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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Pegasus (trademark) launch operations and the PegaStar integrated spacecraft bus

The Pegasus air launched space booster, which successfully flew its maiden flight on 5 Apr. 1990, provides the international satellite community with a flexible cost effective means for delivering small payloads into low Earth orbit. The vehicle's simple, robust design and horizontal integration methods ensure maximum reliability and significantly reduce launch base infrastructure requirements. The vehicle's air launched approach and ability to launch over open ocean regions provide unmatched flexibility in launch location and approach used to ensure range safety. The PegaStar integrated spacecraft bus, which complements the Pegasus launch system, can provide a turnkey means for delivering instrument and sensor packages into low Earth orbit and providing extended (5 to 10 year) on orbit operational support. Pegasus and PegaStar are described, including payload interfaces, delivery capability; integration methods, facility and ground support equipment requirements; and typical launch operations.

Mosier, Marty↗
NASA NTRS1992

Overview of National Launch System with emphasis on cargo transfer vehicle

As a result of the Augustine Committee's recommendation to the National Space Council, NASA and the DOD have embarked on a joint program to provide a new capability for transporting payloads into space. Vehicles within the National Launch System (NLS) family are to be robust designs allowing more streamlined ground processing with corresponding reductions in operations cost. A primary NASA objective is access to space and the space station independent of the Space Shuttle. This requires the program to provide more than a simple payload-to-orbit capability. This capability is provided in large part by the cargo transfer vehicle.

Buchanan, Harry↗
NASA NTRS1992

Pilot-in-the-loop analysis of propulsive-only flight control systems

Longitudinal control system architectures which directly couple flight stick motions to throttle commands for a multi-engine aircraft are presented. This coupling enables positive attitude control with complete failure of the flight control system. The architectures chosen vary from simple feedback gains to classical lead-lag compensators with and without prefilters. Each architecture is reviewed for its appropriateness for piloted flight. The control systems are then analyzed with pilot-in-the-loop metrics related to bandwidth required for landing. Results indicate that current and proposed bandwidth requirements should be modified for throttles-only flight control. Pilot ratings consistently showed better ratings than predicted by analysis. Recommendations are made for more robust design and implementation. The use of quantitative feedback theory for compensator design is discussed. Although simple and effective augmented control can be achieved in a wide variety of failed configurations, a few configuration characteristics are dominant for pilot-in-the-loop control.

Chou, Hwei-Lan↗
NASA NTRS1993

A passivity based controller for free base manipulators

A feedback linearization technique is used in conjunction with passivity concepts to design robust controllers for free base robots. It is assumed that bounded modeling uncertainties exist in the inertia matrix and the vector representing the coriolis, centripetal, and friction forces. Under these assumptions, the controller guarantees asymptotic tracking of the joint variables. A Lagrangian approach is used to develop a dynamic model for space robots. Closed-loop simulation results are illustrated for a simple case of a single link planar space manipulator with freely floating base.

Chuang, C.-H.↗
NASA NTRS1995

Liquid crystal point diffraction interferometer

A new instrument, the liquid crystal point diffraction-interferometer (LCPDI), has been developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point diffraction interferometer (PDI) and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wavefronts with very high data density and with automated data reduction. This dissertation describes the theory of both the PDI and liquid crystal phase control. The design considerations for the LCPDI are presented, including manufacturing considerations. The operation and performance of the LCPDI are discussed, including sections regarding alignment, calibration, and amplitude modulation effects. The LCPDI is then demonstrated using two phase objects: defocus difference wavefront, and a temperature distribution across a heated chamber filled with silicone oil. The measured results are compared to theoretical or independently measured results and show excellent agreement. A computer simulation of the LCPDI was performed to verify the source of observed periodic phase measurement error. The error stems from intensity variations caused by dye molecules rotating within the liquid crystal layer. Methods are discussed for reducing this error. Algorithms are presented which reduce this error; they are also useful for any phase-stepping interferometer that has unwanted intensity fluctuations, such as those caused by unregulated lasers.

Mercer, Carolyn R.↗
NASA NTRS1995

Robust Quantitative Measurement of Flows and Transparent or Highly Reflective Objects

The liquid crystal point diffraction interferometer (LCPDI) is a new instrument that has been developed for the measurement of phase objects. The LCPDI uses the compact, robust design of Linnik's point diffraction interferometer and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wave-fronts. A solid state camera provides very high data density and automated data reduction. The instrument can measure either transparent objects like fluids and lenses, or highly reflective opaque objects like mirrors. In the former case, the refractive index distribution is measured and then related to various properties like temperature, density, chemical composition, or thickness. In the latter case, the measured phase distribution is related to the object shape. The objects measured must be stationary or quasisteady state because the measurement requires the acquisition of several frames of image data during which time the object's properties must not have changed. The data acquisition time depends on the speed of the frame grabber and the required number of data frames. Typically, three to five frames taking 1 to 2 seconds are required. The potential for faster data acquisition exists.

