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We are in 2038. After 18 months of life and work on the surface of Mars, a crew of six explorers board a space rocket and depart for Earth. No humans are left behind, but the work continues without them: autonomous robots will continue to operate a chemical and chemical synthesis plant that they started years before this first crewed mission ever put them on the road. feet on the planet. The plant produces water, oxygen and fuel for rockets using local resources and will methodically build all necessary supplies for the next Mars mission, which is expected to arrive in two years time.
This robot factory is not fiction: It is developed jointly by several NASA teams. One of them is the Swamp Works Lab at NASA's John F. Kennedy Space Center in Florida, where I am a team leader. Officially, it is an in situ resource utilization system (ISRU), but we like to call it factory because it turns a simple dust into rocket fuel. This technology will one day allow humans to live and work on Mars – and return to Earth to tell the story.
But why synthesize elements on Mars instead of shipping them from Earth? NASA invokes the "transmission ratio problem". According to some estimates, to carry a kilo of fuel from Earth to Mars, the current rockets must burn 225 kilos of fuel in transit: they launch into a low Earth orbit, move to Mars and slow down to enter Martian orbit, then slow down to land safely on the surface of Mars. We would start with 226 kg and finish with 1 kg, which gives a transmission ratio of 226: 1. And the ratio stays the same no matter what we ship. We would need 225 tons of fuel to send a ton of water, a ton of oxygen or a ton of machinery. The only way to get around this harsh arithmetic is to put our water, oxygen and fuel on the site.
Different NASA research and engineering groups have been working on different parts of this problem. More recently, our Swamp Works team began integrating many distinct work packages to demonstrate the entire closed-loop system. It's still a prototype, but it shows all the parts needed for our dust factory to become a reality. And although the long-term plan is on Mars, NASA is focusing its attention on the moon. Most of the equipment will be tested and developed on the lunar surface, which will help reduce the risk of sending everything directly to Mars.
The dirt or dust of any celestial body is commonly called regolith. . It is most often volcanic rock that has been crushed or altered over time into a fine powder. On Mars, under a layer of rusty ferrous minerals that gives the planet its famous reddish hue, lies a thicker layer of silicates with names such as feldspar, pyroxene and olivine, made up of silicon and oxygen structures bonded to metals such as iron, aluminum and magnesium.
The excavation of this material is difficult because its consistency and compactness vary from one place to another on Mars. But what makes the task even more difficult is the low gravity of the planet, which makes it difficult to push a shovel into the ground without using your weight to counteract this force. On Earth, when we dig in the ground, we often use large vehicles, as their heavy bodies respond appropriately to the forces of the digging bucket much smaller. But remember the problem of the transmission ratio: every ounce launched on Mars is precious and very expensive. So we had to find a way to dig on the surface of Mars with very light equipment.
Enter RASSOR, or Regolith Advanced Surface System Exploitation Robot, an autonomous mining vehicle designed for a specific purpose: digging or excavating the regolith in low gravity conditions. When designing RASSOR, said the "razor", NASA engineers paid close attention to its actuation system. Robot actuators include motors, gearboxes, and other mechanisms that account for a large percentage of the final mbad of the system. In our design, we used frameless motors, electromagnetic brakes, and 3D printed titanium housings, among other things, to keep weight and volume to a minimum. This effort paid off: our design uses about half of the mbad of current standard actuators with similar characteristics.
To dig, RASSOR uses two opposed bucket drums, each equipped with several small digging tanks. When RASSOR's bucket drums spin and the arms holding them down, they only collect a small amount of regolith in each dig as it moves slowly. This creates a shallow trench rather than a deep hole. These rotating bucket and digger drums are hollow inside, allowing them to collect and retain the excavated regolith. Another key feature of RASSOR is that while digging, bucket drums rotate in opposite directions. This cancels out a large part of the digging forces and will allow RASSOR to carry out low gravity excavations.
