Cislunar Corridors

The two-map problem

Why Cislunar Space Needs Two Transfer Maps

The map you need depends on the engine you carry.

In two-body orbital mechanics, Δv is the universal currency. A Hohmann transfer from LEO to GEO costs about 3.9 km/s regardless of propulsion type — engine choice determines propellant fraction, not the shape of the route.

In the three-body cislunar regime, that equivalence breaks. Impulsive transfers — brief high-thrust burns — still scale with Δv. But low-thrust spirals scale more closely with orbital energy, and the two quantities diverge sharply in the Earth-Moon system. A route that looks only three times harder in Δv can take eight times as long under continuous low thrust.

This is why cislunar logistics requires two maps: a Δv topology for chemical and nuclear-thermal vehicles that maneuver in brief impulses, and a specific-energy topology for solar-electric and ion-drive vehicles that thrust continuously at low levels. The same two nodes can sit close together on one map and far apart on the other.

Most published cislunar Δv diagrams show only the first map. For freight — which has no schedule and no crew — the second map often determines which corridor is actually cheapest.

Impulsive transfers

Hohmann, Free-Return, and Direct Injection

Fast, expensive, and you know where you are going.

The standard Hohmann-like transfer from a 200 km LEO to low lunar orbit takes roughly five days and costs about 3.9 km/s for trans-lunar injection (TLI) plus roughly 0.8 km/s for lunar orbit insertion — about 4.7 km/s total. Every Apollo mission flew a variant. The corridor is fast, well-characterized, and expensive.

Free-return trajectories add a safety constraint: if the lunar orbit insertion burn fails, the vehicle’s unaltered path swings it around the Moon and back to an Earth-entry corridor. Apollo 13 demonstrated this was not a theoretical nicety. The free-return imposes a narrower departure geometry and slightly higher Δv, but for crewed missions the safety trade is straightforward.

Direct injection eliminates the parking orbit. The launch vehicle fires continuously from ascent through TLI, saving the coast-and-restart sequence. Starship’s lunar architecture depends on direct injection from a refueled stack in LEO.

All three are impulsive-map corridors. They are fast (≤ 5 days), require high-thrust engines, and map cleanly onto the standard Δv diagram.

Low-energy transfers

Ballistic Lunar Transfers and Manifold Riding

Trade time for propellant — let the Sun do part of the work.

A ballistic lunar transfer (BLT) exploits the Sun’s gravitational perturbation. Instead of flying a direct Hohmann arc to the Moon, the spacecraft is lofted past the Moon toward the Sun-Earth weak stability boundary — roughly 1.5 million km out — where solar gravity bends the trajectory back toward Earth-Moon space. The vehicle arrives at the Moon with lower relative velocity, reducing the capture burn.

The cost is time. A BLT takes roughly three to four months instead of five days. CAPSTONE, launched in June 2022 on a Rocket Lab Electron, demonstrated the first operational BLT to an NRHO, arriving in November 2022 after a roughly four-month low-energy transit. The spacecraft — a 25 kg CubeSat — could not have reached the Moon on a Hohmann arc with the propulsion it carried. The BLT was the enabling corridor.

Invariant-manifold transfers are the three-body generalization. The unstable periodic orbits around EML1 and EML2 have associated stable and unstable manifolds — dynamical tubes that thread through phase space. A spacecraft that enters a stable manifold tube rides it toward the target orbit with minimal propulsion. The Δv savings can reach 15–40% relative to Hohmann, at the cost of transit times measured in weeks to months.

For freight with no schedule — propellant slugs, structural mass, shielding — manifold transfers are the natural corridors. For crew, the time penalty is rarely acceptable.

Low-thrust spirals

Solar-Electric Spirals: The Specific-Energy Map

High specific impulse buys efficiency. Low thrust buys patience — and a conjunction-management problem.

At high specific impulse — 2,000 to 5,000 seconds — a solar-electric stage can capture lunar cargo with a small propellant fraction. But low thrust stretches the maneuver over months. Using a reference 120 kW, 1.70-tonne solar-electric vehicle:

The numbers show why propellant fraction and transit time cannot be optimized independently. Higher I_sp saves propellant but multiplies flight time — and flight time multiplies the fleet. Every vehicle simultaneously in transit crosses operational conjunction-management shells in LEO and MEO. The cost appears not only in inventory but in the traffic-management burden on the receiving regime.

The scaling trap: Impulsive transfers scale intuitively with Δv. Low-thrust spirals scale with orbital energy. The ratio between the two diverges as you move deeper into the gravity well. That is why the Δv diagram — on its own — is the wrong map for electric vehicles.

