Minimum energy-loss guidance for aeroassisted orbital plane change
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Hull, D. G.↗
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New analytical results for AOTV guidance
Minimum energy-loss turns of an Aero-assisted, Orbital Transfer Vehicle (AOTV) performing the atmospheric portion of an orbital-plane-change maneuver are developed using the heading angle as the independent variable. Because the heading angle is monotonic, several difficulties previously encountered using the flight path angle, which is not monotonic, as the independent variable are eliminated. In addition, the solution of the optimal control problem reduces to the solution of a fourth-order polynomial which can be accomplished analytically.
Hull, D. G.↗
Measurement of ultrasonic velocity using phase-slope and cross-correlation methods
Computer implemented phase-slope and cross-correlation methods are introduced for measuring time delays between pairs of broadband ultrasonic pulse-echo signals for determining velocity in engineering materials. The phase-slope and cross-correlation methods are compared with the overlap method which is currently in wide use. Comparison of digital versions of the three methods shows similar results for most materials having low ultrasonic attenuation. However, the cross-correlation method is preferred for highly attenuating materials. An analytical basis for the cross-correlation method is presented. Examples are given for the three methods investigated to measure velocity in representative materials in the magahertz range.
Hull, D. R.↗
Aero-assisted orbital plane change using an elliptic drag polar
A three-impulse, aero-assisted maneuver is used to change the plane of a circular orbit. The guidance law used during the atmospheric phase is based on the repetitive use of an approximate optimal control law. The approximations include Loh's term being constant, an exponential atmosphere, and a constant-coefficient drag polar. Whereas the true optimal trajectory is flown at maximum lift-to-drag ratio, simulation results for a parabolic drag polar show the angle of attack becoming large near the end of the trajectory. Here, the approximate optimal control rule is developed for an elliptic polar which has maximum lift coefficient and higher values of the drag coefficient at high values of the lift coefficient than the parabolic polar. Simulation results show that the angle of attack still increases to high values near the end of the trajectory and that, overall, the parabolic drag polar produces better results. Finally, it is shown that Loh's term is not constant over the ascent portion of the atmospheric turn and is the probable cause of high angles of attack. However, the guidance laws developed by assuming Loh's term to be constant work well.
Hull, D. G.↗
FORTRAN Algorithm for Image Processing
FORTRAN computer algorithm containing various image-processing analysis and enhancement functions developed. Algorithm developed specifically to process images of developmental heat-engine materials obtained with sophisticated nondestructive evaluation instruments. Applications of program include scientific, industrial, and biomedical imaging for studies of flaws in materials, analyses of steel and ores, and pathology.
Roth, Don J.↗
Fatigue failure of regenerator screens in a high frequency Stirling engine
Failure of Stirling Space Power Demonstrator Engine (SPDE) regenerator screens was investigated. After several hours of operation the SPDE was shut down for inspection and on removing the regenerator screens, debris of unknown origin was discovered along with considerable cracking of the screens in localized areas. Metallurgical analysis of the debris determined it to be cracked-off-deformed pieces of the 41 micron thickness Type 304 stainless steel wire screen. Scanning electron microscopy of the cracked screens revealed failures occurring at wire crossovers and fatigue striations on the fracture surface of the wires. Thus, the screen failure can be characterized as a fatigue failure of the wires. The crossovers were determined to contain a 30 percent reduction in wire thickness and a highly worked microstructure occurring from the manufacturing process of the wire screens. Later it was found that reduction in wire thickness occurred because the screen fabricator had subjected it to a light cold-roll process after weaving. Installation of this screen left a clearance in the regenerator allowing the screens to move. The combined effects of the reduction in wire thickness, stress concentration (caused by screen movement), and highly worked microstructure at the wire crossovers led to the fatigue failure of the screens.
Hull, David R.↗
Observations of directional gamma prime coarsening during engine operation
Two alloys with negative mismatch parameters, NASAIR 100 and a modified NASAIR 100 called Alloy 3 were run as turbine blades in an experimental ground based Garret TFE731 engine for up to 200 hr. The directional coarsening of gamma prime (rafting) that developed during engine testing was analyzed and compared to previous research from laboratory tests. The blades were found to be rafted normal to the centrifugal stress axis over much of the span, but near the surfaces, the blades were found to be rafted parallel to the centrifugal stress axis for certain cycles. Representative photomicrographs of the blades and the effects of stress and temperature on raft formation are shown.
