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At least 829 records · Page 46

Feasibility of Decentralized Linear-Quadratic-Gaussian Control of Autonomous Distributed Spacecraft

A distributed satellite formation, modeled as an arbitrary number of fully connected nodes in a network, could be controlled using a decentralized controller framework that distributes operations in parallel over the network. For such problems, a solution that minimizes data transmission requirements, in the context of linear-quadratic-Gaussian (LQG) control theory, was given by Speyer. This approach is advantageous because it is non-hierarchical, detected failures gracefully degrade system performance, fewer local computations are required than for a centralized controller, and it is optimal with respect to the standard LQG cost function. Disadvantages of the approach are the need for a fully connected communications network, the total operations performed over all the nodes are greater than for a centralized controller, and the approach is formulated for linear time-invariant systems. To investigate the feasibility of the decentralized approach to satellite formation flying, a simple centralized LQG design for a spacecraft orbit control problem is adapted to the decentralized framework. The simple design uses a fixed reference trajectory (an equatorial, Keplerian, circular orbit), and by appropriate choice of coordinates and measurements is formulated as a linear time-invariant system.

Carpenter, J. Russell↗

On Heating the Sun's Corona by Magnetic Explosions: Feasibility in Active Regions and prospects for Quiet Regions and Coronal Holes

We build a case for the persistent strong coronal heating in active regions and the pervasive quasi-steady heating of the corona in quiet regions and coronal holes being driven in basically the same way as the intense transient heating in solar flares: by explosions of sheared magnetic fields in the cores of initially closed bipoles. We begin by summarizing the observational case for exploding sheared core fields being the drivers of a wide variety of flare events, with and without coronal mass ejections. We conclude that the arrangement of an event's flare heating, whether there is a coronal mass ejection, and the time and place of the ejection relative to the flare heating are all largely determined by four elements of the form and action of the magnetic field: (1) the arrangement of the impacted, interacting bipoles participating in the event, (2) which of these bipoles are active (have sheared core fields that explode) and which are passive (are heated by injection from impacted active bipoles), (3) which core field explodes first, and (4) which core-field explosions are confined within the closed field of their bipoles and which ejectively open their bipoles. We then apply this magnetic-configuration framework for flare heating to the strong coronal heating observed by the Yohkoh Soft X-ray Telescope in an active region with strongly sheared core fields observed by the MSFC vector magnetograph. All of the strong coronal heating is in continually microflaring sheared core fields or in extended loops rooted against the active core fields. Thus, the strong heating occurs in field configurations consistent with the heating being driven by frequent core-field explosions that are smaller but similar to those in confined flares and flaring arches. From analysis of the thermal and magnetic energetics of two selected core-field microflares and a bright extended loop, we find that (1) it is energetically feasible for the sheared core fields to drive all of the coronal heating in the active region via a staccato of magnetic microexplosions, (2) the microflares at the feet of the extended loop behave as the flares at the feet of flaring arches in that more coronal heating is driven within the active bipole than in the extended loop, (3) the filling factor of the X-ray plasma in the core field microflares and in the extended loop is approximately 0.1, and (4) to release enough magnetic energy for a typical microflare (10^27 - 10^28 erg), a microflaring strand of sheared core field need expand and/or untwist by only a few percent at most. Finally, we point out that (1) the field configurations for strong coronal heating in our example active region (i.e., neutral-line core fields, many embedded in the feet of extended loops) are present in abundance in the magnetic network in quiet regions and coronal holes, and (2) it is known that many network bipoles do microflare and that many produce detectable coronal heating. We therefore propose that exploding sheared core fields are the drivers of most of the heating and dynamics of the solar atmosphere, ranging from the largest and most powerful coronal mass ejections and flares, to the vigorous microflaring and coronal heating in active regions, to the multitude of fine-scale explosive events in the magnetic network. The low-lysing exploding core fields in the network drive microflares, spicules, global coronal heating, and ,consequently, the solar wind.

Moore, Ronald L.↗

D-21B RBCC Modification Feasibility Study

This report presents a feasibility study on the modifications required to re-engine the Lockheed D-21 Drone for use as a NASA RBCC engine. An introduction, background information, engine configuration and performance, propulsion system integration, loads/thermal analysis, avionics/systems, flight test results, costs and work schedule, and some conclusions are presented.

