Cislunar refers to the vast region of space between Earth and the Moon, extending outward to include the Moon’s orbit and the gravitational sweet spots surrounding it. The term comes from the Latin “cis” (on this side of) and “lunar” (the Moon). It covers roughly 384,400 kilometers (about 239,000 miles) from Earth to the Moon, though the full region of interest stretches even farther depending on how you define the boundary.
How Big Cislunar Space Actually Is
The Moon orbits Earth at an average distance of about 384,400 kilometers, but that distance changes. At its closest (perigee), the Moon swings to roughly 363,300 kilometers from Earth. At its farthest (apogee), it drifts out to about 405,500 kilometers. Cislunar space encompasses all of this range and more.
To put the scale in perspective, geostationary orbit, where most communications satellites sit, is about 35,786 kilometers above Earth. The Moon is roughly nine times farther out than that. And the full sphere of Earth’s gravitational dominance, called the Hill sphere, extends to approximately 1.5 million kilometers, about 42 times the distance of geostationary orbit. Beyond the Hill sphere, the Sun’s gravity takes over and you’re in what’s considered heliocentric (Sun-centered) space. Cislunar space sits well inside this boundary, in the zone where Earth and Moon gravity interact most meaningfully.
Lagrange Points: The Gravitational Sweet Spots
One of the most important features of cislunar space is a set of five locations called Lagrange points, where the gravitational pull of Earth and the Moon balance out in useful ways. A spacecraft placed at one of these points can hold its position with minimal fuel.
Three of them, labeled L1, L2, and L3, sit along the line connecting Earth and the Moon. These are unstable, meaning a spacecraft parked there will slowly drift away and needs small course corrections roughly every 23 days. L1 sits between Earth and the Moon, L2 is on the far side of the Moon, and L3 is on the opposite side of Earth from the Moon.
The other two, L4 and L5, are stable. They form the tips of two equilateral triangles with Earth and the Moon at the base. Objects at L4 and L5 naturally stay put without correction, as long as the mass ratio between the two large bodies exceeds a specific threshold, which the Earth-Moon system comfortably meets. In 1956, the Polish astronomer Kordylewski discovered large concentrations of dust lingering at these two points, confirming their stability in a tangible way.
Key Orbits for Lunar Missions
Getting to the Moon isn’t just about flying in a straight line. Different orbits within cislunar space offer different advantages, and mission planners choose carefully based on what they need.
One orbit getting significant attention is the near-rectilinear halo orbit (NRHO), which NASA selected for the Gateway space station. NRHO is a one-week loop that hangs almost like a necklace from the Moon, balanced between Earth’s and Moon’s gravity. It combines the surface access of a low lunar orbit with the fuel efficiency of a more distant path. The orbit periodically brings a spacecraft close enough to reach the Moon’s south pole, where astronauts will eventually test long-duration habitation technologies. It also allows access to other landing sites across the lunar surface, not just the poles.
NRHO has a practical bonus for communications: it keeps a continuous line of sight to Earth, so there’s no blackout period when a spacecraft swings behind the Moon. That means uninterrupted contact between crews and mission control. The deep-space environment of NRHO also opens the door to radiation research that isn’t possible in low Earth orbit, giving scientists a better picture of how space weather affects people and instruments over time.
Some transfer trajectories through cislunar space are surprisingly long and indirect. Certain missions have used low-energy paths that swing well beyond the Moon, out to distances exceeding 1.5 million kilometers, taking months or even years to reach their final orbit. These routes trade speed for fuel savings, which matters enormously when every kilogram of propellant costs thousands of dollars to launch.
Why Cislunar Space Is Strategically Important
Until recently, most human activity in space took place within about 36,000 kilometers of Earth’s surface. Cislunar space represents a roughly 1,000-fold expansion in the volume that governments and companies now operate in. The U.S. Space Force, for example, was originally focused on protecting assets out to geostationary range. With new public and private missions pushing into cislunar space, that sphere of interest has jumped to over 272,000 miles and beyond.
Economically, cislunar activity is still in its early stages. State-sponsored contracts remain the primary driver for lunar landers, rovers, and related hardware. The World Economic Forum projects that commercial revenues from lunar and cislunar applications, things like data collection, transport services, and resource utilization demonstrations, could reach around $2 billion annually by 2035. Longer-term ambitions include fuel mining from lunar resources and establishing permanent research bases, but those depend on technologies still being developed.
The Challenge of Tracking Objects
Keeping tabs on what’s moving through cislunar space is far harder than tracking satellites in low Earth orbit. Three factors make it difficult. First, the sheer distance between ground-based sensors and cislunar objects means the signal reflected back is much weaker. Second, the Moon itself creates optical background noise that interferes with telescope observations. Third, the orbital dynamics are more complex because objects in cislunar space are influenced by both Earth’s and the Moon’s gravity simultaneously, creating unpredictable paths that are harder to model than the relatively clean two-body physics of near-Earth orbits.
This matters because as more nations and companies send hardware into cislunar space, the ability to detect, identify, and predict the movement of those objects becomes a security and safety concern. Current space surveillance networks were built for tracking things much closer to Earth, and extending that capability outward is an active area of development.
Building a Communications Network
GPS doesn’t work near the Moon. Astronauts and robotic missions in cislunar space need a new navigation and communications infrastructure, and multiple teams are working on designs. The core idea, first proposed by researcher Robert Farquhar in 1969, is to place relay satellites at or near the Earth-Moon Lagrange points.
One approach uses halo orbits around the L1 and L2 points to position navigation satellites that can provide coverage for spacecraft traveling between Earth and the Moon. Another concept places satellites at L3, L4, and L5 in a triangular configuration to achieve broad coverage of the entire cislunar region. More recent proposals combine low-energy transfer orbits with halo orbits to create constellations that offer high-precision positioning data, similar to what GPS provides on Earth, along with relay communication support for complex lunar surface missions.
These constellations would serve a dual purpose: helping spacecraft navigate autonomously in cislunar space, and maintaining continuous data links between the lunar surface, orbiting stations, and Earth. As the number of missions to the Moon increases over the next decade, some form of this infrastructure will be essential.