The Concept For An ISRU And Grown On A Destination Surface Structure For A Lunar Habitat

Introduction

The Moon is very far from Earth, it has extremely harsh environment and the lunar missions might be long. Yearning for family and friends left on Earth would be an impactful psychological discomfort for astronauts. That is why an idea for a lunar habitat which would soothe this effect is needed. In this paper I discuss the concept for an ISRU and grown on a destination surface structure for a lunar habitat, which I have named ‘Lunar Light House’. I present how this concept provides a simple approach to producing vertical structures on the Moon, protecting the crew form external conditions, and allows for introduction of natural sun light to the habitat structure.

Lunar environment

The lunar environment consists of a hard vacuum so in order to enable humans to live there, it requires highly pressurized structures. The lunar surface is dominated by electrically charged dust grains and is exposed to harmful solar and cosmic radiation and to impact with micrometeorites. Therefore, the whole base needs to be protected. Moon does not have any protection from the solar and cosmic radiation and is constantly being stricken by asteroids, meteoroids and comets. A safe lunar habitat for the astronauts would have to ensure protection from the extreme temperatures and hard vacuum and would have to provide radiation and micrometeorites shielding. The structure would have to sustain high internal pressure to maintain right atmosphere, high temperature gradients and vacuum effects. Also astronauts would have to deal with dust contamination and one-sixth terrestrial gravity.

Site selection

Self-sustaining lunar outpost needs energy, water and shelter. These resources need to be renewable or exist in immense quantities in order to be considered useful by the lunar outpost. Changes in temperature on the lunar surface may cause the contraction and expansion of materials and thus materials might change their dimensions. To allow materials to be used for a longer duration, saving money and time, locations with the smallest temperature variations should be chosen for a lunar outpost. Due to the moon’s spin axis, which is less than 2 degrees relative to its orbital plan, the inside of many low-points on the surface of the Moon never see light. Those regions are very cold and permanently dark. That is why there is a big possibility of the presence of water in the form of ice, which is a crucial element for survival.

On both of the Moon’s poles these regions exists. Therefore both are seriously considered as possible starting locations for the Lunar Outpost. The Shackleton Crater on the south pole, thanks to its characteristics, is one of the most relevant locations for a lunar base. The crater stays in shadow almost all the time and that makes it a good potential site for the lunar base, due to the possible presence of the ice. Crater rim on the other hand is a site with sun light present for almost 90% of the time. It was chosen for the location for the Lunar Light House, being one of the 'peaks of eternal light’.

Concept - Lunar Light House

The Lunar Light House project is driven by the need to develop a novel system of protection against cosmic radiation for the ‘surface’ Lunar base, which would allow for more freedom in shaping the base structure. The other goal was to allow for introduction of natural sun light to the structure. The proposed structural system of the base also should allow for the autonomous construction. The challenge of the Lunar Light House project is to propose a use of already existing systems and materials in a novel way that would bring new qualities and possibilities.

Freedom of shape, building upwards, vertical

The main idea standing behind the project and development of the base is to create a structural system that would make building on the Moon more flexible compared to the ‘traditional’ concepts of designing for a lunar surface. Tall structure built on a Moon would overcome the obstacles given by the dust, floating above the surface, raised by the engines and mechanical works.

Introduction of the natural light

A lot of lunar base concepts are proposing to bury the base under the ground or cover it fully with the regolith layer. This approach however makes creating any windows hardly possible. Therefore, designing such a habitat involves taking into the account the problem of how to mitigate claustrophobia. NASA Johnson Space Center investigates the strategies for compensation for the lack of outside views, like flat panel monitors working as a virtual windows or upper-surface penetrations for optic-fibre light source. From the psychological point of view it is very important to have the possibility to look ‘outside’. Also, it is simply one of the most repeatable request of the users - the astronauts. From technical point of view, placing windows in space habitat is very hard because of the protective aspects and engineers are willing to avoid that. With Lunar Light House I am trying to resolve this issue, introducing a novel system, that would allow for the daylight to pass into the base structure, without any losses on protective capabilities.

