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| The Cryobot method of "drilling" is more effective than conventional augering because it uses less power than mechanical cutting. Melting the ice and moving through the resulting liquid makes it easier for the probe to make its journey Credit: NASA JPL |
An adventurous science team recently returned from the deep Norwegian glacial fields, having tested an instrument which may one day be used to explore areas beneath the frozen surfaces of other worlds. As demonstrated by the Jet Propulsion Lab and Caltech, their robotic ice-pick, dubbed Cryobot, sports a heated nose-cone especially designed to melt frozen ground and drill cryogenically. Their most recent depths broke through the equivalent of an ice sheet the size of an eight-story building, or 23 meters (75 feet) into a glacier.
Glacier cutting combines an extreme operating environment with new technology to navigate and image the ice sheet below. The team hopes a frontier lies beneath the exploration of what previously relied on orbital or surface observation, but now can include sub-surface drilling probes. "If you want to learn about the climate history of Mars, which is important in the search for life, you want to examine the layers of the polar caps, and this is how you can do it," said Scott Anderson, a geophysicist on the Cryobot field-test team.
The Cryobot itself is a hip-high, cylindrical probe about 1 meter (3.3 feet) long and 12 centimeters (5 inches) in diameter. Minimizing power and size in their design, the Cryobot team has shaped a nearly self-propelled drill. Heated water at the downward end melts ice below, and gravity provides the pull to great depths. From the back of the robot, a tether or wired umbilical to the surface keeps its electronic links alive. Even if the drilling hole begins to refreeze on top of the Cryobot, the robotic probe can remain in contact with the surface and continue to send valuable exploration data to the researchers. This design minimizes possible contamination during the exploration of pristine environments.
In addition to exploring ancient glaciers and their buried underground lakes on Earth for signs of ancient life, the success of these early Cryobot tests also extends the possible range of mission options for exploring Mars and Europa. Notes Wayne Zimmerman, lead engineer for the task, "there's never been a probe before that does what this one can."
Race for the Pole
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| JPL Cryobot Research Team in the Field. Team members from JPL included (from left) Robert Ivlev, Daniel Helmick, Wayne Zimmerman and Lloyd French. Credit: NASA JPL |
Testing the feasibility of such a warm-nosed drill required travel to a glacier on the island of Spitsbergen, far north of the Arctic Circle in the Norwegian-administered international territory of Svalbad. Although not as challenging as remote robotics on another planet or moons, the researchers still faced challenges working in the polar north. "The north pole is home to the polar bear. We were careful to test at a site to not disturb their environment and the Norwegian Polar Institute provided safety from polar bears," said Dr. Lloyd French, Cryobot task manager and team leader for the Jet Propulsion Cryobot researchers. "We did not see any polar bears during our stay. We did experience ‘ice quakes’ or occasional fracturing of the glacier and heavy snowfall. We had to dig to get into our tents, and dig to get out of our tents."
To help with the tests, the team relied on help from the Norwegian Polar Institute and Norwegian Space Center to verify that the ice-penetrating robot could drill 8-stories below the glacier. "In the past, the United States and Norway participated in a global race for the North Pole on Earth," said French. "Now, with the help of the Norwegian Polar Institute and Norwegian Space Center, we're cooperating on a possible way to explore another North Pole, on Mars."
Breaking the Ice: From Europe to Europa
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| Lake Vostok is believed to contain water millions of years old, which may be the home of ancient organisms. This hidden body of freshwater is the size of Lake Ontario and is the largest of 70 bodies of water first detected under the polar ice-sheet in the 1970s. The plan is to send a Cryobot down through the ice 2.5 miles (4 kilometers) to visit this body of water. Credit: LDEO Columbia University |
"Initially, Europa exploration was a main driver to Cryobot specifications, "says French. Europa, one of Jupiter’s moons, is believed to have a saltwater ocean beneath its icy surface. "Salty environments, like Earth's oceans, have corrosion issues. Oceanography instruments have given us design insights. Radiation is also a factor at the surface of Europa. The effect of radiation is reduced at depth because the ice would shield the hardware from radiation." As if coping with corrosive salt from Europa’s possible ocean and high radiation from Jupiter wasn't challenging enough, the estimated temperature on Europa is likely -190 C, or nearly -400 F.
Deploying the Cryobot may provide just the technology needed as a new way to break up the ice. But if the team deploys such cryobots in other extreme environments both on Earth or elsewhere, even deeper drilling will be required. To drill to the ancient Antarctic fresh-water deposits like Lake Vostok, the fourth largest Lake on Earth, then depths of more than 2.5 miles (4 km) will have to be reached. The salty frozen surface of Europa is estimated to range up to 10 miles in depth.
But in laboratory tests so far, "the depth limitations for the Cryobot have been more dependent on time," says Dr. French. "It took approximately 4 days to melt to a depth of 23m or ~75ft during our engineering test in Svalbard, Norway. This depth is 5 times farther that our lab tests of 5m or ~15ft. The limitations of (the lab) depth is that we can only build a tower of ice 5m tall. So we needed to go out to the field for deeper depths."
Previous probes operating to great glacial depths suffered from a host of engineering shortcomings: high power needs, poor navigation, lack of excavation when holes began to fill in behind, or large probe sizes combined with little room for science payloads. "As applications to Earth and Mars developed, the common environmental elements drove specifications in temperature and pressure," says French. "The specifications for power and communications are dependent upon the three different environments"--terrestrial, Martian and Europan.
In terms of sending a Cryobot-type probe to an extraterrestrial environment, "Size is a big issue," says Dr. French. "This issue drives mission capability and science return. This development is for surface planetary applications, so this instrument platform will need to have a small landed mass. The various instruments need to be small enough to package tightly inside the instrument bay. Increasing the diameter for instruments could result in a 40% jump in heater power."
What's Next
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| Concept artwork shows the Active Thermal Probe (Mars Cryobot) melting downg through the northern ice cap on Mars. Credit: NASA JPL |
Since taking the Cryobot 8 stories below the Norwegian glacier, next steps likely are to continue to press the envelope of extreme engineering tests. According to French, their tests have already "established a bold foothold for opening up new, below-the-surface environments for scientific study." Further instrumenting of the robot will prepare it for deployment and remote operations to explore the Martian ice cap or the salty oceans on Europa.
Instrumenting a Cryobot with cameras and chemical sensors is a likely next step for the researchers. "Typically a camera system is ideal to image layering and deposits," says French, "and a chemistry sensor for pH and salts."
"We desire to look into augmenting the Cryobot with a subsurface sample return capability," concludes French. "One promising method is to use the tether system as a conduit for conveying samples to the surface."
Related Web Pages
Herman Engelhardt's Glaciology resource page