Draper, Susan L.↗
Fatigue failure of regenerator screens in a high frequency Stirling engine
Failure of Stirling Space Power Demonstrator Engine (SPDE) regenerator screens was investigated. After several hours of operation the SPDE was shut down for inspection and on removing the regenator screens, debris of unknown origin was discovered along with considerable cracking of the screens in localized areas. Metallurgical analysis of the debris determined it to be cracked-off-deformed pieces of the 41 micron thickness Type 304 stainless steel wire screen. Scanning electron microscopy of the cracked screens revealed failures occurring at wire crossovers and fatigue striations on the fracture surface of the wires. Thus, the screen failure can be characterized as a fatigue failure of the wires. The crossovers were determined to contain 30 percent reduction in wire thickness and a highly worked microstructure occurring from the manufacturing process of the wire screens. Later it was found that reduction in wire thickness occurred because the screen fabricator had subjected it to a light cold-roll process after weaving. Installation of this screen left a clearance in the regenerator allowing the screens to move. The combined effects of the reduction in wire thickness, stress concentration (caused by screen movement), and highly worked microstructure at the wire crossovers led to the fatigue failure of the screens.
Hull, David R.↗
Application of superconducting technology to earth-to-orbit electromagnetic launch systems
Benefits may occur by incorporating superconductors, both existing and those currently under development, in one or more parts of a large-scale electromagnetic launch (EML) system that is capable of delivering payloads from the surface of the Earth to space. The use of superconductors for many of the EML components results in lower system losses; consequently, reductions in the size and number of energy storage devices are possible. Applied high-temperature superconductivity may eventually enable novel design concepts for energy distribution and switching. All of these technical improvements have the potential to reduce system complexity and lower payload launch costs.
Hull, J. R.↗
As-received microstructure of a SiC/Ti-15-3 composite
A silicon carbide fiber reinforced titanium (Ti-15V-3Cr-3Sn-3Al) composite is metallographically examined. Several methods for examining composite materials are investigated and documented. Polishing techniques for this material are described. An interference layering method is developed to reveal the structure of the fiber, the reaction zone, and various phases within the matrix. Microprobe and transmission electron microscope (TEM) analyses are performed on the fiber/matrix interface. A detailed description of the fiber distribution as well as the microstructure of the fiber and matrix are presented.
Lerch, Bradley A.↗
Construction and evaluation of an imaging focussed-mesh electron multiplier for space instrumentation
A focused-mesh electron multiplier (FMEM) has been combined with a wedge and strip position-sensitive anode to create a novel detector that is considered likely to have a number of applications in space astronomy and laboratory image sensing. Results from the first application of a wedge and strip anode to an FMEM are presented including spatial resolution, spatial linearity, background rate, and pulse risetime. The converted multiplier retains the attributes of an FMEM that made it attractive in the first place, such as low background, high speed, and high dynamic range.
Vallerga, J.↗
CLEAR: Communications Link Expert Assistance Resource
Communications Link Expert Assistance Resource (CLEAR) is a real time, fault diagnosis expert system for the Cosmic Background Explorer (COBE) Mission Operations Room (MOR). The CLEAR expert system is an operational prototype which assists the MOR operator/analyst by isolating and diagnosing faults in the spacecraft communication link with the Tracking and Data Relay Satellite (TDRS) during periods of realtime data acquisition. The mission domain, user requirements, hardware configuration, expert system concept, tool selection, development approach, and system design were discussed. Development approach and system implementation are emphasized. Also discussed are system architecture, tool selection, operation, and future plans.
Hull, Larry G.↗
Aeronautical applications of high-temperature superconductors
The successful development of high-temperature superconductors (HTS) could have a major impact on future aeronautical propulsion and aeronautical flight vehicle systems. A preliminary examination of the potential application of HTS for aeronautics indicates that significant benefits may be realized through the development and implementation of these newly discovered materials. Applications of high-temperature superconductors (currently substantiated at 95 K) were envisioned for several classes of aeronautical systems, including subsonic and supersonic transports, hypersonic aircraft, V/STOL aircraft, rotorcraft, and solar, microwave and laser powered aircraft. Introduced and described are the particular applications and potential benefits of high-temperature superconductors as related to aeronautics and/or aeronautical systems.
