation.

Smith, T.↗
NASA NTRS1993

Three-dimensional solidification and melting using magnetic field control

A new two-fluid mathematical model for fully three dimensional steady solidification under the influence of an arbitrary acceleration vector and with or without an arbitrary externally applied steady magnetic field have been formulated and integrated numerically. The model includes Joule heating and allows for separate temperature dependent physical properties within the melt and the solid. Latent heat of phase change during melting/solidification was incorporated using an enthalpy method. Mushy region was automatically captured by varying viscosity orders of magnitude between liquidus and solidus temperature. Computational results were obtained for silicon melt solidification in a parallelepiped container cooled from above and from a side. The results confirm that the magnetic field has a profound influence on the solidifying melt flow field thus changing convective heat transfer through the boundaries and the amount and shape of the solid accrued. This suggests that development of a quick-response algorithm for active control of three dimensional solidification is feasible since it would require low strength magnetic fields.

Dulikravich, George S.↗
NASA NTRS2020

Modeling and Control of Robot-Structure Coupling During In-Space Structure Assembly

This paper considers the problem of robot-structure coupling dynamics during in-space robotic assembly of large flexible structures. A two-legged walking robot is used as a construction agent, whose primary goal is to stably walking on the flexible structure while carrying a substructure component to a designated location. The reaction forces inserted by the structure to the walking robot are treated as bounded disturbance inputs, and a trajectory tracking robotic controller is proposed that combines the standard full state feedback motion controller and an adaptive controller to account for the disturbance inputs. In this study, a reduced-order Euler-Bernoulli beam structure model is adapted, and a finite number of co-located sensors and actuators are distributed along the span of the beam structure. The robot-structure coupling forces are treated as a bounded external forcing function to the structure, and hence an output covariance constraint problem can be formulated, in terms of linear matrix inequality, for optimal structure control by utilizing the direct output feedback controllers. The numerical simulations show the effectiveness of the proposed robot-structure modeling and control methodology.

Swei, Sean↗
NASA NTRS1966

Spool valve cycles at controlled frequency

Spool valve accurately controls the cycle of a pneumatically-actuated system over long periods. Regulation of pressure from the external source, positioning of the adjusting plugs, and magnet selection, together afford wide variation in cyclic timing and speed of closure in either direction.

Charlton, K. W.↗
NASA NTRS1967

Negative feedback system reduces pump oscillations

External negative feedback system counteracts low frequency oscillations in rocket engine propellant pumps. The system uses a control piston to sense pump discharge fluid on one side and a gas pocket on the other.

Rosenmann, W.↗
NASA NTRS1974

Develop minimum thrustor control laws and select orbits for a geodesy drag-free satellite

The original motivation for studying control laws for pulse plasma systems was based on the improved life characteristics possible with pulse plasma jets. These pulse plasma units are relatively massive compared with cold gas thrustors. As a result, therefore, significant mass savings can be achieved by minimizing the the number of thrustors. The control laws, therefore, were developed for thrust available from two thrustors only. In a spinning satellite, these thrustors are sufficient to completely control the vehicle as long as the spin rate is sufficiently high for a given level of external disturbance. The thrustors are canted so that a component of each is along the plus and minus spin axis. The other component of each thrustor acts in the radial direction. It is sufficient to analyze the behavior in the plane of spin assuming a single thrustor.

Breakwell, J. V.↗
NASA NTRS1976

The effects of pressure, temperature, and pore water on velocities in Westerly granite

A description is presented of an experimental assembly which has been developed to conduct concurrent measurements of compressional and shear wave velocities in rocks at high temperatures and confining pressures and with independent control of the pore pressure. The apparatus was used in studies of the joint effects of temperature, external confining pressure, and internal pore water on sonic velocities in Westerly granite. It was found that at a given temperature, confining pressure has a larger accelerating effect on compressional waves in dry rock, whereas at a given confining pressure, temperature has a larger retarding effect on shear waves.

Spencer, J. W., Jr.↗
NASA NTRS1981

Automotive Stirling reference engine design report

The reference Stirling engine system is described which provides the best possible fuel economy while meeting or exceeding all other program objectives. The system was designed to meet the requirements of a 1984 Pontiac Phoenix (X-body). This design utilizes all new technology that can reasonably be expected to be developed by 1984 and that is judged to provide significant improvement, relative to development risk and cost. Topics covered include: (1) external heat system; (2) hot engine system; (3) cold engine system; (4) engine drive system; (5) power control system and auxiliaries; (6) engine instalation; (7) optimization and vehicle simulation; (8) engine materials; and (9) production cost analysis.