Once RASSOR has filled his bucket drums, he raises his arms and goes to a treatment facility. To unload the regolith, the robot simply turns the drums in the opposite direction and the regolith comes out of the same teaspoons where it entered. Another piece of equipment, a robotic hopper lift arm, handles the next task. He lifts a load of regolith on the deck of the plant and transfers it to an oven that closes and begins to heat up. Any molecule of water attached to the regolith is driven off by a dry gas fan and then collected with the help of a condensing tube called cold finger.
You may be wondering, "But is the regolith on Mars not dry?" The answer is … it's complicated. It mostly depends on where you dig and how deep you dig. Some areas on Mars seem to have almost solid ice sheets a few feet below the surface. At low latitudes, there are gypsum sand dunes composed of about 8 percent water by weight.
Once cleared of water, the regolith is thrown to the ground so that the RASSOR robot can pick it up and carry it. This "waste" can actually be used for building protective structures or even roads and landing strips, using the 3D printing methods being developed at NASA.
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1. MINES: A wheeled robot digs the regolith by rotating bucket drums equipped with toothed buckets. All illustrations: James Provost
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2. TRANSPORTING: Turning the drums in the opposite direction, the robot unloads the regolith collected in a robotic hopper lift arm.
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3. TREATMENT: An oven heats the regolith to extract water that is electrolysis in H 2 and O 2 . A Sabatier reactor combines H 2 with CO 2 collected in the atmosphere to produce methane.
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4. TRANSFER: A robotic umbilical arm – equipped with a set of lockable doors to prevent dust – from transferring fluids to a mobile tanker.
6 USE AND STORAGE: Astronauts consume water and oxygen – also used for growing plants – while fuel is stored as cryogenic liquids for future use. "/>
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5. DELIVERY: The petroleum robot supplies water, oxygen and methane to human habitats and long term storage tanks.
6. USE AND STORAGE: Astronauts consume water and oxygen – also used for growing plants – while the fuel is stored as a cryogenic liquid for future use.
All water extracted from the regolith is then purified. The cleaning module uses a multi-stage filtration system as well as several deionization beds.
Water is not just for drinking; it is also the key ingredient of rocket fuel. By splitting the molecules H 2 O with an electrolyser into molecules of hydrogen gas (H 2 ) and gaseous oxygen molecules (O 2 ) , then compressing and liquefying These two gases separately, we can synthesize the fuel and oxidant most commonly used in liquid fuel rocket engines.
The problem is that liquid hydrogen has to be stored at extremely low temperatures. This is why NASA plans to turn hydrogen into a much easier fuel to store: methane (CH 4 ). You can get it by combining hydrogen and carbon. But where do we get carbon on Mars?
Fortunately, Mars has a lot of carbon. The Martian atmosphere is composed of 96% of carbon dioxide molecules. Capturing this carbon is the job of a carbon dioxide freezer; this essentially produces dry ice from thin air.
Once we have collected gaseous hydrogen from the electrolyzer and carbon dioxide from the atmosphere, we can combine them into methane through a chemical process called Sabatier's reaction. A special reactor designed by NASA creates the pressure and temperature needed to maintain this reaction and turn hydrogen and carbon dioxide into methane, with water as a byproduct.
The following equipment in our factory is a robotic umbilical arm. to transfer fluids to an external tanker. The peculiarity of this system is that its umbilical is specially designed to prevent dust from entering. The regolith dust is very fine and penetrates everything. And since the regolith is composed of crushed volcanic rock, it is very abrasive and hard enough for the material. (NASA's lunar missions have shown that the regolith was at the root of many problems, including false instrument readings, fouling mechanisms, joint failure, and control problems. It is therefore essential to keep it out of reach of umbilicals, electrical connectors and fluids and any sensitive electronics.
Each side of the umbilical contains a set of doors that acts a bit like an airlock to prevent dust from entering. Making a connection requires three distinct steps: the first is to squeeze the closed doors on each side, so that a special perimeter seal creates a completely dust-proof barrier around the two sets of umbilical gates. In the second step, the doors located on either side of the umbilical interface open inside the dust seal, thus revealing the actual connectors, mounted on a movable plate. The final step is to bademble the plates and physically connect all the electrical, electrical and fluid connectors.
