Patent ID: 8196481

Claim:
Apparatus for measuring the amount of fuel aboard a spacecraft under weightless conditions, said apparatus comprising: at least one orifice; at least one flow latch valve for selecting an orifice; at least one control valve for releasing a stream of a pressurizing gas from at least one high-pressure tank to supply pressure to at least one fuel tank that contains said fuel, via said orifice that is selected; and measurement and calculation means for determining an amount of fuel of the at least one fuel tank based on a measured first pressure, a measured first temperature, and a measured first vapor pressure of the at least one fuel tank prior to releasing the stream of pressuring gas from the at least one high-pressure tank, a measured time period of the supply of pressurizing gas from the at least one high-pressure tank to the at least one fuel tank, a measured second pressure, a measured second temperature, and a measured second vapor pressure of the at least one fuel tank after completion of the supply of pressurizing gas from the at least one high-pressure tank to the at least one fuel tank, a measured third averaged pressure, a measured third averaged temperature, and a fuel tank volume as a function of the internal pressure of the high-pressure tank, and a temperature-dependent fuel density, an orifice coefficient and a parameter that takes into account the dependence of the critical flow on the supply pressure.