The subsurface ice probe (SIPR) is a proposed apparatus that would bore into ice to depths as great as hundreds of meters by melting the ice and pumping the samples of meltwater to the surface. Originally intended for use in exploration of subsurface ice on Mars and other remote planets, the SIPR could also be used on Earth as an alternative to coring, drilling, and melting apparatuses heretofore used to sample Arctic and Antarctic ice sheets.
The SIPR would include an assembly of instrumentation and electronic control equipment at the surface, connected via a tether to a compact assembly of boring, sampling, and sensor equipment in the borehole (see figure). Placing as much equipment as possible at the surface would help to attain primary objectives of minimizing power consumption, sampling with high depth resolution, and unobstructed imaging of the borehole wall. To the degree to which these requirements would be satisfied, the SIPR would offer advantages over the aforementioned ice-probing systems.
The tether would include wires for power, wires or optical fibers for control and sensor data, and a narrow tube through which meltwater would be pumped to the surface. A unit containing a heater, a cam-driven agitator, and an auxiliary pump (a small peristaltic pump) would be submerged in a small pool of water at the bottom of the borehole. The heater in this unit would melt ice at the bottom of the hole. The agitator would prevent settling of any suspended sediment to the bottom of the hole. The auxiliary pump would quickly transfer the meltwater and any sediment to a small holding tank above the water surface. To minimize unwanted loss of energy through side melting and to optimize the depth resolution of meltwater samples, only a small amount of water would be left at the bottom of the hole.
The heart of the down-hole assembly would be a small well pump that would force the water and sediment from the holding tank, up through the tube, to the instrumentation assembly at the surface. The pump must provide sufficient head to lift the water from the greatest anticipated borehole depth. Alternatively, the downhole assembly could be made smaller by placing a pump on the surface and using a two-way fluid or pneumatic loop to drive the liquid to the surface. The inevitable dissipation of electric energy in the power cables could be utilized as auxiliary heating to prevent freezing of the water in the tube. Either above or below the pump there could be an electronic camera to acquire images of the borehole wall and/or a nephelometer for acquiring data on sediment particles trapped in the wall.
The design of the tube is anticipated to demand a major part of the overall design effort. The bore of the tube must be narrow enough that the mixing length within the tube corresponds to a short column of water in the hole: this length defines the depth resolution of the system (intended to be of the order of centimeters). At the same time, the bore must not be so narrow that the consequent resistance to flow exceeds the capability of the well pump, and the bore must be wide enough to accommodate suspended particles. The tube must not kink or fracture at low temperatures. It should be sufficiently insulated to prevent freezing during normal operation and it should tolerate inadvertent freezing.
This work was done by Michael Hecht and Frank Carsey of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tspunder the Physical Sciences category. NPO-40031