Rock Abrasion Tool for Mars Exploration

At Honeybee Robotics in Greenbelt, MD, Steven Indyk, Director of Space Systems, reflected on one of the company’s most celebrated contributions to space exploration: the Rock Abrasion Tool (RAT). Developed for NASA’s Spirit and Opportunity Mars Exploration Rovers, the RAT was a first-of-its-kind instrument designed to expose the untouched interiors of Martian rocks.

Mounted at the end of each rover’s robotic arm, the RAT functioned as what Indyk calls “the geologist’s hammer” of the mission. The compact, three-degree-of-freedom system was engineered to grind through Mars’ oxidized crust, which are layers that obscure the chemical and mineral story beneath. 

“It’s there to open up the rocks on the surface of Mars to get past any of the oxidized and weathered layers,” he explained.

By exposing fresh rock faces, the tool allowed other instruments to analyze their true composition. The reddish, weathered exteriors often held little scientific value, but the interiors contained a treasure trove of data. 

“If you can look on the inside, you can get a lot more valuable scientific information,” Indyk said. “Basically revealing the secrets of the rock.”

Built on earth, proven on mars

Before ever leaving Earth, the RAT underwent hundreds of rigorous tests in Honeybee’s labs. Engineers used basalt from California’s Mojave Desert to simulate the conditions the rovers would face millions of miles away.

“We did a whole test series of over 300 tests using different Earth environments and Mars ambient environments, using a vacuum chamber and thermal conditions,” Indyk recalled.

At the core of the tool was a small but powerful cutting bit embedded with diamond and resin. It rotated about its own axis while orbiting a larger one, creating perfectly round, 45-millimeter openings on rock surfaces. The RAT’s twin brushes cleared debris as it worked, leaving behind what Indyk describes as “the highest accuracy polish that has ever been accomplished off the planet Earth.”

The instrument’s precision came from a combination of mechanics and control. The RAT was positioned on the Martian surface using two stabilizing arms that were nicknamed “butterflies,” which pressed against the rock to ensure a steady, controlled grind. 

“The robotic arm would place the RAT onto the rock and apply a known force,” Indyk said. “That way, we would know our position very precisely and would not slip off the surface.”

Designed to remove just the outer rind, the RAT could grind as deep as 12 millimeters when needed. Each carefully abraded circle gave scientists a clear view of Mars’ true geology.

When Spirit and Opportunity landed in 2004, each equipped with a RAT, the mission was expected to last 90 days. Instead, the rovers kept operating for years—far beyond expectations. 

“This year marks the 20th anniversary of a very successful mission that was originally designed to last 90 days,” Indyk noted.

Commanding from 140 million miles away

Operating a robotic tool on Mars required an intricate communication network and extensive planning. Teams at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena wrote daily command sequences that were transmitted through NASA’s Deep Space Network, a trio of massive antenna arrays in the U.S., Spain, and Australia. Those signals were then relayed to orbiters circling Mars before reaching the surface.

“There’s a common misconception that operating a rover on another planetary surface is like using a joystick,” Indyk said. “The truth is, it takes many days of planning, and it’s done autonomously.”

Due to the roughly half-hour communication delay between Earth and Mars, the RAT could not be operated in real time. Instead, Honeybee and JPL teams scripted multi-day sequences in advance. 

“It’s almost impossible to tele-operate something on the surface of Mars,” Indyk explained. “But we have a very reliable team and system that’s been tested for years and years.”

As the Payload Uplink and Downlink Lead (PUL and PDL) for the RAT, Indyk oversaw both the sending of commands to the rover and the interpretation of data it returned. 

“It was my responsibility to send the commands for everything that the RAT would do,” he said. 

Once the data arrived back on Earth, his team verified whether the operations succeeded and adjusted for the next cycle if needed.

The science that stayed on mars

The RAT didn’t collect or store material. Instead, it ground away the weathered outer layers so other instruments could analyze the newly revealed surfaces in situ. 

“The RAT grinds material, removing the outside layer of the rock,” Indyk said. “Then the other science instruments would look at the inside surface of that RAT hole.”

All of this science stayed on Mars, since none of the samples were returned to Earth. 
“That would be a different mission,” Indyk noted, as he referred to the long-anticipated Mars Sample Return project.

Even without bringing home physical samples, the RAT’s impact was profound. The tool’s performance validated Honeybee Robotics’ approach to planetary surface engineering and helped define how future missions would study extraterrestrial geology.

“The Spirit and Opportunity Mars Rover Mission was extremely successful,” Indyk said. “It really set the pace and raised the bar for all future Mars exploration missions.”

Twenty years later, the circular abrasions left behind by the RAT remain visible on the Martian surface—each one a mark of human ingenuity and mechanical precision.

“Simply speaking, the RAT was the geologist’s hammer on Mars,” he said. “It revealed the planet’s true secrets, one grind at a time.”

Video by ASME’s Video Production Team. Article by Aida M. Toro.