June 17, 2012
Dr. Greg Zimmerli presented to the Academy students on Tuesday about his work in cryogenic propulsion. Contrary to popular belief, space isn’t cold – at least not enough for grade-A rocket fuel. Considerable efforts have and are being made to keep liquid H2 and O2 condensed over an extended, and potentially indefinite, amount of time. Dr. Zimmerli’s work focused on instrumenting the fuel remaining inside the tanks, a feat which becomes more challenging in microgravity with fuel adhering to the walls and cavities forming in the center. Several previous efforts include measuring the pressure in the chamber, or performing a Burn Time Integration (add up how long one has burnt fuel times the approximate fuel consumption rate.) The latter is something we’ve all tried in our cars from time to time, so the potential issues there should be obvious.
Dr. Zimmerli’s work is a new method that uses an antenna deployed inside the tank to deliver a broad spectrum signal and measure the resonant effects on the metal containers. As the amount of fuel decreases in each of the tanks, and the characteristic response at each fuel level from each frequency is matched, the amount of fuel remaining can be determined accurately.