Liquid oxygen/liquid hydrogen auxiliary power system thruster investigation

The design, fabrication, and demonstration of a 111 newton (25 lb) thrust, integrated auxiliary propulsion system (IAPS) thruster for use with LH2/LO2 propellants is described. Hydrogen was supplied at a temperature range of 22 to 33 K (40 to 60 R), and oxygen from 89 to 122 K (160 to 220 R). The thruster was designed to operate in both pulse mode and steady-state modes for vehicle attitude control, space maneuvering, and as an abort backup in the event of failure of the main propulsion system. A dual-sleeve, tri-axial injection system was designed that utilizes a primary injector/combustor where 100 percent of the oxygen and 8 percent of the hydrogen is introduced; a secondary injector/combustor where 45 percent of the hydrogen is introduced to mix with the primary combustor gases; and a boundary layer injector that uses the remaining 45 percent of the hydrogen to cool the thrust throat/nozzle design. Hot-fire evaluation of this thruster with a BLC injection distance of 2.79 cm (1.10 in.) indicated that a specific impulse value of 390 sec can be attained using a coated molybdenum thrust chamber. Pulse mode tests indicated that a chamber pressure buildup to 90 percent thrust can be achieved in a time on the order of 48 msec. Some problems were encountered in achieving ignition of each pulse during pulse trains. This was interpreted to indicate that a higher delivered spark energy level ( 100 mJ) would be required to maintain ignition reliability of the plasma torch ignition system under the extra 'cold' conditions resulting during pulsing

Study of advanced techniques for determining the long-term performance of components

A study was conducted of techniques having the capability of determining the performance and reliability of components for spacecraft liquid propulsion applications for long term missions. The study utilized two major approaches; improvement in the existing technology, and the evolution of new technology. The criteria established and methods evolved are applicable to valve components. Primary emphasis was placed on the propellants oxygen difluoride and diborane combination. The investigation included analysis, fabrication, and tests of experimental equipment to provide data and performance criteria

Development of a novel gerotor pump for lubrication systems of aeronautic engines

The technology of lubrication systems for aircrafts engines has seen significant development during the history of aeronautics and has progressed in parallel with the evolution of the engines themselves. Starting from the first, wetsump schemes derived from automotive applications, more complex systems and components have been introduced. The progressive increase of aeronautic engines’ power and speed, as well as that of the maximum operative altitude of the aircraft, have increased the lubricant flow rate required to avoid severe mechanical issues that can cause dangerous conditions for the vehicle and its users. Currently, the main focus on the development of novel lubrication pumps is aimed at reducing the pumps’ weight and envelope while maintaining, or possibly increasing, their reliability. The first two objective could be pursued by searching for novel pump types and/or increasing the pump speed in order to downsize its required capacity, but the low-pressure environment, typical of the lubrication circuits, over imposes a few, severe, limitations to avoid cavitation occurrence that decrease the effectiveness of this approach. The central aim of the presented research, performed within the program “Greening the Propulsion”, is to provide a theoretical framework to help in the development of a novel gerotor pump for the lubrication of aeronautic engines.The first step of the research involves the study of the state of the art of aeronautic engines’ lubrication systems, providing particular care to the effect that any design choice and possible operational condition may have on the lubrication pump design. Hence, the state of the art for gerotor pumps is investigated; results of this study are used, along with catalogue comparisons, to build simplified sizing tools to perform a benchmarking activity involving gerotors and other low pressure pumps type. This activity, performed to position gerotor pumps in the aeronautic engine lubrication market, is then used as a starting point to highlight the weak points of gerotors traditional design and to propose some possible solutions to enhance the pumps performances. To study the outcomes of these modifications, a rigorous theoretical framework is required; sizing and modeling criteria, based on the theory of gearing and compressible fluids, are hence detailed and used to build an Automatic Design and Simulation Framework, able to automatically design, validate and simulate a novel gerotor pump given a minimum number of geometrical and physical input parameters. This design and simulation tool is then used to evaluate the performance boost provided by the proposed variations and to optimize the gears profiles by pairing it with a multiobjective algorithm based on evolutionary strategies. Another critical component of any lubrication system is the pressure relief valve used to avoid the occurrence of dangerous conditions for the pipes integrity. A side activity involving the study of a preliminary sizing tool for pressure relief valve is hence performed. A preliminary design framework is presented and discussed, highlighting the importance of the valve discharge coefficient. To study its dependence on the valve’s geometry, a lengthy CFD simulation campaign is performed varying the poppet shape and the fluid Reynolds’ number. Results are hence discussed and used inside the design framework

