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Pressurized systems' development and operation are presented for effective use in design. Article reviews and accesses current design practices to establish guidance to achieve greater consistency in design, product, and greater efficiency in design effort.
A survey of studies into hazards associated with closed or pressurized system rupture and preliminary guidelines for the performance design of primary, secondary, and protective receptors of these hazards are provided. The hazards discussed in the survey are: blast, fragments, ground motion, heat radiation, biological, and chemical. Performance guidelines for receptors are limited to pressurized systems that contain inert gas. The performance guidelines for protection against the remaining unaddressed degenerative hazards are to be covered in another study.
The general physics of pressure transients, sources of pressure transients, and major factors influencing pressure transients are addressed. Mitigation strategies that aid in reducing the magnitude of pressure transients are discussed. Methods to characterize pressure transients and their effects on the structure are presented. Case studies illustrate the structural analysis methodology used to predict the structural dynamic response. The structural verification process involves formulating acceptance and qualification programs, which requires knowledge of the stress state. The maximum expected operating pressure (MEOP) is established such that the maximum stress produced by static pressure is equivalent to the maximum stress at the same critical location produced by the combined effect of steady state pressure and the magnitude of the pressure transient. A roadmap on how to treat transient pressures in the structural verification process of spaceflight pressurized systems (e.g., valves, lines, pressure vessels, pressurized structures) is presented.
The Space Shuttle Orbit Maneuvering System and Reaction Control System are pressure-fed rocket propulsion systems utilizing earth storable hypergolic propellants and featuring engines of 6000 lbs and 900 lbs thrust, respectively. The helium pressurization system requirements for these propulsion systems are defined and the current baseline pressurization systems are described. An advanced helium pressure regulator capable of meeting both OMS and RCS helium pressurization system requirements is presented and its operating characteristics and predicted performance characteristics are discussed.
The use of Tri‐gas in rocket propulsion systems is somewhat of a new technology. This paper defines Tri‐gas as a mixture of gases composed largely of helium with a small percentage of a stoichiometric mixture of hydrogen and oxygen. When exposed to a catalyst the hydrogen and oxygen in the mixture combusts, significantly raising the temperature of the mixture. The increase in enthalpy resulting from the combustion process significantly decreases the required quantity of gas needed to pressurize the ullage of the vehicle propellant tanks. The objective of this effort was to better understand the operating characteristics of Tri‐gas in a pressurization system with low temperature applications. In conjunction with ongoing programs at NASA Marshall Space Flight Center, an effort has been undertaken to evaluate the operating characteristics of Tri‐gas through modeling and bench testing. Through improved understanding of the operating characteristics, the risk of using this new technology in a launch vehicle propulsion system was reduced. Bench testing of Tri‐gas was a multistep process that targeted gas characteristics and performance aspects that pose a risk to application in a pressurization system. Pressurization systems are vital to propulsion system performance. Keeping a target ullage pressure in propulsions tanks is necessary to supply propellant at the conditions and flow rates required to maintain desired engine functionality. The first component of testing consisted of sampling Tri‐gas sources that had been stagnant for various lengths of time in order to determine the rate at which stratification takes place. Second, a bench test was set up in which Tri‐gas was sent through a catalyst bed. This test was designed to evaluate the performance characteristics of Tri‐gas, under low temperature inlet temperatures, in a flight‐like catalyst bed reactor. The third, most complex, test examined the performance characteristics of Tri‐gas at low temperature temperatures in a test configuration built to more closely resemble a vehicle pressurization system. The results of these bench tests address various risks that all relate to underperformance of Tri‐gas pressurization systems.
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Pressurization system for liquid rockets, analyzing inert weight and complexity reduction using Saturn 5 S-4B stage
Pressurization system for liquid rockets, analyzing inert weight and complexity reduction using Saturn 5 S-4B stage
A pressurization system model was developed for a crossfeed subscale water test article using the EASY5 modeling software. The model consisted of an integrated tank pressurization and pressurization line model. The tank model was developed using the general purpose library, while the line model was assembled from the gas dynamic library. The pressurization system model was correlated to water test data obtained from nine test runs conducted on the crossfeed subscale test article. The model was first correlated to a representative test run and frozen. The correlated model was then used to predict the tank pressures and compared with the test data for eight other runs. The model prediction showed excellent agreement with the test data, allowing it to be used in a later study to analyze the pressurization system performance of a full-scale bimese vehicle with cryogenic propellants.