Source record↗

Validated Feasibility Study of Integrally Stiffened Metallic Fuselage Panels for Reducing Manufacturing Costs

The continual need to reduce airframe cost and the emergence of high speed machining and other manufacturing technologies has brought about a renewed interest in large-scale integral structures for aircraft applications. Applications have been inhibited, however, because of the need to demonstrate damage tolerance, and by cost and manufacturing risks associated with the size and complexity of the parts. The Integral Airframe Structures (IAS) Program identified a feasible integrally stiffened fuselage concept and evaluated performance and manufacturing cost compared to conventional designs. An integral skin/stiffener concept was produced both by plate hog-out and near-net extrusion. Alloys evaluated included 7050-T7451 plate, 7050-T74511 extrusion, 6013-T6511 extrusion, and 7475-T7351 plate. Mechanical properties, structural details, and joint performance were evaluated as well as repair, static compression, and two-bay crack residual strength panels. Crack turning behavior was characterized through panel tests and improved methods for predicting crack turning were developed. Manufacturing cost was evaluated using COSTRAN. A hybrid design, made from high-speed machined extruded frames that are mechanically fastened to high-speed machined plate skin/stringer panels, was identified as the most cost-effective manufacturing solution. Recurring labor and material costs of the hybrid design are up to 61 percent less than the current technology baseline.

Pettit, R. G.↗

Integral Airframe Structures (IAS): Validated Feasibility Study of Integrally Stiffened Metallic Fuselage Panels for Reducing Manufacturing Costs

The Integral Airframe Structures (IAS) program investigated the feasibility of using "integrally stiffened" construction for commercial transport fuselage structure. The objective of the program was to demonstrate structural performance and weight equal to current "built-up" structure with lower manufacturing cost. Testing evaluated mechanical properties, structural details, joint performance, repair, static compression, and two-bay crack residual strength panels. Alloys evaluated included 7050-T7451 plate, 7050-T74511 extrusion, 6013-T6511x extrusion, and 7475-T7351 plate. Structural performance was evaluated with a large 7475-T7351 pressure test that included the arrest of a two-bay longitudinal crack, and a measure of residual strength for a two-bay crack centered on a broken frame. Analysis predictions for the two-bay longitudinal crack panel correlated well with the test results. Analysis activity conducted by the IAS team strongly indicates that current analysis tools predict integral structural behavior as accurately as built-up structure. The cost study results indicated that, compared to built-up fabrication methods, high-speed machining structure from aluminum plate would yield a recurring cost savings of 61%. Part count dropped from 78 individual parts on a baseline panel to just 7 parts for machined IAS structure.

Munroe, J.↗

Heat Sink Welding for Preventing Hot Cracking in Alloy 2195 Intersection Welds: A Feasibility Study

Two concepts, stationary cooling and trailing cooling, were proposed to prevent weld intersection cracking. Finite element analysis was used to demonstrate the potential effectiveness of those two concepts. Both stationary and trailing heat sink setups were proposed for preventing intersection cracking. The cooling media could be liquid nitrogen, or pressured air knife. Welding experiments on the small test panel with the localized heat sink confirmed the feasibility of using such a stationary cooling technique. The required cooling was achieved in this test panel. Systematic welding experiments should be conducted in the future to validate and refine the heat sink technique for preventing intersection cracking.

Yang, Yu-Ping↗

Feasibility Study of Thin Film Thermocouple Piles

Historically, thermopile detectors, generators, and refrigerators based on bulk materials have been used to measure temperature, generate power for spacecraft, and cool sensors for scientific investigations. New potential uses of small, low-power, thin film thermopiles are in the area of microelectromechanical systems since power requirements decrease as electrical and mechanical machines shrink in size. In this research activity, thin film thermopile devices are fabricated utilizing radio frequency sputter coating and photoresist lift-off techniques. Electrical characterizations are performed on two designs in order to investigate the feasibility of generating small amounts of power, utilizing any available waste heat as the energy source.

