Review and test of chilldown methods for space-based cryogenic tanks

Abstract

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...

Development and validation of an analytical charge–hold–vent model for cryogenic tank chilldown

“…[2] Chato and Sanabria experimentally investigate the feasibility of the CHV cryogenic tank chill down technique using liquid hydrogen and a 4:96 m 3 Aluminum 2219 tank. The tank was able to be cooled from an initial wall temperature of 244 K in six CHV cycles.…”

“…Re jet and Pr jet , defined in Eqs. (2) and (3), refer to the jet Reynolds number and Prandtl number respectively. Re jet is calculated with the hydraulic diameter of the nozzle acting as the characteristic length.…”

“…Based off the experimental configuration from Ref. [2], a specific CHV model is developed to compare with the only available set of data, a sampling of which is shown and explained in Figs. 2 and 3.…”

Cryogenic fluid transfer for exploration

“…The propellant required to chill the tanks down represents another mass loss (ground testing has shown a 149 kg tank can be chilled down with 14.5 kg of liquid hydrogen (ref. 20).) Several strategies are available to avoid this loss entirely.…”

“…Nevertheless the Progress module includes resupply tanks holding about 870 kg of propellant (two tanks of nitrogen tetroxide and two of UDMH hydrazine). This module and system were first used on Saylut 6 on January 20,1978 10), which looked at a vane device to separate gas and liquid during transfer. Figure 2 shows inflow into one of the VTRE tanks during a fluid transfer.…”