The lava fields of Hawaii. The peaks of the Himalayas. The crowds of a Justin Bieber concert. These are among the most perilous of environments on planet Earth, places where few humans dare tread. They ain’t got nothin’, though, on waters of our planet’s polar regions, where frigid temperatures and considerable pressures would snuff a puny human like you in a heartbeat.

Robots, though? This is the stuff their tough-as-hell bodies were made for. This is the domain of Seabed, the sensor-packed machine that dives over a mile deep into the polar seas—autonomously—collecting invaluable data. But it comes at a price: Getting the bot back to its icebreaking boat alive can be more challenging than communicating with a Mars rover millions of miles away.

Seabed doesn’t swim like your typical autonomous underwater vehicle. Most are shaped like torpedoes, which allows them to efficiently cut through the water like jets. Seabed instead can use its propellers to hover in the water column like a helicopter. This allows it to hang over the seafloor and map it with sonar, or cozy up next to ice to measure its thickness.

The robot can’t be tethered for hardwired communication, on account of the ice, and radio waves don’t work underwater. So instead, Seabed sends signals of sound (like MIT’s hypnotic fish robot). Even then, the robot isn’t always a reliable communicator. “If we are lucky, we get a 256 byte packet once every minute,” says Northeastern University roboticist Hanumant Singh, who developed Seabed. “And there are no guarantees that we can get it.” Compare that to how NASA scientists communicate with Mars rovers: The signal takes an average of 20 minutes to get from the robots to Earth, but at least it’s consistent. If Singh needs to ping Seabed, the signal might not get there.

To account for the dropped signals, Singh gives the robot a course to, say, run along a particular stretch of the seafloor and map it with sonar. If something appears to be going awry, like colder weather blows in and starts freezing over the ice hole Seabed’s supposed to surface in, Singh can send a signal to cut the mission short. Ideally, it reaches the recipient quickly. (He’s only lost one of these robots, by the way, not because of a communication breakdown but because an intense current swept it away.)

If Seabed comes up in the wrong spot under thick ice, there’s also no guarantee its operators can get it out of the water. It may come up near the icebreaker, like on one mission in 2010. You can’t go breaking ice willy-nilly near a $500,000 robot, so the researchers had to dig a small hole in the ice. This gave them access to the vehicle, to which they attached weights to sink it a bit, but also a float to keep it from plummeting to the bottom of the sea. Then the ship could crack open up the ice further—carefully still, of course—and pull the robot out. On another nearly ill-fated mission, the researchers had to deploy a smaller tethered ROV to grab Seabed and tow it safely to open water.

Generally, though, Seabed returns to within just a few meters of where operators expect it to surface. Again, if the robot weren’t reliably autonomous, this environment would eat it alive.

And once Seabed is in the water, it’s happy as a fish in … water. It’s sealed up nice and tight to keep freezing water from infiltrating the electronics. So if you bring it out of a warm ship hangar and drop it in the sea quickly, it’ll be alright. Where things get problematic is when you have to pull the robot out of the water, then expect to use it again right away.