Robust Liquid Volume Sensor for Flexible Bladders in Microgravity

The Portable Life Support System (PLSS) on the Advanced Space Suit (AEMU) will carry consumable cooling water maintained at ambient pressure within an array of soft-walled, flexible reservoirs known collectively as the Feedwater Supply Assembly (FSA). To ensure uninterrupted thermal control, it is critical to monitor the volume of water remaining for the duration of an extra-vehicular activity (EVA), but no known sensor is suitable for this task. Existing measurement techniques are unacceptably sensitive to the motion and varying geometry of the reservoir in microgravity, or to electromagnetic interference within the suit environment. This represents a critical technology gap for NASA’s suit development. We have developed a compact, low power sensor that accurately measures the volume of liquid in the FSA or any soft-walled bladder. The novel acoustic detection technique provides a measurement of absolute liquid volume that is insensitive to gravity, the motion and geometry of the reservoir, the presence of gas pockets, and electromagnetic interference. In ground tests, the sensor achieved continuous measurement with accuracy on the order of 5% full scale under prototypical EVA conditions. These results were fully repeatable over six long duration experiments conducted on different days without recalibration. We are currently developing a pre-production version of the sensor and planning a sub-orbital spaceflight qualification test