Transfer reference

Cislunar Transfer Corridors: Δv, Time, and Heritage

The menu of routes from Earth orbit to the cislunar nodes.

The aiming problem

Mass-Driver Aiming Precision: Where Error Amplifies

A meter per second of launch error shifts the perigee by 220 kilometers.

A lunar mass driver is extraordinarily sensitive to muzzle velocity. Near the 2.52 km/s design point, each meter per second of launch error shifts the eventual Earth-perigee by roughly 220 km. The reason: the payload leaves the Moon only modestly above lunar escape velocity, so small errors in muzzle speed are amplified roughly threefold in the excess velocity that shapes the Earth-return ellipse.

The tolerance depends on destination. Direct LEO delivery requires roughly ±1.3 m/s — about five parts in 10,000, with the dangerous error direction capable of dropping perigee into the atmosphere. GEO tolerates roughly ±32 m/s. EML1 and EML2, which accept manifold insertion rather than aerodynamic capture, are the most forgiving targets.

That is another reason the first lunar exports want to stop high. Tight aiming is an engineering constraint on the track. Loose aiming is a property of the destination.

The tug problem

The Tug with No Propellant: The Noble-Gas Dependency

The obvious architecture fails on the propellant it needs.

The straightforward logistics architecture is to stop lunar cargo at EML1 or EML2 and let a reusable electric tug carry it inward to LEO or GEO. Then the propellant ledger fails.

A reusable electric tug cycling EML1 ↔ a 2,000 km Starmind shell pays roughly 3 km/s in each direction. Hall-effect and gridded-ion thrusters can perform this efficiently, but their propellants — xenon, krypton, argon — are all noble gases. None has a demonstrated off-Earth production source anywhere in the industrial architecture.

The Moon can plausibly supply oxygen and hydrogen. Using them chemically for the same round trip drives the propellant fraction toward three-quarters of departure mass — a reusable vehicle that is mostly propellant on every sortie.

The alternatives are unattractive. Aerobraking can save the downleg burn, but a low-density cargo structure now needs a very large thermal-protection system capable of entering near 10 km/s — essentially the same unsolved large-ferry aerobraking problem encountered at Mars. Or each package carries its own expendable capture stage, which gives up the reusable tug entirely.

The noble gases are not a footnote. They are a gating terrestrial stock for electric propulsion until an off-Earth supply chain is demonstrated.

The catch problem

Who Catches: The Narrowest Dependency in Lunar Export

The Moon can throw the mass. The unresolved question is who catches it.

The current lunar-export concept contains an unusually narrow dependency. Direct delivery to low orbital shells assumes a Starship-derived vehicle — SpaceX’s AI1-class cargo variant — can self-capture with roughly a six-percent propellant fraction. That is a spacecraft-design choice being made by SpaceX for reasons unrelated to lunar logistics.

If the design changes, the arrival architecture changes with it. No alternative self-capture stage exists at the required scale. No alternative aerobraking system has been demonstrated at the required entry velocity. The mass driver can be built to demonstrated engineering tolerances. The receiver — the vehicle that matches velocity with arriving cargo and delivers it to a customer orbit — does not yet have a second source.

This is a single-vendor chokepoint in what would otherwise be a multi-operator logistics network.

Strategic corridors

Cislunar Corridors as Strategic Infrastructure

Movement from cislunar space to GEO is less fuel-intensive than movement from GEO to LEO.

Every corridor described above also works in reverse. The U.S. Space Force formalized cislunar space as an operational domain in March 2026, establishing a Cislunar Coordination Office and codifying requirements for space domain awareness (SDA) through a 2040 roadmap. The AFRL Oracle Prime satellite — an experimental platform designed to monitor objects near a Lagrange point — is the first dedicated cislunar surveillance asset.

The military logic follows from the corridor physics. Descending from cislunar space to GEO requires less Δv than climbing from GEO to LEO. A vehicle parked quietly in a stable DRO — requiring almost no station-keeping maneuvers that would announce its presence — sits on a corridor that opens downhill toward the most valuable orbital real estate on Earth.

China has flown test articles in cislunar space. Every major space power now treats the corridors not only as trade routes but as approach vectors. A January 2026 White House executive order, “Ensuring American Space Superiority,” mandated DOD to establish capabilities for detecting and countering threats within the cislunar regime.

The corridors page in the system-level corridor index treats all regimes together. This page covers only the cislunar segment — the transfer routes, their physics, and the dependencies they carry.