The researchers working on the project known as SIMPLE will tell you that it’s anything but.
It is no small undertaking to design and build a 25-foot-long underwater robot, launch it through a narrow hole drilled through 20 feet of sea ice, allow it to maneuver it autonomously through several kilometers of Antarctic Ocean for hours at a time and program it to pilot itself back to within a few feet of where it started.
The simple part is that it at least takes place on planet Earth.
Though still many years away from their ultimate goal, the team members are using their underwater robot named ARTEMIS to develop the technology that they hope will one day explore the vast ocean covering Jupiter’s icy moon Europa.
“The idea here is to get in on the ground level and push the technology forward,” said Britney Schmidt, a professor of planetary science at the Georgia Institute of Technology (Georgia Tech) and principal investigator for the project. “ARTEMIS itself won’t be going to Europa but the technologies and the ideas and the way that we’ve used them and some of the engineering decisions and some of the science hypotheses, those are what will be migrated forward into future hopefully underwater exploration in Europa.”
ARTEMIS is the latest in a series of robots that’s part of the Sub-ice Investigation of Marine and Planetary-analog Ecosystems (SIMPLE) project. It’s a NASA-funded effort to build machines that can explore the harsh environments on Earth that most closely mimic those of the icy worlds of the outer solar system.
The National Science Foundation, which manages the U.S. Antarctic Program, is supporting the Antarctic field operations of the project.
Europa is near the top of a short list of spots in the solar system that could realistically harbor life beyond Earth. It’s Jupiter’s fourth largest moon and completely covered in an ocean up to 60 miles deep.
Jupiter and its moons are more than five times farther away from the sun than Earth, and at that distance, temperatures along Europa’s equator never rise above minus 250 degrees Fahrenheit. These frigid conditions freeze the top 10 to 20 miles of ocean into a thick layer of ice. Yet planetary models and flyby probes have shown that tidal forces from Jupiter’s gravitational field keep the deep interior warm enough for a liquid ocean, where scientists hope to discover extraterrestrial life.
“When we think about ingredients for life and the things that we might need to host a biosphere outside of Earth, Europa kind of rises to the top because we have a big global ocean, it’s hidden by an ice shell…. [but] underneath that, it may be very Earth like,” Schmidt said.
The Ross Ice Shelf near McMurdo Station is among the best terrestrial stand-ins for the Jovian moon. It’s a permanently frozen ice shelf roughly the size of Texas, more than 2,000 feet thick in places. Abutting the shelf is seasonal sea ice, which freezes during the austral winter and clears out in the late summer. It’s an ideal launch site for the robot, and these two ice coverings together make for the best place on Earth to learn more about what it takes to pilot a robot under the frozen surface of an alien ocean.
Fortunately for the team, Antarctic sea ice is thinner than on Europa. They only had to drill through about 20 feet of sea ice where they set up their ‘bot camp.
“Getting something to go through a drilled hole in the ice and then go off on long range missions is something that nobody has done here before,” said Bill Stone, president of Stone Aerospace, which built the robot. “It can be programmed to go along a series of directional points, wherever you want it to go. And it will execute a series of behaviors that we want it to do along the way.”
Making the vehicle as autonomous as possible is a key part of the project. Remotely piloting a probe under Europa’s deep oceans from as far away as Earth is impossible. Any interplanetary ocean vehicle will need to be able to explore on its own, establish its own maps, and automatically investigate anything that looks interesting along the way.
ARTEMIS is programmed with a prototype system to help develop such onboard programming. Once it enters the water, the researchers indicate a point on the map, and more than 300,000 lines of code automatically guide the robot to where it needs to go.
“It is in a class of vehicles that are technically termed HROVs or Hybrid [Remote Operating Vehicles],” Stone said. “It’s a vehicle that can be both autonomous as well as being operated from a remote station like an ROV.”
When it’s on manual mode, the pilot guides the robot using an X-Box video game controller. They watch its progress through the water from a live video feed carried along a 15 kilometer-long spool of fiber optic cable.
The robot is part also of the design process to figure out what kinds of hardware a future interplanetary submarine might need.