Sisk, R. C.↗

Exoskeletal Engine Concept: Feasibility Studies for Medium and Small Thrust Engines

The exoskeletal engine concept is one in which the shafts and disks are eliminated and are replaced by rotating casings that support the blades in spanwise compression. Omission of the shafts and disks leads to an open channel at the engine centerline. This has immense potential for reduced jet noise and for the accommodation of an alternative form of thruster for use in a combined cycle. The use of ceramic composite materials has the potential for significantly reduced weight as well as higher working temperatures without cooling air. The exoskeletal configuration is also a natural stepping-stone to complete counter-rotating turbomachinery. Ultimately this will lead to reductions in weight, length, parts count and improved efficiency. The feasibility studies are in three parts. Part 1: Systems and Component Requirements addressed the mechanical aspects of components from a functionality perspective. This effort laid the groundwork for preliminary design studies. Although important, it is not felt to be particularly original, and has therefore not been included in the current overview. Part 2: Preliminary Design Studies turned to some of the cycle and performance issues inherent in an exoskeletal configuration and some initial attempts at preliminary design of turbomachinery were described. Twin-spoon and single-spool 25,800-lbf-thrust turbofans were used as reference vehicles in a mid-size commercial subsonic category in addition to a single-spool 5,000-lbf-thrust turbofan that represented a general aviation application. The exoskeletal engine, with its open centerline, has tremendous potential for noise suppression and some preliminary analysis was done which began to quantify the benefits. Part 3: Additional Preliminary Design Studies revisited the design of single-spool 25,800-lbf-thrust turbofan configurations, but in addition to the original FPR = 1.6 and BPR = 5.1 reference engine. two additional configurations used FPR = 2.4 and BPR = 3.0 and FPR = 3.2 and BPR = 2.0 were investigated. The single-spool 5.000-lbf-thrust turbofan was refined and the small engine study was extended to include a 2,000-lbf-thrust turbojet. More attention was paid to optimizing the turbomachinery. Turbine cooling flows were eliminated, in keeping with the use of uncooled CMC materials in exoskeletal engines. The turbine performance parameters moved much closer to the nominal target values, demonstrating the great benefits to the cycle of uncooled turbines.

Halliwell, Ian↗

Exoskeletal Engine Concept: Feasibility Studies for Medium and Small Thrust Engines

The exoskeletal engine concept is one in which the shafts and disks are eliminated and are replaced by rotating casings that support the blades in spanwise compression. Omission of the shafts and disks leads to an open channel at the engine centerline. This has immense potential for reduced jet noise and for the accomodation of an alternative form of thruster for use in a combined cycle. The use of ceramic composite materials has the potential for significantly reduced weight as well as higher working temperatures without cooling air. The exoskeletal configuration is also a natural stepping-stone to complete counter-rotating turbomachinery. Ultimately this will lead to reductions in weight, length, parts count and improved efficiency. The feasibility studies are in three parts. Part I-Systems and Component Requirements addressed the mechanical aspects of components from a functionality perspective. This effort laid the groundwork for preliminary design studies. Although important, it is not felt to be particularly original, and has therefore not been included in the current overview. Part 2-Preliminary Design Studies turned to some of the cycle and performance issues inherent in an exoskeletal configuration and some initial attempts at preliminary design of turbomachinery were described. Twin-spoon and single-spool 25.800-lbf-thrust turbofans were used as reference vehicles in a mid-size commercial subsonic category in addition to a single-spool 5,000-lbf-thrust turbofan that represented a general aviation application. The exoskeletal engine, with its open centerline, has tremendous potential for noise suppression and some preliminary analysis was done which began to quantify the benefits. Part 3-Additional Preliminary Design Studies revisited the design of single-spool 25,800-lbf-thrust turbofan configurations, but in addition to the original FPR = 1.6 and BPR = 5.1 reference engine, two additional configurations used FPR = 2.4 and BPR = 3.0 and FPR = 3.2 and BPR = 2.0 were investigated. The single-spool 5,000-lbf-thrust turbofan was refined and the small engine study was extended to include a 2,000-lbf-thrust turbojet. More attention was paid to optimizing the turbomachinery. Turbine cooling flows were eliminated, in keeping with the use of uncooled CMC material in exoskeletal engines. The turbine performance parameters moved much closer to the nominal target values, demonstrating the great benefits to the cycle of uncooled turbines.

Halliwell, Ian↗

The Feasibility of a Galileo-Style Tour of the Uranian Satellites

Gravity-assist trajectories have been a key to outer Solar System exploration. In particular, the gravity-assist tour of the Jovian satellites has contributed significantly to the success of the Galileo mission. A comparison of the Jovian system to the Uranian system reveals that the two possess similar satellite/planet mass ratios. Tisserand graphs of the Uranian system also indicate the potential for tours at Uranus. In this paper. We devise tour strategies and design a prototypical tour of the Uranian satellites, proving that tours at Uranus are feasible.

