Exploring Mars caves, leaving ‘breadcrumbs’

Exploring Mars caves: Underground cave with shafts of sunlight from openings in top, and small robotic rovers on the ground.
View larger. | This is an artist’s depiction of small autonomous rovers inside an ancient lava tube on Mars. Researchers at The University of Arizona have developed a new system of such rovers for exploring Mars caves or lava tubes. Like in the fairy tale Hansel and Gretel, they would leave “breadcrumbs” – communication nodes – to help maintain contact with each other and a mother rover on the surface. Image via John Fowler/ Wikimedia Commons/ Mark Tarbell/ Wolfgang Fink/ The University of Arizona.

Future astronauts on Mars might use caves or lava tubes as habitats. They could provide shelter from the harsh conditions on the surface, the intense radiation in particular. On March 1, 2023, researchers at the University of Arizona said they’ve developed a new technology where small autonomous robot rovers could start exploring caves on Mars. The rovers – inspired by the fairy tale Hansel and Gretel – would drop high-tech “breadcrumbs” to find their way.

In this case, the “breadcrumbs” would be miniature sensors, which the robots would deploy within the caves in order to monitor their environment and remain in contact with each other. In this way, they could scout for suitable underground places for future astronauts to live and work.

The journal Advances in Space Research published the peer-reviewed details of the proposed new technology as a pre-proof on February 11, 2023.

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Exploring Mars caves, with inspiration from Hansel and Gretel

Current rovers are too large to explore caves easily. A flock of smaller robots, however, could do so, and engineers would design them for just that purpose. Also, in those dark subsurface environments, they would need to be able to efficiently monitor their surroundings and stay in contact with each other. The newly devised system is called the dynamically deployed communication network (DDCN).

Additionally, they would also require a “mother rover” that remains on the surface. This is where Hansel and Gretel comes in. As lead author Wolfgang Fink at the University of Arizona explained:

If you remember the book, you know how Hansel and Gretel dropped breadcrumbs to make sure they’d find their way back. In our scenario, the ‘breadcrumbs’ are miniaturized sensors that piggyback on the rovers, which deploy the sensors as they traverse a cave or other subsurface environment.

The University of Arizona also tweeted about the newly developed system on March 1:

Exploring Martian caves: Crater seen from above with deep round hole in its center.
View larger. | NASA’s Mars Reconnaissance Orbiter (MRO) took this photo of a crater on the slope of the Pavonis Mons volcano in 2011. In the bottom of the crater is a deep hole that scientists say is a cave or lava tube. In the future, flocks of small autonomous rovers could explore these underground environments. Exploring Martian caves or similar subsurface environments would be exciting … what might we find? Image via NASA/ JPL/ University of Arizona/ APOD.

Fully autonomous rovers

The little rovers are autonomous and depend on each other to do their mission. So, if one rover gets far away from another, but is still within communications range, it will drop a breadcrumb, aka a communication node. Fink refers to these breadcrumbs as “opportunistic deployment.” He said:

One of the new aspects is what we call opportunistic deployment, the idea that you deploy the ‘breadcrumbs’ when you have to and not according to a previously planned schedule.

The exploratory rovers don’t even need the mother rover to communicate with each other. Indeed, they can do that quite easily on their own. The mother rover is more of a passive recipient, collecting data transmitted by the smaller rovers. In this case, it acts as the orchestrator, controlling the rovers’ movements.

Since 2001, Fink and his colleagues have been working on something called tier-scalable reconnaissance. This involves teams of robots working together but at different levels. As a current example, the Perseverance rover on Mars controls the smaller Mars helicopter called Ingenuity. Generally speaking, the small autonomous rovers would work the same way. But in the breadcrumb scenario, this ability would be enhanced, allowing the rovers to operate underground.

Small robotic rover with tractor-like treads for wheels and 2 cameras.
An experimental rover used for testing hardware and software related to autonomous exploration. Image via Wolfgang Fink/ The University of Arizona.

Sending information to the surface

The exploratory rovers are always in contact with the mother rover. Therefore, they can send their data to the mother rover without ever having to go back up to the surface themselves. In fact, they would remain down in the subsurface until they died. Fink said:

They’re designed to be expendable. Instead of wasting resources to get them into the cave and back out, it makes more sense to have them go as far as they possibly can and leave them behind once they have fulfilled their mission, run out of power or succumbed to a hostile environment.

Astrobiologist Dirk Schulze-Makuch in Germany added:

The communication network approach introduced in this new paper has the potential to herald a new age of planetary and astrobiological discoveries. It finally allows us to explore Martian lava tube caves and the subsurface oceans of the icy moons, places where extraterrestrial life might be present.

Victor Baker at the University of Arizona also noted that:

The most amazing discoveries in science come about when advances in technology provide both first-time access to a thing or place and the means of communicating what is thereby discovered to creative minds that are seeking understanding.

Habitats for future astronauts

One of the primary objectives would be to find subsurface caverns that astronauts could use as shelters. As the paper explains:

Subterranean caverns, and in particular relatively deep lava tube caves, provide a possible refuge for life under otherwise challenging planetary surface conditions, and, as such, are of prime astrobiological relevance.

Lava tube caves or other subsurface environments may also be suitable habitats for astronauts and subsequent human settlement but are yet to be explored, in part due to difficulties ensuring continued communication with a robotic probe inside these environments.

Small rover with 6 wheels and flat top.
View larger. | This was NASA’s first and smallest Mars rover, called Sojourner. It was only 26 inches (65 cm) long! The larger Mars Pathfinder “mother lander” took this image in 1997. In the future, similar but significantly more advanced mini-rovers could explore caves and lava tubes on Mars. Image via NASA/ JPL/ NASA Photojournal.

Exploring Mars caves … and beyond

Other similar but even more advanced missions could involve robotic explorers underwater. This could include the icy ocean moons in the outer solar system.

For example, small robotic probes could explore the methane lakes on Saturn’s moon Titan or even the subsurface oceans of Europa or Enceladus. As with Mars, a mother probe could float on the surface on a Titanian lake or sit on the ice above a subsurface ocean. In this case, the communication nodes would act as repeaters, boosting the signal in regular intervals. This would help prevent the signal from degrading. Even the nodes could gather data, such as measuring pressure, salinity, temperature and other chemical and physical parameters. On these worlds, however, the nodes would send the data back to the surface lander by using a cable. As Fink noted:

Imagine you make it all the way to Europa, you melt your way through miles of ice, make it down to the subsurface ocean, where you find yourself surrounded by alien life, but you have no way of getting data back to the surface. That’s the scenario we need to avoid.

Bottom line: Researchers have developed a “breadcrumb” system that small autonomous robot rovers might use in exploring Mars caves and lava tubes.

Source: A Hansel & Gretel Breadcrumb-Style Dynamically Deployed Communication Network Paradigm using Mesh Topology for Planetary Subsurface Exploration

Via the University of Arizona

March 10, 2023

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