The Space Development Agency awarded contracts worth $1.75 billion to build 36 new sensor satellites in support of the Pentagon’s Golden Dome missile defense shield.

18 satellites each will be supplied by L3Harris and by Sierra Space. They will be part of the Tranche 3 of the SDA’s Missile Defense, Warning and Tracking layer, a constellation of satellites in low-Earth orbit. Launch will potentially follow in autumn 2028, already.

The SDA award is intended to “accelerate” the deployment of the “Tracking Layer” constellation to provide “the homeland, our deployed forces, and allies with global, persistent indications, detection, identification warning, tracking, and defense against advanced and evolving missile threats”, in the words of SDA Director GP Sandhoo, who is also the Space Force’s Portfolio Acquisition Executive for Missile Warning and Tracking.

This new acquisition is specifically known as the “Accelerated Missile Defense Tranche 3”, or AMDT3 and rapidly adds satellites to 72 sensor spacecrafts that were ordered back in December 2025 to Lockheed Martin, Rocket Lab, Northrop Grumman, and L3Harris. This brings the total of Tracking Layer satellites on order/in build to 104. 

The Tracking Layer constellation is part of a wider, proliferated, multi-layered system known as the Proliferated Space Warfighter Architecture, or PWSA. The system comprises separate constellations of data transport satellites (forming the Transport Layer) and one of missile warning and defense satellites, all in low-Earth orbit.

To keep pace with a changing threat environment and evolving technology, the agency intends to field the satellites in batches, or tranches, approximately every two years. PWSA has already gone through 2 Tranches: Tranche 0, “experimental”, saw the placing into orbit of 8 missile warning and tracking satellites and 19 transport spacecrafts. Tranche 1 more recently saw multiple launches that are due to deliver into orbit 28 more missile warning and tracking satellites plus 126 communication sats.

Tranche 2 saw awards placed in 2024 for 54 missile warning, tracking, and advanced fire-control satellite prototypes to be built, 18 each, by L3Harris, Lockheed Martin and Sierra Space. Another Tranche2 award went to Rocket Lab for designing and building 18 data transport satellites.

For this new, Tranche 3 award, L3Harris announced that AMDT3 satellites “build on the successful on-orbit demonstration of an L3Harris Hypersonic and Ballistic Tracking Space Sensor (HBTSS) satellite and infrared sensor payload the company developed for the Missile Defense Agency (MDA)”. L3Harris and Northrop Grumman each built one HBTSS prototype for the Missile Defense Agency, both of which launched as part of the first batch of SDA missile defense satellites.

The new satellites are “equipped with medium-field-of-view payloads designed to provide fire control quality data for missile defense.”

L3Harris now has more 70 missile tracking and defense satellites on order, including 5 already on orbit. It has invested in expanding its space manufacturing facility in Indiana and in a new satellite integration facility in Florida which it says will allow manufacture to start “immediately”.

Sierra Space’s own satellites will be missile warning and tracking spacecraft. The design is “based” on Sierra Space’s ‘Horizon’ spacecraft, a a customizable modular satellite platform. As mentioned previously, the company is already on contract to build 18 satellites as part of Tranche 2 as well.

Golden Dome Director Michael Guetlein said in March this year that $10 billion were being added to “accelerate” some of the space-based sensing elements of the intended missile defence system architecture.

The Senate Armed Services Committee, on its part, used its draft of the fiscal year 2027 National Defense Authorization bill to introduce a request for SDA to field “at least 45 HBTSS-like satellites as part of Tranche 3”.

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