There was no margin for error and the group did not have the luxury of exploration for its own sake in this first crucial trek. They carried enough equipment to scout out their most promising site and, if all went well, to install what would be the first two airlocks on a section of the underground cavern that would become the first “room” of their new home. If all went as planned, they would leave the ARU to pump oxygen into the first section of the reclaimed natural tunnel while simultaneously compressing methane gas into storage tanks that would fuel the first generator already tethered to the ARU they carried and which would be left just outside of the reclaimed space in the former underground river to generate and store the power the colonists would need for light and to power most of the equipment and tools with which they hoped to improve and expand their new home into a workable life-sustaining environment.

As the group approached what should be the outlet of the former aquifer that eons ago had carried underground water to what would have been a very large, deep lake but was now as dry as the rest of the nearby terrain, they could see what appeared to be an opening above a smooth outcrop of rocks forming a natural ramp rising to approximately two meters off the ground. At one time, the opening would have been at the floor of the lake, approximately 90 meters below the water line, one of several underground rivers that fed a large natural lake that expanded for at least 250 kilometers to the South and west held in by the natural rock outcroppings that now appeared as tall canyon walls around the rim of the long-dry lakebed.

Nowhere would the lake have been as deep as at this spot, and the natural rock face of the steep hill towered just over 100 meters above the opening of the tunnel. Fortunately, thousands of years of windstorms had sandblasted the surrounding rocky surfaces leading up to the outlet into a smooth ramp with a rise of less than 20 degrees that would facilitate moving the necessary equipment up to the cave without much difficulty. This natural ramp was one of the reasons this particular site had been chosen. As the group climbed up to the natural cave’s entrance draped in shadows under the glare of a Martian midday sun, the dimensions of the cave’s opening could be better gauged as an ovoid shape nearly three meters tall by approximately seven meters wide. It was large enough to accommodate a group twice the size of the current expedition with their spacesuits walking side by side without feeling claustrophobic. Once inside, the walls reflected the smooth surface originally carved out by torrents of water flowing for millennia when Mars more closely resembled the Earth the colonists had recently left behind while it too still retained its former splendor.

The entrance receded as far as flashlight beams could probe, its smooth floor slanting upwards at a gentle slope of approximately five degrees. The cave walls and ceiling seemed devoid of large cracks or other imperfections that would pose an immediate problem for their terraforming efforts by allowing large quantities of oxygen to escape. Tests would need to be run once preliminary airlocks could be installed to learn the airtight quality of the rock and what efforts would be required to allow it to retain a breathable atmosphere with an acceptable amount of leakage, but upon their first visual inspection, it looked very encouraging. If the natural tunnel walls could retain an atmosphere with an acceptable amount of leakage that could be addressed through topical sealants, the hundreds of miles of its length would provide all the space the colonists would need for any foreseeable future expansion.

The most critical part of this first expedition to what was destined to become the site of this tiny subset of humanity’s new Martian home was to test the ability of the natural cave system carved by the ancient aquifer to sustain a breathable atmosphere. To that end, the group would need to close off a section of the broad natural tunnel whose length was as yet undetermined but suspected to run for hundreds of miles based on ground penetrating radar images taken from orbital satellites that had mapped significant sections of the underground terrain in a search for water and other useful resources.

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The first order of business was to close off a section of the tunnel approximately 50 meters in length by placing two permanent airlocks to allow the section to be imbued with a breathable atmosphere after first suctioning the thin Martian atmosphere in that isolated section of tunnel in order to measure the rate at which the atmosphere would reintroduce itself through the rock of unknown porosity or through cracks and other natural imperfections. The viability of the mission and survival of the colony would depend in no small part on these test results as the resources available to the colonists both from their irreplaceable stock of precious cargo and those that might be adapted from local materials to effectuate airtight seals would be very limited.

Working diligently and keeping a close eye on their available oxygen reserves, the team first set to work identifying a suitable tunnel section by carefully inspecting every inch of the tunnel floor, ceiling and walls for cracks and other obvious imperfections that might leak oxygen. To the delight of the team, the tunnel was found to be as smooth as glass and without any visible imperfections. It was decided that the first airlock would be installed approximately 70 meters from the entrance of the tunnel, providing close proximity to the surface and enough room to set up generators and the ARU equipment that would extract from the atmosphere oxygen, hydrogen, carbon and methane for fuel and breathable air from the inhospitable Martian atmosphere. The plentiful CO2 would provide the carbon and oxygen necessary for water, air, and reconstitution of methane. Hydrogen and nitrogen could also be extracted in more than ample quantities for their needs. Later, water could be extracted directly from the soil if not found naturally in underground aquifers. But in the early stages of colonization, the necessary resources and equipment for those tasks would be unavailable.

Thanks to the use of carbon fiber manufacturing processes mastered on earth not long before this mission and which made the modified space elevator a reality for the colonists, the installation of airlocks was a relatively simple matter as these were made from incredibly thin, light, and nearly indestructible carbon nanotubes weaved into a Mylar-like substance that was light, flexible, and as tough as diamonds. The fabric, with a thicker reinforced weave for the airlock doors, was thinner than silk and fashioned like a round raft section that could be inflated and would accommodate itself to nearly any shape up to its maximum diameter. The colonists possessed scores of these in various diameters as large as ten meters. And more could be manufactures as needed. The airlock “doors” were simple flaps of reinforced carbon fiber that felt as pliant and slippery as the cartilage of a squid, could be zippered closed for a perfect airtight seal and provided a fairly transparent seal along with the rest of the thinner material beyond the airlock flaps. But it could be darkened if needed through the application of a small current to its photosensitive coating, making it adjustable from perfectly clear, nearly invisible state to a black that would block out all light and dangerous UV radiation. The airlock flaps gained rigidity through the same process that darkened them with the application of an electric current and could be opened by pressing a switch on either side of the door flap as well as manually in an emergency by unzipping the material in its less rigid state in much the same way as one would a zippered baggie. Installation of these required nothing more than a careful placing of the flat package in the middle of the floor where one wished the airlock flap to be located and the pulling of a tab that released a mixture of pressurized gas rigid seal as it hugged the sides of the tunnel walls along its contours. If a too large package were used, the material would flatten against the outer walls, floor and ceiling running along it until it was perfectly stretched to its intended size, leaving a slight concave airlock that would work as well as a perfectly sized one, though it may be a few centimeters or a few meters nearer or farther from the precise intended point of deployment as the airlock used up its longer than necessary size by hugging the outer walls for whatever distance was necessary until it became fully inflated. As with any airlock, two of these were needed to provide space between them for the equalizing of pressure and expulsion of atmospheric gasses from the Martian atmosphere in order to replace these with breathable air.