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A government, industry, and university cooperative is developing an advanced hybrid electric city transit bus. Goals of this effort include doubling the fuel economy compared to current buses and reducing emissions to one-tenth of current EPA standards. Unique aspects of the vehicle's power system include the use of ultra-capacitors as an energy storage system, and a planned natural gas fueled turbogenerator developed from a small jet engine. Power from both the generator and energy storage system is provided to a variable speed electric motor attached to the rear axle. At over 15000 kg gross weight, this is the largest vehicle of its kind ever built using ultra-capacitor energy storage. This paper describes the overall power system architecture, the evolution of the control strategy, and its performance over industry standard drive cycles.

In February 2004 NASA released “The Vision for Space Exploration.” The important goals outlined in this document include extending human presence in the solar system culminating in the exploration of Mars. Unprocessed waste poses a biological hazard to crew health and morale. The waste processing methods currently under consideration include incineration, microbial oxidation, pyrolysis and compaction. Although each has advantages, no single method has yet been developed that is safe, recovers valuable resources including oxygen and water, and has low energy and space requirements. Thus, the objective of this project is to develop a low temperature oxidation process to convert waste cleanly and rapidly to carbon dioxide and water. In the Phase I project, TDA Research, Inc. demonstrated the potential of a low temperature oxidation process using ozone. In the current Phase II project, TDA and NASA Ames Research Center are developing a pilot scale low temperature ozone oxidation system.

Two separate experimental rigs used in tests on NASA and Zero-G Corporation aircrafts flying low-gravity trajectories, and in the NASA 2.2 Second Drop Tower have been developed to test the functioning of the Flexible Membrane Commode (FMC) concept under reduced gravity conditions. The first rig incorporates the flexible, optically opaque membrane bag and the second rig incorporates a transparent chamber with a funnel assembly for evacuation that approximates the size of the membrane bag. Different waste dispensers have been used including a caulking gun and flexible hose assembly, and an injection syringe. Waste separation mechanisms include a pair of wire cutters, an iris mechanism, as well as discrete slug injection. The experimental work is described in a companion paper. This paper focuses on the obtained results and analysis of the data.

Of the many competing technologies for resource recovery from solid wastes for long duration manned missions such as a lunar or Mars base, incineration technology is one of the most promising and certainly the most well developed in a terrestrial sense. Various factors are involved in the design of an optimum fluidized bed incinerator for inedible biomass. The factors include variability of moisture in the biomass, the ash content, and the amount of fuel nitrogen in the biomass. The crop mixture in the waste will vary; consequently the nature of the waste, the nitrogen content, and the biomass heating values will vary as well. Variation in feed will result in variation in the amount of contaminants such as nitrogen oxides that are produced in the combustion part of the incinerator. The incinerator must be robust enough to handle this variability. Research at NASA Ames Research Center using the fluidized bed incinerator has yielded valuable data on system parameters and variables.

Dielectric heating via microwave irradiation of contaminant laden sorbents offers distinct advantages in comparison to conventional thermal regeneration techniques. High temperatures may be achieved very rapidly because electromagnetic energy is absorbed directly by the sorbent material. A Technology Demonstrator, incorporating efficient rectangular waveguide based sorbent cartridge designs and effective microwave transmission systems was designed, fabricated and tested. Importantly, the performance of the Molecular Sieve 13X Waveguide Cartridge for the removal of water vapor, the Molecular Sieve 5A Waveguide Cartridge for the removal of CO2, and the Activated Carbon Waveguide Cartridge for removal of volatile organics from air, were each validated by successive sorption/ microwave desorption cycles.

This paper explains why a spark ignited gasoline engine, intake pressurized with three cascaded stages of turbocharging, was selected to power NASA's contemplated next generation of high altitude atmospheric science aircraft. Beginning with the most urgent science needs (the atmospheric sampling mission) and tracing through the mission requirements which dictate the unique flight regime in which this aircraft has to operate (subsonic flight @ >80 kft) we briefly explore the physical problems and constraints, the available technology options and the cost drivers associated with developing a viable propulsion system for this highly specialized aircraft. The paper presents the two available options (the turbojet and the turbocharged spark ignited engine) which are discussed and compared in the context of the flight regime.

