A Hopping Robot to Enhance Europa’s Exploration Using Locally Harvested Water
Key Takeaway
The SPARROW project, developed by engineers from NASA’s Jet Propulsion Laboratory, Purdue University, and Honeybee Robotics, envisions a steam-propelled hopping robot capable of exploring the harsh terrain of Europa, Jupiter’s icy moon. Utilizing locally harvested water for propulsion, SPARROW could revolutionize the way we explore ocean worlds by overcoming terrain obstacles that ground-based robots cannot.
Summary
- SPARROW stands for Steam Propelled Autonomous Retrieval Robot for Ocean Worlds.
- The robot is designed to be “terrain agnostic,” capable of navigating Europa’s harsh surface.
- It requires a lander for deployment, refueling, and sample storage.
- Europa Clipper, a NASA mission to Europa, is not suitable due to its lack of a lander.
- SPARROW’s propulsion system uses a “hot water thruster,” heating water to create thrust.
- The robot’s gimballed design allows for trajectory correction and sample collection.
- Challenges include preventing ice blockages in the propulsion system.
- Phase II funding is needed for further development, but the project is currently stalled.
Introduction
Various forms of hopping robots have crept into development for use in different space exploration missions. We’ve reported on their use on asteroids and even our own Moon. However, a study funded by NASA’s Institute for Advanced Concepts (NIAC) in 2018 planned a mission to a type of world where hopping may not be as noticeable an advantage—Europa.
The mission, developed by engineers at NASA’s Jet Propulsion Laboratory, Purdue University, and Honeybee Robotics, is known as the Steam Propelled Autonomous Retrieval Robot for Ocean Worlds, or SPARROW. It’s about the size and shape of a soccer ball, with the logic, power, and control systems inside a spherical outer hollow shell.
The Concept of SPARROW
Design and Deployment
SPARROW wouldn’t be able to operate on its own, however. It would require a lander to deposit it onto the surface and serve as a refueling and sample collection storage base. Europa Clipper, the only currently planned NASA mission to the icy moon, would have been good for hitching a ride, but its lack of a lander made it unsuitable for SPARROW.
Budget Constraints
Budget constraints are always a problem for innovative missions. However, the hopping robot itself is well-suited for the environment on Europa. Its designers intended to make it “terrain agnostic,” meaning it could traverse even the harshest terrain the icy moon could throw at it. These would include penitentes, shards of ice that could be meters tall and difficult for ground-based robots to traverse.
SPARROW could fly over them, collect interesting samples, and return to the lander to refuel and deposit them. Then, it could go out again in a different direction. To model this system architecture, the JPL team spent Phase I trying to determine the best propulsion system for the robot and modeling control algorithms for the flights.
Propulsion System
First, let’s tackle the propulsion system. The lander accompanying SPARROW would have to mine ice off the moon’s surface, then heat it and store it as water. When SPARROW returned from a hop, it would use the water to refuel. Five different propulsion methods were considered as part of the study. Still, the best turned out to be a “hot water thruster,” where SPARROW would internally heat the water supplied by the lander, then eject that out in a burst of propulsive force to launch the robot off the surface.
Control System
The second major part of the paper was controlling that propulsion. Trajectory correction is critical to mission success, but in this case, the designers believe that no matter where the robot ends up, it will be able to collect a sample and return to the lander. This is due to its gimballed design, which allows the robot to consistently orient correctly, even after bouncing along a frozen surface for a while.
Challenges and Future Prospects
Ice Blockages
There is still much work to do before the mission is ready to go, though. Some of the most pressing questions are how to stop ice from forming in the robot’s propulsion nozzle and throughout its structural cage. Such blockages could easily throw off any existing trajectory calculations and theoretically immobilize the hopper entirely if they were severe enough.
Funding and Progress
However, no work is planned to solve those problems for now as the project has yet to receive Phase II funding from NIAC, and work on it appears to have stalled. Dr. Gareth Meirion-Griffith, the primary investigator on the project, has moved on from JPL to take a job at Collins Aerospace. Even so, someday, the author’s ideas might be integrated into a Europa lander mission—we’ll have to wait and see.
Technical Details
Propulsion System Analysis
Table 1: Propulsion Methods Considered
| Propulsion Method | Description | Suitability for Europa |
|---|---|---|
| Hot Water Thruster | Heats water and ejects it for thrust | High |
| Cold Gas Thruster | Uses compressed gas for propulsion | Moderate |
| Electric Propulsion | Uses electric fields to accelerate ions | Low |
| Chemical Propulsion | Combines fuel and oxidizer for a chemical reaction | Low |
| Nuclear Thermal Propulsion | Uses a nuclear reactor to heat a propellant | Very Low |
The hot water thruster was chosen for its efficiency and the availability of water on Europa’s surface.
Control System Design
The gimballed design of SPARROW allows it to maintain orientation and control its trajectory even after bouncing on the icy surface. This system ensures that the robot can always return to the lander for refueling and sample deposit.
Table 2: Gimballed Design Features
| Feature | Description |
|---|---|
| Orientation Control | Maintains correct orientation after bouncing |
| Trajectory Correction | Allows for mid-hop adjustments to ensure accurate landing |
| Sample Collection | Ensures samples are collected regardless of final landing position |
| Refueling Capability | Returns to lander for refueling and sample deposit |
Potential Impact and Future Missions
Advancing Exploration
Exploring the surface of Europa is only one part of its mystery. The potential to discover signs of life or understand the moon’s geological history could provide invaluable insights into the broader field of astrobiology.
Future Missions
Future missions could incorporate SPARROW into more comprehensive exploration plans, using its hopping capability to cover large areas of Europa’s surface. This could complement other landers and orbiters, providing a multi-faceted approach to studying the icy moon.
Conclusion
The SPARROW project offers a new way to explore Europa’s harsh and fascinating terrain. It uses water found on the spot for propulsion. Propulsion means moving something forward. SPARROW also has a gimballed design to correct its path. A gimballed design is a setup where something can move in different directions to stay balanced. This design helps SPARROW navigate the icy surface of Europa. Although there are still funding and technical challenges, this technology could greatly change how we explore ocean worlds.
References
- This Hopping Robot Could Explore the Solar System’s Icy Moons
- SPARROW: Steam Propelled Autonomous Retrieval Robot for Ocean Worlds
- A Robot Hopper to Explore the Moon’s Dangerous Terrain
- Miniaturized Jumping Robots Could Study An Asteroid’s Gravity
