This probe would overcome some of the deficiencies of prior ice-melting probes.
An improved probe has been proposed for burrowing vertically into ice for scientific exploration of polar icecaps, glaciers, and the like. The predecessor of the improved probe is a Philbert probe, which contains an electric heater to melt the ice in contact with it and thereby make it descend through the ice under its own weight. A Philbert probe also contains a mechanism from which the wires for the electric heater and any sensors in the probe are paid out behind the probe; these wires become sealed into the overlying ice as the probe descends. The two major drawbacks of a Philbert probe are that (1) it tends not to go straight down and (2) a plug of dust, sand, rock, and/or other debris tends to build up in the meltwater ahead of the probe, eventually becoming large enough to halt the descent by interrupting the heat-transfer interface between the vehicle nose and the ice. The improved probe is designed to eliminate these drawbacks.
Like a Philbert probe, the improved probe would include an electric heater and a mechanism for paying out wires connecting the probe to instrumentation on the surface. However, the manner of heating and the means of propulsion would differ greatly from those of a Philbert probe. Moreover, propulsion would involve cyclic (rather than continuous) operation. In comparison with a Philbert probe or other probe that depends on continuous melting, the improved probe would be more energy-efficient because less energy would be lost to the far field through gradual conduction; instead of melting the surrounding ice continuously at a slow rate, the improved probe would aggressively apply intense heat and melt only small portions of the ice for short intervals. In this manner, less heat would be lost to the far field.
The probe would contain a plug of ferrous metal that would be free to move vertically in a cavity within the probe. The plug would be heated by a resistive heating coil; this coil would also serve as an electromagnet coil that, when energized, would hold the plug at the top of the cavity. When the coil was de-energized, the hot plug would fall down in the cavity, which would be partly filled with water. Contact between the plug and the water would cause an explosion of super-saturated steam that would increase the pressure in the reservoir significantly, which in turn, would expel hot water/steam through orifices at the base of the reservoir leading to the nose.
These orifices would lie in a spherical nosepiece that would be free to spin, and the orifices would direct the flow of hot water/steam in the manner of turbine blades to make the nosepiece spin. The spin would ensure that the jets play over the entire frontal face of ice below the probe, melting the ice and stirring up any nonmelting debris so that the debris would become suspended in the liquid water and would be displaced by the probe as it moved down. The spherical nosepiece could be counterweighted, so that it would always cut downward in the absence of any nonmelting obstacle and would return the vehicle to downward movement immediately after passing an obstacle.
There would be another cavity rearward of (above) the water/steam cavity wherein the plug moves. This upper cavity would be kept filled with hydrogen and oxygen gases generated by electrolysis of water. Passages in the side wall of the probe would allow flow between this cavity and the front (lower) end of the probe. During the steam explosion, most of the hot water forced out of the water/steam cavity would rise along these passages, heating the side wall well above the melting temperature and pressurizing the gas in the upper cavity. This gas would act somewhat as a regulator that would maintain the probe at a modest overpressure relative to the ambient ice.
The electrolysis electrodes would be energized via the same wires as those for the heater/magnet. When the upper cavity was full of gas, the water level in the cavity would fall below the electrodes, stopping the electrolysis; thus, the volume of gas would, in effect, regulate itself. If the passages leading to the electrolysis chamber became clogged with debris, the debris could be cleared by sparking a hydrogen/oxygen explosion in the chamber.
The heating of the side wall would melt the ice in contact with the side wall, freeing the probe to fall into the cavity excavated below by the jets of hot water. Upon completion of expulsion of water from the water/steam cavity, the probe would have descended by an amount comparable to the dimension of the water/steam cavity. The next operating cycle would then begin.
This work was done by Brian Wilcox, Partha Shakkottai, and Wayne Zimmerman of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Machinery/Automation category. NPO-20894
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Ice-Melting Probe Using Steam and Jets of Hot Water (reference NPO-20894) is currently available for download from the TSP library.
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