Mercer, Carolyn R.↗
NASA NTRS1995

High data density temperature measurement for quasi steady-state flows

A new optical instrument, the liquid crystal point diffraction interferometer (LCPDI), is used to measure the temperature distribution across a heated chamber filled with silicone oil. Data taken using the LCPDI are compared to equivalent measurements made with a traversing thermocouple and the two data sets show excellent agreement This instrument maintains the compact, robust design of Linnik's point diffraction interferometer and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wavefronts with very high data density and with automated data reduction.

Mercer, Carolyn R.↗
NASA NTRS1996

Pilot-in-the-Loop Analysis of Propulsive-Only Flight Control Systems

Longitudinal control system architectures are presented which directly couple flight stick motions to throttle commands for a multi-engine aircraft. This coupling enables positive attitude control with complete failure of the flight control system. The architectures chosen vary from simple feedback gains to classical lead-lag compensators with and without prefilters. Each architecture is reviewed for its appropriateness for piloted flight. The control systems are then analyzed with pilot-in-the-loop metrics related to bandwidth required for landing. Results indicate that current and proposed bandwidth requirements should be modified for throttles only flight control. Pilot ratings consistently showed better ratings than predicted by analysis. Recommendations are made for more robust design and implementation. The use of Quantitative Feedback Theory for compensator design is discussed. Although simple and effective augmented control can be achieved in a wide variety of failed configurations, a few configuration characteristics are dominant for pilot-in-the-loop control. These characteristics will be tested in a simulator study involving failed flight controls for a multi-engine aircraft.

Chou, Hwei-Lan↗
NASA NTRS1996

High Data Density Temperature Measurement for Quasi Steady-State Flows

A new optical instrument, the liquid crystal point diffraction interferometer (LCPDI), is used to measure the temperature distribution across a heated chamber filled with silicone oil. Data taken using the LCPDI are compared to equivalent measurements made with a traversing thermo-couple and the two data sets show excellent agreement. This instrument maintains the compact, robust design of Linniks point diffraction interferometer and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wave-fronts with very high data density and with automated data reduction.

Mercer, C. R.↗
NASA NTRS1996

Liquid-Crystal Point-Diffraction Interferometer for Wave-Front Measurements

A new instrument, the liquid-crystal point-diffraction interferometer (LCPDI), is developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point-diffraction interferometer and adds to it a phase-stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wave fronts with very high data density and with automated data reduction. We describe the theory and design of the LCPDI. A focus shift was measured with the LCPDI, and the results are compared with theoretical results,

Mercer, Carolyn R.↗
NASA NTRS1998

Assessment Study of the State of the Art in Adaptive Control and its Applications to Aircraft Control

Many papers relevant to reconfigurable flight control have appeared over the past fifteen years. In general these have consisted of theoretical issues, simulation experiments, and in some cases, actual flight tests. Results indicate that reconfiguration of flight controls is certainly feasible for a wide class of failures. However many of the proposed procedures although quite attractive, need further analytical and experimental studies for meaningful validation. Many procedures assume the availability of failure detection and identification logic that will supply adequately fast, the dynamics corresponding to the failed aircraft. This in general implies that the failure detection and fault identification logic must have access to all possible anticipated faults and the corresponding dynamical equations of motion. Unless some sort of explicit on line parameter identification is included, the computational demands could possibly be too excessive. This suggests the need for some form of adaptive control, either by itself as the prime procedure for control reconfiguration or in conjunction with the failure detection logic. If explicit or indirect adaptive control is used, then it is important that the identified models be such that the corresponding computed controls deliver adequate performance to the actual aircraft. Unknown changes in trim should be modelled, and parameter identification needs to be adequately insensitive to noise and at the same time capable of tracking abrupt changes. If however, both failure detection and system parameter identification turn out to be too time consuming in an emergency situation, then the concepts of direct adaptive control should be considered. If direct model reference adaptive control is to be used (on a linear model) with stability assurances, then a positive real or passivity condition needs to be satisfied for all possible configurations. This condition is often satisfied with a feedforward compensator around the plant. This compensator must be robustly designed such that the compensated plant satisfies the required positive real conditions over all expected parameter values. Furthermore, with the feedforward only around the plant, a nonzero (but bounded error) will exist in steady state between the plant and model outputs. This error can be removed by placing the compensator also in the reference model. Design of such a compensator should not be too difficult a problem since for flight control it is generally possible to feedback all the system states.

