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.


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