Why here
Empty space with an address.
There is nothing at EML-1 — no surface, no resource, no ground to stand on. Its value is entirely positional. It sits at the top of the Earth’s gravity well and the top of the Moon’s, which makes it the cheapest place to change your mind about where you are going. A depot here is closer in energy to the lunar surface, to GEO, and to a Mars departure than any of those are to each other.
That is why cislunar space is the second regime and the first genuinely strategic one. The gear-ratio table makes the case in one line: a tonne of propellant delivered to EML-1 from the lunar surface displaces 17 tonnes lifted from Earth. Hold the depot and you hold the interchange.
Envelope
What bounds it.
The constraint fingerprint — the parameters that are fixed, time-invariant, and must be designed around rather than defended against. Each is paired with the consequence it forces.
| Parameter | Value | Consequence |
|---|---|---|
| Transport Δv | 3.8 km/s from LEO | Cheap to reach, cheaper to leave |
| Power | Solar, continuous | No eclipse penalty at the libration points |
| Light time | 1.3 s round trip | Ground control still works; barely inside the teleoperation window |
| Local resource | None on site | Depends on lunar water arriving; the depot has no well of its own |
| Gravity | Micro | Free-flying assembly and transfer; no landing, no launch |
Hazards
What damages it.
Hazards are not constraints. A constraint bounds what is possible; a hazard accumulates, has a return period, and is defended against. Kept in a separate table on purpose — the distinction is the point.
| Hazard | Character | Defence |
|---|---|---|
| Galactic cosmic rays | Continuous, outside the belt | Shielding mass; the first regime without the Earth’s magnetic cover |
| Solar particle events | Episodic, severe | Storm shelter; the dose spikes that a station cannot outrun |
| Station-keeping | Continuous | Fuel budget; the libration points are unstable and must be actively held |
| Micrometeoroids | Continuous, low rate | Shielding; the same background as all free space |
Four readings
The same place, four questions.
Each of the four topologies asks a different question of the same body. A destination that looks marginal under one can look essential under another, which is the reason the maps are kept separate.
Continuous solar, no eclipse. The libration points never fall into shadow the way low orbits do.
Pure interchange. Nothing is made here; everything is transferred, fuelled, and re-aimed.
Light time is 1.3 s — the last address where ground control still works without autonomy.
The first regime outside the magnetosphere. Cosmic rays and solar storms both switch on here.
Matter inventory
What is actually here.
Cislunar space has no matter of its own — it is a volume, not a body. What makes it an economic object is that it is the natural destination for lunar water: the Moon exports up its shallow well to the depot, and the depot fuels everything outbound. The entire matter argument for cislunar space is really an argument about the Moon, read from the delivery point rather than the source.
Corridors
Where it connects.
The edges into and out of this node, with the Δv and status each carries. Full detail on the corridors page.
| Corridor | Δv | Carries | Status |
|---|---|---|---|
| LEO → EML-1 | 3.8 km/s | The way up from the near shore | Flown |
| Lunar surface → EML-1 | 2.5 km/s | The export leg — 17.4× gear ratio | Planned |
| EML-1 → Mars transfer | 0.8 km/s | Departure from the shallow end of the well | Planned |
Contested
Deliberately Not Claimed
The load-bearing uncertainties, stated as uncertainties. Each is tagged with the confidence it actually earns rather than the confidence the argument would prefer.
The depot depends on a well that is not yet flowing. Every cislunar economic case assumes lunar water arriving at the libration point. Until the Moon exports, the depot is stocked from Earth and the gear ratio runs the wrong way.
Which libration point wins is unsettled. EML-1, EML-2 and the lunar distant retrograde orbit each have advocates. The choice depends on the mission mix, and the mission mix does not exist yet.
Record
Provenance.
- Presence
- Crewed transits; no permanent station yet
- Anchor points
- EML-1, EML-2, LDRO
- Sources
- The Free-Fall Regimes; the Earth–Moon System interstitial
- Reviewed
- Q3 2026