The U.S. Space Force has completed the critical design review for the first two orbital planes of its Epoch 2 medium Earth orbit missile-warning and tracking constellation, Space Systems Command announced Sept. 8. The review covers 10 satellites being developed with BAE Systems Space & Mission Systems and clears the program to begin spacecraft assembly, integration and testing in 2027.
Epoch 2 is the second increment of the Space Force’s Resilient Missile Warning and Tracking Medium Earth Orbit program. The satellites will use infrared sensors to detect and maintain custody of threats ranging from bright intercontinental ballistic missile launches to dimmer, maneuvering hypersonic vehicles.
The new spacecraft will occupy two MEO orbital planes, building on the two planes and 12 satellites associated with Epoch 1. Distributing sensors across several planes is intended to improve global coverage, revisit rates and resilience while providing additional sources of battlespace awareness and technical intelligence.
Space Systems Command completed the critical design review five months after the preliminary design review and 14 months after the initial Epoch 2 contract award. The service attributed the schedule to digital engineering tools that allowed government and industry teams to evaluate the system-level design, identify interface conflicts and assess mission performance before hardware integration.
A critical design review confirms that the spacecraft, payload, communications interfaces and supporting systems are sufficiently mature to proceed toward fabrication and integration. It does not represent completion of the satellites, but it reduces design risk before production and environmental testing begin.
BAE Systems received a $1.2 billion firm-fixed-price Other Transaction Authority agreement in May 2025 for 10 Epoch 2 space vehicles. The company’s Space & Mission Systems business includes the former Ball Aerospace operations acquired by BAE Systems in 2024.
The Space Force plans to field the MEO architecture in successive epochs, with each increment introducing additional coverage and more mature capabilities. The first delivery under the BAE Systems Epoch 2 award is planned for fiscal 2029.
BAE Systems is the first of two planned Epoch 2 vendors. Space Systems Command said source selection for the second supplier remains underway, with an award targeted for early fiscal 2027. The service has not disclosed the number of spacecraft that would be ordered from the second contractor.
The MEO layer forms part of a wider multi-orbit missile-warning architecture rather than a stand-alone replacement for existing systems. Medium Earth orbit offers a different balance of coverage, sensor range and persistence from geosynchronous satellites and the larger low Earth orbit tracking constellation being deployed by the Space Development Agency.
MEO satellites can provide broader regional coverage per spacecraft than platforms in low Earth orbit while operating closer to potential targets than geosynchronous sensors. Combining measurements from multiple orbital layers is intended to improve the ability to detect launches, maintain tracks on maneuvering vehicles and pass timely data to command-and-control and missile-defense systems.
Space Systems Command is coordinating the program with the Space Development Agency and Missile Defense Agency. In March 2026, the command awarded Kratos Technology & Training Solutions a $446.8 million agreement for ground management and integration supporting Epoch 1 and Epoch 2 launches and operations.
The next major industrial step will be the start of assembly, integration and testing in 2027. That phase will bring together the satellite buses, infrared payloads, communications equipment and flight software before the spacecraft undergo environmental and system-level qualification for delivery.