Analysis of recirculating type external pressurization systems for use in pressure control of cryogenic hydrogen, oxygen, and nitrogen storage systems
Two transient operational modes of the X-34 pressurization system were analyzed using the ROCket Engine Transition Simulation (ROCETS) program. The first operational mode considers the normal operation. For the engine burn period, the required helium mass and pressure of each propellant tank were calculated. In the second case, the possibility of failure of the pressurization system solenoid valves, its consequence on the over-pressurization, and simultaneous operation of pressurization and vent/relief systems were evaluated.
A pressurization system model was developed for a generic bimese Two-Stage-to-orbit Reusable Launch Vehicle using a cross-feed system and operating with densified propellants. The model was based on the pressurization system model for a crossfeed subscale water test article and was validated with test data obtained from the test article. The model consists of the liquid oxygen and liquid hydrogen pressurization models, each made up of two submodels, Booster and Orbiter tank pressurization models. The tanks are controlled within a 0.2-psi band and pressurized on the ground with ambient helium and autogenously in flight with gaseous oxygen and gaseous hydrogen. A 15-psi pressure difference is maintained between the Booster and Orbiter tanks to ensure crossfeed check valve closure before Booster separation. The analysis uses an ascent trajectory generated for a generic bimese vehicle and a tank configuration based on the Space Shuttle External Tank. It determines the flow rates required to pressurize the tanks on the ground and in flight, and demonstrates the model's capability to analyze the pressurization system performance of a full-scale bimese vehicle with densified propellants.
An analysis of transient pressures in externally pressurized cryogenic hydrogen and oxygen tanks was conducted and the effects of design variables on pressure response determined. The analysis was conducted with a computer program which solves the compressible viscous flow equations in two-dimensional regions representing the tank and external loop. The external loop volume, thermal mass, and heat leak were the dominant design variables affecting the system pressure response. No significant temperature stratification occurred in the fluid contained in the tank.
Langley Research Center pressure systems are being recertified to ensure safe operation of these systems. The procedures for recertifying these pressure systems are reviewed. Generally, the analysis and inspection requirements outlined in the appropriate national consensus codes are followed. In some instances where the requirements of these codes are not met. The systems are analyzed further, repaired, modified and/or tested to demonstrate their structural integrity.
NASA has provided little guidance for determining and implementing appropriate filtration of spaceflight propulsion and pressurant systems. Additionally, industry standards typically used for building and verifying filter performance are antiquated and lack applicability to propulsion systems. The NASA Engineering and Safety Center (NESC) was requested to perform a gap analysis, identify risks, and develop a mitigation plan for spaceflight propulsion filtration. This report contains the outcome of the NESC analysis.
Guidelines for the successful design of pressurization systems for main propulsion, auxiliary propulsion, and attitude control systems for boosters, upper stages, and spacecraft were presented, drawing on the wealth of design experience that has accumulated in the development of pressurization systems for liquid rockets operational in the last 15 years. The design begins with a preliminary phase in which the system requirements are received and evaluated. Next comes a detail-design and integration phase in which the controls and the hardware components that make up the system are determined. The final phase, design evaluation, provides analysis of problems that may arise at any point in the design when components are combined and considered for operation as a system. Throughout the monograph, the design tasks are considered in the order and manner in which the designer must handle them.
A transient model of the propulsion test article (PTA) helium pressurization system was developed using the generalized fluid system simulation program (GFSSP). The model included pressurization lines from the facility interface to the engine purge interface and liquid oxygen (lox) and rocket propellant-1 (RP-1) tanks, the propellant tanks themselves including ullage space, and propellant feed lines to their respective pump interfaces. GFSSP's capability was extended to model a control valve to maintain ullage pressure within a specified limit and pressurization processes such as heat transfer between ullage gas, propellant, and the tank wall as well as conduction in the tank wall. The purpose of the model is to predict the flow system characteristics in the entire pressurization system during 80 sec of lower feed system priming, 420 sec of fuel and lox pump priming, and 150 sec of engine firing.
A transient model of the Propulsion Test Article 1 (PTA1) Helium Pressurization System was developed using the Generalized Fluid System Simulation Program (GFSSP). The model included feed lines from the facility interface to the engine purge interface and Liquid Oxygen (LOX) and Rocket Propellant 1 (RP-1) tanks, the propellant tanks themselves including ullage space and propellant feed lines to their respective pump interfaces. GFSSPs capability was extended to model a control valve to maintain ullage pressure within a specified limit and pressurization processes such as heat transfer between ullage gas, propellant and the tank wall. The purpose of the model is to predict the flow system characteristics in the entire pressurization system during 80 seconds of pre-pressurization operation, 420 seconds of pressurization stand-by operation and 150 seconds of engine operation. Subsequent to the work presented here, the PTA1 model has been updated to include the LOX and RP-1 pumps, while the pressurization option itself has been modified to include the effects of mass transfer. This updated model will be compared with PTA1 test data as it becomes available.