The success of NASA's Mars rovers Spirit and Opportunity has scored high points for the wheeled automatons, but another plan may one day have their robotic successors hopping.

That plan, according to its research team, calls for a swarm of small, spherical robots the size of tennis balls to hop across another world exploring caves, nooks and other crannies that past mobile robots have been too large to study.

"The individual units are very cute and very adorable," Penelope Boston, one of two researchers spearheading an effort to study the hopping microbots, told SPACE.com. "But the function of them as an ensemble is where the real strategy lies."

Boston and microbots principal investigator Steven Dubowsky - head of the Field and Space Laboratory at the Massachusetts Institute of Technology (MIT) - won $400,000 in funding this year from the NASA Institute for Advanced Concepts (NIAC) to push their research forward.

"It's rather a unique robot concept," said Robert Casanova, NIAC director, in a telephone interview. "Most others have been either wheeled vehicles or walking or staggering ones. The hoppers have the advantage of getting into very difficult, tight spaces, say in caves, whereas one of the larger rovers might be cumbersome."

It is precisely the microbots potential for planetary spelunking - on Mars, Earth, the Moon or otherwise - that grabbed Boston's attention.

"I want to try and get into those kinds of places," said Boston, who directs cave and Karst studies at the New Mexico Institute of Mining and Technology, adding that they could be a vital tool to detect organisms on Earth or in space. "It's very important to make devices for life detection on Mars, for example...Any planet or moon with a solid surface will do."

Swarming Mars

A single golf-cart sized Mars rover weighs about 384 pounds (174 kilograms) and includes a sophisticated suite of cameras, spectrometers and other geological tools to study the red planet's surface.

"We (put) about 1,000 of these microbots into that mass," Boston said. "And that would allow a great diversity of robots."

The microbots envisioned by Dubowsky and Boston would push themselves along using a polymer-based artificial muscle that would kick them about one meter forward about once every hour. They would also be capable of carrying a miniaturized suite of science instruments, such as cameras, spectrometers or other sensors, that could be tailored for a specific mission.

"The instruments to study the surface would be different that if you were aiming at a lava tube," Boston said, adding that a proper fuel cell and hardy, resistant shell are vital foundations for a viable microbot system. "They have to be big enough to carry the kind of fuel cell that can power their systems, but not be too small that they get wedged into everything."

Current plans call for microbots that could be deployed via lander, rover, aerial vehicles, orbital platforms or even an astronaut scattering the automatons by hand.

An open line

The other benefit of a microbot swarm is redundancy, Boston said.

Not only could a series of individual units be lost without compromising a mission's integrity, a network of functional microbots could provide a vital relay link to a remote base or orbital craft during subsurface exploration.

"These guys need to keep in communication with each other," Boston said. "So they could set up a node-to-node communications system a lot like a cellular [phone] network. Everybody will know where everybody else is."

From that base, the microbots could eventually be capable of complex behavior, she added.

Earthly cave dwellers

Before they set hopper on another world, microbots will likely make their first jumps through terrestrial caves on Earth, researchers said.

"I think we'll come out of this with unique technology and units that we can test in the lava tube caves here," Boston said. "We've already done some testing to look at the size of the units and how they would bounce on a rugged surface."

An actual working, instrumented microbot is at least a few years off depending on the level of funding, but would prove a vital resource in studying hazardous regions within Earthly caves, according to Boston.

"One of our caves in New Mexico is sulfuric acid-filled, and others have really small passages that humans can't get into," she said. "I can't wait to have my own fleet of these guys."