Icy moon explorers may someday hunt for life using an old-fashioned method: steam power.
A conceptual robot being investigated at NASA's Jet Propulsion Laboratory (JPL) would release soccer ball-sized machines to hop on the surface and fly through the air, using steam produced by melting ice.
The early-stage idea is called Steam-Propelled Autonomous Retrieval Robot for Ocean Worlds (SPARROW). On an icy moon such as Jupiter's Europa or Saturn's Enceladus, SPARROW could potentially travel several miles in the moon's low-gravity environment — with no thick atmosphere to slow it down.
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"The terrain on Europa is likely highly complex," Gareth Meirion-Griffith, JPL roboticist and lead researcher of the concept, said in a JPL statement. Examples of the challenges a robot like SPARROW may encounter include crevasses, porous and treacherous ice, or penitentes, long blades of ice that typically form at high latitudes on Earth. SPARROW, however, could navigate these obstacles, Meirion-Griffith added. "It has complete freedom to travel across an otherwise inhospitable terrain."
SPARROW received Phase I funding from the NASA Innovative Advanced Concepts program, which specializes in technology that would push the bounds of traditional design, in 2018, allowing the design team to explore ideas and advance the technology readiness level of the mission for spaceflight. SPARROW's team could propose a follow-on Phase II study for further development, too.
So far, the team has been evaluating different ideas for water-based propellant systems that produce steam efficiently. Using computer simulations, SPARROW investigators also examined how the robot will tumble and move while exploring the ice. Their concern is making sure that the robot uses the most efficient launch angles and hop speeds to move around.
"From this, and related propulsion calculations, we were able to determine that a single long hop would be more efficient that several smaller hops," Meirion-Griffith said.
While a potential SPARROW mission is years or perhaps decades from launch (if it happens at all), the researchers already have some ideas about how the exploration would proceed. A lander would potentially bring down swarms of SPARROWs to do independent investigations on a moon's surface. The lander would delve into the ice and melt the ice to fuel the individual SPARROWs.
Each little hopping robot would then heat the water inside its engines to make the steam it needs to jump off the surface. The SPARROWs would range a safe distance from the lander, allowing them to return to home base whenever they need a refuel — and also, to drop off scientific samples for analysis.
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