Cislunar Surveillance

The unwatched volume

The Unwatched Volume: 1,000 Times GEO and Barely Monitored

The U.S. military’s space tracking network was built for LEO and GEO. Cislunar space is a tenfold increase in range and a thousandfold expansion in volume.

The geostationary belt sits roughly 35,786 km above Earth’s equator. The U.S. Space Surveillance Network and its allied counterparts are architected to catalog and maintain custody of objects from LEO through GEO. Beyond GEO, capability drops sharply. EML1 is roughly 326,000 km from Earth — about nine times farther than GEO. The volume of space between Earth and the Moon is over 1,000 times the volume enclosed by the geostationary shell.

That volume is not empty. China has flown test articles in cislunar space. Queqiao-1 operated in an EML2 halo orbit from 2018. CAPSTONE has occupied an NRHO since November 2022. Commercial lunar landers transit the regime regularly. And movement from cislunar space to GEO is less fuel-intensive than movement from GEO to LEO — enabling strategic surprise from less-tracked regions.

No comprehensive catalog of cislunar objects exists. No sensor network provides continuous custody. The regime is watched the way the open ocean was watched before radar: sporadically, opportunistically, and with long gaps.

Stability as surveillance

Stability Is a Surveillance Property

An unstable orbit announces itself. A stable orbit does not.

A spacecraft in an unstable halo orbit around EML1 or EML2 must maneuver periodically to maintain its position. Those station-keeping burns produce thrust signatures, radio emissions, and predictable orbital corrections. Each event is a detection opportunity.

A spacecraft in a distant retrograde orbit (DRO) can remain dynamically stable with almost no station-keeping — tens of thousands of kilometers from the Moon, hundreds of thousands from Earth, with no maneuvers that announce its presence. It is dark, cold, and quiet.

This is why the warehouse-and-junction framework has a security dimension. Junctions are visible. Warehouses are not — unless someone is specifically looking.

Stability is therefore not only a propellant property. It is a surveillance property. The orbit families that are cheapest to occupy are also the hardest to monitor.

Why cislunar SDA is hard

Five Reasons Cislunar Space Domain Awareness Is Harder Than GEO

Every tool that works at GEO degrades or fails at cislunar distances.

Distance. EML1 is roughly nine times farther than GEO. Optical signal strength falls with the square of distance; radar returns fall with the fourth power. A sensor designed for GEO-class brightness sees nothing at EML1 without a fundamental redesign.

Volume. The cislunar regime is over 1,000 times the volume of the geostationary shell. Covering it with a search beam requires either enormous field-of-view sensors or constellations of narrow-field sensors with coordinated tasking.

Non-Keplerian dynamics. Below GEO, orbital mechanics are effectively two-body — a spacecraft’s position can be predicted with standard Keplerian propagation. In cislunar space, the Moon’s gravity makes orbits chaotic. Traditional catalog-maintenance algorithms break. New propagation models, new association algorithms, and new custody metrics are required.

Exclusion zones. Ground-based optical telescopes lose cislunar targets when they pass near the Moon or Sun in the sky — the scattered light overwhelms the signal. Solar and lunar exclusion zones create regular gaps in coverage.

Custody. In the GEO tracking regime, “custody” means continuous awareness of an object’s position over time. In cislunar space, the combination of distance, volume, exclusion zones, and chaotic dynamics means custody is routinely lost. Reacquiring a lost object in a 1,000×-GEO volume is a search problem, not an update problem.

Ground-based limits

Ground-Based Cislunar Tracking: What Works and What Doesn’t

Small telescopes can detect cislunar spacecraft. They cannot maintain continuous custody.

Los Alamos National Laboratory demonstrated ground-based cislunar tracking using 36 cm telescopes with back-side-illuminated CMOS imagers, detecting CAPSTONE at roughly 440,000 km (apparent magnitude ~19.6) and Artemis Orion at roughly 320,000 km (~15.5 magnitude). ExoAnalytic Solutions used its global network of over 350 telescopes at 35 sites to track the Artemis 1 mission through its cislunar trajectory.

These demonstrations confirm that detection is possible. But detection is not custody. A single telescope loses the target when the Earth rotates, when the Moon or Sun creates an exclusion zone, and when weather intervenes. A global network can extend coverage but cannot eliminate the geometry gaps. And at cislunar distances, a spacecraft that maneuvers even slightly between observations may not be in the predicted search volume on the next pass.

Ground-based sensors are a floor. Persistent cislunar SDA requires space-based sensors positioned in the regime itself.

Oracle Prime

AFRL Oracle Prime: The First Dedicated Cislunar Surveillance Satellite

The first satellite designed specifically to search for, detect, and track objects in cislunar space.

