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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Water-Searchers: A Reconfigurable and Self Sustaining Army of Subsurface Exploration Robots Searching for Water/Ice Using Multiple Sensors

Perhaps the most promising site for extant life on Mars today is where subsurface water has been maintained. Therefore, searching for underground water will provide a good chance to find evidence of life on Mars. The following are scientific/engineering questions that we want to answer using our approach: (1) Is there subsurface water/ice? How deep is it? How much is there? Is it frozen? (2) What kinds of underground layers exist in the Martian crust? (3) What is the density of Martian soil or regolith? Can we dig into it? Should we drill into it? (4) Can a sudden release of underground water occur if a big asteroid hits Mars? Our approach provides essential information to answer these questions. Moreover, dependence on the water content and depth in soil, not only resultant scientific conclusions but also proper digging/drilling methods, are suggested. 'How much water is in the Martian soil?' There can be several possibilities: (1) high water content that is enough to form permafrost; (2) low water content that is not enough to form permafrost; or (3) different layers with different moisture contents. 'How deep should a rover dig into soil to find water/ice?' The exact size-frequency distribution has not been measured for the soil particles. On-board sensors can provide not only the water content but also the density (or porosity) of Martian soil as a function of depth.

Youk, G. U.↗
NASA NTRS2000

Evidence for a Sudden Magnetic Field Reconfiguration in SGR 1900+14

We report on the detection of large flux changes in the persistent X-ray flux of SGR 1900+14 during its burst active episode in 1998. Most notably, we find a factor of approximately 700 increase in the non-burst X-ray flux following the August 27th flare that decayed in time as a power-law. Throughout the decay of this flux enhancement, our measurements indicate that the pulse fraction remains constant. This indicates a global flux enhancement as a consequence of the August 27th flare rather than localized heating. While the persistent flux has since recovered to the pre-outburst level, the pulse profile has not. The pulse shape changed to a near sinusoidal profile within the tail of the August 27th flare (in gamma-rays) and this effect has persisted for more than 1.5 years (in X-rays). The results presented here suggest the magnetic field of the neutron star in SGR 1900+14 was significantly altered (perhaps globally) during the giant flare of August 27.

Woods, Peter M.↗
NASA NTRS2001

Evidence for a Sudden Magnetic Field Reconfiguration in Soft Gamma Repeater 1900+14

We report the detection of large flux changes in the persistent X-ray flux of soft gamma repeater (SGR) 1900 + 14 during its burst active episode in 1998. Most notably, we find a factor of approx. 700 increase in the nonburst X-ray flux following the August 27 flare, which decayed in time as a power law. Our measurements indicate that the pulse fraction remains constant throughout this decay. This suggests a global flux enhancement as a consequence of the August 27 flare rather than localized heating. While the persistent flux has since recovered to the preoutburst level, the pulse profile has not. The pulse shape changed to a near sinusoidal profile within the tail of the August 27 flare (in gamma-rays), and this effect has persisted for more than 1.5 years (in X-rays). The results presented here suggest that the magnetic field of the neutron star in SGR 1900 + 14 was significantly altered (perhaps globally) during the giant flare of August 27.

Woods, Peter M.↗
NASA NTRS2002

MIMO Sliding Mode Control for a Tailless Fighter Aircraft, An Alternative to Reconfigurable Architectures

A frequency-domain procedure for the design of sliding mode controllers for multi-input, multi-output (MIMO) systems is presented. The methodology accommodates the effects of parasitic dynamics such as those introduced by unmodeled actuators through the introduction of multiple asymptotic observers and model reference hedging. The design procedure includes a frequency domain approach to specify the sliding manifold, the observer eigenvalues, and the hedge model. The procedure is applied to the development of a flight control system for a linear model of the Innovative Control Effector (ICE) fighter aircraft. The stability and performance robustness of the resulting design is demonstrated through the introduction of significant degradation in the control effector actuators and variation in vehicle dynamics.

Wells, S. R.↗
NASA NTRS2002

Sliding Mode Control Applied to Reconfigurable Flight Control Design

Sliding mode control is applied to the design of a flight control system capable of operating with limited bandwidth actuators and in the presence of significant damage to the airframe and/or control effector actuators. Although inherently robust, sliding mode control algorithms have been hampered by their sensitivity to the effects of parasitic unmodeled dynamics, such as those associated with actuators and structural modes. It is known that asymptotic observers can alleviate this sensitivity while still allowing the system to exhibit significant robustness. This approach is demonstrated. The selection of the sliding manifold as well as the interpretation of the linear design that results after introduction of a boundary layer is accomplished in the frequency domain. The design technique is exercised on a pitch-axis controller for a simple short-period model of the High Angle of Attack F-18 vehicle via computer simulation. Stability and performance is compared to that of a system incorporating a controller designed by classical loop-shaping techniques.

Hess, R. A.↗
NASA NTRS2002

Autonomous Reconfigurable Control Allocation (ARCA) for Reusable Launch Vehicles

The role of control allocation (CA) in modern aerospace vehicles is to compute a command vector delta(sub c) is a member of IR(sup n(sub a)) that corresponding to commanded or desired body-frame torques (moments) tou(sub c) = [L M N](sup T) to the vehicle, compensating for and/or responding to inaccuracies in off-line nominal control allocation calculations, actuator failures and/or degradations (reduced effectiveness), or actuator limitations (rate/position saturation). The command vector delta(sub c) may govern the behavior of, e.g., acrosurfaces, reaction thrusters, engine gimbals and/or thrust vectoring. Typically, the individual moments generated in response to each of the n(sub a) commands does not lie strictly in the roll, pitch, or yaw axes, and so a common practice is to group or gang actuators so that a one-to-one mapping from torque commands tau(sub c) actuator commands delta(sub c) may be achieved in an off-line computed CA function.

