Rob Mueller is the Lead Senior Technologist for the RASSOR (Regolith Advanced Surface Systems Operations Robot) project, as well as all Kennedy Space Center (KSC) Human Robotics Systems. The RASSOR mining robot will collect soil (known as regolith) on the moon or Mars so it can be processed into rocket propellants, breathable air, water, and other consumable commodities as well as manufacturing and construction materials feed stocks.
NASA Tech Briefs: Rob, How is the RASSOR designed, and what is it able to do?
Rob Mueller: Traditionally, the construction equipment on Earth is called heavy equipment. The reason it’s called heavy equipment is because the reaction force required to dig soil on the Earth is quite large, and the weight of the machine provides the reaction force. Typically, you’ll see these big yellow machines on construction sites doing excavation.
On the moon, we don’t have that luxury. On the moon, the gravity is one sixth the gravity on Earth, so everything is very light. If you had a small, traditional front-end loader on the moon, and you tried to dig up the regolith, or the lunar soil, it wouldn’t actually penetrate the soil. It would just do a push-up. There wouldn’t be enough reaction force on the machine, so we have to think about ways to do things differently. That means reconsidering the whole design of excavation and construction equipment on the moon.
NTB: How does the moon's reduced gravity produce challenges for the machine? Does that affect the wheels and other parts of the design?
Mueller: The problem is the same on the moon, or Mars, or asteroids, or any reduced gravity environment; basically, it’s this problem of not having enough reaction force. Another problem that we have is that the regolith is very abrasive. It’s a powder. Think of it as being like crushed glass. It’s basically basalt that is crushed by meteorites that have impacted the moon and other bodies over 4.5 billion years. This regolith is very difficult to work with. It’s also electrostatically charged, and it’s highly abrasive.
So if you combine the different environment and new materials, it’s a new problem. To tackle that new problem, we designed new kinds of machines. And one example of those machines that we designed is the RASSOR robot. The RASSOR robot completely rethinks the way we do excavation. Instead of using the weight of the machine to push against the bucket driving into the soil, we’ve come up with a new configuration that’s called a bucket drum. The bucket drum has lots of little scoops, and each scoop has a very small force. Then we have two bucket drums with counter rotating forces, so the forces cancel each other out. Now you don’t need a heavy machine. Now a small machine that weighs about 50 kilograms can do a similar job to a very heavy machine.
NTB: How does this robot differ from rovers of the past?
Mueller: NASA rovers of the past have been very slow, very precise, and they carry very delicate instruments and very highly technological devices that cannot take much punishment. What we need when we’re digging regolith is a very lightweight machine that’s extremely robust. This RASSOR robot is designed to be very fault-tolerant. It can actually tumble. If it falls, it can pick itself up. It can flip itself over. It can do acrobatics. It has very few instruments on it. It’s more of a digging machine than a scientific robot like we’ve built in the past.
NTB: What kinds of commodities can be made with the moon's resources?
Mueller: The recent [Lunar CRater Observation and Sensing Satellite] LCROSS mission has shown us that almost every element we need exists on the moon. The LCROSS mission showed in the plume that carbon monoxide was present and also large quantities of water ice, about 5.6 percent. We could extract oxygen from the regolith. Forty-two percent of most of the lunar regolith (by mass) is oxygen.
We also now know that there is water ice in the regolith at the poles of the Moon and Mars, and possibly asteroids as well like Ceres. If we can extract the water ice from the regolith, that’s extremely valuable. Water ice can be used in propellant. It is also used for drinking water, for life support, and for growing plants. Water is the key to surviving in the solar system for humans. So if we can build robots that can mine the water ice out of the regolith, that is the first step towards expanding civilization into the solar system.
NTB: How will it actually work, when the RASSOR robot actually lands on the moon?
Mueller: The first step in any mining operation is prospecting. The first thing we would do is use robots like RASSOR and similar robots like the Regolith and Environment Science and Oxygen and Lunar Volatiles Extraction (RESOLVE] rover, which has a drill attached to it, and we would actually do some prospecting. Once we’ve identified the exact location of the ore, which is the water ice, then we start digging.
We would use the RASSOR robot to dig a trench. We suspect that the water ice is underneath an overburden of regolith. If you can dig down below 30 cm, between 30 cm and 1 meter, thermal projections show that water ice could be stable in those kinds of environments. So if we could dig a trench and dig down to 1 meter, we suspect that we’ll find large quantities of water ice at those depths in permanently shallow craters. Once we discover the water ice, we can acquire the water ice, mine it, and bring it back to the lander. And on the lander, we’ll have a processing machine. In that processing chemical plant, we’ll extract the water, we’ll clean it up, we’ll electrolyze it, and then we’ll use it in terms of hydrogen and oxygen and other feed stocks.