Predictions from GLIMPS and HFAST design codes are compared with experimental data for the RE-1000 and SPRE free-piston Stifling engines. Engine performance and available power loss predictions are compared. Differences exist between GLIMPS and HFAST loss predictions. Both codes require engine-specific calibration to bring predictions and experimental data into agreement.

This paper summarizes the approach being used by the NASA Lewis Research Center for the long-term durability assessment of the Stirling engine hot-section components. The approach consists of: (1) preliminary Structural assessment; (2) development of a viscoplastic constitutive model to accurately determine material behavior under high-temperature thermomechanical loads, such as creep and plasticity interaction, and creep-ratcheting; (3) an experimental program to characterize material constants for the viscoplastic constitutive model, and for the short-time verification of specific materials of interest; (4) finite-element thermal analysis, and structural analysis using a viscoplastic constitutive model to obtain stress/strain/temperature at the critical location of the hot-section components for life assessment; and (5) development of a life prediction model applicable for long-term durability assessment at high temperatures.

A test facility at NASA Lewis has been assembled for evaluating: free-piston Stirling engine/linear alternator control options, and interaction with various electrical loads. This facility is based on a “SPIKE” engine/alternator. The paper describes the engine/alternator, a multi-purpose load system, a digital computer based load and facility control, and a data acquisition system with both steady-periodic and transient capability. Preliminary steady-periodic results are included for several operating modes of a digital AC parasitic load control. Preliminary results on the transient response to switching a resistive AC user load are discussed.

Under the Department of Energy's (DoE) Solar Thermal Technology Program, Sandia National Laboratories is evaluating heat engines for terrestrial Solar Distributed Heat Receivers. The Stirling engine has been identified by Sandia as one of the most promising heat engines for terrestrial applications. The Stirling engine has the potential to meet DoE's performance and cost goals [1]. The NASA Lewis Research Center is providing management of the Advanced Stirling Conversion System (ASCS) Project through an Interagency Agreement with the DoE. NASA Lewis is conducting technology development for Stirling convertors directed toward a dynamic power source for space applications. Space power requirements include high reliability with long life, high system efficiency and low vibration. The free-piston Stirling engine has the potential for both solar and nuclear space power applications.

The combination of an inherently robust asynchronous (induction) electrical machine with the rapid control of energy provided by a high frequency resonant ac link enables the efficient management of higher power levels with greater versatility. This could have a variety of applications from launch vehicles to all-electric automobiles. These types of systems utilize a machine which is operated by independent control of both the voltage and frequency. This is made possible by using an indirect field-oriented control method which allows instantaneous torque control in all four operating quadrants. Incorporating the ac link allows the converter in these systems to switch at the zero crossing of every half cycle of the ac waveform. This “zero loss” switching of the link allows rapid energy variations to be achieved without the usual frequency proportional switching loss.

To support the Space Exploration Initiative, studies were performed to investigate and characterize Dynamic Isotope Power System (DIPS) alternatives for the surface mission elements associated with a lunar base and subsequent manned Mars expedition. A key part of this characterization was to determine how the mission environment affects system design. The impact of shielding to provide astronaut protection from power system radiation was also examined. Impacts of mission environment and shielding were examined for two representative DIPS types (closed Brayton cycle and Stirling cycle converters). Mission environmental factors included: (1) thermal background; (2) dust and atmospheric corrosion; (3) meteoroid damage; and (4) presence of an atmosphere on Mars. Physical effects of these factors on thermal power systems were identified and their parametric range associated with the mission and mission environment were determined.

The National Aeronautics and Space Administration (NASA) is funding research to characterize Stirling machine thermodynamic losses. NASA's primary goal is to improve Stirling design codes to support engine development for space and terrestrial power. However, much of the fundamental data is applicable to Stirling cooler and heat pump applications. The research results are reviewed. Much has been learned about oscillating-flow hydrodynamics, including laminar/turbulent transition, and tabulated data has been documented for further analysis. Now, with a better understanding of the oscillating-flow field, it is time to begin measuring the effects of oscillating flow and oscillating pressure level on heat transfer in heat exchanger flow passages and in cylinders. This critical phase of the work is just beginning.