Heaton, Andrew F.↗

Feasibility Study of Laboratory Simulation of Single-Stage-to-Orbit Vehicle Base Heating

The feasibility of simulating in a laboratory the heating environment of the base region of the proposed reusable single-stage-to-orbit vehicle during its ascent is examined. The propellant is assumed to consist of hydrocarbon (RP1), liquid hydrogen (LH2), and liquid oxygen (LO2), which produces CO and H2 as the main combustible components of the exhaust effluent. Since afterburning in the recirculating region can dictate the temperature of the base flowfield and ensuing heating phenomena, laboratory simulation focuses on the thermochemistry of the afterburning. By extrapolating the Saturn V flight data, the Damkohler number, in the base region with afterburning for SSTO vehicle, is estimated to be between 30 and 140. It is shown that a flow with a Damkohler number of 1.8 to 25 can be produced in an impulse ground test facility. Even with such a reduced Damkohler number, the experiment can adequately reproduce the main features of the flight environment.

Park, Chung Sik↗

Using Wearable Computers in Shuttle Processing: A Feasibility Study

Shuttle processing operations are performed following prescribed instructions compiled in a Work Authorization Document (WAD). Until very recently, WADs were printed so that they could be properly executed, including the buy off of each and every step by the appropriate authorizing agent. However, with the development of EPICs, Maximo, and PeopleSoft applications, some of these documents are now available in electronic format; hence, it is possible for technicians and engineers to access them on line and buy off the steps electronically. To take full advantage of these developments, technicians need access to such documents at the point of job execution. Body wearable computers present an opportunity to develop a WAD delivery system that enables access while preserving technician's mobility, safety levels, and quality of work done. The primary objectives of this project were to determine if body wearable computers are a feasible delivery system for WADs. More specifically, identify and recommend specific brands of body wearable computers readily available on the market. Thus, this effort has field-tested this technology in two areas of shuttle processing, and it has examined the usability of the technology. Results of two field tests and a Human Factors Usability Test are presented. Section 2 provides a description of the body wearable computer technology. Section 3 presents the test at the Space Shuttle Main Engine (SSME) Shop. Section 4 presents the results of the integration test at the Solid Rocket Boosters Assembly and Refurbishing Facility (SRBARF). Section 5 presents the results of the usability test done at the Operations Support Building (OSB).

Centeno, Martha A.↗

Finding Feasible Abstract Counter-Examples

A strength of model checking is its ability to automate the detection of subtle system errors and produce traces that exhibit those errors. Given the high computational cost of model checking most researchers advocate the use of aggressive property-preserving abstractions. Unfortunately, the more aggressively a system is abstracted the more infeasible behavior it will have. Thus, while abstraction enables efficient model checking it also threatens the usefulness of model checking as a defect detection tool, since it may be difficult to determine whether a counter-example is feasible and hence worth developer time to analyze. We have explored several strategies for addressing this problem by extending an explicit-state model checker, Java PathFinder (JPF), to search for and analyze counter-examples in the presence of abstractions. We demonstrate that these techniques effectively preserve the defect detection ability of model checking in the presence of aggressive abstraction by applying them to check properties of several abstracted multi-threaded Java programs. These new capabilities are not specific to JPF and can be easily adapted to other model checking frameworks; we describe how this was done for the Bandera toolset.

Pasareanu, Corina S.↗

Feasibility of Surfactant-Free Supported Emulsion Liquid Membrane Extraction

Supported emulsion liquid membrane (SELM) is an effective means to conduct liquid-liquid extraction. SELM extraction is particularly attractive for separation tasks in the microgravity environment where density difference between the solvent and the internal phase of the emulsion is inconsequential and a stable dispersion can be maintained without surfactant. In this research, dispersed two-phase flow in SELM extraction is modeled using the Lagrangian method. The results show that SELM extraction process in the microgravity environment can be simulated on earth by matching the density of the solvent and the stripping phase. Feasibility of surfactant-free SELM (SFSELM) extraction is assessed by studying the coalescence behavior of the internal phase in the absence of the surfactant. Although the contacting area between the solvent and the internal phase in SFSELM extraction is significantly less than the area provided by regular emulsion due to drop coalescence, it is comparable to the area provided by a typical hollow-fiber membrane. Thus, the stripping process is highly unlikely to become the rate-limiting step in SFSELM extraction. SFSELM remains an effective way to achieve simultaneous extraction and stripping and is able to eliminate the equilibrium limitation in the typical solvent extraction processes. The SFSELM design is similar to the supported liquid membrane design in some aspects.

