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The Space Shuttle Orbiter Atmospheric Revitalization Pressure Control System (ARPCS) and the Fuel Cell System (FCS) use a hot wire anemometer type of gas mass flow sensor for flow measurement. In the ARPCS oxygen and nitrogen mass flows are measured and in the FCS oxygen and hydrogen mass flows are measured. The existing flow sensors suffer from certain accuracy limitations and potential failure modes. A new type of commercially developed solid state micro-machined silicon gas mass flow sensor developed by Honeywell was adapted to allow the technology to be assessed for the application. A demonstration test program has been conducted to evaluate the performance characteristics of the new sensor for space system applications and environments. The testing was sponsored by the National Aeronautics and Space Administration (NASA) at the Johnson Space Center (JSC).

The early external active thermal control system (EEATCS) is designed to cool the U.S. Laboratory (USL), during early assembly stages of the International Space Station (ISS), to support assured early research (AER). The ISS is assembled on orbit over a period of about 5 years and over 40 stages. During later stages, about half way through the assembly, the USL is cooled by the external active thermal control system (EATCS), but that system is not available during early stages. To assure research, during early stages, the USL is cooled by the EEATCS; at a later stage, the USL cooling is switched to EATCS. During early stages, electric power is provided by the integrated truss segment (ITS) P6, which consists of photovoltaic (PV) arrays to convert sunlight into direct current power, an integrated equipment assembly (IEA) to support hardware required to store and condition electric power, and a long spacer to provide spacing between outboard power modules.

This paper presents classical control algorithms design for the solar array pointing system of the Space Station Freedom (SSF). This development is based on continuous, rigid body model of the solar array beta gimbal assembly (BGA) containing both linear and nonlinear dynamics due to various friction components. Optimum sets of controller parameters were obtained based on integral performance criteria through EASY5 simulations in the time domain. Classical sensitivity studies conducted in EASY5 indicated that the worst potential problem (possible system instability) is due to the variations in the electric motor dead-zone characteristics. After incorporation of an alternate static friction model, a Taguchi based tolerance design sensitivity study was conducted. Results indicated that the voltage variance, torque sensitivity constant and the motor resistance are the most important tolerances investigated with respect to integral square error (ISE).

Mathematical modeling of the Ni-H2 cell based on the fundamental electrochemical processes is necessary for accurately simulating the battery behavior on Space Station Freedom. Accurate predictions are incorporated as part of the development of the Space Station Electric Power System simulation. This simulation will be used to develop and test control algorithms which will maximize the available power in the most efficient way. This is a deviation from the approach used on smaller satellite power systems which are designed with substantial margin. Hence, the use of an empirical battery model is not feasible due to its low fidelity. This paper covers the electrochemical theory related to the Ni-H2 cells, and the analysis of experimental data used to develop relations between the cell state of charge and certain cell properties. Theoretical results are compared against well-documented experimental data.

The Rocketdyne Division of Rockwell International Corporation is currently researching and evaluating the use of Artificial Intelligence and in particular Expert System technologies for the monitoring of large space-based electric power systems such as NASA's Space Station Freedom (SSF). Power System Security of space borne and lunar based electrical power systems provide unique challenges to power system software design engineers. The major responsibility of Power System Security is the monitoring of the state of health of the Power Distribution System. The role of system security is to ensure that uninterrupted electrical power of high quality is distributed to all the load centers [1]. Voltage, current, power source reliability, and power quality are main components that describe the integrity of an electrical power system and fall into the area of security control.

Future space exploration missions will require new and innovative approaches to supplying electric power. Due to the very high transportation cost associated with the lunar and Mars missions, the mass of these power systems will be a critical factor. Power systems currently being considered for these applications include both nonnuclear and nuclear systems. For lunar applications, the 354-hour-long nighttime presents a formidable challenge to energy storage technology for nonnuclear power systems. Because of their low energy densities, energy storage systems can be prohibitively massive at higher power levels. Consequently, the nonnuclear power systems may be limited to low-power mission applications on the surface of the Moon. Eliminating or greatly reducing the need for energy storage makes these systems competitive with nuclear power systems. A Free Electron Laser (FEL) power system based in lunar orbit was examined for providing power by beaming energy to the lunar surface.