Kaufman, Howard↗
NASA NTRS1999

Spaceliner Class Operability Gains Via Combined Airbreathing/ Rocket Propulsion: Summarizing an Operational Assessment of Highly Reusable Space Transports

In discussing a new NASA initiative in advanced space transportation systems and technologies, the Director of the NASA Marshall Space Flight Center, Arthur G. Stephenson, noted that, "It would use new propulsion technology, air-breathing engine so you don't have to carry liquid oxygen, at least while your flying through the atmosphere. We are calling it Spaceliner 100 because it would be 100 times cheaper, costing $ 100 dollars a pound to orbit." While airbreathing propulsion is directly named, rocket propulsion is also implied by, "... while you are flying through the atmosphere." In-space final acceleration to orbital speed mandates rocket capabilities. Thus, in this informed view, Spaceliner 100 will be predicated on combined airbreathing/rocket propulsion, the technical subject of this paper. Interestingly, NASA's recently concluded Highly Reusable Space Transportation (HRST) study focused on the same affordability goal as that of the Spaceliner 100 initiative and reflected the decisive contribution of combined propulsion as a way of expanding operability and increasing the design robustness of future space transports, toward "aircraft like" capabilities. The HRST study built on the Access to Space Study and the Reusable Launch Vehicle (RLV) development activities to identify and characterize space transportation concepts, infrastructure and technologies that have the greatest potential for reducing delivery cost by another order of magnitude, from $1,000 to $100-$200 per pound for 20,000 lb. - 40.000 lb. payloads to low earth orbit (LEO). The HRST study investigated a number of near-term, far-term, and very far-term launch vehicle concepts including all-rocket single-stage-to-orbit (SSTO) concepts, two-stage-to-orbit (TSTO) concepts, concepts with launch assist, rocket-based combined cycle (RBCC) concepts, advanced expendable vehicles, and more far term ground-based laser powered launchers. The HRST study consisted of preliminary concept studies, assessments and analysis tool development for advanced space transportation systems, followed by end-to-end system concept definitions and trade analyses, specific system concept definition and analysis, specific key technology and topic analysis, system, operational and economics model development, analysis, and integrated assessments. The HRST Integration Task Force (HITF) was formed to synthesize study results in several specific topic areas and support the development of conclusions from the study: Systems Concepts Definitions, Technology Assessment, Operations Assessment, and Cost Assessment. This paper summarizes the work of the Operations Assessment Team: the six approaches used, the analytical tools and methodologies developed and employed, the issues and concerns, and the results of the assessment. The approaches were deliberately varied in measures of merit and procedure to compensate for the uncertainty inherent in operations data in this early phase of concept exploration. In general, rocket based combined cycle (RBCC) concepts appear to have significantly greater potential than all-rocket concepts for reducing operations costs.

Nix, Michael B.↗
NASA NTRS2000

Generation of a Cold Atom Beam from a Pyramidal Magneto-Optical Trap

Techniques to generate cold atom beams are of great interest in a variety of applications, from atomic frequency standards and atom optics to experimental studies of Bose-Einstein condensation. Cold atom beams have been produced by slowing thermal atomic beams using the Zeeman-slowing technique or chirped lasers, or using laser-cooling techniques to extract a slow atomic beam from the background gas in a low-pressure vapor cell. These laser-cooling techniques include "atomic funnels" or two-dimensional magneto-optical traps, as well as a variation of the conventional vapor cell magneto-optical trap called the "low-velocity intense source" (LVIS). Variations of the LVIS have been realized with unique trap geometries such as conical or pyramidal mirror traps. The present work implements a simple and robust design based on the pyramidal trap geometry and allows use of a single large diameter (<less than or = 20 cm) laser beam to obtain large capture rates of atoms from the background vapor. The four 45 deg mirrors are truncated just before the apex of the pyramid, and the 1 sq cm region at the center of the incident laser beam is retro-reflected by lambda /4 plate with a high-reflectance gold coating on the second surface. A small (1 mm diameter) hole in this retro-optic forms an extraction column for the atoms while maintaining a low conductance between the source region and an adjacent UHV chamber.

