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Radio Frequency Mass Gauge on Parabolic

Completed Technology Project

Project Introduction

Radio Frequency Mass Gauge on Parabolic
Propellant quantity gauging is a critical function for space vehicles, yet the only way to gauge the amount of propellants in a low-gravity environment is to "settle" the liquid in the tanks by accelerating the vehicle and measuring the liquid level. Although this settled-gauging technique works well in many instances, e.g. during launch or main engine burns, it has drawbacks and penalties. At a low settling thrust the liquid slosh times are long, leading to inaccurate level sensor data. The penalty for this propellant gauging inaccuracy is additional propellant load, to cover the uncertainty margin. Without a settling thrust, the propellant quantity is even more uncertain. These difficulties could be overcome with a low-gravity propellant gauging technology, such as the Radio Frequency Mass Gauge (RFMG). The RFMG is a technology being developed at NASA to gauge cryogenic propellants in low-gravity, or under low settling thrust conditions where sloshing is also an issue. The technique has been proven to work very well in ground tests using liquid hydrogen and liquid oxygen, but lacks substantial low-g testing. The RFMG was successfully tested on a low-g aircraft in 2010 (Figure 1), under the NASA Facilitated Access To The Space Environment For Technology (FAST) program, but low-g data was acquired at only three different fluid fill levels during the flight week, and data for one of the fill levels was gathered only during one zero-g parabola at the end of a lunar-g flight campaign. The low-g aircraft tests demonstrated that the RFMG can accurately gauge the liquid quantity provided some filtering or averaging is used (sloshing in the tank increases the gauge noise level, but the uncertainty can be reduced by averaging). In this second round of lowg testing, we propose to increase the fidelity of the test by including hardware elements inside the tank, such as a tube along the long axis of the tank to mimic a spray bar, and a slosh baffle. The spray bar and slosh baffle are realistic tank hardware elements that are likely to be included in a space-based cryogenic propellant tank. Because the hardware elements affect the RF modes of the tank, they were not included in the 2010 flight tests in order to simplify the RF modeling. Similar hardware elements have been successfully incorporated in other 1g ground-based tests of the RFMG. In addition to adding internal hardware, the new low-g test data will be collected at different fill levels than tested previously, thereby providing increased confidence that the RFMG can accurately operate at any fill level. The tests will be conducted with the same tank, fluid (Fluorinert FC-77), and rig as used during the 2010 test flights. We propose to collect low-g data using at least two different fluid fill levels on at least two different flight days (one fluid fill level per flight day). Multiple parabolic flights at a fixed fluid quantity will provide a multitude of test data at various liquid-vapor configurations, as well as under conditions of sloshing in the tank. The RFMG technique is fast, completing a gauging operation in 2 seconds, so multiple sets of data can also be collected during each parabola. Acquiring low-gravity test data with the RFMG and demonstrating that it works with internal hardware elements and at multiple fill levels will mature the flight readiness of the RFMG, thereby reducing the risk of adopting this technology on a future space vehicle. More »

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Technology Maturity (TRL)

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Light bulb

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