Source record↗
NASA NTRS1982

RAXJET: A computer program for predicting transonic, axisymmetric flow over nozzle afterbodies with supersonic jet exhausts

A viscous-inviscid interaction method to calculate the subsonic and transonic flow over nozzle afterbodies with supersonic jet exhausts was developed. The method iteratively combines a relaxation solution of the full potential equation for the inviscid external flow, a shock capturing-shock fitting inviscid jet solution, an integral boundary layer solution, a control volume method for treating separated flows, and an overlaid mixing layer solution. A computer program called RAXJET which incorporates the method, illustrates the predictive capabilities of the method by comparison with experimental data is described, a user's guide to the computer program is provided. The method accurately predicts afterbody pressures, drag, and flow field properties for attached and separated flows for which no shock induced separation occurs.

Wilmoth, R. G.↗
NASA NTRS1981

Studies of high latitude current systems using MAGSAT vector data

The magnetic disturbance fields caused by global external current systems are considered with particular emphasis on improving the understanding of the physical processes which control high latitude current systems. Following processing the MAGSAT data were routinely plotted in the Universal Time (UT) format as well as in a polar plot format. The H'D'U' coordinate system, was adopted as the standard for representing the MAGSAT residual magnetic field vectors. A data file was generated and the TPOLAR computer code was developed to determine from the orbital elements, the time, latitude, and MLT of the extremum latitude of each transpolar segment of orbit. The precision of the vector data set from MAGSAT prompted an extended exploratory phase for data analysis procedures, modeling techniques and phenomenology.

Burrows, J. R.↗
NASA NTRS1982

A Shuttle Derived Vehicle launch system

This paper describes a Shuttle Derived Vehicle (SDV) launch system presently being studied for the NASA by Martin Marietta Aerospace which capitalizes on existing Shuttle hardware elements to provide increased accommodations for payload weight, payload volume, or both. The SDV configuration utilizes the existing solid rocket boosters, external tank and the Space Shuttle main engines but replaces the manned orbiter with an unmanned, remotely controlled cargo carrier. This cargo carrier substitution more than doubles the performance capability of the orbiter system and is realistically achievable for minimal cost. The advantages of the SDV are presented in terms of performance and economics. Based on these considerations, it is concluded that an unmanned SDV offers a most attractive complement to the present Space Transportation System.

Tewell, J. R.↗
NASA NTRS1987

Procedures for Computing Transonic Flows for Control of Adaptive Wind Tunnels

Numerical methods are developed for control of three dimensional adaptive test sections. The physical properties of the design problem occurring in the external field computation are analyzed, and a design procedure suited for solution of the problem is worked out. To do this, the desired wall shape is determined by stepwise modification of an initial contour. The necessary changes in geometry are determined with the aid of a panel procedure, or, with incident flow near the sonic range, with a transonic small perturbation (TSP) procedure. The designed wall shape, together with the wall deflections set during the tunnel run, are the input to a newly derived one-step formula which immediately yields the adapted wall contour. This is particularly important since the classical iterative adaptation scheme is shown to converge poorly for 3D flows. Experimental results obtained in the adaptive test section with eight flexible walls are presented to demonstrate the potential of the procedure. Finally, a method is described to minimize wall interference in 3D flows by adapting only the top and bottom wind tunnel walls.

Rebstock, Rainer↗
NASA NTRS1988

Evaluation and application of a new interferometry technique for compressible flow research

A new method for obtaining large scale interferograms of flow fields in real time was investigated. The method was based on the point diffraction interferometry technique. The method was modified to accommodate the higher laser power required in recording transonic and supersonic flow fields. Basic tests were conducted in unsteady flows and flows about circulation control airfoils at transonic speeds. It was found that vibration was not a significant factor in the application of the system. In the case of the circulation control airfoils, the real-time viewing allowed the identification of the Coanda jet interaction with the external flow and the shedding of large scale vortices. The method proved to be very sensitive to the optical quality of the wind tunnel windows. The results obtained were compared with earlier interferograms obtained using interferometry. These results were in qualitative agreement.

Bachalo, William D.↗
NASA NTRS1994

Pulley With Active Antifriction Actuator And Control

Torque actuator and associated control system minimizes effective friction of rotary bearing. Motor exerts compensating torque in response to feedback from external optical sensor. Compensation torque nearly cancels frictional torque of shaft bearings. Also useful in reducing bearing friction in gyro-scopes, galvanometers, torquemeters, accelerometers, earth-motion detectors, and balances.

Ih, Che-Hang C.↗
NASA NTRS1998

Sufficient Conditions for the Stability of a Lur'e System With Two Nonzero Inputs Based on Lyapunovs Direct Method

The Lur'e problem is a famous problem in nonlinear control theory. The analysis of this system is usually restricted to Lur'e systems in which the external input is zero. One form of this problem involves the stability analysis of the Lur'e system with two nonzero inputs. The stability analysis of this type of system is traditionally performed based on L stability theory. The objective of this paper is to present sufficient conditions for the stability of this system based on Lyapunov's direct method. This is a conceptually simpler approach to the existing analysis based on L stability theory and it provides some additional information about the stability of the system.

Adetona, Olawale↗