Why the pad comes first
A lander touching down on unprepared regolith is the single most destructive event that can happen to a lunar base. The exhaust plume excavates the surface and throws material outward at speeds the plume models put above two kilometres per second for the finest grains, and with no atmosphere to slow it, that material travels ballistically until it hits something.
Apollo 12 landed 155 metres from the Surveyor 3 probe and sandblasted it badly enough to pit the camera housing and strip paint; the pits on the parts the crew brought home bound the impact speed between about 300 metres a second and two kilometres a second. That was a small lander. A cargo vehicle delivering the next habitat module is very much larger.
So the sequence is forced: survey, grade, sinter a pad, raise a berm, and only then land anything else nearby. Everything in the construction programme follows from that ordering.
Laser vitrification
Lunar regolith is largely silicates and metal oxides. Heat it past roughly 1,200 °C and it does not burn, it melts, and on cooling it forms a glass ceramic with useful compressive strength. In laser tests on a south pole simulant, sintering begins near 1,180 °C and a full melt needs about 1,360 °C, and melting proved about ten times more energy efficient per unit of consolidated material than sintering, which is why the head here melts rather than sinters. No cement, no water, no binder, nothing shipped from Earth.
This is the process NASA's MMPACT programme (Moon to Mars Planetary Autonomous Construction Technology) and ICON are developing under a 57.2 million dollar award, marketed as Laser Vitreous Multi material Transformation. It is the most credible surface construction technique currently funded.
Grade and compact
A blade flattens the site and a roller closes the voids. Sintering an uncompacted surface leaves a crust over cavities, which cracks the first time a lander puts weight on it. This step is skipped by nobody twice.
Melt with a directed beam
A high power laser on the gantry raises the top 30 to 50 mm past 1,200 °C. The head tracks back and forth laying one course at a time.
Cool by radiation alone
In vacuum there is no convection, so the melt sheds heat only by radiating and by conducting into the soil beneath. Cooling is slow and even, which is exactly what gives the slab its strength. Rushing it introduces thermal stress and the slab fails on the first landing.
Inspect
An ultrasonic head checks the course for voids before another goes on top. Cheap now, impossible later.
Index and repeat
The gantry steps one course forward. Eleven square metres of finished slab a day.
What gets built, and in what order
| Structure | Increment | Area or mass | Rate | Why it is at this point in the order |
|---|---|---|---|---|
| Graded pad bedsite prep | 1 | 380 m² | 8 days | Nothing can land safely until this exists |
| Sintered apron22 m diameter | 1 | 380 m² | 35 days | The slab itself |
| Module skirtscompacted regolith to a fifth of hull height | 1 | not yet budgeted | not yet budgeted | Anchors each hull and protects its foot once the modules are down; the only regolith against the vessels in the built increment |
| Blast berm29 m outer | 2 | 1,400 pavers | 36 days | Catches what the apron does not |
| Module shielding2 m over five vessels, planned | 2 | 1,850 t | 310 days | The single largest earthmoving job on the site, not yet started in the built increment |
| Graded roadsfour routes | 3 | 2,100 m² | 190 days | Cuts dust generation and rover wear |
| Equipment padsplant and array | 3 | 260 m² | 24 days | Stops the plant settling |
| Printed shell trialtest article | 4 | 18 m² | 60 days | The step that decides whether volume is launched or made |
Module shielding will dominate everything once it starts. Eighteen hundred tonnes of regolith moved by a machine handling six tonnes a day is most of a year of continuous operation, and it is why the excavator is the busiest thing on the site and why autonomy matters so much. The site is shown before that job: the vessels stand on their skirts and the cover is still to come.
Rate and energy
Material properties, honestly
Sintered regolith is not concrete and should not be described as though it were. It is a glass ceramic: strong in compression, weak in tension, and brittle.
| Property | Sintered regolith | Portland concrete | Implication |
|---|---|---|---|
| Compressive strength | 20 to 45 MPa | 20 to 40 MPa | Comparable. Good for pads and footings. |
| Tensile strength | 2 to 4 MPa | 2 to 5 MPa | Both are weak. Neither spans without reinforcement. |
| Density | 2.4 to 2.8 g/cm³ | 2.4 g/cm³ | Similar |
| Thermal shock resistance | Poor | Moderate | The reason cooling cannot be rushed |
| Reinforcement available | ISRU iron alloy (in situ resource utilisation) | Steel | The alloy from the plant is the rebar |
A pressurised shell needs tensile capacity, and sintered regolith does not have it. The increment four trial is a shell with ISRU iron reinforcement, and whether that works is genuinely unknown. Everything up to increment three, which is pads, berms, shielding and roads, is compression only and well inside what the material can do.
What is not yet known
Nothing in this document has been done on the Moon. The MMPACT and ICON work is funded development on Earth; the November 2022 award pays for the construction system, and no slab has yet been laid on the surface. The 11 square metres a day is an allocation for a gantry that does not exist, and the strength table comes from simulant tests, not from lunar regolith, with recent cryogenic cycling tests showing sintered simulant losing strength over repeated cold soaks. The excavator rate is the largest assumption in the build order: six tonnes a day is an allocation, while NASA's ISRU Pilot Excavator (IPEx) demonstration target is ten tonnes over eleven days, under a tonne a day, for a machine of the class the site shows, so the 310 day shielding job assumes either a larger machine or several of them, and neither has flown. The 65 metre pad distance rests on the sintered apron and the berm catching the low angle fan; the only measured ejecta case is Apollo 12 at 155 metres, and the landers this base expects are far larger than the lunar module. The compacted skirts at the foot of each hull are not yet budgeted for mass or placement time. A pressurised shell needs tensile capacity and sintered regolith does not have it; whether a shell reinforced with ISRU iron works is genuinely unknown, and that is the increment four trial. Everything before it is compression only and inside what the material can do.
Increment plan
Increment 1, survey, grade and pad
The site is surveyed on composition and slope, graded flat, and the apron laid. Nothing else lands until it exists. Once the modules are down, a compacted regolith skirt is built against the foot of each hull to about a fifth of its height.
Increment 2, berms and shielding
The blast berm around the pad, then two metres of regolith over every pressure vessel. This is the longest single job in the programme, and the base is shown before it: each hull stands clear on its skirt.
Increment 3, roads and equipment pads
The four routes, and footings for the plant and the array. Dust generation across the site falls sharply once these are down.
Increment 4, printed pressure shell
A reinforced test article, pressurised and instrumented but not crewed. If it holds, habitat volume stops being launched and starts being made.
Sources and further reading
Every figure in this document traces to one of these. Agency documents and peer reviewed work first, reporting only where it is the primary record.