NTB: How long is it meant to operate for?
Mueller: We’ve done our calculations, and we think that to support a crew of four, we’ll need about ten metric tons of oxygen per year. So if you do the projections based on that, a robot the size of RASSOR would have to work 16 hours a day all year long. Not only that, you’d need four of those machines to achieve those quantities. These machines have to be very robust and be actually capable of working basically two shifts a day, every day.
We have also designed the robot to work for 5 years, almost every day. That’s a very tall command for a machine in a very difficult and extreme environment. It’s an engineering challenge, and we’re building prototypes to test the prototypes. Then, by incrementally increasing the fidelity of the prototypes, we can achieve designs that have this capability of being able to operate for 5 years in an extreme environment such as Mars or the moon.
NTB: How has the most recent testing gone, and have there been modifications to the design because of the testing?
Mueller: We’ve done some testing in lunar regolith simulant. Not in a vacuum. Just in the earth environment with lunar regolith simulant. And we’ve learned a lot. The first thing we’ve learned is that the mobility aspect is extremely difficult. You’re digging a trench, and driving in and out, and the slopes can be higher than 30 degrees, and the regolith is also very loose. When the regolith is loose in a reduced-gravity environment, it is very difficult to achieve traction. We have tried to solve that problem with tracks. Similar to Caterpillar tracks, we’ve discovered that the tracks are quite prone to jamming and difficult to operate in a dusty environment such as regolith. Our recent test experience has shown the tracks are challenging, and the next prototype will probably use wheels to try to solve the same problem.
NTB: Is that the RASSOR 2?
Mueller: The RASSOR 2 prototype will be redesigned to incorporate all the lessons learned from RASSOR 1, and we will improve the digging mechanism, we will make it lighter, we’ll use advanced materials, and we’ll use a new mobility system.
NTB: When will this be space ready?
Mueller: Typically, we design machines on the Technology Readiness Level (TRL) scale. The TRL scale goes from a 1 to 9 — 1 being when you have a new idea and 9 when it’s flown in space and proven. Typically, we develop a technology until we achieve TRL 6. At TRL 6, it becomes a candidate for a mission. Right now RASSOR is at about TRL 4, so we probably have a few more years of work to achieve TRL 6, and then we would start thinking about using it in a real mission.
NTB: What do you think is the RASSOR’s most innovative features?
Mueller: The most innovative features are the fact that it doesn’t have a separate dump bin. Most machines dig and transfer soil from the bucket to the dump bin. Then, they drive and dump the soil into the end device, like a hopper on a chemical plant. What we’ve done is we’ve incorporated everything into the bucket drum so that it has a very low digging force (because the bucket drum has small scoops), and then the regolith can be carried by the bucket drum. It doesn’t have a separate mechanism to carry it, and then it can actually be delivered.
The most innovative feature of the whole design is the counter-rotating bucket drums, which completely cancel out the horizontal digging force. It combines the load/haul/dump functions into the one extremely simple mechanism, inspired by Occam’s Razor line of reasoning that says the simplest answer is often correct. It should be able to dig on an asteroid, which is extremely challenging.
NTB: What is a typical day for you? What kinds of work do you do with the RASSOR?
Mueller: We always try to come up with new innovative ideas, and that involves a lot of brainstorming. We have a special environment that we built out in our facility called the Swamp Works. The Swamp Works has a special location called the “innovation space.” In the innovation space, we have a lot of whiteboards, tools, and devices designed to stimulate and promote innovation. What it boils down to is a facilitated innovation process of brainstorming, and we get the team together and we really try to think of new ways to meet our requirements.
Once we’ve finished the brainstorming, we’ll do a very quick, efficient prototype to prove the concept. Once the concept is proven, we’ll start designing an actual machine and build it to test it. Then we’ll repeat that cycle several times before we actually have a real robot that’s ready to go to outer space.
NTB: How do you see the RASSOR contributing to space exploration in the future? What do you see as the possibilities?
Mueller: In the past, we’ve talked about big missions delivering a lot of hardware and Constellation-class landers, which deliver up to 15 metric tons to the surfaces of other planets. The reality is: The recent Mars Science Lander mission, for example, could only land about 1000 kilograms on Mars. The reality is we can only deliver small payloads to other planetary surfaces. What that means is we have to shrink the size of our machines down, and be able to do the job with smaller machines, or even swarms of small machines. So we think we have to develop new robots that are small and lightweight and still do the job.
NTB: What is your favorite part of the job?
Mueller: My favorite part is the creative aspect of being able to design new devices and solve problems. We have taken the first small steps to making humanity a spacefaring civilization. If we can actually harness the resources in our solar system and in the universe, that’s the key to being able to exist in outer space as a spacefaring civilization. That’s why it’s so important to acquire these resources with robots like RASSOR.
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