Feasibility demonstration of cryogenic fluid gauging for space vehicle applications

This article describes a gauging concept for determining the mass of liquid contained in a tank in a low-gravity environment. The concept, which is referred to herein as the 'compressibility gauge', is based on the thermodynamic principle that the pressure of gas or vapor changes when its volume changes. In operation, the tank volume is changed slightly by an oscillating bellows (pulser), and the corresponding change in tank pressure is measured. The primary objective of the present investigation of this concept was to explore the effects specific to gauging cryogenic fluids, such as heat, mass, and momentum transport at the liquid-vapor-tank interfaces, on the accuracy of the gauge. Freon-11 was used as a convenient laboratory fluid to simulate liquid hydrogen and other cryogens. The test results and analyses indicate that cryogenic effects can have a significant effect on gauging accuracy. Nonetheless, it is concluded that the gauge has the potential of high accuracy in low gravity, to use simple hardware, and to be lightweight for space vehicle applications. (Author)