If the future unfolds as experts predict, the moon will become a bustling spaceport.
Spacecraft will regularly land on the Moon’s surface and launch on rockets, part of a supply chain that will supply human camps, service scientific facilities, and drop off equipment for extraterrestrial mining operations. Initially, the rockets are expected to be a big mess of kicking up dust and flying debris. A recent meeting of experts discussed what we know, and don’t know, about how to handle an “airport-like” operation on the Moon’s surface.
The Lunar Innovation Consortium held a workshop on Lunar Launch and Landing Facilities on July 23, 2024. The consortium is managed by the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. Experts from government, universities and the private sector shared ideas on the design, analysis and construction of launch and landing facilities, and identified technology gaps for establishing a sustainable presence on the lunar surface.
Group Effort
Important decisions are coming up about how to create the infrastructure needs. if Earth’s celestial partner would become a major transportation route and would sustain long-term human habitation there.
“Establishing human habitation on the moon is going to be a collaborative effort,” says Ian Jeng, a structural engineer and doctoral student at the Colorado School of Mines who focuses on safe and sound lunar infrastructure.
“We will need to launch and deliver significant amounts of material to the lunar surface before we can have a significant human presence there,” Jen told Space.com. “We will need experts from across industries working together to create a successful and capable lunar infrastructure.”
Rocket smoke
Jen expects to see larger launch and lander vehicles on the moon, which means more rocket traffic will mean bigger rocket plumes interacting with the lunar surface.
“Mitigating the effects of rocket outgassing is currently a popular area of research, as it can create craters on surfaces or produce high-velocity regolith ejections that can damage the vehicle or anything in the vicinity of the landing site,” he said.
To limit the impact of such explosions, the construction and use of launch landing pads (LLPs) is on the list of topics for discussion. Any landing pad surface designer worth contributing to the “exhausting” design task needs to know what craft class the lunar lander falls into.
Reusable and easily repairable
“The LLP will need to be reusable or easily repairable to safely and efficiently transport people, mission assets and supplies to and from the lunar surface,” Jen said.
Jehn explains that the LLP system can leverage established design and construction methods from the terrestrial civil engineering industry. Civil and structural engineers have designed systems similar to those currently used at the SpaceX Falcon and Blue Origin New Shepard landing zones.
According to Jen, any structural system relies on two elements to be able to design: the expected loading conditions and the material properties.
Jen said there is significant work underway to develop structural materials for the lunar terrain, which is a work in progress.
But it also has its pitfalls.
Rugged Construction
“The problem is that rocket jet loading standards are proprietary,” Jen noted. But currently, those standards are kept secret by NASA’s Commercial Lunar Payload Services (CLPS) and the Human Landing System manufacturers, and can only be accessed through legally binding non-disclosure agreements, Jen said.
To that end, Jen is working with the American Society of Civil Engineers, which has begun developing guidelines for “Engineering, Design, Analysis and Construction of Lunar Infrastructure.”
Considerations include what type of construction and materials will be needed, the environmental impact, and how to handle the lunar regolith and rocks to ensure a robust structure can be produced.
It’s common for rocket plumes from vertical takeoff and vertical landing maneuvers to impose physical pressures and heat fluxes on interacting surfaces during landing and launch, Jeng noted. Different rocket nozzles, orientations, and sizes result in different concentrations of pressure and heat.
“In my opinion, establishing the loading conditions is now the top priority. Without loading criteria, you can’t design a structural system like the Lunar LLP,” said Jeng, who said it’s like trying to design a highway overpass without knowing what types of vehicles will be crossing it.
Source of speculation
During the six Apollo missions between 1969 and 1972, 12 moonwalkers left the moon’s surface and returned safely, so why was there so much fuss and indignation about the moon landings and departures?
The Apollo landings have created more questions than they answer, says John Connolly, a professor of practice in the aerospace engineering department at Texas A&M University, who worked at NASA for 35 years, including on the space agency’s Artemis Human Landing System program and with private lunar lander contractors.
“We know that the moon’s surface has a top layer of loose regolith that would be blown away by most lander propulsion systems, but the mechanisms behind what happens below that – that the regolith layer gets denser and more cohesive as you go deeper – are still a source of speculation and require many hours of computer simulation,” Connolly told Space.com.
Density Change
Connolly reports that the “fluffy” regolith on the moon’s surface is like a top layer covering denser, “hard-packed” lunar soil that lies a few feet or less deep.
“We know that the geotechnical properties of the lunar surface change rapidly within the first metre, which complicates the task of modelling the surface as we must account for changes in density, cohesion, porosity and shear strength,” Connolly said. “Even after blowing away the top layer of loose regolith, the lunar lander’s engine fumes will continue to interact with the exposed regolith in a variety of ways.”
This is not an easy problem to model analytically, Connolly added: it requires accurately modeling the flow of the engine’s exhaust gases, and then how those gases interact with the lunar regolith.
“So we need to almost individually model how regolith particles detach from the soil matrix, accelerate within the plume, collide with other particles, and finally fall into a ballistic trajectory,” Connolly said. And this requires huge amounts of computational fluid dynamics run time on a supercomputer, he said.
A spray-on solution?
Should the launch pad/landing pad be prepared to prevent the lander from continuing to scrape up lunar regolith and ejecting it at high speed onto valuable nearby surface hardware?
“I think the answer is yes, but maybe not anytime soon,” Connolly advises. Initially, the lunar terrain itself could be used as a “bank” to protect surface assets, he says. Landing sites could simply be chosen where there’s a hill or ridge between them and extraterrestrial supplies and services.
But if it wants to keep landing in the same place, it may need to undergo procedures to clean up the impact of the landing rocket’s ejecta, Connolly said.
If so, you could inject yourself with “Rhino Snot.” Yes, you read that correctly. The military has named it “Rhino Snot,” a commercially available spray-on polymer used to treat dusty areas that binds soil particles together and strengthens the soil.
“The military sprays liquid polymers on dirt roads and helicopter landing pads to quickly stabilise them, and a lunar-compatible version of this technology could potentially be used for landing pads,” Connolly said.
Connolly added that if a more long-term solution is needed, such as for a permanent lunar base with landers arriving and departing periodically, surface treatments such as deeply sintered regolith pads may be the right answer.
Mission Successful
“A safe and secure lunar landing and ultimately launch is critical to the success of the mission,” said Rob Mueller, senior engineer at NASA’s Swamp Works Granular Mechanics and Regolith Operations Laboratory at the Kennedy Space Center in Florida.
Mueller told Space.com that data coming from NASA’s Commercial Lunar Payload Services (CLPS) lander will provide new insights into how rocket engine ejection affects materials on the lunar surface.
With that knowledge, it’s clear what’s possible in the long term, Mueller said.
“In the future, spaceports will be developed on the moon and other orbital and surface destinations in the solar system, using locally derived propellants such as hydrogen and oxygen derived from water,” Mueller said. “These are the first steps in opening up transportation routes in the solar system for humans and resource-mining robots.”
