How can we build landing and launch pads on the moon?

If the future unfolds like some experts forecast, the moon is going to be one bustling spaceport. 

Vehicles will routinely blast in and rocket off the lunar surface, part of a supply chain that caters to human encampments, equips science facilities and plops down gear for extraterrestrial mining operations. Early on, it's projected to be a rocket ruckus of kicked-up dust and flying debris. A recent gathering of experts grappled with what we know, what we don't know about how to handle "airport-like" operations on the moon. 

The Lunar Surface Innovation Consortium held a moon launch and landing facilities workshop on July 23, 2024. The consortium is administered by the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. Government, university, and private sector specialists shared ideas on the design, analysis and construction of launch and landing facilities, as well as identify technology gaps in order to establish a sustainable presence on the moon.

Group effort

Major decisions are forthcoming on how to create the infrastructure need if Earth's celestial partner is to become a major thoroughfare and keep up any long-term human habitation there.

"Establishing a human presence on the lunar surface is a group effort," said Ian Jehn, a structural engineer focused on safe and sound infrastructure for the moon. He's also a PhD candidate at the Colorado School of Mines.

"It is likely that before any prominent human presence occurs on the moon, significant mass will need to be launched and delivered to the lunar surface," Jehn told Space.com. "We need professionals from all industry areas to collaborate to produce successful and well-performing lunar infrastructure."

Rocket plumes

Jehn foresees larger launch and landing vehicles on the moon. Those comings and goings mean larger rocket plumes interacting with the lunar landscape. 

"Mitigating the effects of rocket plume forces is currently a popular study area, as plume gas has the potential to cause cratering of the surface and generate high-speed regolith ejecta that can damage the structure of the vehicle or anything in the surrounding vicinity of the landing zone," he said.

To curb those blast effects, on the discussion topic list is the construction and use of launch and landing pads, or LLPs. Any landing pad surface designer worth his or her "exhausting" design work contribution needs to know what craft class a moon lander falls into.

Reusable, easily repairable

"LLPs will likely need to be reusable or easily repairable," Jehn said, "to ensure the safe and efficient transport of people, mission assets, and material to and from the moon's surface."

LLP systems can leverage some very well-established design and construction practices from the terrestrial civil engineering industry, Jehn explains. Civil and structural engineers have been designing similar systems that are being used right now for SpaceX Falcon and Blue Origin New Shepard landing zones. 

Any structural system relies on two components to enable design, Jehn said, and those are anticipated loading conditions and material properties. 

Jehn said that for the moon's terrain, a significant effort is underway to develop structural materials. That's work in progress. 

But that's also a catch.

Sturdy structures

"The issue is the proprietary nature of rocket plume loading criteria," Jehn points out. However, at present these criteria are being withheld by the NASA's Commercial Lunar Payloads Services (CLPS) and human landing system manufacturers, he said, and they can only be accessed through legally binding non-disclosure agreements.

To that end, Jehn is engaged in work by the American Society of Civil Engineers. That group has initiated the development of "Lunar Infrastructure Engineering, Design, Analysis, and Construction" guidelines. 

On the table are such things as what type of construction and materials are required, environmental effects, and dealing with lunar regolith and rocks to assure the fabrication of sturdy structures. 

It is typical for rocket plumes from vertical takeoff/vertical landing operations to apply physical pressure and heat flux to the landing and launch interaction surface, Jehn points out. Different rocket nozzles, orientations, and sizes will result in differing pressure and heat concentrations.

"In my opinion, establishing loading conditions is now the priority. You can't design a structural system, like a lunar LLP, without loading criteria," said Jehn. An analogy is trying to design a highway overpass without knowing what type of vehicle is driving over that bridge, he said.

Source of speculation

Given six Apollo missions between 1969-1972 that deposited and safely returned a dozen moonwalkers, why all the fuss and fuming about touching down and departing the moon?

Those Apollo landings created more questions than answers, responds John Connolly, a professor of practice at Texas A&M University's Aerospace Engineering department. His prior NASA career of 35 years included work on the space agency's Artemis human landing system program, where he also worked with commercial lunar lander contractors. 

"We know that there is an upper layer of loose lunar regolith that will be blown away by almost any lander propulsion system. But the mechanics of what happens below that — as the regolith layer gets more dense and more cohesive with depth — are still the source of speculation and expenditure of hours of computer simulation time," Connolly tells Space.com. 

Changing density

The moon's topside "fluffy" regolith is an overcoat for a "hard packed" denser lunar soil that is less than a few feet below, Connolly reports.

"Knowing that the lunar surface geotechnical properties change rapidly within this first meter complicates our efforts to model the surface because you have to take into account changing density, cohesion, porosity and shear strength," said Connolly. "The engine plume of a lunar lander, after blowing off the loose upper layer of regolith, will continue to interact with the exposed regolith in a number of ways." 

It isn't an easy problem to model analytically, Connolly added. There's need to correctly model the engine plume gas flow and then model how the gas will interact with the lunar regolith.

"So you almost need to model each regolith particle individually as it is dislodged from the soil matrix, accelerates in the plume, bumps into other particles, and eventually ends up on a ballistic trajectory," said Connolly. And this would require a huge amount of computational fluid dynamics run time on a supercomputer, he said.

Spray-on solution?

Do we need to prepare a launch/landing pad to keep landers from continuing to scour the lunar regolith and eject it at high velocities at valuable, neighboring surface hardware?

"I believe the answer is yes, but maybe not immediately," Connolly advises. You can initially use the topography of the moon itself as a "berm" to protect surface assets, he said. Just pick a landing site that has a hill or ridge between it and other off-worldly goods and services.

But if you want to continue to land at the same site, you may need to treat it to eliminate the effects of lander rocket plumes, Connolly said.

If that's the case, you could call for shots of "Rhino Snot" — yes, you're reading that correctly. The military dubbed it Rhino Snot — a commercial spray-on polymer used to treat dust-prone areas that increases the soil strength by interconnecting soil particles together.

"The military sprays liquid polymers to quickly stabilize dirt roads and helicopter landing pads, and a lunar-qualified version of this technology could be used for landing pads," said Connolly. 

If a longer-term solution is needed, Connolly continued, as in the case of a permanent moon base with regularly arriving and departing landers, a surface treatment such as a deeply sintered regolith pad may be the right answer.

Mission success

"Safe and reliable landings, and eventually launches, on the moon are necessary for mission success," said Rob Mueller, a senior technologist in the granular mechanics and regolith operations lab within NASA's Swamp Works at the Kennedy Space Center in Florida.

Mueller told Space.com that the data output from NASA's Commercial Lunar Payloads Services (CLPS) landers will provide new insights into how rocket engine plumes impact lunar surface materials. 

With that knowledge in hand, what's possible in the far term is clear, Mueller said. 

"In the future we will see spaceports developing on the lunar surface and other solar system orbital and surface destinations. They will use in-situ derived propellant such as hydrogen and oxygen from water," Mueller said. "These are the first steps to opening up the solar system transportation routes to humanity and resource mining robots."