Advanced hydraulic systems for next generation of skid steer loaders

Fluid power systems have been extensively used in off highway applications like skid steer loaders, wheel loaders, excavators since many years. Work has been done by both industry and academia to improve efficiency, reduce noise and leakages in these systems. With increasing competition in the market, importance is now also given to operator comfort and machine productivity in off highway applications. Mobile, off – highway vehicles like Skid-steer loaders are widely used in labour saving applications like loading earth into a truck, dig and move material on construction sites to, clean roads, clear snow from roads etc. To carry out these jobs in limited spaces, skid steer loaders need tight turning radius. For this reason, these machines have a short wheelbase which prevents the use of suspensions in these vehicles. The absence of a suspension system exposes the vehicle to ground vibrations of high magnitude and low frequency. Vibrations reduce operator comfort, productivity and life of components. This thesis will discuss control strategies for vibration damping of skid steer loader using the hydraulic boom cylinder as the active suspension element, which is equivalent to a spring–damper. Along with vibrations, the machine productivity is also hampered by material spillage which is caused by the tilting of the bucket due to the extension of the boom. This dissertation will discuss the development of a robust path-planning control algorithm which adapts to the position of the boom to maintain a level load to achieve bucket self-leveling. Another reason for reduced productivity in skid steer loaders is slow in site travel speeds. This dissertation also concentrates on reducing the in-job cycle time by developing a control strategy to smooth speed shift the drive motors keeping the pump flow constant. To synthesize these proposed control algorithms, high fidelity hydraulic and mechanical models of the skid steer loader are created. Ultimately, the control algorithms derived in this dissertation help in improving operator comfort and machine productivity

Advances in Fluid Power Systems

The main purpose of this Special Issue of “Advances in Fluid Power Systems” was to present new scientific work in the field of fluid power systems for hydraulic and pneumatic control of machines and devices used in various industries. Advances in fluid power systems are leading to the creation of new smart devices that can replace tried-and-true solutions from the past. The development work of authors from various research centres has been published. This Special Issue focuses on recent advances and smart solutions for fluid power systems in a wide range of topics, including: • Fluid power for IoT and Industry 4.0: smart fluid power technology, wireless 5G connectivity in fluid power, smart components, and sensors.• Fluid power in the renewable energy sector: hydraulic drivetrains for wind power and for wave and marine current power, and hydraulic systems for solar power. • Hybrid fluid power: hybrid transmissions, energy recovery and accumulation, and energy efficiency of hybrid drives.• Industrial and mobile fluid power: industrial fluid power solutions, mobile fluid power solutions, eand nergy efficiency solutions for fluid power systems.• Environmental aspects of fluid power: hydraulic water control technology, noise and vibration of fluid power components, safety, reliability, fault analysis, and diagnosis of fluid power systems.• Fluid power and mechatronic systems: servo-drive control systems, fluid power drives in manipulators and robots, and fluid power in autonomous solutions

Variable Structure Feedback Control with Application to Spacecraft with Small Thrust Propulsion Systems