Free-piston Stirling power converters are a candidate for high capacity space power applications. The Space Power Research Engine (SPRE), a free-piston Stirling engine coupled with a linear alternator is being tested at the NASA Lewis Research Center in support of the Civil Space Technology Initiative. The SPRE is used as a test bed for evaluating converter modifications which have the potential to improve converter performance and for validating computer code predictions. Reducing the number of cooler tubes on the SPRE has been identified as a modification with the potential to significantly improve power and efficiency. This paper describes experimental tests designed to investigate the effects of reducing the number of cooler tubes on converter power, efficiency and dynamics. Presented are test results from the converter operating with a reduced number of cooler tubes and comparisons between this data and both baseline test data and computer code predictions.

The steady-state and dynamic performance of a candidate aircraft power distribution system is considered. The system features distribution of both single phase 20-kHz and three-phase 400-Hz power. It is shown that unlike some other recent 20-kHz systems, the power quality of the 20-kHz bus is not a concern due to the use of a synchronous bi-directional rectifier (SBR) as the primary interface to the 20-kHz bus. In addition to showing that the system behaves adequately in the steady-state, the dynamic performance of the system is considered during step changes in load, bolted faults, and sudden variations in jet engine speed.

Jet Engines may experience severe vibration due to the sudden imbalance caused by blade failure. This research investigates employment of on board magnetic bearings or piezolectric actuators to cancel these forces in flight. This operation requires identification of the source of the vibrations via an expert system, determination of the required phase angles and amplitudes for the correction forces, and application of the desired control signals to the magnetic bearings or piezo electric actuators. This paper will show the architecture of the software system, details of the control algorithm used for the sudden imbalance correction project described above, and the laboratory test results.

The Spacelab Life Sciences 2 (SLS-2) mission became NASA's longest duration Shuttle mission, lasting fourteen days, when Columbia landed on November 1, 1993. Located within the Spacelab were a total of 48 laboratory rats which were housed in two Research Animal Holding Facilities (RAHFs) developed by the Space Life Sciences Payloads Office (SLSPO) at Ames Research Center. In order to properly maintain the health and well-being of these important research animals, sufficient quantities of food and water had to be available for the duration of the mission. An Inflight Refill Unit was developed by the SLSPO to replenish the animals' drinking water inflight using the Shuttle potable water system in the middeck galley as the source of additional water. The Inflight Refill Unit consists of two major subsystems, a Fluid Pumping Unit (FPU) and a Collapsible Water Reservoir (CWR).

This report discusses application of a new lightweight carbon-carbon (C-C) space radiator technology developed under the NASA Civil Space Technology Initiative (CSTI) High Capacity Power Program to a 20 kWe lunar based power system. This system comprises a nuclear (SP-100 derivative) heat source, a Closed Brayton Cycle (CBC) power conversion unit with heat rejection by means of a plane radiator. The new radiator concept is based on a C-C composite heat pipe with integrally woven fins and a thin walled metallic liner for containment of the working fluid. Using measured areal specific mass values (1.5 kg/m2) for flat plate radiators, comparative CBC power system mass and performance calculations show significant advantages if conventional heat pipes for space radiators are replaced by the new C-C heat pipe technology.

A high fidelity, direct-interface, fusible heat sink for cooling astronauts during extravehicular activity was constructed and tested. The design includes special connectors that allow the coolant loop to be directly connected to the fusible material, in this case water. Aspects tested were start-up characteristics, cooling rate, and performance during simulated heat loads. A simplified math model was used to predict the effect of increasing the effective thermal conductivity on heat sink freezing rate. An experiment was designed to measure the effective thermal conductivity of a water/Aluminum foam system, and full gravity tests were conducted to compare the freezing rates of water and water/foam systems. This paper discusses the results of these efforts.

Dante II, an eight-legged walking robot developed by the Dante project, explored the active volcanic crater of Mount Spurr in July 1994. In this paper, we describe the operator interfaces and the network-based participation methods used during the Dante II mission. Both virtual environment and multi-modal operator interfaces provided mission support for supervised control of Dante II. Network-based participation methods including message communications, satellite transmission, and a World-Wide Web server enabled remote science and public interaction. We believe that these human-machine interfaces represent a significant advance in robotic technologies for exploration.