Researchers are developing an innovative insect-like robot with extendable legs to explore the challenging terrain of caves and lava tubes on the Moon and even Mars.

"These are... very interesting spaces to explore. They're relatively sheltered. If there are any signs of previous life, that's a good place to look for them. Also, if we're thinking eventually about human habitation, that's a good place to build a shelter," said Mark Cutkosky, professor of mechanical engineering at Stanford University School of Engineering.

While Martian caves are a tantalizing goal of future exploration of the Red Planet, we don't yet have a definite idea of their structure. The Stanford University-built ReachBot robot is designed to have the adaptability for whatever cave structure it may find itself in.

"The goal of ReachBot is to develop a robot that can access extreme environments on other planets such as Mars or the moon, where typically robots cannot really go," said Marco Pavone, associate professor of aeronautics and astronautics at Stanford University School of Engineering.

ReachBot was inspired by the structure of an arachnid, featuring a small body and long extendable appendages equipped with grippers. These grippers can latch onto rocky surfaces, allowing the robot to effectively navigate these difficult environments.

It's being developed by the Biomimetics and Dextrous Manipulation Lab at Stanford who are experimenting with different prototypes. The Mars-ready robot will have custom-engineered extendable booms, but its prototypes start out more modestly using humble tape measures for testing.

"These arms are made out of space booms. Just imagine them as a 3D tape measure," said team member Tony Chen.

"To prototype ReachBot we actually used a lot of tape measures in these because they serve functionally almost identical to space booms."

The cave-crawling ReachBot is equipped with sensors and a contact-before-motion planner, enabling it to scan its surroundings and identify graspable features on rocky surfaces. This technology allows the robot to maintain tension in its appendages, similar to the mechanism of a multi-fingered hand.

"A robot needs to reason about all the different possibilities and all these different uncertainties in order to compute an effective and safe path. And to this task, the plan is to use different techniques from optimization and artificial intelligence to reason on the fly about all of these different possibilities," added Pavone.

To validate the performance of ReachBot, a field test was conducted in a lava tube in the Mojave Desert, California. The test confirmed the robot's ability to identify and securely grasp multiple sites, demonstrating its potential for future exploration missions in the challenging terrains of the Moon and Mars.

Further prototyping is planned to refine the design, while the researchers say similar long-limbed robots could have a variety of applications in space.

"The end goal, at least for planetary exploration, is to go places where no robot has been able to go before," added Cutkosky.

"What else out there in space is an application for which having a small body with a very long reach could be useful? Could it be useful for maintaining structures in space? Or in orbit? Could it be useful for exploring certain parts of the moon or for asteroids?"