Small spacecrafts requiring small propulsion systems are becoming more popular for low Earth orbit. It is important for these research satellites to have accurate guidance and control systems. Small propulsion systems will also be beneficial for multiple small spacecrafts used future exploration expeditions beyond low Earth orbit. These small spacecrafts benefit from the simplicity of low thrust cold gas propulsion systems. Additionally, large spacecrafts using low thrust, high specific impulse propellants for main propulsion systems, such as ion engines, allow longer and more flexible missions, including Earth orbiting spacecraft and interplanetary spacecraft. In order to extend the life of future planetary exploration missions, it becomes necessary to use In-Situ Resource Utilization (ISRU) to be able to extract resources such as water, oxygen, propellants, and building materials from the local target environment. Small free flying vehicles can be used for quickly surveying planetary surfaces in order to search for potential resource locations. These surveying vehicles can also use such extracted propellants if their propulsion system is designed for it. Cold gas propulsion provides a flexible system to use locally extracted or manufactured propellants. This dissertation investigates nonlinear feedback control techniques for spacecraft with low thrust, cold gas thrust, and spacecraft with cold gas thrust. A model for a cold gas propulsion system is developed for designing control systems for multiple types cold gas thrusters. The model is also used for testing control algorithms in simulation. The cold gas model is validated from a cold gas propulsion hardware testing, and a control law is tested on hardware

Hypergolic Propellants: The Handling Hazards and Lessons Learned from Use

Several unintentional hypergolic fluid related spills, fires, and explosions from the Apollo Program, the Space Shuttle Program, the Titan Program, and a few others have occurred over the past several decades. Spill sites include the following government facilities: Kennedy Space Center (KSC), Johnson Space Center (JSC), White Sands Test Facility (WSTF), Vandenberg Air Force Base (VAFB), Cape Canaveral Air Force Station (CCAFS), Edwards Air Force Base (EAFB), Little Rock AFB, and McConnell AFB. Until now, the only method of capturing the lessons learned from these incidents has been "word of mouth" or by studying each individual incident report. Through studying several dozen of these incidents, certain root cause themes are apparent. Scrutinizing these themes could prove to be highly beneficial to future hypergolic system testing, checkout, and operational use

Integrated control and health management. Orbit transfer rocket engine technology program

To insure controllability of the baseline design for a 7500 pound thrust, 10:1 throttleable, dual expanded cycle, Hydrogen-Oxygen, orbit transfer rocket engine, an Integrated Controls and Health Monitoring concept was developed. This included: (1) Dynamic engine simulations using a TUTSIM derived computer code; (2) analysis of various control methods; (3) Failure Modes Analysis to identify critical sensors; (4) Survey of applicable sensors technology; and, (5) Study of Health Monitoring philosophies. The engine design was found to be controllable over the full throttling range by using 13 valves, including an oxygen turbine bypass valve to control mixture ratio, and a hydrogen turbine bypass valve, used in conjunction with the oxygen bypass to control thrust. Classic feedback control methods are proposed along with specific requirements for valves, sensors, and the controller. Expanding on the control system, a Health Monitoring system is proposed including suggested computing methods and the following recommended sensors: (1) Fiber optic and silicon bearing deflectometers; (2) Capacitive shaft displacement sensors; and (3) Hot spot thermocouple arrays. Further work is needed to refine and verify the dynamic simulations and control algorithms, to advance sensor capabilities, and to develop the Health Monitoring computational methods

Digital displacement hydrostatic transmission systems

Digital Displacement pumps and motors are a new type of hydraulic machine, in which fluid commutation and displacement control are achieved by solenoid actuated valves under the command of a microprocessor, rather than mechanical means. The thesis is that radial piston machines, built according to this principle, offer energy efficiency and control advantages over variable stroke axial piston pumps, when applied to hydrostatic vehicle transmissions.Experimental results on the efficiency of prototypes are analysed and compared to published results from swashplate machines, showing an improvement in energy efficiency. Loss models are proposed and compared with experiment.A Digital Displacement motor suitable for propelling a vehicle is described and the design and development of the mechanics, electro-magnetics and embedded software are described. Experimental results are also presented, illustrating the performance of a demonstrator vehicle driven by the motor, in particular demonstrating the closed-loop regulation of vehicle speed using motor displacement control.A demonstrator vehicle is described which features a hydrostatic transmission using both a Digital Displacement pump and an axial piston motor. Experimental results of pump performance are presented with specific focus on vehicle propel. A control technique is described which increases the sensitivity of the pump at low speeds. Results are presented of tests on the prototype transmission system, focussing on the time-domain system dynamics. A computer simulation model of the vehicle is presented and results compared to experiment