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Home , Lander (spacecraft)

Lunar Architectures Jeffrey Montes, Fellow, Open Lunar Foundation

Background / Motivation

Lunar (a.k.a.. launch/ profit organization working on policy and pads) will be a cornerstone of partnerships that support a sustainable all but the most anemic lunar futures. lunar settlement driven by open values. Undoubtedly they are critical to any Consistent with this , this is a working sustainable presence. The central problem document for designers, engineers, and spaceports address is the detrimental policy-makers interested in understanding effects of ejecta, the global dispersal of this problem or applying the approach to lunar surface material (rocks, dust, etc.), other problems. caused by landing on and launching atop unprotected lunar ground. Because the This isn't an engineering trade study, has no , ejecta goes it isn't built on previously unpublished fast and far—potentially blanketing the information, and it isn't intended as a set globe at velocities that could damage of ready-made designs to choose from. infrastructure and undermine science, It is an architectural and conceptual and reaching altitudes where exploration through geometry, and orbital habitats live. This document mechanism, and concept of operation is the output of a research fellowship (CONOPS). taking a new look at lunar spaceports with Open Lunar Foundation, a non-

Fig. 1: Stages of exhaust ejecta beneath an (Metzger et al., 2011).

1 Design Spaces Lunar Spaceport Architecture

In The Theoretical Minimum Susskind and bounded by four designs as four corners A spaceport is a kind of armor for the There is increasing attention on in-Space Hrabovsky define a concept called a state define a square room. Each design lunar surface in that it protects the ground resources as they relate to the hopeful space: represents a corner of that space, an from the destructive force of rocket cis-lunar economy and to lunar surface extreme value. None of the designs engine exhaust and prevents the ground infrastructure. Among that infrastructure, "...the collection of all states occupied by a from becoming a spray of high-velocity spaceports stand out. For the "vibrant system is its ...state space. The state space is ought to be taken as the solution; instead not ordinary space; it's a mathematical set they should aid designers in inventing projectiles. In the absence of this surface Earth-Moon future" NASA has outlined whose elements label the possible states of the unexpected hybrids. armor, everything around the landing with the , shuttling to and system. [p.3] site would need to be armored and thus from the surface will be foundational and Design spaces are useful for early stage more massive, indiscriminately driving commonplace. A spaceport might itself be Similar to a state space, a design space problems. For a technology that does engineering margins. While many surface a product of an indigenous lunar material is a solution domain defined by relatively not yet exist a design space paints the assets will need to be engineered against economy, or it might, like a , detailed designs aimed at a common scene and sets the ground for informed the likelihood of micrometeorite impact be a product of Earth and imported to problem. The one-dimensional space scrutiny. For problems without real-world and other incidental damage, the risk of the Moon. The structural, material and between 0 and 1 is a continuum with an solution precedents a design space ejecta damage will result in unnecessarily production differences between in situ infinite number of values. For difficult and can guide debates. It can be helpful for large margins that levy substantial and imported artifacts has a fundamental important problems at an early stage of problems where a design framework has penalties felt at the system level. For this effect on their design and is the first of two development (such as lunar spaceports), not been established. Designers flourish on reason, investing in spaceports early is axes of the design space. fleshing out the extreme cases (the 0 and constraints because they need a working critical for asset longevity, risk reduction, the 1) can more be effective at moving a model of a problem and its boundaries to coordination and policy, human safety, In Pad for Humanity: Lunar Spaceports as community of designers towards discovery understand which of those boundaries to and programmatic durability. Critical Shared Infrastructure, Montes et al. and invention than prescribing an push, which to bend or break, and which inevitably wrong goldilocks. to respect. Finally, when open-sourcing a problem, a design space leaves room for This document maps a two-dimensional future work to build upon. design space, which is by definition

RD DS

Fig. 2: One-dimensional reference design (left); multi-dimensional design space (right) Fig. 3: A map of spaceport design considerations. (Montes, et al., 2020).

2 3 The Four Designs defined spaceports as “a facility providing visiting vehicles. Beyond that, spaceports Four designs, defining a two-dimensional carrier and a commercial airport differ in a site for vertical rocket transport to and can get more sophisticated; offering “drive design space, are explored. The differences performance and circumstance but share from the lunar surface and supporting thru” services to visiting vehicles such as between the four designs are essentialized the same essential function, the following services including but not limited to refueling, recharging and maintenance. in the design space plot diagram. All emerge designs do not perform equally but rather refueling, recharging and maintenance.” The impact feature-richness has on design from the same need to mitigate ejecta but are intended to embody the essence of their The most basic spaceport imaginable is and complexity make it the second design exist under distinct circumstances. As such, boundary-defining point in a shared design nothing more than ground armor - a flat space axis. all of the designs are structures that perform space. pad engineered to resist lunar weathering this basic function. Just as an aircraft and the thermal and mechanical loads of

we are going feature-rich here The Machine The Works

imported in-situ

Apollo 12 Surveyor III LM plume center location (155m) The Skinny The Brute y = 0 y = -6m feature-poor we are Figure 3: A polar graph showing the size of particles blown (red dots, to scale) as a function of distance from the here center of the exhaust plume (concentric rings) for a 40 t lander. The dashed line marks the threshold beyond which 126 micron particles cease to be blown. Figure by author after Van Susante & Metzger (2014).

Figure 4: The main “sheet” of ejecta (dust, sand, gravel and rocks) traveling upward at an approximately 1-3 degree slope and away from the Apollo 12 LM. was located beneath the main sheet so was only damaged by a fraction of the impacts that would have occurred if directly exposed. Figure following Tosh, et al., (2011).

4 5 The Skinny is a lightweight spaceport imported from Earth and deployed on the lunar surface. It performs only the essential function of a spaceport.

Architecture CONOPS

The Skinny has two zones - a central Delivered to the lunar surface as lander "bullseye" and an outer "apron". The payload, it is hoisted from the lander bullseye, which sit directly under the lander using a crane, which places it on prepared engines, must withstand the thermal and (leveled and flattened) ground. The mechanical loads of the deployment sequence begins with the exhaust. This zone is made of metal panels expansion of the outer tube, which tensions that unfold from a stowed configuration the apron. The bullseye is then deployed by into an octagonal platform. The apron panel hinge actuation. A rover may be used borders the bullseye and extends out. It is to secure the apron rim to the ground using made of a heat-resistant textile deployed soil anchors. into shape by an expanding tube filled with gas or an expanding foam. While the The Skinny may alternatively be lowered apron will experience lesser loads than the to the surface by the maiden lander bullseye, the fringes of the engine exhaust while hovering above the altitude that retain enough energy to create ejecta of creates ejecta. This would require an smaller particles sizes (Fig. 3) unconventional engine configuration combined with a wire system to lower payloads. This may eliminate the need for a crane to pick and place the artifact from the payload bay of a lander onto the surface and may enable said vehicle to land on the pad it deploys.

7 The Machine is a feature-rich spaceport imported from Earth and deployed on the lunar surface. It offers visiting vehicles additional services and protection.

Architecture CONOPS

Featuring subsystems and , Delivered to the lunar surface as lander The Machine is a spacecraft onto itself. payload, it is hoisted from the lander using It is elevated above the ground on legs, a crane. The legs deploy from their stowed which earns it volume under the deck position prior to placement on an ideal for an exhaust duct. This duct captures or prepared (leveled and flattened) site. the exhaust gases in continuum and Once on the surface, the platforms open transitional flow and redirects them via panel hinge actuation. An existing utility down and laterally away from the vehicle connects power and fuel lines from lander, protecting it. A hatch on the main the base. deck conceals a robotic arm the offers automated refueling and/or recharging for The Machine may alternatively be lowered a visiting vehicle. Since it interfaces directly to the surface by the maiden lander with fuel and power lines, it removes the while hovering above the altitude that need and associated risk for other vehicles creates ejecta. This would require an to refuel each cycle. Due to its elevation unconventional engine configuration off of the ground and the dimensional combined with a wire system to lower constraints of stowage, it does not have an payloads. This may eliminate the need extended apron to protect the ground from for a crane to pick and place the artifact lower energy exhaust. from the payload bay of a lander onto the surface and may enable said vehicle to land on the pad it deploys.

9 The Brute is a simple in situ-made spaceport. It performs the essential function of a spaceport.

Architecture CONOPS

The Brute consists of a printed pad After a site is selected, a mound is created elevated on a mound of regolith with a using regolith - ideal volumes that have road leading up to it. The pad is made of already been excavated for base-building a single material and process: additively purposes. After the desired height and constructed high-temperature polymer. slope is reached, construction of the road A promising candidate is geopolymer, begins, layer by layer, up the slope. Once inorganic ceramics that can be made the road is completed, the same robotic of silicon, oxygen, aluminum, and iron printer can park at the top of the road and (all found on the Moon). The pad has print the pad. Once complete, the printer an upturned profile, ensuring that high reverse down the road it printed. velocity gases and ablated material do not induce shear forces on the down-sloped mound. The road, not required to sustain the acute thermal and mechanical loads of the engine exhaust, can be made from a less resilient polymer. The slope of regolith mound is likely driven by the maximum desire slope of the road.

11 The Works is a full-featured, in-situ made spaceport. It requires a proper civil engineering effort.

Architecture CONOPS

The Works consists of an intricate, Roads are completed first to mitigate multi-zone pad, an ejecta shield, and dust. Setts are removed from their ovens subterranean systems for refueling and onto a pallet, which is loaded until full. In capturing exhaust gases all connected parallel, an excavator digs a trench for the with roads. The pad is constructed in three subterranean fuel line and exhaust pipe. zones made of grouted, oven-sintered The fuel line (likely imported from Earth) basalt setts (deep blocks) of varying depth. and the pipe are laid in the trench and The ejecta shield is additively constructed covered. The roads are made be removing from polymer and made with integrated regolith overburden leaving a hard layer voids which backfilled with regolith. A which can be optionally paved or covered. subterranean pipe, assembled from segments, is used to direct engine exhaust The first pallet of setts is moved to a to where it might be captured, protecting prepared (leveled and flat) site where a the lunar vacuum from contamination. sett-laying machine places them into or onto the ground. After all setts are laid, Setts are laid in a hexagonal grid with a robotic printer filling the gaps with the deepest in the central zone and the grout. The same printer used to grout the shallowest in the outer zones. Their heft, setts can be used to print the wall, whose hardness and depth into the ground make hollow cavities are filled with regolith by a them resistant to cracking, wear, and conveyor/ excavator. dislodging. The gaps between the setts are injected with liquid geopolymer that sets in place, creating a seal that prevents the high-pressure exhaust gases from disassembling the setts. Geopolymers would offer unrivaled fire-resistance and may be best suited for the central zone. Less resistant polymers may be used for the ejecta shield and outer zone grouting.

13 Notes Assumptions Conclusions

Ejecta shields Time span All spaceports in the design space leverage worth solving together. a set of technologies and practices that will A well designed and sufficiently large The most challenging design (The Works) be required for any lunar future: sitework. All design directions imply socio-economic pad combined with a perfect landing is bounded at 2120, 100 years from this Sitework includes excavating, leveling, incentive structures regarding cost and (vertical descent from the a non-ejecta- writing. and moving large volumes of regolith. benefit sharing, which deserve greater blowing distance and laterally accurate) attention. These initial directions may Lunar scarcity If the sitework required for the different does not need an ejecta shield. However, designs is more similar than the designs provide a starting point for such an accidents happen. Vehicles may explode Regardless of their position on the design are, this could translate to lower long term analysis. and engines may malfunction, causing space plot, each design is bounded by cost for in-situ spaceports. Multiple simple a crash that threatens the base and its the limitations of a world of inherent spaceports can be traded against investing inhabitants. Once the exhaust plume scarcity, the Moon. Indeed, any artifact on in a fully featured one. References leaves the continuum flow regime, it enters the lunar surface is inevitably bound by into free molecular flow, where it tends to Lightweight, imported spaceports could scarcity. The rocket equation guarantees Metzger, P., Smith, J.,, Lane, J.,(2011) Phenomenology bounce and scatter rather than flow. In this this for imported artifacts. For in situ- mean that every large mass lander could of soil erosion due to rocket exhaust on the Moon and situation, shields may reflect high-velocity made artifacts, this is based in a unique be required to ride share with one that the Mauna Kea lunar test site. Journal of Geophysical gases and ejecta back at the vehicle. geological reality. What is valuable on self-lands or is lowered down to the Research: Planets 116, no. E surface prior to landing. There is more the Moon is locked in rocks found in a Montes, J., Schingler, J.K., Metzger, P. Pad for Lander design work to be done to explore dust mitigation high entropy distribution on the surface. Humanity: Lunar spaceports as Critical Shared When engines turn off during landing, the This applies equally to water: The Moon approaches implied within this technology Infrastructure, Proc. of the 17th Int'l Conf. on Eng'g, release of pressure in the load on the pad may have many gigatons of water but direction, such as the dis-incentive Sci., Constr. & Operations in Challengeing Env's. may liberate material and cause it to shoot that water is dirty, in low concentrations, structure associated with user-pays. (2020). upwards. This is a reason to armor the and scattered. Because the Moon lacks Larger, more complex, spaceports would NASA’s Lunar Exploration Program Overview bottom of the lander. hydrological, aeolian, or biological prompt cooperative use to bring down (September 2020), NASA, https://www.nasa.gov/ specials/artemis/ processes that pool, collect, deposit, the per user cost. This may be interesting Engine configuration can have a big effect separate, and concentrate raw materials, it to explore in the small regions with Susskind, L., Hrabovsky, G., The Theoretical on the thermal and mechanical loads on is a land of functional scarcity. a pad. For example, laterally mounted, concentrations of resources deemed Minimum. Basic Books, 2014. valuable with the combined intent to canted, raised or multiple smaller engines Landing Precision Heiken, Grant H., David T. Vaniman, and Bevan protect the precious areas, and enable can reduce or favorably distribute these M. French. Lunar Sourcebook: A User's Guide to the loads. Vehicle guidance, spatial awareness and greater ease of access to such a unique Moon. Cambridge University Press, 1991. landing accuracy and precision has been location. perfected to a landing tolerance of 1 meter. Van Susante, Paul and Metzger, Phillip T. Design, Design spaces deserve to be used more Test and Simulation of Lunar and Landing Pad frequently by the lunar infrastructure Soil Stabilization Built with In-Situ Rock Utilization industry to help collaborate on which (2016). ASCE Earth and Space, Orlando, FL problems are worth solving in which ways Tosh, Abhijit, Peter A. Liever, Robert R. Arslanbekov, before commitment to greater R&D. and Sami D. Habchi (2011). Numerical analysis of spacecraft rocket plume impingement under lunar Designing in the open can help the lunar environment. Journal of Spacecraft and community realize what problems are 48(1): 93-102

14 15 This work is the result of a 2019−2020 research fellowship at Open Lunar Foundation. I am grateful to OLF for their support and for their brave commitment in putting forth smart, pragmatic, and actionable models for our collective Space future. I am also grateful to the growing OLF community and especially to Chelsea Robinson and Jessy Kate Schingler.

2020