The size of a space-based missile defense constellation depends on how many interceptors can reach an attacking missile before its rocket finishes accelerating. An interceptor elsewhere in orbit cannot contribute to that engagement simply because it belongs to the same system.
Frederick Lamb and Laura Grego apply this constraint to Golden Dome in an October 15, 2026, analysis published by War on the Rocks. They calculate that approximately 24,000 orbital interceptors would be required in one scenario involving four closely timed missile launches. The figure is their scenario estimate, not an announced Golden Dome procurement quantity.
Position and Available Flight Time
A boost-phase interception targets a missile during powered flight, before it releases its warheads. Placing interceptors in low Earth orbit can avoid the geographical restrictions that affect weapons stationed on land or ships. However, orbital motion continually changes which interceptors are close enough to a launch location.
The American Physical Society’s February 2025 report explains this coverage requirement. The spacecraft travel around Earth, Earth rotates beneath them, and an attacker can choose when to launch. Maintaining an interceptor within reach at every relevant time requires a population distributed around the planet. Several missiles launched close together increase the number needed locally, even though most of the constellation remains too distant to participate.
The short engagement period also includes the time required to detect a launch, determine its trajectory, decide whether it is an attack, and authorize a response. Only the remaining time is available for the interceptor to travel to the missile. Faster detection and faster interceptors change the calculation, but neither eliminates the need to have weapons positioned within reach.
Lamb and Grego’s 24,000-interceptor calculation assumes four solid-propellant intercontinental ballistic missiles launched within roughly 200 seconds from the same area of North Korea or a missile installation in northern Russia. It considers defense of the contiguous United States, assigns one interceptor to each missile, and assumes interceptor acceleration of five times Earth’s gravity and a speed of five kilometers per second when its motor finishes burning. Alaska is excluded.
Those assumptions define what the number represents. Assigning multiple interceptors to each attacking missile changes the requirement. Changing the attacking missile’s powered-flight duration changes how far a defensive weapon can travel before the opportunity closes. Lamb and Grego argue against proceeding with the proposed space-based interceptor program.
Boost-phase defense differs from interception after warheads have separated. During the midcourse phase, warheads move through space alongside discarded rocket components and potentially deliberate decoys. The American Physical Society report explains that identifying the warhead among these objects is a separate technical problem. A longer engagement window does not remove the need to distinguish the target.
How Constellation Requirements Affect Cost
The Congressional Budget Office examined a different question in its May 12, 2026, report: the potential cost of a national missile defense architecture consistent with the executive order that preceded Golden Dome. It estimated approximately $1.2 trillion in 2026 dollars to develop, deploy, and operate its modeled system over 20 years.
The budget office used a notional design because the Defense Department had not released the planned system’s detailed composition. Its architecture included an orbital interceptor layer, two wide-area surface layers, a regional surface layer, and supporting sensors, communications, and battle-management systems. The space-based interceptor component accounted for about 70% of acquisition costs and 60% of total costs.
New Space Economy’s account of the national missile defense cost estimate explains how the orbital component contributes to that spending. The budget office’s modeled architecture and Lamb and Grego’s engagement calculation address different assumptions and should not be treated as interchangeable estimates of one finalized system.
The direct procurement consequence is that interceptor inventory must cover periods and locations where most spacecraft cannot engage. Manufacturing and launch requirements follow from the number of weapons needed within reach, the number of simultaneous targets, and the performance assumed for each interceptor.