A robotic arm installed aboard the propellant plant will pick up the umbilical and place it in a mobile tank robot. then connect and unload the finished products. In this respect, the surface treatment system looks a lot like a service station here on Earth, but instead of gasoline, it could distribute water. Or liquid oxygen. Or liquid methane. Or all three!
We recently presented a demonstration of this ISRU plant at the Swamp Works Lab in Florida. At this point, we had to simulate the oven and electrolyser to reduce costs and complexity. We also simulated the three different finished products using water for all three. But we used prototypes of hardware and software for all the other parts.
By badembling these subsystems, we investigated problems and failures throughout this process. We performed our system integration only at the end of our development and testing process. This is one of the fundamental principles of Swamp Works: rapid prototyping and early integration, enabling rapid proof of concept and early failures.
The idea of this March rocket fuel plant is that it will be packaged in a small box plant, sent to Mars, and then deployed and started on the Martian surface well before the explorers arrive. Human missions on Mars will depend on this factory to independently produce and store the fuel needed for their return journey, even before these astronauts leave the Earth. There are also NASA teams looking for ways to grow all kinds of different things during transit and on Mars. Including potatoes.
So, what must happen before then? Well, a lot.
NASA has years of experience with autonomous landers and independent rovers operating on the surface of Mars. And our newest rovers – Curiosity, which landed in 2012, and the March 2020 rover, for launch in 2020 – have some built-in autonomy. But the complexity of this rocket fuel fabrication plant, as well as its long life The level of autonomy required for such a system will bring things to a whole new level.
In the meantime, many technical challenges must be overcome before a mission like this one can succeed. One of the most critical issues is whether each subsystem of our current Mars surface treatment system can be upgraded to meet the needs and throughput required by a human mission on Mars. Recent studies by NASA estimate that a system of this type will have to produce about 7 tons of liquid methane and about 22 tons of liquid oxygen in about 16 months. Next, we need to determine where to land and dig to optimize our performance, how many RASSOR excavators we will need and how many hours per day will be needed. We also need to determine the size of the carbon dioxide freezer and the Sabatier reactor, as well as the amount of energy required for all this equipment.
In addition, we must anticipate problems by identifying unique point failures that may interrupt surface treatment and thereby delay future human mission. We will need to evaluate the probabilities of each of these failures in order to add to the system the appropriate amount of duplication and redundancy.
That robotic technologies can support this mission for years without maintenance or repair. we will have to design them according to very strict specifications. All moving parts must stay out of these tiny particles of destructive regolith dust. Reinforcing sealing technologies or strengthening moving parts to tolerate dust will add complexity and weight unless we can find an ingenious solution to the problem.
We also need to determine how compact or hard the mixture of regolith and ice is below the surface of Mars, and then design the digging tools appropriately. The scoops and teeth of our RASSOR excavation robot are best suited for packaged regolith mixed with ice chips. But this design will not be suitable for breaking large sheets of hard and hard ice. We will need definitive evidence of the composition of the ice and the regolith beneath the surface on Mars in order to design the most appropriate and effective digging equipment. Either this, or we will have to design more complex and robust tools capable of handling a variety of soil densities and ice densities.
We must also meet the challenges of long-term storage of super-cold liquids. Technologies and materials for pressure vessels and insulation are constantly improving, but will current technologies work on the surface of Mars for long periods of time?
Over the next few years, NASA will look at all these challenges. And we will continue to increase the capacity and readiness of all our prototype components. We will make the RASSOR robot stronger and lighter and test it in environments similar to those of Mars. We will continue to test and integrate the furnace and the electrolyser, and we will try to increase the capacity of the carbon dioxide freezer and the Sabatier reactor to verify that they can meet the needs of a Mars crewed mission. All this work and many more will continue so that our dust-push prototype can one day become a fully operational Mars system.
This article appeared in the print edition of November 2018 under the title "From dust to thrust. "
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