Structural system

1. ISRU

Due to the payload restrictions local materials should be used where and when possible. To achieve inexpensive construction, as much ISRU must be applied as possible. In the end, the base should be self-sustainable, requiring virtually no additional resources from Earth. All amenities and necessary facilities ought to be fabricated from local materials derived from mining or gathering. Building materials may be prone to damage. On the lunar surface they would be exposed to a vacuum, severe temperature variations, radiation, micrometeorite impacts, high outward forces from pressurized structures. It all must be taken under consideration when choosing the right materials.

2. Lunar regolith

Almost the entire lunar surface is covered by the lunar regolith. It is electrically charged, abrasive and is a bad heat conductor. It can be used to cover parts of habitats to ensure protection against radiation for the base. According to studies, a regolith thickness of 2-3 meters is required to protect the human body from the hazardous radiation. A lot of the concepts for the lunar bases assume that the regolith shell structures covers inflatable modules. However, this solution does not allow for a lot of freedom in shaping the structure. Double-curved morphology of inflatable structures, covered with the regolith tends to shed loose regolith coverings. The biggest challenge is to construct the shell using optimal geometry. At this moment none of the previous approaches work sufficiently enough.

3. Reinforcement

Any kind of soil, weather it is sand, earth or lunar regolith, is not strong enough to act as a construction material itself. The reason why soils hold together is that they have high values of their coefficients of friction. Soil strength almost completely depends on internal friction between the soil particles themselves. To avoid sliding, the frictional force can be considered the shear strength. The more friction, the more strength against shearing. The shear strength of soil depends on the internal forces. But unlike other materials, soils have an infinite number of potential sliding planes all at once.

In this project the use of geotechnical engineering is proposed, in order to make the use of regolith to build up a lunar base structure possible. With a use of geo-synthetic material to reinforce the soil mass it is possible to build stable structure with smaller amount of the material used. Such a structure, in which tension is transferred to the soil reinforcement, relies on self-weight to resist the destabilizing soil forces acting at the back of the reinforced soil zone. Structures constructed this way may be inclined steeper than 70 degrees from horizontal. To achieve freedom in designing shape and to introduce natural light to the structure, in-situ grown nano-cellulose is proposed to be used. Together with the lunar regolith, nano-cellulose membranes would create a composite system, based on the soil reinforcement principles. It is a mechanical technique used to stabilize the soil structure. It can be conducted by the inclusion of short randomly distributed fibres or of continuous strips or sheets within the soil mass. It stabilizes unstable slopes and helps to retain the soil on steep slopes and under crest loads. To ensure lateral stabilization, nano-cellulose reinforcement is designed as a continuous surface, climbing in the form of a spiral along the whole structure, instead of being divided into separate layers. hanks to the use of nano-cellulose, Lunar Light House can be built tall and stay stable without using as much material.

The reinforced regolith idea has been tested on the simple mold and the results were very promising. The structure which did not have any reinforcement fell apart, even without any additional forces applied. The structure with reinforcement layers made out of cellulose withstood given pressure, only with slight deformation, but no soil particles falling apart.

4.Habitat Elements

The base consists of two structure systems. To ensure a working life support system, a tight structure able to hold pressure, temperature etc. is needed. Torus shaped inflatable modules brought form Earth are stacked vertically, one on top of another, creating a habitat for the crew with all of the necessary functions, laboratories, greenhouses, workshops etc. The inflatable modules and the production module deploy automatically and the production of the cellulose starts. In order to gather and assemble regolith layers additional robots would be needed. They can work all the time, while the cellulose layers are being produced, so the regolith would be ready to put on place, with every ‘layer’ of the cellulose which is ready. Since the base modules are built vertically, it requires minimum site preparation and ground manipulation to start construction.

The other structure is rigid regolith-nano-cellulose shell build around inflatable modules.

5. Production module

To enable in-situ production of nano-cellulose membrane the production module is needed. It ensures right conditions for the growth. It provides oxygen water (extracted from the crater) and C02 (first brought from Earth but later produced by human presence). Geometry of the production membrane is based on the Miura-Ori fold, similarly to the Origami inspired solar array. Unfolded structure appears to be divided evenly into a checkerboard of parallelograms. It’s great asset is the ease of deployment. There is only one way to open and close it. The mechanical structure of a device that folds this way can be very simple, only one input is required to deploy it. On top of it there is inflatable membrane, keeping the right atmosphere and conditions for the nano-cellulose growth.