Kohel, J.↗
NASA NTRS2000

Generation of a Cold Atom Beam from a Pyramidal Magneto-Optical Trap

We have built an atomic beam source utilizing a simple and robust design based on the pyramidal trap geometry of Kim et al. Our design allows use of a single large diameter (\le20 cm) laser beam to obtain large capture rates of atoms from a background vapor. A small (about 1mm diameter) hole in the retro-optic at the apex of the pyramid provides an extraction column for the atoms. We have operated the apparatus both as a magneto-optical trap (using an auxiliary plug laser beam), and as a cold atomic beam source. The characterization of this large pyramidal beam source will be reported, including an investigation of scaling to very large (10--20cm) high power (about 1W) laser beams which should allow significant improvements in atomic beam flux.

Bliss, J. L.↗
NASA NTRS2000

Influence of Tooth Spacing Error on Gears With and Without Profile Modifications

A computer simulation was conducted to investigate the effectiveness of profile modification for reducing dynamic loads in gears with different tooth spacing errors. The simulation examined varying amplitudes of spacing error and differences in the span of teeth over which the error occurs. The modification considered included both linear and parabolic tip relief. The analysis considered spacing error that varies around most of the gear circumference (similar to a typical sinusoidal error pattern) as well as a shorter span of spacing errors that occurs on only a few teeth. The dynamic analysis was performed using a revised version of a NASA gear dynamics code, modified to add tooth spacing errors to the analysis. Results obtained from the investigation show that linear tip relief is more effective in reducing dynamic loads on gears with small spacing errors but parabolic tip relief becomes more effective as the amplitude of spacing error increases. In addition, the parabolic modification is more effective for the more severe error case where the error is spread over a longer span of teeth. The findings of this study can be used to design robust tooth profile modification for improving dynamic performance of gear sets with different tooth spacing errors.

Padmasolala, Giri↗
NASA NTRS2000

Third Computational Aeroacoustics (CAA) Workshop on Benchmark Problems

The proceedings of the Third Computational Aeroacoustics (CAA) Workshop on Benchmark Problems cosponsored by the Ohio Aerospace Institute and the NASA Glenn Research Center are the subject of this report. Fan noise was the chosen theme for this workshop with representative problems encompassing four of the six benchmark problem categories. The other two categories were related to jet noise and cavity noise. For the first time in this series of workshops, the computational results for the cavity noise problem were compared to experimental data. All the other problems had exact solutions, which are included in this report. The Workshop included a panel discussion by representatives of industry. The participants gave their views on the status of applying computational aeroacoustics to solve practical industry related problems and what issues need to be addressed to make CAA a robust design tool.

Dahl, Milo D.↗
NASA NTRS2001

Use of System Safety Risk Assessments for the Space Shuttle Reusable Solid Rocket Motor (RSRM)

This paper discusses the System Safety approach used to assess risk for the Space Shuttle Reusable Solid Rocket Motor (RSRM). Previous to the first RSRM flight in the fall of 1988, all systems were analyzed extensively to assure that hazards were identified, assessed and that the baseline risk was understood and appropriately communicated. Since the original RSRM baseline was established, Thiokol and NASA have implemented a number of initiatives that have further improved the RSRM. The robust design, completion of rigorous testing and flight success of the RSRM has resulted in a wise reluctance to make changes. One of the primary assessments required to accompany the documentation of each proposed change and aid in the decision making process is a risk assessment. Documentation supporting proposed changes, including the risk assessments from System Safety, are reviewed and assessed by Thiokol and NASA technical management. After thorough consideration, approved changes are implemented adding improvements to and reducing risk of the Space Shuttle RSRM.

Greenhalgh, Phillip O.↗
NASA NTRS2002

Oxidation- and Creep-Enhanced Fatigue of Haynes 188 Alloy-Oxide Scale System Under Simulated Pulse Detonation Engine Conditions

The development of the pulse detonation engine (PDE) requires robust design of the engine components that are capable of enduring harsh detonation environments. In this study, a high cycle thermal fatigue test rig was developed for evaluating candidate PDE combustor materials using a CO2 laser. The high cycle thermal fatigue behavior of Haynes 188 alloy was investigated under an enhanced pulsed laser test condition of 30 Hz cycle frequency (33 ms pulse period, and 10 ms pulse width including 0.2 ms pulse spike). The temperature swings generated by the laser pulses near the specimen surface were characterized by using one-dimensional finite difference modeling combined with experimental measurements. The temperature swings resulted in significant thermal cyclic stresses in the oxide scale/alloy system, and induced extensive surface cracking. Striations of various sizes were observed at the cracked surfaces and oxide/alloy interfaces under the cyclic stresses. The test results indicated that oxidation and creep-enhanced fatigue at the oxide scale/alloy interface was an important mechanism for the surface crack initiation and propagation under the simulated PDE condition.

Zhu, Dongming↗