NASA begins sub-surface icy moon explorer tests

When NASA’s Europa Clipper arrives at its destination in 2030, the spacecraft will conduct 49 flybys of Jupiter’s moon, Europa, using an array of advanced scientific instruments to search for signs that the ocean beneath the moon’s icy surface might support life. The spacecraft, launched on 14th October, carries some of the most sophisticated scientific tools ever sent to the outer solar system. Meanwhile, NASA is already working on the next wave of robotic technologies to further explore Europa and other ocean worlds, potentially venturing into their hidden watery depths.

One such concept is the SWIM (Sensing With Independent Micro-swimmers) project, which envisions deploying a swarm of self-propelled, mobile robots, each about the size of a smartphone. These micro-swimmers would be delivered to subsurface oceans by an ice-melting cryobot, where they could navigate the water autonomously, searching for chemical and temperature signals that might indicate life.

Ethan Schaler, Principal Investigator for SWIM at NASA’s Jet Propulsion Laboratory (JPL) in Southern California, explained: “People might ask, why is NASA developing an underwater robot for space exploration? It’s because there are places we want to go in the solar system to look for life, and we think life needs water. So we need robots that can explore those environments — autonomously, hundreds of millions of miles from home.”

Prototypes for the SWIM concept are under development at JPL and have already undergone testing in a 25-yard (23-metre) competition swimming pool at Caltech in Pasadena, yielding promising results.

SWIM Practice

The latest version of the SWIM prototype is a 3D-printed plastic robot built with low-cost, commercially available motors and electronics. Propelled by two small propellers and guided by four steering flaps, the robot successfully demonstrated precise manoeuvrability. It autonomously maintained its course, corrected its direction when needed, and executed a back-and-forth "lawnmower" exploration pattern — all without direct human intervention. It even managed to spell out "J-P-L" during the trials.

For added security, the robot was tethered to a fishing line, with an engineer following along poolside with a fishing rod in hand, ready for retrieval if needed. Meanwhile, a team member monitored the robot's movements and sensor data in real time using a laptop. Over the course of testing, the team ran more than 20 trial sessions, both in the Caltech pool and in specialised tanks at NASA’s Jet Propulsion Laboratory (JPL).

Ethan Schaler, the Principal Investigator for SWIM at JPL, commented: “It’s awesome to build a robot from scratch and see it successfully operate in a relevant environment. Underwater robots are inherently challenging to develop, and this is just the beginning of a series of designs we’ll need to refine for a mission to an ocean world. But this prototype proves that we can equip these robots with the essential capabilities and begin tackling the unique challenges they’d face on a subsurface mission.”

Swarm Science

The prototype used in most pool tests was a wedge-shaped device measuring 16.5 inches (42 centimetres) in length and weighing 5 pounds (2.3 kilograms). For space missions, however, the final design envisions much smaller robots—roughly one-third the size of the prototype. These palm-sized swimmers would feature custom-built, miniaturised components and utilise an innovative underwater acoustic communication system to transmit data and determine their positions.

While the physical prototype underwent pool testing, digital versions of the robots were evaluated through computer simulations. These virtual tests replicated the extreme pressure and gravity conditions the robots might face on Europa. In the simulation, a swarm of 5-inch (12-centimetre) robots explored an unknown environment, searching for potential signs of life. The tests revealed the robots’ scientific capabilities and informed the development of algorithms to optimise their efficiency during missions.

The simulations also helped refine trade-offs between the robots’ battery life (up to two hours), their exploration range (approximately 3 million cubic feet or 86,000 cubic metres of water), and the number of robots in a swarm (typically a dozen, deployed in four or five waves).

Collaborators at Georgia Tech further advanced the concept by developing a compact ocean composition sensor. This tiny chip, just a few millimetres across, is the first of its kind to combine multiple measurements in a single package, allowing each robot to simultaneously assess temperature, pressure, pH levels, conductivity, and chemical composition.

Despite its promise, the SWIM concept remains in the early stages of development, requiring several more years of refinement before it could be considered for a potential mission to an icy moon. In the meantime, Ethan Schaler, Principal Investigator for SWIM, sees potential applications closer to home. He envisions the robots being adapted for oceanographic research or for collecting critical data beneath polar ice sheets, demonstrating their versatility beyond space exploration.