Turney, George E.↗
Soft X-ray and extreme utraviolet quantum detection efficiency of potassium chloride photocathode layers on microchannel plates
The quantum detection efficiency (QDE) of KCl photocathodes in the 44-1460 A range was investigated. An opaque layer of KCl, about 15,000-A-thick, was evaporated and applied the surface of a microchannel plate (MCP), and the contribution of the photocathode material in the channels (and on the interchannel web) to the QDE was measured using a Z stack MCP detector. It is shown that KCl is a relatively stable photocathode material, with the QDE equal to 30-40 percent in the EUV. At wavelengths above 200 A, the QDE is slightly better than the QDE of CsI, as reported by Siegmund et al. (1986). While the shape of the QDE curve as a function of wavelength is similar to those reported for CsI and KBr, KCl was found to lack the high QDE peak found in the curves of CsI and KBr at about 100 A. A simple QDE model is described, the predictions of which were found to agree with the measurements on the KCl photocathode.
Siegmund, Oswald H. W.↗
Observations of directional gamma prime coarsening during engine operation
Two alloys, NASAIR 100 and a modified NASAIR 100 called Alloy 3, were run as turbine blades in an experimental ground-based Garrett TFE731 engine for up to 200 hours. The stress induced directional coarsening of gamma-prime (rafting) that developed during engine testing was analyzed and compared to previous research from laboratory tests. The blades were found to have formed a lamellar structure, the lamellae being normal to the centrifugal stress axis over much of the span. However, near the surfaces, the blades were found to have formed lamellae parallel to the centrifugal stress axis for certain cycles. Representative photomicrographs of the blades and the effects of stress and temperature on lamellae formation are shown.
Draper, S.↗
Perturbation guidance for aerocruise with bounded control
A perturbation guidance algorithm is developed for the constant-altitude portion of the orbital-plane change maneuver, called aerocruise. It is obtained by solving a linear-quadratic regulator problem in terms of the perturbed state and control variables. The regulator problem with hard control-variable constraints is then studied. For the two-control-variable case, the simulation results show that the bounded-control algorithm gives better performance than that obtained using a limiter for the case where control variables exceed the bounds.
Hull, David G.↗
Aeronautical applications of high-temperature superconductors
The successful development of high-temperature superconductors (HTS) could have a major impact on future aeronautical propulsion and aeronautical flight vehicle systems. A preliminary examination of the potential application of HTS for aeronautics indicates that significant benefits may be realized through the development and implementation of these newly discovered materials. Applications of high-temperature superconductors (currently substantiated at 95 k) were envisioned for several classes of aeronautical systems, including subsonic and supersonic transports, hypersonic aircraft, V/STOL aircraft, rotorcraft, and solar, microwave and laser powered aircraft. Introduced and described are the particular applications and potential benefits of high-temperature superconductors as related to aeronautics and/or aeronautical systems.
Turney, George E.↗
Real-time approximate optimal guidance laws for the advanced launch system
An approach to optimal ascent guidance for a launch vehicle is developed using an expansion technique. The problem is to maximize the payload put into orbit subject to the equations of motion of a rocket over a rotating spherical earth. It is assumed that the thrust and gravitational forces dominate over the aerodynamic forces. It is shown that these forces can be separated by a small parameter epsilon, where epsilon is the ratio of the atmospheric scale height to the radius of the earth. The Hamilton-Jacobi-Bellman or dynamic programming equation is expanded in a series where the zeroth-order term (epsilon = 0) can be obtained in closed form. The zeroth-order problem is that of putting maximum payload into orbit subject to the equations of motion of a rocket in a vacuum over a flat earth. The neglected inertial and aerodynamic terms are included in higher order terms of the expansion, which are determined from the solution of first-order linear partial differential equations requiring only quadrature integrations. These quadrature integrations can be performed rapidly, so that real-time approximate optimization can be used to construct the launch guidance law.
Speyer, Jason L.↗