For most space operations, the statement “What goes up, up, and remains” is ideal. Just 10 years ago, most of the systems and devices sent from Earth into space, including orbit (except for the ISS) and other planets, never returned. Of course, space debris often leaves orbit and burns up in the Earth's atmosphere, but it's hard to call it a full return.
Now reusable rockets have appeared, one of the space expeditions ended with the collection of asteroid samples with their return to Earth. But nevertheless, this principle remains relevant in our time. And if the inhabitants of the Earth can put up with it, then for a future mission with the landing of people on Mars, this principle is absolutely not suitable. The reason is simple: humans must be able to return to Earth. There are several options to ensure the return, but the main problem is the lack of fuel. The ideal option is to produce fuel right there on the Red Planet. The Perseverance rover and its MOXIE module will help you find out if this scenario is real.
Isn't it easier to take fuel from Earth? No, it’s not easier. After landing on Mars, the colonists / marsonauts will have no fuel left for their way home, so they will either have to wait for the delivery of additional cargo, or generate fuel on their own. And this can be done only if oxygen is produced on Mars. Perseverance's job is to run several tests to prove that the Red Planet can produce fuel. All this will be implemented as part of the MOXIE (Mars Oxygen ISRU Experiment) experiment.
What is this experiment?
This is one of the most promising experiments from the point of view of science, conducted outside the Earth. Yes, many of us are attracted by the flying drone tests that are about to take place. But still, from a scientific point of view, MOXIE is more important.
MOXIE Module - Appearance
If everything goes smoothly, then NASA scientists and engineers will be able to prove the possibility of producing the most important resource - fuel - outside our planet. Scientists hope to start producing fuel on Mars using components that are already on the Red Planet. Otherwise, long-term travel of people to other planets, including Mars, may be impossible or extremely unlikely.
According to preliminary calculations, the Marsonauts will need about 30 tons of liquid oxygen to return to Earth.
The whole secret of the experiment is in ceramics
If aliens decided to land on Earth and try to find oxygen, they would have succeeded without any difficulty. The Earth's atmosphere contains about 21% of this element, so only the simplest scientific equipment is needed to detect it. Oxygen can be removed from water by electrolysis, in which case the equipment is even simpler.
But with Mars it is different. If it is possible to find reserves of ice or water (data from some studies suggest that there is ice in bulk, but this has yet to be proven), then the rest is a matter of technology, fuel can be produced. So far, everything is complicated with Martian water.
Therefore, scientists hope to establish the process of extracting oxygen from the atmosphere of Mars. 95% of its atmosphere is carbon dioxide. MOXIE will help test the ability to extract oxygen from the atmosphere using solid oxide electrolysis. It will be just carbon dioxide that will break down, with reaction derivatives in the form of oxygen and carbon monoxide (carbon monoxide).
The principle here is the same as in conventional electrolysis - the decomposition of chemical compounds into individual elements using electricity. But there is a very important component here - the ceramic elements in the cells of the solid oxide electrolyzer. The cells are composed of zirconium oxide stabilized with a small amount of scandium. This material is known as ScSZ. It allows electrolysis to be carried out, having such qualities as heat resistance, high strength, light weight.
The oxygen production cycle begins with the operation of the air compressor and dust filters. MOXIE uses a scroll compressor in which two scroll elements are connected to form a single system. The task of the compressor is to increase the pressure in the module to the ground. This is not easy because Mars' atmosphere is about 100 times more rarefied than Earth's.
Compressor for MOXIE
An important nuance - for the electrolysis of solid oxides, high temperatures of about 800 ° C are required. Compressed to the density of Earth's atmosphere, the gas passes through a series of 3D-printed heat exchangers. The high temperature is achieved thanks to electricity - what else. And the MOXIE consumes more power than a rover RTG produces in one sol. Accordingly, the experiment was planned as carefully as possible.
Act like a tree
Its creators sometimes call the module "artificial tree", because carbon dioxide is absorbed with the production of oxygen. But the process itself is
The gas heated to a high temperature, which is 98% carbon dioxide, enters the SOXE cells. Each cell is a "sandwich" of porous metal electrodes on each side of the ScSZ plates, which act as a solid electrolyte. A current is supplied through the cell, as a result of which the reduction reaction is carried out under the action of the catalyst:
The oxygen ions then react with each other in the immediate vicinity of the porous anode as follows:
The module's sensors evaluate the quality and progress of the response. The capacity of the module is about 12 g / h at a maximum current of 4A. Upon completion of the reaction, all of its derivatives are returned to the atmosphere. The device itself is a proof of concept, its main task is to prove the possibility of producing oxygen on Mars. There is no point in storing oxygen now.
If the capacity of the module is increased 200 times, then it will be able to generate exactly the same 30 tons of oxygen that was mentioned at the beginning.
The MOXIE module is pretty simple, there is nothing like that. But in some cases, side reactions can occur, as a result of which the pores of the cathode are clogged with solid carbon. This is the main problem, since there is no operator nearby who can clean the electrodes and restore the module to work. Well, if a full-scale module appears, there will already be people nearby. And they will be able to ensure the normal operation of the "big MOXIE", since their return to Earth will depend on it.