Hodel, A. S.↗
NASA NTRS2003

Investigations of Relatively Easy To Construct Antennas With Efficiency in Receiving Schumann Resonances: Preparations for a Miniaturized Reconfigurable ELF Receiver

Relatively little is known about the cavity between the Earth and the ionosphere, which opens opportunities for technological advances and unique ideas. One effective means to study this cavity is with extremely low frequency (ELF) antennas. Possible applications of these antennas are global weather prediction, earthquake prediction, planetary exploration, communication, wireless transmission of power, or even a free energy source. The superconducting quantum interference device SQUID) and the coil antenna are the two most acceptable receivers discovered for picking up ELF magnetic fields. Both antennas have the potential for size reduction, allowing them to be portable enough for access to space and even for personal ware. With improvements of these antennas and signal processing, insightful analysis of Schumann resonance (SR) can give the science community a band of radio frequency (RF) signals for improving life here on Earth and exploring beyond.

Farmer, Brian W.↗
NASA NTRS2004

Applying a Genetic Algorithm to Reconfigurable Hardware

This paper investigates the feasibility of applying genetic algorithms to solve optimization problems that are implemented entirely in reconfgurable hardware. The paper highlights the pe$ormance/design space trade-offs that must be understood to effectively implement a standard genetic algorithm within a modem Field Programmable Gate Array, FPGA, reconfgurable hardware environment and presents a case-study where this stochastic search technique is applied to standard test-case problems taken from the technical literature. In this research, the targeted FPGA-based platform and high-level design environment was the Starbridge Hypercomputing platform, which incorporates multiple Xilinx Virtex II FPGAs, and the Viva TM graphical hardware description language.

Wells, B. Earl↗
NASA NTRS2004

Development of a Multi-bus, Multi-source Reconfigurable Stirling Radioisotope Power System Test Bed

The National Aeronautics and Space Administration (NASA) has typically used Radioisotope Thermoelectric Generators (RTG) as their source of electric power for deep space missions. A more efficient and potentially more cost effective alternative to the RTG, the high efficiency 110 watt Stirling Radioisotope Generator 110 (SRG110) is being developed by the Department of Energy (DOE), Lockheed Martin (LM), Stirling Technology Company (STC) and NASA Glenn Research Center (GRC). The SRG110 consists of two Stirling convertors (Stirling Engine and Linear Alternator) in a dual-opposed configuration, and two General Purpose Heat Source (GPHS) modules. Although Stirling convertors have been successfully operated as a power source for the utility grid and as a stand-alone portable generator, demonstration of the technology required to interconnect two Stirling convertors for a spacecraft power system has not been attempted. NASA GRC is developing a Power System Test Bed (PSTB) to evaluate the performance of a Stirling convertor in an integrated electrical power system application. This paper will describe the status of the PSTB and on-going activities pertaining to the PSTB in the NASA Thermal-Energy Conversion Branch of the Power and On-Board Propulsion Technology Division.

Coleman, Anthony S.↗
NASA NTRS2006

Reconfigurable Control with Neural Network Augmentation for a Modified F-15 Aircraft

Description of the performance of a simplified dynamic inversion controller with neural network augmentation follows. Simulation studies focus on the results with and without neural network adaptation through the use of an F-15 aircraft simulator that has been modified to include canards. Simulated control law performance with a surface failure, in addition to an aerodynamic failure, is presented. The aircraft, with adaptation, attempts to minimize the inertial cross-coupling effect of the failure (a control derivative anomaly associated with a jammed control surface). The dynamic inversion controller calculates necessary surface commands to achieve desired rates. The dynamic inversion controller uses approximate short period and roll axis dynamics. The yaw axis controller is a sideslip rate command system. Methods are described to reduce the cross-coupling effect and maintain adequate tracking errors for control surface failures. The aerodynamic failure destabilizes the pitching moment due to angle of attack. The results show that control of the aircraft with the neural networks is easier (more damped) than without the neural networks. Simulation results show neural network augmentation of the controller improves performance with aerodynamic and control surface failures in terms of tracking error and cross-coupling reduction.

Burken, John J.↗
NASA NTRS2001

Reconfigurable robots for all terrain exploration

While significant recent progress has been made in development of mobile robots for planetary suface exploration,there remain major challenges. These include increased autonomy of operation, traverse of challenging terrain, and fault-tolerance under long, unattended periods of use.

mobile robots multi-robot cooperation robotic arch↗
NASA NTRS1996

A Reconfigurable Testbed Environment for Spacecraft Autonomy

A key goal of NASA's New Millennium Program is the development of technology for increased spacecraft on-board autonomy. Achievement of this objective requires the development of a new class of ground-based automony testbeds that can enable the low-cost and rapid design, test, and integration of the spacecraft autonomy software. This paper describes the development of an Autonomy Testbed Environment (ATBE) for the NMP Deep Space I comet/asteroid rendezvous mission.

testbed autonomy New Millennium Program (NMP) Auto↗