Oracle Prime (Oracle-P) is an Air Force Research Laboratory program with Advanced Space as prime contractor, Terran Orbital providing the spacecraft bus, and a Leidos-built optical imaging payload. The satellite will operate in a halo orbit near Earth-Moon Lagrange Point 1 (EML1) — roughly 326,000 km from Earth — for a two-year on-orbit experiment. Preliminary design review was completed in December 2025, and launch is planned for 2027.

Oracle Prime’s mission is to demonstrate the ability to discover unknown or lost objects and maintain custody of known objects in cislunar space. Because EML1 is approximately eight times farther from Earth than GEO, communications will be less frequent and at lower data rates than Earth-orbit sensors — the satellite must perform substantial on-board processing to send manageable data volumes back to ground.

Advanced Space brings flight-proven cislunar experience from CAPSTONE. The program name was changed from Cislunar Highway Patrol System (CHPS) to Oracle — shifting the emphasis from policing to observation and foresight.

One sensor is not a network. Oracle Prime is a pathfinder, not an operational architecture. A single space-based sensor provides detection opportunities but not persistent coverage. The U.S. Air Force has funded studies for cislunar sensor constellations, but no operational network has been approved or funded.

The Space Force pivot

U.S. Space Force Cislunar Strategy: From Theory to Acquisition

In 2024, cislunar SDA was a research topic. In 2026, it is an acquisition program.

In March 2026, the U.S. Space Force formalized cislunar space as an operational domain, establishing a Cislunar Coordination Office led by Jamie Stearns of the AFRL Space Vehicle Directorate. The office brings together program managers and engineers to build acquisition roadmaps and timelines for cislunar capabilities through 2040.

The pivot followed two forcing events. A January 2026 White House executive order, “Ensuring American Space Superiority,” mandated the Department of Defense to establish capabilities for detecting and countering threats within the cislunar regime and called for initial elements of a permanent lunar outpost by 2030. NASA’s March 2026 decision to pause Gateway and redirect toward a lunar surface base gave the military a concrete surface asset to protect.

The Space Force’s “Objective Force” document envisions sustained military presence through 2040, providing positioning, navigation, and timing (PNT) infrastructure and telecommunications to support allied interests in cislunar space. The requirements are being codified into acquisition programs rather than research projects.

Corridors as approach vectors

The Downhill Corridor: Why Cislunar Space Is a Strategic Approach

Descending from cislunar space to GEO costs less Δv than climbing from GEO to LEO.

Every transfer corridor described elsewhere on this site works in reverse. A vehicle parked 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 in the Earth-orbit regime.

The Δv from EML1 to GEO is roughly 0.8 km/s. From GEO to LEO is roughly 3.9 km/s. A cislunar vehicle has more energy available than a GEO vehicle, and reaches its target faster. The less-monitored region is also the region with the easier approach to the most protected assets.

This is the strategic logic driving the Space Force’s urgency. Cislunar SDA is not a distant concern about lunar mining. It is a near-term concern about approach vectors to GEO.

The mass-driver question

Mass Drivers as a Dual-Use Capability

An electromagnetic launcher that can throw shielding mass can also throw projectiles.

A lunar mass driver designed to export regolith, structural stock, or shielding to EML1 is also — by its physics — capable of launching kinetic projectiles. A 2026 strategic assessment noted that mass drivers “could serve as valuable first-strike weapons systems” by launching projectiles at orbital or even terrestrial targets. The Outer Space Treaty prohibits weapons of mass destruction in space but does not specifically address kinetic launchers on the lunar surface.

The dual-use property is inherent. A mass driver capable of reaching EML1 at 2.52 km/s can also deliver mass to any Earth-return trajectory. Aiming precision of ±1.3 m/s is tight enough for LEO delivery — tight enough for targeting. The distinction between a logistics tool and a weapon is the intent at the control console, not the design of the track.

That makes mass-driver governance inseparable from cislunar surveillance. The monitoring infrastructure that watches for unauthorized objects in cislunar space must also watch the surface installations that could produce them.

Who watches

The Current State: Who Watches Cislunar Space

The warehouses hold mass. The junctions sell Δv. And most of the volume between them remains a place nobody can continuously watch.

The table makes the gap visible. Ground-based demonstrations have proven that detection works. A single space-based pathfinder is in development. No operational network exists. The regime that is 1,000 times the volume of GEO has fewer dedicated sensors than any single orbital shell inside GEO.

The first cislunar economy will be built from warehouses and junctions. The warehouses hold mass. The junctions sell Δv. And unlike low Earth orbit, most of the volume between them remains a place nobody can continuously watch.