The Mars VerSatile Underground Building ProjeCt (Mars SUBsPaCe) is a habitat designed to support a large population of people on Mars in a substainable and scalable manner. We believe an underground habitat has significant advantages over above ground structures. Being underground means that the surrounding material offers somekind of protection against the increased cosmic radiaition due to the thinner Martian atmosphere. The surrounding material around the habitat also serve as instulation preventing heat loss. Since the structure is expanding underground, the above-ground profile of the habitat is small. This reduces the problem posed by violent dust storm and meteorite strikes.

The design of SUBsPaCe is based on the working principle of an earth auger. It consists of a central shaft surrounded by a helical structure. At the base of the central shaft there is a massive boring head to remove the material from beneath it. Similarly there are four overlapping boring heads at the end of the helical structure. The lobby block which serves as the main entrance to the habitat also contains powerful hydraulic ramps to assist in the boring motion of the whole structure.

The key to the versatility of our habitat lies in the modular design of the habitation block . As the whole structure bores into the ground, space is created between the lobby and the first habitation block at the beginning of the helical structure. As the whole structure turns, a new habitation block can then be installed periodically. This allows a scalability in terms of space in the habitat.

For every complete round in the central shaft there are 10 habitation blocks. Access to each habitation block is via the main spiral ramp (1:12 gradient) which runs throughout the building. An integrated elevator and stairwell allows occupants to access each habitation block no more than 5 blocks away. At the back of each habitation block is a massive service corridor which also runs throughout the length of the bulding. It is used to tranport the excavated soil to the surface and serves as an evacuation route in case of emergency.

To further drive home the message that 3D printing can be an efficient mean of manufacturing, these modular habitation blocks can conceivably be constructed via concrete-like material (derived from the Martian enviroment) 3D printing at an offsite location. The central shaft can also be printed in a similar fashion (small box in Fig. 3) by a printer running along the circumference of the shaft. We believe large scale implementation of 3D printing here will bring down the construction time for the habitat by allowing automonous construction operation.

The whole underground building is covered by an umbrella-shaped structure. The hexagonal structures are solar panels which will produce power to augment the usage by the occupants. It also contains a few airlocks for transfer in and out of the habitat (in the model it has been raised up so that the habitat is visible). The central column serve as a structure for a massive hanging hydroponics bay which both serve to provide food, water and air purification and recycling. More importantly the column also divert sunlight into all parts of the habitat during daytime for illumination, thus mitigating the negative psychological impacts with prolonged underground habitation.

The scale of our design here is 1:266. Each habitation approximately contains a living space of 150 m2. There are 40 blocks in the building, including the lobby block and two maintainance and boring block at the bottom of the helical structure. The model is sectioned so that the internal layout is visible.

1. Design Process

The very first conceptualizations were done on paper . All subsequent CAD designs and test assembly were done in Solidworks. The main difficulty faced in the design phase lies in establishing the dimensions of the structure. For that we took inspiration from notably the Pearl Bank Apartment (Singapore) and Ponte City (Johannesburg, South Africa).

1. Fabrication Process

The 3D printing facilities were kindly provided by Hwa Chong Institution.

Our architectural model was fabricated using the process of fused deposition material (FDM). Printing were done on two Panther 3D printers manufactured by a company with the same name (based in Singapore). The printers have the following specification:

1. Position Accuracy: X/Y: 0.025mm and Z: 0.005mm
2. Print Nozzle Diameter: 0.4mm (compatible with 1.75mm diameter PLA and ABS plastic filament)
3. Build Volume: 202mm (X) x 162mm (Y) x 157mm (Z)

Earlier work done to characterize the printers has revealed that they can print reliably down to a resolution of at most 1 mm. Therefore during the CAD design phase, all the interlocking parts were given 0.5 mm clearance on each side and that no structures were smaller than 1 mm.

Removal of the supporting structure was of a great concern to us, as it might potentially interfere with the actual model. Initially, we planned to print each of the habitaion block in two parts, a top and bottom section. These would eliminate the need for support structure for the over-hanging roof. We deemed that the assembly of the two half and the central column adds negligibly to the total time taken.

However, when we started our printing we found that at the optimized printer setting, each block took approximately 3 hours to complete. Due to student usage in the day time, only one of the printer is avalaible. Thus we made the decision to assemble the structure in Solidworks and scale it by 55% for printing in 4 blocks. This resulted in the loss of some minute details in the model and damages due to support removal.

The model was printed with white 1.75mm PLA extruded at a temperature of 195 oC on to a Kapton tape covered platform heated to 55 oC .

The .SLDPRT files (Solidworks parts file) for the designs were converted to .STL files. These files were later converted to gcode via Cura which also generated the print instructions for the filling structures in the solid portion of the model and the supports for the overhanging structures in the model. The gcodes were then ported over to repetier-host interface with the actual printer.

Combined printing time of approximately 48hrs. Layer height of 0.1mm and a fill factor of 20% for fast printing. For our print, we used a pair of printers. The printed models were then post-processed with just the removal of support materials. The four main section are then assembed by means of glueing with cyanoacrylate adhesive.