Construction of the Inflatable Habitat ECHO for Inside a Lunar-analogue Lava-tube

Introduction; In the summer of 2021, the analogue astronaut mission “CHILL-ICE” shall be carried out inside the Stefanshellir cave system. This short term 2-night mission has the objective to put up an inflatable habitat inside a Lunar-analogue Lava tube within 8 hours. This 8h requirement simulates the lifespan of the oxygen tank that astronauts would have, during an emergency Extra Vehicular Activity (EVA).

Requirements; For the CHILL-ICE mission, a habitat prototype has been developed by the Wilson School of Design, Kwantlen Polytechnic University Canada. The habitat, named acronymically ECHO (Extreme Cave Habitat One) needed to fulfil the following mission requirements:

• 8H put up/ Take down
  • Essential for the astronauts to stay alive.
• Portable for 2 persons to carry inside the selected lava tube
  • 38° slope / 11 m and max. weight 50 kg
• Free standing
  • Fidelity for an analogous mission and no reliance on ground conditions.
• Habitable for 3 persons [2]
  • Min. 8 m³ but preferred >21 m³
• Re-deployable
  • Needs to be used for recurring phases of analogue missions.
• Airlock
  • Fidelity in simulating the ingress/egress process and the design of the structure.
• Water-resistant
  • Interior needs to stay dry. The caves on Earth can be subject to high humidity and cave rain.
• Dimensional restrictions due to cave location.
  • 7.5 x 4.6 x 4.15 m

(Figure 1: Habitat material properties hierarchy.)

For this analogue mission and the construction of this habitat, the influence of gravity and space vacuum has been neglected. For the design of the habitat, all spaces shall require multiple functions to provide enough space for a sleeping, bathroom, working and experiment station. Furthermore, as the Stefanshellir cave system consist of a rocky basaltic terrain, the floor of the habitat needs to be able to withstand possible ruptures. The material priority hierarchy can be found in figure 1.

All materials selected for the habitat have been subjected, prior of usage, to testing to comply with the material hierarchy as mentioned in figure 1.

ECHO Habitat; The final result of the habitat can be seen in figure 2 and figure 3. The technical overview of the habitat features is given in table 1.

(Figure 2: The habitat ECHO (Extreme Cave Habitat One) in a deployed state with airlock.)

(Figure 3: Interior design of the ECHO habitat with Airlock door provided and mylar pillows for thermal insulation.)

Habitat features
Mass	30 kg
Capacity	40 m3
Dimension	4.0 x 3.5 x 2.1 m
Dim. Airlock	1.1 x 3.5 m
Max. persons	3
Fly material	Nylon
Shell material	Tyvek (spun-bound polyethylene)
Floor	-        Cordura nylon -        Mylar -        Open Cell Polyurethane foam
Free standing	Yes
Portal for cabling	Yes

(Table 1: Overview of habitat features.)

The selected form of the habitat is a 'barrel vault' or 'Quonset' archetype. This shape aligns with the available space left in the selected spot inside the terrestrial lava tube. The structure of the habitat consists of four air members and two poles. This combination results in a redundancy in the event of air member failure and/or leakage. The skin is constructed of Tyvek (spun-bound polyethylene) building membrane material. This material is chosen upon its lightweight and economical benefits.

In addition, to protect ECHO and the analogue astronauts against any lightweight falling debris from the cave an external lightweight fly has been added to the shell. The floor is constructed of 3 layers and is removable. These layers will provide thermal insultation, some protection from the uneven/basalt cave floor and a durable surface for the range of activities.

As mentioned in table 1, the habitat offers accommodation for 3 crew members comfortably. Inside the airlock, 1 crew member can get changed in their EVA suits, provided by the Astroland Interplanetary Agency. When not in use, the EVA suits can be stored in the airlock. The airlock room has a multifunction as it is also the private bathroom area.

Lastly, there is a set of mylar pillows (see figure 2) that serve as thermal insulation and are reflective of light sources. These pillows are to be filled with air, secured and placed against the walls, as needed, to achieve and retain thermal comfort. To hold the pillows in place, a set of diagonally placed elastics are used. In addition, these elastics can also hold deployed sleeping mattresses during the day. For storing lightweight items, a set of pockets that run lengthwise in the main volume of the habitat are made.

Acknowledgements;

First, we would like to thank the FULLAIR and ECHO teams from Wilson School of Design (S. Fairburn, S. Phillips, L. Norris, B. van Rikxoort, M. Alary, K. Langer, J. Legoff, A. Nelmes, D. Seriani, A. Sullivan, G. Wong, C. Michel, W. Tsz Long Lo) for their amazing work in research and developing this habitat for the CHILL-ICE mission, during this difficult COVID period. They have been the key factor for the success of this mission and therefore this research.

In addition, we would like to thank the whole CHILL-ICE team for their remote support during the development of this habitat.

Lastly, we acknowledge the ILEWG EuroMoonMars manager B. Foing for making this research possible.

References;

[1] M.V. Heemskerk et al., EGU2020-901-1, (2020)

[2] NASA STD-3000-90 8.6.2.1

[3] 2021LPI....52.2762H2021/03

CHILL-ICE (Construction of a Habitat Inside a Lunar-Analogue Lava Tube): Building and Testing of a Deployable Habitat in Icelandic Lava Tubes for Space Exploration Purposes

Heemskerk, M. V.; Pouwels, C. R.; Heemskerk, R. S.; Kerber, S.; Foing, B. H.

[4] 2021LPI....52.2502F2021/03

Life and Research at SouthPole Moonbase: EuroMoonMars Campaigns Results 2019-2020

Foing, B. H.; Rogers, H.; Musilova, M.; Weert, A.; Mulder, S.; Kerber, S.; Castro, A.; Pouwels, C.; Das Rajkakati, P.; Heemskerk, M.; et al