The cryo-hydro integrated robotic penetrator system (CHIRPS) is a partially developed instrumentation system that includes a probe designed to deeply penetrate the Europan ice sheet in a search for signs of life. The CHIRPS could also be used on Earth for similar exploration of the polar ice caps — especially at Lake Vostok in Antarctica. The CHIRPS probe advances downward by a combination of simple melting of ice (typically for upper, non-compacted layers of an ice sheet) or by a combination of melting of ice and pumping of meltwater (typically, for deeper, compacted layers). The heat and electric power for melting, pumping, and operating all of the onboard instrumentation and electronic circuitry are supplied by radioisotope power sources (RPSs) and thermoelectric converters energized by the RPSs. The instrumentation and electronic circuitry includes miniature guidance and control sensors and an advanced autonomous control system that has fault-management capabilities.

The CHIRPS probe is about 1 m long and 15 cm in diameter. The RPSs generate a total thermal power of 1.8 kW. Initially, as this power melts the surrounding ice, a meltwater jacket about 1 mm thick forms around the probe. The center of gravity of the probe is well forward (down), so that the probe is vertically stabilized like a pendulum. Heat is circulated to the nose by means of miniature pumps and heat pipes.

The probe melts ice to advance in a step-wise manner: Heat is applied to the nose to open up a melt void, then heat is applied to the side to allow the probe to slip down into the melt void. The melt void behind the probe is allowed to refreeze. Four quadrant heaters on the nose and another four quadrant heaters on the rear (upper) surface of the probe are individually controllable for steering: Turning on two adjacent nose heaters on the nose and two adjacent heaters on the opposite side at the rear causes melt voids to form on opposing sides, such that the probe descends at an angle from vertical. This steering capability can be used to avoid debris trapped in the ice or to maneuver closer to a trapped object of scientific interest.

The probe contains a system that ingests meltwater, heats the water, and pumps the heated water to form a jet out of a central orifice on the nose. The jet removes debris and contributes to the melting of ice in front of the probe. The external pressure of the ice is utilized to drive some of the meltwater into a channel on the outside of the probe shell, across a membrane, into miniature pumps, which supply water samples to the onboard scientific instruments.

The guidance and control sensors include a three-axis inclinometer, a forward- looking acoustic imager, and sensors for measuring temperature, pressure, flow rate, and pump-motor current. There is also a tether-payout encoder and a tetheractuator/ brake current sensor for use in the event that the probe is connected to surface instrumentation via a tether cable (typically, for a shallow penetration). The electronic circuitry includes a power conditioner, telemetry driver, master controller, digital-to-analog and analog-to-digital converters, instrument drivers, and memory circuits, including data buffers.

At the rear (upper end) of the fully developed probe, for radio communication with the surface instrumentation in the event that a tether cable was not used (typically, during a deep penetration), there would be a primary radio transceiver and its antenna. Behind this antenna there would be 13 radio relay units, denoted ice transceivers, each between 2 and 3 cm thick and about 10 cm in diameter. The transceivers would be released, one at a time, into the rear slush and allowed to become frozen in place for relaying signals between the probe and the surface. The release depths would be chosen on the basis of signal strength and of the temperature and electrical conductivity of the ice.

In the event of an ice sheet over a body of liquid water (as in Lake Vostok), as the probe approached the ice/liquid interface, the acoustic imager would sense the interface. At this point, the front portion of the probe carrying the heat source and instruments would separate from the rear portion of the probe. The ice would refreeze around the aft body, which would thereafter serve as an anchor and a communication relay. The front portion would descend through the water on a tether, sampling the water for signs of life.

This work was done by Wayne Zimmerman, Frank Carsey, and Lloyd French of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Electronics/ Computers category. NPO-40747


This Brief includes a Technical Support Package (TSP).
Ice-Penetrating Robot for Scientific Exploration

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This article first appeared in the February, 2007 issue of NASA Tech Briefs Magazine.

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