Hu, Shih-Yao B.↗

Preliminary Design, Feasibility and Cost Evaluation of 1- to 15-Kilometer Height Steel Towers

Design and construction of tall towers is an on-going research program of NASA. The agency has already done preliminary review in this area and has determined that multi-kilometer height towers are technically and economically feasible. The proposed towers will provide high altitude launch platforms reaching above eighty percent of Earth's atmosphere and provide tremendous gains in the potential energy as well as substantial reduction in aerodynamic drag. NASA has also determined that a 15-KM tower will have many useful applications in: (i)Meteorology,(ii)Oceanography, (iii)Astronomy, (iv)High Altitude Launch, (v)Physics Drop Tower, (vi) Biosphere Research, (vii) Nanotechnology, (viii) Energy/Power, (ix)Broadband Wireless Technology, (x)Space Transportation and (xi)Space Tourism.

Shanker, Ajay↗

Trailing Ballute Aerocapture: Concept and Feasibility Assessment

Trailing Ballute Aerocapture offers the potential to obtain orbit insertion around a planetary body at a fraction of the mass of traditional methods. This allows for lower costs for launch, faster flight times and additional mass available for science payloads. The technique involves an inflated ballute (balloon-parachute) that provides aerodynamic drag area for use in the atmosphere of a planetary body to provide for orbit insertion in a relatively benign heating environment. To account for atmospheric, navigation and other uncertainties, the ballute is oversized and detached once the desired velocity change (Delta V) has been achieved. Analysis and trades have been performed for the purpose of assessing the feasibility of the technique including aerophysics, material assessments, inflation system and deployment sequence and dynamics, configuration trades, ballute separation and trajectory analysis. Outlined is the technology development required for advancing the technique to a level that would allow it to be viable for use in space exploration missions.

Miller, Kevin L.↗

Engineering Feasibility and Trade Studies for the NASA/VSGC MicroMaps Space Mission

Knowledge of airborne CO concentrations is critical for accurate scientific prediction of global scale atmospheric behavior. MicroMaps is an existing NASA owned gas filter radiometer instrument designed for space-based measurement of atmospheric CO vertical profiles. Due to programmatic changes, the instrument does not have access to the space environment and is in storage. MicroMaps hardware has significant potential for filling a critical scientific need, thus motivating concept studies for new and innovative scientific spaceflight missions that would leverage the MicroMaps heritage and investment, and contribute to new CO distribution data. This report describes engineering feasibility and trade studies for the NASA/VSGC MicroMaps Space Mission. Conceptual studies encompass: 1) overall mission analysis and synthesis methodology, 2) major subsystem studies and detailed requirements development for an orbital platform option consisting of a small, single purpose spacecraft, 3) assessment of orbital platform option consisting of the International Space Station, and 4) survey of potential launch opportunities for gaining assess to orbit. Investigations are of a preliminary first-order nature. Results and recommendations from these activities are envisioned to support future MicroMaps Mission design decisions regarding program down select options leading to more advanced and mature phases.

Abdelkhalik, Ossama O.↗

Initial Feasibility Assessment of a High Altitude Long Endurance Airship

A high altitude solar powered airship provides the ability to carry large payloads to high altitudes and remain on station for extended periods of time. This study examines the feasibility of this concept. Factors such as time of year, latitude, wind speeds and payload are considered in establishing the capabilities of a given size airship. East and West coast operation were evaluated. The key aspect to success of this type of airship is the design and operation of the propulsion and power system. A preliminary propulsion/power system design was produced based on a regenerative fuel cell energy storage system and solar photovoltaic array for energy production. A modular system design was chosen with four independent power/propulsion units utilized by the airship. Results on payload capacity and flight envelope (latitude and time of year) were produced for a range of airship sizes.

Colozza, Anthony↗