In previous blogs I’ve talked about how Lunar Starship can save the Artemis program to build a sustainable Lunar base. I’ve discussed how a Lunar Starship can deliver roughly 210 T to the Lunar surface if traveling one way. And I’ve talked a bit about some of the challenges of managing electricity generation during the Lunar night.
One missing piece of the puzzle is speculation about how a Lunar base assembled from Starships might actually look. What would it be like to live there? This is a fun question, and this blog is intended to discuss some aspects of the problem. It’s also a less serious question as the particulars of interior design are dependent, in large part, upon individual taste. Unlike, for example, hard numbers about Lunar transfer orbits and mass allotments, there is considerable latitude here for speculation and flights of fancy. The Lunar Starship represents approximately 2000 cubic meters of pressurizable volume, which is more than 4x the size of my house.
My intention with this post is to discuss some existing ideas and talk about some of the more obvious design considerations and constraints. Let’s not take this too seriously!
I’m not the first person to develop concepts in this area! Here’s a post at HumanMars with a list of speculative designs, and Google Image Search turns up a variety of other concepts. Many of these look pretty cool and draw on older concept art developed by SpaceX. In particular, they often feature capsule-like sleeping areas, reclining couches, lounge areas, at least one deck devoted to treadmills, and a large central tunnel with ladders for moving between floors.
When I think about Starship Lunar Base interior design, I think about how the space will be used, what its mission might be, and what mechanical constraints exist on the design.
In terms of space utilization, a well designed base should support the daily flow of activities from sleep and self care, to eating, recreation, work, and maintenance. People will need private space and public space, and some common areas will be noisier than others at different times of day. If the base, or part of it, is operating on shifts, how will that work?
Is the design so mass and volume constrained that we need to draw on submarine design language and have one hundred sweaty people sharing two showers (one of which is full of food) and hot bunking in shifts? Or do we turn to the design of Antarctic research stations, which must support teams of variable size performing multiple independent and extended missions in a deeply hostile environment?
The mission of the Lunar base at the Lunar south pole is to support science and technology objectives. Over time, the base will grow but it is also necessary that each Starship be capable of operating as an independent and self-sufficient surface space station. Long term, larger facilities may be build directly on the surface but with 2000 cubic meters per lander, and 210 T of cargo to play with, I don’t think that there’s a strong forcing function to start digging tunnels through Lunar rock. This would be different if the largest possible lander was another HLS contender or a tiny Skylab variant, like Jamestown Base in the first season of “For All Mankind”.
Finally, let’s consider mechanical constraints. The Starship is nominally a stainless steel tube about 50 meters long and 9 meters in diameter. The top half is payload volume, and the bottom half is divided between two tanks for oxygen and methane fuel. These fuel tanks can also support pressurized habitable volume after landing, but would arrive as little more than empty caverns with, perhaps, airlocks and mesh flooring built in.
The Starship’s load paths are through the skin. Therefore loads on the structure, such as heavy cargo and human passengers (if present during launch) should be mounted closer to the edge. Starship can support something like 15 decks from top to bottom, but mass and geometry constraints preclude any of these (except the prop tank domes) being 1 bar-capable pressure bulkheads. So keep the floors thin, and put heavy stuff near the walls.
This structural constraint is similar to silos or lighthouses. In both cases, access throughout the structure is effected not by a central shaft with incandescently hazardous unfenced edges and ladders, but gently curving spiral staircases running around the perimeter. In the case of Starship, the stairs could include runner tracks and rack/pinion for moving heavier cargo, and could taper towards the top to reflect reduced traffic at the extremities of the structure. Outside the main airlock just forward of the fuel dome, a spiral access ramp could be deployed on the exterior of the vehicle with fold-out slats. Similar fold-out or keyed structures could support external loading with sandbags containing Lunar regolith for thermal, radiation, and micro meteoroid protection.
A spiral stair access strategy also raises the design possibility of using split levels to take advantage of relative heights. For example, a level devoted to being a dormitory needs less head room than a basketball court, and there’s no rule stating that each sub-system or separate function needs exactly one (1.0) deck worth of floor space. Here’s another approach to helical and redundant stairs for Starship.
So, how does internal space usage break down? What is the optimal population per Lunar Starship base?
Let us consider the floor plan of the Amundsen-Scott South Pole Station, which can house up to 150 people. During busy summers with even more people, the overflow are housed in tents! My wife Dr Christine Moran spent most of 2016 there so I’ve some second hand familiarity with how it works.
The image below shows a plan view of the main part of the station. There are various satellite buildings, storage, telescopes, runways, ruins, crashed planes, and tunnels not shown here. But it presents a good summary of the core functions of the station. The triple structure to the bottom right (“the arches”) is devoted to logistics. There is a garage, power plant, cargo storage, and space for 600,000 gallons of jet fuel.
The quadruple structure to the upper left is the elevated station, and exists on two floors, with a plan given in the next image.
The elevated station, which is the newest part, is given in rough plan view below. Much more detailed design documents are available for the interested reader. The structure consists of two core structures end to end, with four wings on the north side. Three of the four contain single bedrooms roughly 2.5 m x 3.3 m, while the fourth contains a gym and basketball court, which seems extravagant but going outside requires procedures to avoid becoming an ice block.
The core contains offices, laboratories, computer facilities, medical facilities, dining, kitchen, a sauna, post office, store, greenhouse, laundry, and recreation specific rooms devoted to quiet reading, arts and crafts, music, TV, and games.
