The thing designated SPARROW that engineers from NASA’s Jet Propulsion Laboratory want to send to the icy moons of Enceladus and Europa has nothing at all in common with its namesake bird. Americans and scientists love acronyms, and the designation SPARROW came from the name “Steam Propelled Autonomous Retrieval Robot for Ocean Worlds.” The project is part of the “NASA Innovative Advanced Concepts” program (NIAC), whose current candidates were announced by NASA earlier in Spring 2020.
SPARROW stands out because it uses a very old propulsion solution from the start of the Industrial Age. But instead of coal for steam locomotives, it uses steam for a rocket propellant. To do this, SPARROW heats and melts the abundantly plentiful ice. With short bursts of steam, the approximately soccer ball-sized robot can then make large hops in the low gravity of the icy moons. The concept involves a lander base unit releasing and coordinating several SPARROWs.
Here is a video that the engineers made to illustrate their proposal: