Could plastics help create an inflatable lunar habitat?

Austrian architect Thomas Herzig had a vision of a self-sustaining habitat able to withstand the harsh environment of space. Having pitched his ideas to the European Space Agency, could that vision soon become a reality? Rob Coker spoke to Herzig to find out.

The colonisation of the Moon has been a dream for many people for centuries. How did it feel winning a contract from the European Space Agency (ESA) that could help make it a reality?

I felt extremely fortunate to have the support of ESA, allowing me to develop my concept intensively and providing theoretical proof that this concept actually works and has many significant advantages over other previously published lunar habitat designs.

What steps did you take that helped draw ESA's attention to your product?

I had previously designed a Mars habitat on my own initiative with the support of the two Astrophysicists Gabor Bihari and Norbert Kömle, which had not yet been worked out in such detail, but was based on the same principle: A prefabricated ultralight inflatable membrane structure covered with loose regolith for protection against cosmic particle radiation, plus reflective foils that direct only the useful spectrum of sunlight inside.

I submitted this design to ESA's OSIP (Open Space Innovation Platform) channel with the note that I would like to develop a modified lunar habitat version.

Tell me about the Pneumocell concept and the reasons why ESA is interested in it for this project.

The selection process had two stages. Already in the feedback after the first selection stage, our concept was described as ‘potentially disruptive’ by the jury.

ESA had already received two commissioned lunar habitat concepts by two other very well-known architectural offices, SOM and Foster & Associates.

Not based on a 3D-printed structure and not on a prefabricate hard shell structure, our concept was very different – and new.

Apparently, the ESA jury had recognised the potential of our concept and was curious to see how expandable it would be with further development, as well as how well it would stand up to scientific, technical and economic scrutiny.

Which materials make up the fabric of the habitat?

After our materials research, two membrane materials are now on the short list: Mylar (BOPET) and aliphatic TPU (thermoplastic polyurethane).

Reflective Mylar is already being used in space for satellites. It has higher tensile strength than TPU and has a wider temperature range. However, no large inflatable walk-in structure has ever been produced from Mylar.

On the other hand, we have already erected several larger inflatable buildings on Earth using TPU. It is easier and cheaper to process and there are already a lot of industrially produced components on the market, such as valves and cable holders. Tests on prototypes will show which of the two is the better option.

Since the homogenous, transparent Mylar or TPU membrane would not be strong enough to withstand the high inner pressure, the whole structure is reinforced by a net of Dyneema (an ultra-high molecular weight polyethylene (UHMwPE)) ropes. This material features the highest tensile strength versus weight and is flexible enough in the required temperature range. For the mirrors, a silver coated Kapton membrane is the best option.

Roughly how many square metres will the habitat occupy once inflated?

The central element of each unit consists of the torus-shaped greenhouse, which has a floor area of ​​245 square metres and is five metres high.

Sleeping compartments, sanitary rooms and tunnels are connected to these greenhouses, and rooms for work and daily needs are connected to the tunnels. These add another 50-100 square metres to each unit.

A habitat unit consists of a CFRP-truss frame tower with reflective foil, a greenhouse plus various adjoining rooms with building services and has a total payload of approximately 4,000kg.

How many humans could exist comfortably in there and for how long?

One greenhouse can provide enough oxygen and food for two humans. By adding more units, we can create a village housing up to at least 100 more inhabitants.

As long as the ecological cycle within the greenhouse is stable, the team can self-sufficiently provide itself with food, oxygen and energy for an unlimited period of time.

Does it worry you that perhaps some critics may see the project as humans bringing plastics pollution to the Moon?

My intention is to install a functioning ecological cycle on the moon in which all waste is recycled. Plastic foils, of which we only need very little material, make this technically possible.

For each kilogram of building material that we bring to the moon, we need 300kg of fuel. For this reason alone, we will not be able to afford to produce garbage on the moon.

What is the lifespan of the product and how do you foresee it being reused or recycled following its primary function?

The materials are UV-resistant and also shielded from UV light and cosmic radiation. However, we do not yet know how Mylar and TPU resist microbes and fungi in contacting soil over a long time.

We will gain experience by testing prototypes that will help us to make a prognosis about the lifespan.

For recycling of plastic and metal, these can be molten in a solar oven and casted or 3D printed. To produce recycled membrane material of the same quality, we would need a factory as on Earth. But that effort probably would not make sense.

Also, since there is no carbon in the moon, the production of plastics only with resources from the moon is impossible.

How many years of scientific research went into the development of the prototypes? How many iterations have there been to date?

I started developing the Mars habitat in 2018 and worked intensively together with Kömle and Bihari on the lunar habitat study from March 2021 to May 2022. Several other scientists and technicians from universities and private institutions also generously supported us with their expertise. FInally, it also incorporates 15 years of experience and research into inflatable structures that I have previously produced on Earth. 

I worked on a prototype of an inflatable underground terrestrial greenhouse in 2020 that has some conceptual similarities, but no prototype for the lunar habitat yet. This is the next step that we would like to take now after having completed the design study. But to do this, we need significantly more resources.

However, no functional prototypes have yet been made of the other design concepts presented so far – only mock-ups that demonstrate the 3D printing technology.

The race as to who will build a lunar habitat first and with which design is still in its infancy and completely open.

Finally, what would you like to see as a name for an established 'Moon Village'?

We have given our design the name ‘PNEUMO PLANET’ because it is a pneumatic structure within which we create an ecological cycle in which people can live without external supplies, just like on our planet.

If such a habitat is actually set up on the moon, which of course I very much wish, it will only be possible with the co-operation of many entities. Each of them will have wishes and reasons regarding the naming. The name doesn't really matter to me as long as it is realised.

And when it happens, as a responsible Moon-architect, I am definitely excited to supervise the construction on site.