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This paper reviews the literature for tank chilldown methods applicable to cryogenic tankage in the zero gravity envirormnent of earth orbit, selects one method for demonstration in ground based test, and then reports the results of that test. The method selected for investigation was the change-hold-vent method which uses repeated injection of liquid slugs, followed by a hold to allow complete vaporization of the liquid and a vent of the tank to space vacuum, to cool tankage to the desired temperature. The test was conducted on a 175 cubic foot, 2219 aluminum walled tank weighing 329 pounds, which has been previously outfitted with spray systems to test nonvented fill technologies. To minimi ze hardware changes a simple control-by-pressure scheme was implemented to control injected liquid quantities. The tank cooled from 440 R sufficiently in six charge-hold-vent cycles to allow a complete nonvented fill of the test tank. Liquid hydrogen consstuaed in the process is estimated at 32 pounds. IrTIRODU=ONThe current interest in pressurized transfer of cryogenic fluids stems in part from NASA's plans for an ambitious human Space Exploration Initiative (CIAO) including manned voyages to the Moon and Mars. These activities will require enormous amounts of propellant stored as cryogenic liquids. The ability to efficiently transfer these cryogen between earth-to-orbit tanker vehicles, orbiting depots, and space transportation vehicles is required for mission success. Current transfer concepts include a tank chilldown stage to remove the majority of the thermal enemy stored in the wall. This allows the wall energy to be removed, prior to the start of the fill process, rather than forcing it to be absorbed in the incoming liquid cryogen. Note: this paper focuses solely on the chilldown of tank walls, other chilldown processes such as line cooldawn and engine prechilling, although also important will not be addressed.Chilldown of a cryogenic tank in a low-gravity environment has never been done. Although extensive data is available for ground-based tank chilldown of cryogenic tanks (e.g., Centaur upper stage, STS external tank), the techniques required to transfer cryogens in low gravity are quite different fra, those used terrestrially. During a normal-gravity tank chilldown, a vent on top of tank is kept open to vent the vapor generated during the chill process thereby maintaining a low tank pressure. If the normal-gravity technique is used onorbit, the uncertainty of liquid and vapor distributions in low gravity may result in the dining of large amounts of liquid overboard. REVIEW OF THE LITERATURE General Transfer SystemsConcepts for missions involving orbital fluid transfer can be found as early as the planning stages of the Apollo Program (ref. 1). One of the earliest detailed designs of an orbital fluid transfer system is found in reference 2. The reference 2 study proposed designs for LO Z and LHz tankers based on an equilibrium analysis of the thermodynamics of the fill process, including vented and nonven...

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This paper presents experimental design and test results of the recently concluded 1-g inverted vertical outflow testing of two 325x2300 full scale liquid acquisition device (LAD) channels in liquid hydrogen (LH 2 ). One of the channels had a perforated plate and internal cooling from a thermodynamic vent system (TVS) to enhance performance. The LADs were mounted in a tank to simulate 1-g outflow over a wide range of LH 2 temperatures (20.3 -24.2 K), pressures (100 -350 kPa), and flow rates (0.010 -0.055 kg/s). Results indicate that the breakdown point is dominated by liquid temperature, with a second order dependence on mass flow rate through the LAD. The best performance is always achieved in the coldest liquid states for both channels, consistent with bubble point theory. Higher flow rates cause the standard channel to break down relatively earlier than the TVS cooled channel. Both the internal TVS heat exchanger and subcooling the liquid in the propellant tank are shown to significantly improve LAD performance.