“The vehicle that goes to space is going to have to be much smaller and lighter than ARTEMIS,” said Peter Kimball, an engineer at Stone Aerospace. He added that on land, ARTEMIS weighed more than 2,500 pounds. “Sending something like that to Europa is completely infeasible.”
The problem with designing underwater vehicles like ARETMIS is that even the addition of a small instrument comes with a big weight penalty. The larger the robot is, the more energy it takes to propel, which in turn requires bigger batteries, which adds to the overall weight, which again requires more energy to move, and on and on. Figuring out the best ways to slim down the robot’s systems and instruments will go a long way towards making future probes possible.
“A big part of the data analysis here, from a technology development perspective is [determining] what do we really need? What is most important, and what can we get rid of?” Kimball said. “The smaller we make the vehicle, the smaller we can make the batteries.”
For its work in the Antarctic, researchers are using the robot’s large size and long battery life to their advantage. It’s covered with numerous sensors and instruments to capture a broad range of data about the waters of McMurdo Sound.
“What’s unique about ARTEMIS is that it is a relatively long-range vehicle,” Schmidt said. “What the instrument package does for us is give us a kind of robot oceanographer, as well as some information about biology in the area.”
One of the main goals of the project is to help calibrate aerial ice-penetrating surveying technology for a Europa mission that’s already in development. While swimming long distances under the ice, the robot charted a detailed picture of how thick the ice shelf is, and how well researchers had been able to measure it from the air.
“We have sonars that are mapping the topographies of the ice,” Schmidt said. “That data is going to be used to compare to ice penetrating radar of the same environment so we can take what we can do here, and map it to radar data all over the continent, and eventually on Europa.”
NASA plans to launch a probe in the early 2020s to fly around the icy moon. One of the instruments slated for the mission is an ice-penetrating radar to create a cross section of the moon’s icy crust. Dubbed the Europa Multiple-Flyby Mission, the probe will chart the surface and underside of Europa’s ice, looking for spots thin enough that a future lander could drill through the ice to the liquid ocean below.
Part of the SIMPLE team flew a similar ice-penetrating radar over the Ross Ice Shelf in the 2013 and 2014 seasons, led by the University of Texas Institute for Geophysics. ARTEMIS then used sonar waves to map the same spot of the shelf from the underside to see how accurate those radar readings are.
“The data we’re collecting underneath this radar target area are going to provide ground truth for ice thickness so that the radar folks can tune the algorithms for this radar that’s going to Europa,” Kimball said.
The sonar echoes received by the underwater robot appear as a forest of red dots against a black background on one of the screens monitoring the progress of the robot. As the sub moves through the water, more dots appear, resolving themselves into detailed contours of the icescape that covers the ocean.
While it swims under the ice, the sub collects data about the conditions of the water itself. Onboard instruments are constantly gauging how deep the robot is under the surface and measuring the temperature of the water and its salinity.
“There’s a whole range of different water masses, and you can look at how those are interacting underneath,” Schmidt said “You can tell if you have ocean water that’s just ocean water because it’s a certain salinity, or if you have mixed ice melt in there, that’s a different salinity or if it’s bottom water versus shelf water versus Antarctic current water.”
While the sub is in the water, these results are projected live onto a screen over the bank of computers the researchers are using to steer the sub.
On a nearby screen, small sea creatures occasionally swim in front of the camera. Should a chance meeting like that happen in the oceans of Europa, the question about whether life exists beyond of Earth would be settled in an instant. But astrobiologists aren’t banking on such a fortuitous encounter, so they are working to develop ways for a future probe to detect signs of life that are more difficult to see.
“It would go there to search for life, but there is no magical ‘search for life’ sensor that you can buy and put on a robot,” Kimball said. “One of the big questions is what sensors would you put on such a robot and how would you interpret the data from those sensors to know whether what you were seeing in this environment was life or evidence of life.”
One promising tool they tested out was a custom-built protein fluorescence spectrometer. It scanned for protein molecules by shining a carefully calibrated light into the ice and looking for the tell-tale glow that certain proteins emit as a result.
