On July 14, the Space Development Agency (SDA) announced partnerships worth a combined $1.75 billion to develop 36 new Golden Dome missile-defense tracking satellites. Each company is on the hook for 18 spacecraft under Accelerated Missile Defense Tranche 3 (AMDT3), with all 36 expected to be ready for launch by the end of 2028, according to an SDA statement. The prime names are L3Harris Technologies and Sierra Space, and the job is specific: build additional satellites for the SDA Proliferated Warfighter Space Architecture's Tranche 3 Tracking Layer constellation.

This is not a vague “space growth” headline. SDA is using infrared sensors in low Earth orbit to detect and track missiles, then pushing the data in real time over a low-latency communications network to military forces on the ground. The 36 contracted satellites are intended to increase constellation coverage and integrate with the spacecraft of SDA's first three Tranches, tightening the system that feeds warning and tracking for next-generation missile threats.

The contracts are similar in shape but differ in what each variant is “for,” and SDA built those differences into the procurement language. Sierra Space's agreement calls for “18 missile warning and missile tracking variant space vehicles,” while L3Harris is tasked with “18 missile defense variant space vehicles.” Both sets are described as equipped with infrared sensors that will add to the constellation’s global network. In other words, this is a layered architecture, where different satellite “variants” can support different mission elements inside the same tracking layer concept.

Money, too, lands differently across the two awards. L3Harris can receive up to $955 million for its 18 satellites, which the Space Force describes as “Hypersonic and Ballistic Tracking Space Sensor-like” (HBTSS) spacecraft. