GOLDEN, Colorado – Here on Earth, centuries of accumulated engineering knowhow, hard-learned lessons, and societal evolution have shaped a robust framework of building standards that govern how we build and maintain buildings today.
But now, as humanity prepares to put in place a “sustained presence” on the moon, how do we guarantee the safety and integrity of structures built in an environment for which no such tradition exists?
At the 26th Space Resources Roundtable held June 2-5 on the campus of the Colorado School of Mines, one expert says what’s needed is a lunar building code, the development of specific design criteria for the moon.
What’s shaking?
Both NASA and China’s space agency are planning to build habitats, landing pads, equipment shelters, and tall towers on the moon. But all that construction could be off to a shaky start, suggests Nerma Caluk, an engineer and lunar specialist for Skidmore, Owings & Merrill, an architecture and structural engineering firm in San Francisco, California.
Caluk said there’s a need to leverage terrestrial building experiences.
“On Earth, structural systems rely on strong gravitational acceleration to resist seismic lateral forces through both foundation friction and overturning stability. However, on the moon, the gravitational field strength is reduced to just one-sixth of Earth’s surface gravity,” Caluk told Space.com.
Because seismic inertial forces are governed purely by a structure’s mass rather than its weight, the lateral demand on a structure remains fully active while its gravitational restoring capacity is substantially diminished, Caluk added.
“Low-profile surface structures risk translational sliding across poorly characterized regolith interfaces, while taller vertical structures face significant overturning vulnerability, as the moon provides only a fraction of the gravitational restoring moment available in a terrestrial seismic environment,” said Caluk.
Here on Earth, structural engineers routinely design typical building systems to yield, crack, and sustain permanent inelastic deformation during a design-level seismic event.
They intentionally leverage “inelastic energy dissipation” as the primary mechanism for managing seismic demand, Caluk said. But this design philosophy is fundamentally incompatible with a crewed lunar environment, she said.
Take for example a hatch distortion or pressure seal misalignment. They constitute a mission-critical failure, and any structural breach risks catastrophic depressurization, said Caluk.
A group taking on the challenge of shaping guidelines on the building of lunar infrastructure is the aerospace division of the American Society of Civil Engineers.
The group’s technical committee on space engineering and construction has crafted “Infrastructure Engineering, Design, Analysis, and Construction (LIEDAC) guidelines” for the moon, Caluk said, to tackle seismic issues imposed by moonquakes.
The LIEDAC guidelines, Caluk said, characterize the unique lunar hazard environment, classify operational consequences through a risk-categorization hierarchy, and establish target performance objectives “so that safe commercial development can proceed on a defensible technical basis.”
Inherent uncertainties
Caluk also outlined a “Response Spectrum Analysis” supported by NASA Small Business Technology Transfer funding that looked at the inherent uncertainties of the lunar subsurface.
The output of the analysis has developed criteria emphasizing the necessity of a local geotechnical site investigation for all structures, regardless of their seismic design category.
“These investigations are critical for identifying and mitigating risks such as seismic slope stability, seismically induced total and differential settlement, and other geotechnical hazards that may be triggered or amplified by moonquake ground motions,” she reported here at the School of Mines gathering.
Moreover, the framework that Caluk and her associates have pulled together, acknowledges that lunar site conditions are not yet fully understood on a global scale.
Design practices
Not knowing ahead of time what lunar explorers may face is an unsure, shuddering proposition.
“Therefore, responsible design practices must account for this uncertainty through rigorous subsurface investigation whenever feasible,” Caluk added. “By prioritizing localized data collection, engineers can ensure that structural foundations are robust enough to handle the unique physical properties of the lunar regolith and the specific seismic demands of the deployment site.”
Caluk and her team members looked at the maximum considered moonquake, representing a more severe shaking level, to verify collapse prevention and ensure overall structural integrity under extreme lunar seismic events.
“NASA’s deep institutional knowledge of human spaceflight operations and crewed mission safety,” Caluk concluded, “provides the critical foundation upon which structural performance criteria for lunar infrastructure can now be formally established, with terrestrial engineering precedent offering a proven methodology for doing so even under evolving geotechnical and seismic data conditions.”