“Proteins are higher order structures usually created in biochemical reactions and that’s why they’re useful. If you can see evidence that those are there, than that’s suggestive of life. Its’ what we call a biomarker,” Schmidt said. “It doesn’t necessarily mean that life exists, but it means that processes relevant to life, and potentially biological in nature, have occurred.”
They placed the spectrometer on the end of an extendable arm so the robot could place the sensor right against the underside of the ice.
“The idea is to touch the instrument to the ice in order to measure what’s living right on the surface of the ice or right inside of the ice,” Kimball said. “By touching it right to the ice you don’t have any sea water in between. Sea water, here on Earth, is full of proteins that could potentially swamp the signal.”
Another advantage to practicing on Earth is that it’s easy to double-check what the sensors on the robot are reading against a more comprehensive laboratory analysis.
“We can take water samples up at the ice-ocean interface, or anywhere else along our track, and take them back to the lab and analyze what our remote or our onboard instruments are saying, versus the ground truth from water samples,” Schmidt said.
Finding life in the ocean around McMurdo is not difficult. The waters under the sea ice teem with a wide variety of organisms and the robot offered scientists a chance to learn more about them and their environment. The project’s timing was fortuitous because late November, when the team was in the field, is also when the ocean ecosystem undergoes major changes as the austral summer sets in.
“The sub-ice shelf is a non-photosynthetic ecosystem, and where that transition is to the photosynthetic ecosystem is actually only becoming measurable in a big way [in November] because the [sea] ice is getting thinner and the snow is going away,” said Peter Doran, a professor of geology and geophysics at Louisiana State University.
The sunlight that filters through the ice is an important source of nourishment to the organisms that live underneath. As in most ecosystems, photosynthetic plants and algae absorb the rays of the sun and convert them into energy, forming the foundation of the food chain.
In the Antarctic, the cycle is a bit more complicated than at lower latitudes because of the months of total darkness in the winter and constant light in the summer. In addition, snow covers much of the sea ice in the beginning of the summer, blocking sunlight from filtering through. Usually by late November enough light starts to reach the waters beneath the ice that it spurs massive growth in the algae underneath.
“This will be the first time you can actually look at the fine-scaled changes in light conditions under the sea ice covering, and how the organisms respond to those changes in light levels,” Doran said. “You can’t do that without a submarine of some kind.”
ARTEMIS carries a special light sensor to record how much of the light that plants need for photosynthesis passes through the ice. As it moves through the water, the robot collects more data over a greater area than past techniques, which could only observe conditions around gaps in the ice.
“No one’s been able to do that before, because it’s all been hole-driven. One hole here one hole there,” Doran said. “Doing long transects and getting the biogeochemical gradients is a completely novel thing.”
It’s a lot of science to fit into a single season in Antarctica, and the researchers put in long hours to get as much data as they could. Between the robot launch, systems checkout, its ten-hour mission plus recovery, working 20 hours a day or more was not uncommon for the team.
“We got some important data, we checked out the vehicle, got it working and have a lot of lessons for future work,” Schmidt said.
Since returning from Antarctica, the team has been sifting through the vast amounts of data they collected over their three seasons of work. They’re hoping to release the bulk of their work within the next year or so.
“As soon as we have this data processed in interesting ways, we’ll publish it but we’ll also archive the data so other people can use it,” Schmidt said. “We’re trying to get the science out to the community, trying to get the engineering designs out to the community so people can benefit from our lessons learned, and we’re going to try to push these technologies forward in a variety of ways.”
There are still a number of technical challenges that scientists will need to overcome before any future interplanetary submarine can be built, not least of which is building a machine that can drill through miles of ice and deploy a small submarine. Past robots have addressed different parts of this problem individually, in the hopes of eventually putting together a comprehensive robotic system that can do everything.
“What we’re doing here with the SIMPLE program, using ARTEMIS, using SCINI, using Deep-SCINI, using Icefin, using all these underwater vehicles, is to try to push the envelope on the technology,” Schmidt said. “We need underwater and under-ice exploration to get to that point so that we can take those technologies and get to Europa.”