ISRU Space Age Begins

The scary-looking abbreviation ISRU stands for In-Situ Resource Utilization. Maybe the abbreviation IMR will become familiar in Russian, or maybe not. It means the extraction and production of the necessary resources, fuel, building materials, water and oxygen for people, from local – lunar, Martian or asteroid materials, instead of bringing everything from Earth. In 2021, the first technology demonstrator successfully launched on Mars, new missions are planned, and a variety of prototypes are being tested on Earth.

Construction on the Moon using the RASSOR Rover-Excavator-Dump Truck as presented by a NASA artist
Construction on the Moon using the RASSOR Rover-Excavator-Dump Truck as presented by a NASA artist

In real conditions

On the starboard side of the Perseverance rover, there is a technological demonstrator for the production of oxygen from carbon dioxide in the Martian atmosphere MOXIE. The name is assembled from the letters describing the purpose of the unit, and it is also a character trait – audacity, decisiveness, initiative.

MOXIE Cutaway, NASA Animation
MOXIE Cutaway, NASA Animation

The installation works by sucking in the Martian atmosphere through a HEPA filter, compresses it about 100 times with a scroll compressor, heats it up to 800 ° C and feeds it to a block of solid oxide electrolysis printed on a 3D printer. In it, a carbon dioxide molecule on a porous cathode loses an oxygen atom, leaving through a solid-state electrolyte (Yttria-stabilized zirconium dioxide YSZ) to the anode. In total, of two molecules of carbon dioxide CO2 we get two molecules of carbon monoxide CO and an oxygen molecule O2

Solid oxide electrolysis unit, image M. Hecht, J. Hoffman et al.
Solid oxide electrolysis unit, image M. Hecht, J. Hoffman et al.

It should be noted that MOXIE had to be adapted to the capabilities of the rover. For example a scroll compressor was a compulsory measure to meet the limitations of size, weight and energy consumption. And if by simply increasing the cells it is possible to linearly increase the productivity of the electrolysis unit, then the compressor is scaled only 10 times, and then you will have to look for other options. Despite the efforts of the engineers, MOXIE consumes three times more electricity than the Perseverance radioisotope thermoelectric generator produces, so they are going to turn it on only ten times during the Martian year (with a possible, or rather expected, continuation of the mission). At the first stage, the characteristics of the structure will be studied in real conditions, at the second stage it will be tested in different weather conditions, and at the third stage, engineers are going to experiment, for example, comparing work at different temperatures. The MOXIE is expected to be capable of producing up to 10 grams of oxygen per hour.

April 20 unit included for the first time. He received about 5 grams of oxygen, which would be enough for a person for about ten minutes, and there is no need to talk about rocket engines. But, as they say, the beginning is dashing trouble – MOXIE will give the experience of using the installation in real Martian conditions. And the knowledge of how the characteristics of the HEPA filter will change, when it gets clogged, or in what form the degradation of electrolysis cells will manifest itself, will be useful years later when designing already “serious” installations.

Soon on the moon

Image of Space Applications Services
Image of Space Applications Services

The European Space Agency is going to send an automated interplanetary station to the moon in 2025 with a technology demonstrator of the use of local resources. On May 12, it announced that it had entered into a contract with Belgian startup Space Applications Services to build three experimental plants to produce oxygen from lunar regolith.

It is known that the lunar regolith contains up to 45% oxygen, while the rest is also valuable: silicon, iron, calcium, aluminum, titanium. Space Applications Services will have to implement two technologies for oxygen production: the FFC Cambridge process and the hydrogen recovery of ilmenite.

FFC The Cambridge process (FFC – in the first letters of the names of the inventors) was invented in the late 90s and is electrolysis in the presence of molten calcium salts. Lunar regolith is loaded into a bath with molten calcium chloride CaCl2… Metal oxides will be reduced (initially the process was proposed for the production of titanium under terrestrial conditions) at the cathode, and pure oxygen will be obtained at the anode.

On the left is the original regolith, on the right after processing.  Metallic luster means reduction of metal oxides.  Photo by ESA
On the left is the original regolith, on the right after processing. Metallic luster means reduction of metal oxides. Photo by ESA

Hydrogen reduction of ilmenite is another promising technology. If the Cambridge process can be loaded with regolith directly from the surface, then here it is necessary to separate ilmenite (titanium iron ore) from olivine, anorthite, and pyroxene. Then ilmenite FeTiO3 placed in a closed container with hydrogen and heated. It turns out iron, titanium dioxide and water. The water is then decomposed by electrolysis into hydrogen and oxygen. Hydrogen is used to restore a new portion of ilmenite, and oxygen can be used for their own purposes.

Space Applications Services are expected to demonstrate a complete and scalable workflow on the Moon suitable for future missions.

Space excavator

Prototype, first and second versions of RASSOR, photo by NASA
Prototype, first and second versions of RASSOR, photo by NASA

In addition to the factories directly producing oxygen and other useful resources, service equipment is also needed that would be engaged in production and transportation. And NASA has been developing the concept of a high-traffic rover, bulldozer and loader at the same time for many years. It is called RASSOR (Regolith Advanced Surface Systems Operations Robot). In the first version, which was mentioned in 2013, it was tracked, and the second version became wheeled. Interestingly, the drums along the edges serve as both an excavator bucket, a dump truck body and even wheels. During testing, the rover moved over extremely rugged terrain, digging trenches and carrying soil. It is difficult to say what space excavators and dump trucks will look like in a century, but the already tested RASSOR design solutions have a high chance of implementation.

Other projects

In 2021 NASA singled out $ 45 million in SBIR / STTR programs to 289 small businesses and 47 academic institutions. Approximately 11% are related to 3D printing, and some are related to ISRU – projects for the production of blocks for landing sites, the development of a bonding agent for the production of building materials on the Moon, the extraction of oxygen and other resources from regolith, etc. Let me remind you that recently I told about testing a 3D printed landing site and the fact that ICON was engaged in the creation of lunar construction equipment.

European Space Agency experimented with sintering of the regolith by concentrated sunlight.

SpaceX, which is critical for the Starship project to create an infrastructure for the production of fuel on Mars (without refueling, the ship cannot return), is still engaged in higher priority matters. November 2020 Musk toldthat work on technologies for using local resources could begin as early as the end of 2021, depending on how successfully tests of the Starship prototype go. Considering several beautiful explosions of the latter in the first half of 2021, it is logical to assume that the dates have already shifted to 2022. The most likely option is the Sabatier reaction – carbon dioxide reacts with hydrogen in the presence of a catalyst and the output is methane and water. Hydrogen can be obtained by electrolysis of water from reaction products and water ice available in abundance on Mars.

If you think about it, in a global sense, modern astronautics is like a picnic or tourism – they took everything they needed with them, went into space and returned back. It is ISRU technologies, together with closed life support systems, that will transform humanity from a tourist into a full-fledged inhabitant of space.

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