The Global Precipitation Measurement (GPM) mission is an international partnership between NASA and JAXA whose Core spacecraft performs cutting-edge measurements of rainfall and snowfall worldwide and unifies data gathered by a network of precipitation measurement satellites. The Core spacecraft's propulsion system is a blowdown monopropellant system with an initial hydrazine load of 545 kg in a single composite overwrapped propellant tank. At launch, the propulsion system contained propellant in the tank and manifold tubes upstream of the latch valves, with low-pressure helium gas in the manifold tubes downstream of the latch valves. The system had a relatively high beginningof-life pressure and long downstream manifold lines; these factors created conditions that were conducive to high surge pressures. This paper discusses the GPM project's approach to surge mitigation in the propulsion system design. The paper describes the surge testing program and results, with discussions of specific difficulties encountered. Based on the results of surge testing and pressure drop analyses, a unique configuration of cavitating venturis was chosen to mitigate surge while minimizing pressure losses during thruster maneuvers. This paper concludes with a discussion of overall lessons learned with surge pressure testing for NASA Goddard spacecraft programs.
The Global Precipitation Measurement (GPM) mission is an international partnership between the National Aeronautics and Space Administration (NASA) and the Japan Aerospace Exploration Agency (JAXA) whose Core spacecraft will perform cutting-edge measurements of rainfall and snowfall worldwide and unify data gathered by a network of precipitation measurement satellites. Upon launch in early 2014, the Japanese H-IIA launch vehicle will place the Core observatory into its mission orbit, at which point the spacecraft's propulsion system operates to maintain strict orbit requirements for the mission duration. This paper discusses the propulsion system design, assembly, and testing, with an emphasis on the challenges and lessons learned. GPM contains a blowdown monopropellant propulsion system with twelve thrusters, an aluminum-lined composite overwrapped propellant tank, and fluid control components, with a launch propellant load of 545 kg. One of the main technical drivers for the system design is end-of-life disposal, which led to the development of the first design-for-demise propellant tank. The propulsion system assembly was organized to accommodate late component deliveries, and included challenges posed by building an integral propulsion system without use of the spacecraft's primary structures. This paper also includes a description of the testing performed to prove the design and workmanship of the propulsion system, including early benchtop testing, the full systemlevel functional test sequence, and propulsion verifications performed after integration into the observatory.
The Lunar Reconnaissance Orbiter (LRO) is a robotic exploration observatory launched on June 18, 2009. The LRO spacecraft contains a monopropellant propulsion system with twelve thrusters, two propellant tanks, a composite overwrapped pressurant tank, and fluid control hardware to regulate the propellant supply to the thrusters. This paper provides a detailed discussion of the testing process that verified the functionality of the system. Sections in this paper walk through the various component tests performed at the propulsion system level, including pressure transducer calibration, valve leakage tests, pressure regulator performance tests, and thruster gas flow impedance tests. Test descriptions provide test rationale, method and equipment, and approximate duration. This paper also includes descriptions of special propulsion tests, including heater verification testing, propulsion module vibration testing, and propulsion testing performed during the observatory-level thermal vacuum testing. This paper concludes with an explanation of the major lessons learned during functional testing, including intricacies associated with a system that includes diaphragm tanks and pressure regulator testing difficulties associated with a large downstream volume. NomenclatureACS = attitude control system AN = Army-Navy Ar = argon ATK = Alliant Techsystems COPV = composite overwrapped pressure vessel EMI = electromagnetic interference FP = flow panel GHe = gaseous helium GN2 = gaseous nitrogen GSE = ground support equipment GSFC = Goddard Space Flight Center K = thousand LRO = Lunar Reconnaissance Orbiter MEOP = maximum expected operating pressure NASA = National Aeronautics and Space Administration NSI = NASA standard initiator PGSE = pressure ground support equipment psi = pounds per square inch (gauge) RV = relief valve S/C = spacecraft SCCH = standard cubic centimeters per hour SCCS = standard cubic centimeters per second 2 Flight Component Designators AT = attitude control system thruster GFDP = gas fill and drain valve -pyrovalve GFDR = gas fill and drain valve -regulator GFDT = gas fill and drain valve -tank HGF = high-pressure gas filter HLF = hydrazine low-pressure filter -top tank HPD = high-pressure transducer HPLV = high-pressure latch valve HPR = high-pressure regulator LBLF = hydrazine low-pressure filter -bottom tank LFDB = liquid fill and drain valve -bottom tank LFDT = liquid fill and drain valve -top tank LPD = low-pressure transducer MLV = manifold latch valve NT = insertion thruster PV = pyrovalve TLV = tank latch valve
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