MADISON, Wis. -- A robotic submarine that will eventually be used to explore a moon that orbits Jupiter continues to be tested in Madison's Lake Mendota.

The saucer-shaped submersible known as ENDURANCE is cruising the icy depths of the city's largest lake this week at part of $2-million project funded by NASA.

Engineer Bill Stone of Texas-based Shackleton Energy Co. designed and built the deep-diving robot for NASA.

Researchers from NASA and the University of Illinois at Chicago are heading up the test, in which a submersible will dive underneath the ice to map the environment and sample microbial life.

ENDURANCE will eventually be used to explore the frozen oceans on Europa, but that could take another 20 years.

Between now and then, scientists will work on its mapmaking abilities, first in Lake Mendota and then next year in a 130-foot deep frozen lake in Antarctica. In those tests, the submersible would study the landscape and chemical composition of Lake Bonney.

Earlier this week, a 120-foot crane lowered the sphere-like underwater instrument into the icy waters of the lake off the University of Wisconsin-Madison Limnology Lab Tuesday afternoon, successfully starting the first phase of field tests to see if the photography and other scientific instruments on board can withstand the arctic conditions.

Various engineers and scientists watched the robot's sensors and processors churn out a stream of data Tuesday, and they monitored computers to make sure cold temperatures didn't take a toll on the submersible.

The UW-Madison's Center for Limnology is providing logistical support for the $2.3 million effort.

The robot is called ENDURANCE, which stands for Environmentally Non-Disturbing Under-Ice Robotic Antarctic Explorer.