In recent years, we've seen increasing interest in sending aerial drones to astral bodies such as planets, moons, and asteroids. But some groups are developing crafts meant to explore different environments altogether.
Stone Aerospace is a US-based company developing tools for the purpose of exploration in harsh, complex, and dangerous environments such as underwater—more specifically, underwater environments in space.
The Search for Earth-like Planets
But if Earth is the only known planet to have liquid oceans, why are we building devices meant to explore them among the stars? The answer has a more sweeping scope than is initially obvious.
NASA astrobiologists have developed Project SIMPLE—short for Sub-Ice Marine and PLanetary-analog Ecosytems—as part of ASTEP (Astrobiology Science and Technology for Exploring Planets). As the name implies, the field of astrobiology focuses on searching for and (optimistically) preparing to study extraterrestrial life.
Project SIMPLE aims to use the McMurdo Ice Shelf as a proxy for theoretical ocean-like conditions under the ice of Europa, one of the moons of Jupiter where scientists believe we may have the best chance of finding extraterrestrial life (without needing interstellar travel).
According to a 2015 NASA abstract on the SIMPLE project, Europa's "oceans" are an area of intense interest to the field of astrobiology:
"...just below their respective icy crusts, [Earth and Europa] likely share similar oceanic conditions, including temperatures, pressures... and potentially even salinity. Thus the interface between Earth's thick ice shelves and ocean is an important and little-explored analog for the physicochemical, and possibly microbial, characteristics of icy worlds."
Stone's fleet of underwater vehicles are designed to be ready for explorations of these ocean-like environments. The vehicles specialize in autonomous navigation using laser and sonar navigation, machine learning and artificial intelligence, and innovative hardware for computation and propulsion. The team has also been preparing for eventual exploration of the oceans of Europa and elsewhere by testing their fleets in the cenotes of Mexico, the Antarctic, and underwater caves in Florida.
Here is an overview of some of Stone Aerospace's projects and how they might support exploration in the future.
DEPTHX: An Explorer for the Oceans of Europa
DEPTHX is an autonomous underwater vehicle that was designed to be able to explore and map unknown underwater areas, especially those where no direct navigational operation is possible. DEPTHX boasts the title of being the first robotic system to use 3D SLAM for real-time navigation, the first autonomous system to map an underwater cave, and the first robotic system to autonomously decide how to collect a biological sample.
Image courtesy of Stone Aerospace.
The design of the vehicle is meant to minimize the potential of it becoming snagged in an environment with unknown hazards, hence the smooth ellipsoid shape. It comes equipped with an arm that can extend 1.5 meters to collect samples.
DEPTHX uses two separate systems for navigation: the 3D SLAM navigation system and a dead reckoning system with a ring laser gyroscope, depth sensors, and Doppler velocity log with custom software.
Cenote maps produced by DEPTHX. Image courtesy of Stone Aerospace.
In 2007, the team used DEPTHX to autonomously explore the Zacatón hydrothermal spring complex in Mexico.
In relation to eventual space exploration, DEPTHX could be used to explore the oceans of Europa where the capability to autonomously navigate and collect samples would be important.
ARTEMIS: Detecting Signs of Life Underwater
ARTEMIS is another underwater autonomous vehicle that was designed for eventual use in outerspace—however, this project has a focus on astrobiology detection in unexplored underwater environments.
Onboard the ARTEMIS is an array of sensors and tools for navigation and for detecting the signatures of life: a protein fluorescent spectrometer, a water sample collecting port, a port where water can flow through for pH/Oxygen/CTD measurements, an optical triplet to detect organic matter, and HD cameras with LED lighting.
Some of the sensors on ARTEMIS are also able to extend and penetrate overhead ice to collect measurements and samples. The vehicle also uses 3D sonar for mapping and navigation.
ARTEMIS was tested under the Antarctic Murcado Ice Shelf in 2015.
ARTEMIS under the Murcado Ice Shelf. Image courtesy of Stone Aerospace.
Sunfish: Navigating Complex Environments
Sunfish is the most recent addition to Stone Aerospace’s fleet of underwater exploration vehicles. The team recently tested Sunfish in the underwater caves of Florida’s Peacock Springs, a complicated and labyrinth-like environment where divers can easily find themselves lost.
Sunfish is capable of hovering, moving in any direction, and uses 3D navigation with sonar to map and navigate its environment while avoiding hazards. It tracks the route it travels through caves and is able to navigate back to a home base without becoming lost by recognizing the features in the environment.
Sunfish is also capable of being given a goal, like reaching a point that is 1 mile north of its current location, and will navigate and try to determine the best route to accomplish its task. When the vehicle reaches a dead end, it can back up and try a different path.
The test was the first time an autonomous vehicle navigated through Peacock Springs, reached its goal, and returned to its starting point using autonomous navigation--a successful run for the team, and a step closer to the oceans of Europa.
Sunfish in Peacock Springs. Image courtesy of Stone Aerospace.
AUVs represent an exciting new form of space exploration. Combining object detection, motion planning, and accurate sensing into an autonomous vehicle is a complex task. We've seen that Stone Aerospace has accomplished this with their AUVs in bodies of water here on Earth. But how will they fare in space? Stay tuned and hopefully we'll find out.
Updated December 11th, 2017.
Feature image courtesy of Stone Aerospace.