In terms of overall area, roughly half the station is logistics, and half is habitation. Of the habitation, half is private quarters and half is common space, divided up by about a dozen core functions. While I don’t think it’s remotely necessary for the Lunar Starship base to have underutilized rooms for very specific functions, I think there is enough space that it doesn’t have to be run like a WW2 submarine.
In total, the south pole station has about 5000 square meters of floor space. A single Lunar Starship with 15 decks each 3 meters tall has about 900 square meters of floor space. Operating on the Moon presents logistic challenges exceeding even the south pole, so I think it’s reasonable for a single Starship to accommodate between 16 and 20 people. Given that the Lunar Starship mass constraint is less stringent than the volume constraint, it’s not impossible to imagine a stretched Starship providing more living space at the cost of some of that 210 T of cargo.
There is room for seven decks above the methane dome, and nominally eight below, though some of them may have higher ceilings to accommodate bulkier functions.
The top of the Starship should have some kind of oculus or cupola. The uppermost deck is quite small, and makes a natural place for a secluded reading room enjoying natural light and the best views. The next deck down is also smaller and can serve as storage for infrequently required items or matter that can be moved through pipes, such as water and gases.
I generally think there should be a gradient of noise and activity across the Starship, with the sleeping decks positioned a good distance from the machine shop. So the next two decks can be sleeping decks, which are also a natural place to include water storage for additional radiation protection. 16 crew members can be housed in 16 cabins split across two decks. Each cabin is similar in scale to a college dorm room with a bed, desk, chair, porthole, closet, and perhaps a sink. Each sleeping deck also has a small central common lounge area and common bathroom facilities. As the decks are accessed via a helical stair mounted to the inside of the pressure hull, the sleeping deck floor plans are clocked relative to one another.
The next deck down handles the transition between introverted self care and work/life functions, so is the natural place for a “mess”, a large open space used to serve meals, with an adjacent galley, bathroom, food storage, and a variety of wall-mounted cabinets to facilitate the space’s usage for other forms of recreation.
The next deck down is devoted to work functions, and includes office space, a laboratory, a small medical office. This deck can be naturally split into adjacent split levels depending on ceiling height requirements. Remember that in lunar gravity ceilings may have to be a bit higher, and steps can be a bit higher too.
The lowest deck with the habitation part of the base interfaces with the methane tank dome, the primary external airlock, and gravity-fed logistics functions. For example, sumps for gray and black water storage are housed at this level before treatment and pumping back to header tanks beneath the oculus. Being adjacent to the external airlock, this deck is also a natural place to store cargo and equipment, including EVA suits, machine tools, and gym equipment.
The lower part of the Starship, that was formerly devoted to storing liquid oxygen and methane fuel, provides enough room for eight decks with three meters of head room.
Below the thrust puck and oxygen tank lower dome is a space between the skirt and the ground. This space provides additional room for cargo and is also immediately adjacent to the ground. I think this is the natural place to store rovers prior to landing, and to locate a large airlock that can interface with vehicles on the ground. While the airlock 28 meters off the ground can serve well enough for pedestrian access (given an elevator or ramp), driving a fully loaded dump truck up a spiral ramp seems tough. So the space inside the skirt is cleared of raptors and becomes an unpressurized garage.
The inside of the tanks is initially empty. Mesh floors and stairways are compatible with cryogenic fluid flow, as are pre-installed raceways for power and water, hatches, and airlocks. But any desired equipment will have to be moved into and around the space. Therefore the top of each dome should have mounting points for a capable bridge crane and the mesh floors should be locally removable to facilitate access to any point. Pre-loaded equipment and cargo can be stashed in the cargo deck above then, on arrival, lowered through a hatch into pre-built mounting points for easy installation.
The logistics part of the station is responsible for keeping 16 astronauts alive indefinitely, and closing the environment well enough to sustain life support. This requires provisioning of adequate power, atmospheric regulation, water recycling, communications, controls, and thermal control including refrigeration. It also requires the ability to store or fabricate spare parts, support maintenance cycles of all kinds of equipment, and operate space suits and rovers.
What is the mission of the base? As specified, a Lunar Starship base could keep a dozen or so astronauts alive on the surface in comfort for extended periods but what are they there to do? The whole point of using Starship as a lunar base is to jump start surface operational capacity at a sustainable cost. If a Starship base can support a crew of 20 people for 6 months between crew changes, it is conceivable that the whole program could operate below $150,000/person/day, which compares extremely favorably with the ISS program ($10m/person/day), although a LEO space station using similar hardware would be an order of magnitude cheaper if only because the delta-V requirements are lower.
What fraction of the crew is devoted to serving logistics functions and what fraction are research scientists? The south pole overwinter crew of 50 is split roughly 90% logistics to 10% scientists, although if required many more scientists could be housed with little marginal increase in cost. If this pattern repeated on the Moon then each crew might only have two or three rock-obsessed geologists to be gently humored by 15 or so technicians keeping them alive and taking the rovers out for a spin.
Of course, there is no reason to build only one Lunar Starship base, and a sustainable program would aim to deploy them at a cadence of perhaps four per year. Each would be customized to support its specific mission and in response to lessons learned along the way. Combined, they represent a real opportunity to build a series of self-sufficient huts all around the rim of, say, Shackleton Crater. If the landing legs can articulate then they can be walked into closer proximity after landing and joined with pressurized tubes.
Perhaps, down the track, one can be deployed containing only a huge power system and vertically oriented tunnel boring machine, with which it can start excavating the second generation lunar base, complete with enormous underground caverns and Starship-derived towers.