Starship Moonbase

Artemis is the tip of the arrow

NASA’s Artemis program aims to return astronauts to the moon, with the first moon landing scheduled for mid-2027. This Artemis 3 mission will use the Space Launch System (SLS) to send an Orion capsule to a Near-Rectilinear Halo Orbit (NRHO) with 4 NASA astronauts onboard. There Orion will dock with SpaceX’s Human Landing System (HLS), which will carry 2 astronauts to the lunar surface. Ideally they will spend a week exploring the South Pole, before returning to the waiting Orion and Earth. Assuming success, a similar Artemis 4 mission should follow in September 2028, plus deliver a habitation module to NRHO for NASA’s Gateway station. However, these are but trailblazer missions before NASA fulfills its long held ambition to build a sustained moonbase.

Stage 1 Moonbase

Initially NASA intend to use HLS as a foundation habitat for moon operations. It has 1,000m³ of pressurized volume, hence easily accommodates 2-4 NASA astronauts for extended missions. Lunar Terrain Vehicles will be sent on separate cargo vehicles, allowing astronauts to range much farther than previous expeditions. These rovers should allow NASA to identify valuable resources (e.g. water, carbon dioxide/monoxide and metal deposits found in craters) plus survey the best sites for a sustained settlement near the South Pole.

“The Lunar CRater Observation and Sensing Satellite mission launched along with the lunar orbiter was directed to impact the lunar surface. Observations of the resulting 10-mile-high plume showed that nearly five percent of the regolith was composed of water and another five percent contained additional volatiles including methane, ammonia, hydrogen, carbon dioxide, and carbon monoxide.” ~ NASA

Stage 2 Moonbase

SLS is an old-school expendable rocket, which can launch once a year at most, carrying a crew of 4 astronauts. It will require hundreds of people to build a moonbase, which implies SLS will be retired in favor of a more capable vehicle, preferably something reusable to keep costs reasonable. Interestingly HLS is a variant of SpaceX’s Starship, a fully reusable launch vehicle, capable of carrying 100 people or tons of cargo... However, Starship was designed for Mars missions, which will use atmospheric braking to slow the spacecraft and reduce the propellant needed for landing. Unfortunately the moon has no discernible atmosphere, hence it requires even more propellant to land on the moon than on Mars! Fortunately SpaceX devised a workaround for HLS to provide the extra propellant needed for moon landings. For the Artemis 3 and 4 missions HLS will be fully refueled at an orbital propellant depot in Low Earth Orbit (LEO), then use roughly a third of this propellant to enter a highly elliptical Earth orbit, similar to a Geostationary Transfer Orbit (GTO). There it will be topped-up by a tanker Starship, ensuring it has enough propellant to reach NRHO, descend to the surface, and return to orbit again, ready for the next crew to arrive. Hence a conventional Starship could be used for future missions, if it is fully refueled in a higher elliptical orbit, which should provide enough propellant for Starship to return to Earth. Replacing the SLS/HLS combo with a conventional Starship presents many advantages: -

1. Passengers can embark onto Starship at Earth then fly direct to the moon (without having to transfer to a waiting HLS in NRHO), then return direct from the moon to Earth.

2. Starship can carry 200 tons of payload vs 100 tons for HLS.

3. Cargo HLS are single use vehicles, whereas Starships can be reused to save time and cost.

Notably Starship uses flaps and Thermal Protection System (TPS) tiles to enter the atmosphere, giving it a higher dry mass than HLS. However, more propellant can be transferred to compensate for this mass increase and provide the extra needed to leave Low Lunar Orbit (LLO) for the return leg of the journey. Leaving LLO requires relatively little propellant, then Starship essentially falls towards Earth and uses the atmosphere to decelerate before landing.

The Raptor engines used on Starship are extremely powerful (300 tons of thrust for Raptor 3) hence SpaceX will need to clear a landing area on the moon to avoid kicking up large chunks of regolith. No doubt SpaceX engineers will take such issues in their stride, going by past performance and their Mars ambitions...

Considering Starship is designed for rapid reuse, these moon direct missions should increase the payload delivered and significantly reduce costs, allowing base building to proceed at pace.

“SpaceX is excited to integrate things like habitats and rovers and supplies with Starship to make a rich ecosystem of technologies for an incredible moonbase… Thinking about a moonbase analogous to Everest base camp, staffed by hundreds or thousands of scientists and explorers." ~ SpaceX Director of Civil Space Development Nick Cumming/CST2022

The moon has no atmosphere or magnetosphere to protect surface dwellers from solar or cosmic radiation, so surface habitats will need a thick covering of regolith to effectively shield them. Sierra Space produce a Large Integrated Flexible Environment (LIFE), an inflatable habitat whose outer skin is stronger than steel. Their LIFE 5000 habitat has 5,000m³ of pressurized volume and fits a 9m fairing i.e. the cargo space provided by Starship.

“With substantial volume, power, and data capabilities, the [LIFE] habitat is primed for extended human habitation, both for low-Earth Orbit (LEO) missions and for the demanding challenges of long-duration voyages, such as Lunar and Mars surface habitation.” ~ Sierra Space

Considering Starship’s transport efficiency and LIFE’s habitable volume, NASA could complete a sustained moonbase in the 2030s, assuming congress approval.

Stage 3 Moonbase

Surface habitats covered in regolith would provide little protection against strikes from space debris or asteroids, which suggests lunar inhabitants will need to move underground. The moon had volcanic activity in the past, so lava tunnels could provide enough living space for thousands of people. If no suitable tunnels are found at the South Pole, a network of artificial tunnels could be constructed using specialized boring equipment provided by The Boring Company. Note: these artificial tunnels would be quite voluminous as SpaceX intend to transitioned to Mega-Starship, which could swallow an 18m diameter boring machine whole!

These underground complexes will be supplemented by roving habitats, pressurized vehicles designed to climb the highest peaks and descend into permanently shadowed craters, allowing them to fully tap the moon’s resources. These craters at the poles contain large surface deposits of water, carbon dioxide/monoxide and methane, which should be relatively easy to extract. Then the refined materials can be synthesized into methalox propellant, allowing visiting Starships to refuel on the moon, instead of high elliptical orbit.

Because the moon is quite distant from Earth it will likely develop the first space based economy, starting with propellant production. Then food, air, power and water will also be produced in quantity, to support the growing population. Important to note: androids, robots and automated vehicles will far outnumber the human population, which suggests servicing companies will soon spring-up, given the arduous conditions. Shipping anything from Earth would be slow and relatively costly, so eventually most everything could be made on the moon, mostly for local consumption.

In conclusion

What NASA start, commercial entities should complete, creating a robust moonbase capable of supporting itself. Companies like SpaceX, Sierra Space, Tesla and The Boring Company are well placed to oversee this transition – and raring to go.

SLS is a bottleneck, but when NASA transition to Starship they could create a sustained moonbase in less than a decade. Overall the commercial approach promises far more for less, bringing almost anything within our reach. Why choose between the moon and Mars when we can have them both!

Chris Prophet