The elastomeric diaphragm tanks have been in use since the early stages of space flight, and Pressure Systems, Inc. (PSI) has been a long time participant in their application in the Aerospace Industry. This paper presents the history of the elastomeric diaphragm tanks at PSI, covering the program heritage, the evolution of diaphragm material, the tank design philosophy, the manufacturing process, and the testing heritage. Comparison of a diaphragm tank with a simple surface tension Propellant Management Device (PMD) is also made to illustrate the different approaches to their usage.
A titanium-lined, composite overwrapped pressure vessel (COPV) for helium pressurant storage was designed for a commercial spacecraft. This tank has a nominal propellant volume of 81.4 liters (4,967 cubic inches) and a nominal weight of 11.7 kg (25.8 pounds). The maximum expected operating pressure is 331 bar (4,800 psi). Proof pressure requirement is 414 bar (6,000 psi), and the minimum burst pressure is 497 bar (7,200 psi). A complete qualification program was conducted to verify the tank design, including a destructive burst pressure test. The tank successfully completed qualification testing on 03 April, 2002. The production program is in progress. Over 10 flight tanks have been manufactured to date.
For spacecraft propellant tank applications, an all-metal spherical pressure vessel is always the most mass-efficient construction. However, on board spacecrafts where available space is limited, spherical tanks or tanks with spherical heads are not the most efficient packaging solution. This paper summarizes some of the space-efficient tank designs currently being employed or considered by the aerospace industry, including tanks with ellipsoidal heads, common bulkhead tanks, and nested tanks. We will also touch upon the feasibility of Propellant Management Devices (PMDs) within these tanks. Due to the summary nature of this paper, no design details are provided.
A titanium-lined composite overwrapped pressure vessel (COPV) for Xenon storage was designed for the ETS VIII spacecraft. This tank has a nominal propellant volume of 50 liters (3050 cubic inches) and a nominal weight of 7 kg (15.4 pounds). The maximum expected operating pressure is 150 bar (2175 psi), 50 cycles. Proof pressure requirement is 187.5 bar (2719 psi), 5 cycles, and the minimum burst pressure is 225 bar (3264 psi). The tank is designed to hold 89 kg (196 pounds) of Xenon. The ETS VIII Xenon tank design is based on a flight-qualified Xenon tank to take advantage of its design and flight heritage. To minimize risk, the ETS VIII Xenon tank is designed to use only existing manufacturing technology. Manufacturing cost is minimized by using existing tooling. Nonlinear material and geometric modeling techniques were used to analyze this tank. Stress analysis showed positive margins of safety for pressure cycle fatigue, vibration fatigue and minimum burst pressure over the design requirements. Development and Qualification testing verified the design margins and showed the design analyses to be conservative. The liner is constructed from 6AL-4V titanium. This material was chosen due to heritage and for its superb manufacturability, relative high strength, excellent corrosion and oxidation resistance characteristics, good low and high cycle fatigue characteristics, and competitive manufacturing cost. The overwrap consists of high strength Torayca T1000GB carbon fiber and Epon 826 cured resin system. Several composite layers were applied, including helical and hoop wraps. A leak-before-burst (LBB) demonstration program was conducted to verify the LBB characteristics of the Xenon tank. A complete qualification program was conducted to verify the tank design, including a destructive burst pressure test. The tank successfully completed qualification testing on 10 September 1999. The production program completed in December 1999.
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