An integral space power concept provides both the electrical power and propulsion from a common heat source and offers superior performance capabilities over conventional orbital insertion using chemical propulsion systems. This paper describes a hybrid (bimodal) system concept based on a proven, inherently safe solid fuel form for the high temperature reactor core operation and rugged planar thermionic energy converter for long-life steady state electric power production combined with NERVA-based rocket technology for propulsion. The integral system is capable of long-life power operation and multiple propulsion operations. At an optimal thrust level, the integral system can maintain the minimal delta-V requirement while minimizing the orbital transfer time. A trade study comparing the overall benefits in placing large payloads to GEO with the nuclear electric propulsion option shows superiority of nuclear thermal propulsion.

The Dynamic Isotope Power System (DIPS) Demonstration Program is currently focused on the development of a standardized 2.5-kWe portable generator for multiple applications on the lunar or Martian surface. An optimum system configuration has been developed for the 2.5-kWe DIPS module that provides a system with a radiator area which is small and manageable without significantly impacting the system mass, efficiency, and technological risk. The 2.5-kWe DIPS module configuration was developed based on a systematic series of studies. Initially, technology breakpoints in the DIPS component and subsystem designs were identified. Based on the technology assessments, the maximum design temperature for the system was selected and various system and subsystem configurations were evaluated. Finally, the subsystem and system designs for the selected configuration were optimized using a detailed system design optimization computer code.

Significant advancements have been made in the development of lightweight, high performance, carbon-carbon heat pipes for space nuclear power applications. The subject program has progressed through the concept definition and feasibility analysis stages to the current test article component fabrication and assembly phase. This concept utilizes a carbon-carbon tube with integrally woven fins as the primary structural element and radiative surface, Nb-1Zr liners to contain a potassium working fluid, and welded end caps and fill tubes. Various tests have been performed in the development of suitable liner bonding techniques and in the assessment of material stability.

Tests using the Thermogravimetric Analysis (TGA) techniques showed this approach to be a relatively simple and rapid method for assessing the affinity of trace contaminants for a solid amine, CO2 sorbent. Regenerative CO2 sorbents are applicable to many space systems air revitalization applications for removal of CO2. Sorbents may be chemically non-specific as regards reversible adsorption-desorption, chemicals other than CO2 can be regeneratively removed from spacecraft air. These other chemicals, present in trace amounts, may also interfere with the primary CO2 removal function. TGA test procedures were developed to determine adsorption-desorption behavior of trace contaminants on a regenerative solid amine sorbent: Hamilton Standard, material - C (HS-C).

Operating procedures for keyboard data entry in avionics are analyzed. The type of information being entered may be identified either before or after entry of the alphanumeric characters. The keys which are used to identify the type of data may be collected in a centralized control unit or distributed throughout the cockpit adjacent to the associated displays. The Collins NCS-31 and the King KCU 565 navigation and control systems are discussed as illustrations of two sets of choices for operating procedures. Emphasis is placed upon correspondence between the thought processes associated with data entry and the pilot's actions in entering data.

The need for evaluating and optimizing airframes of advanced aircraft configurations with exceptional speed and accuracy has resulted in the development of highly sophisticated computerized techniques. Sensitivity of these programs to advanced materials, construction types, aeroelasticity, structural dynamics, configuration geometry, airloads, missions, and performance has all but obsoleted the statistical approach to the problem solution. The competitive nature of the field has also placed unusually severe demands on calendar time available for such evaluations. This has resulted in the development of integrated analytical computer programs that have the required sensitivity and rapid turnaround time to face the competitive nature of today's environment.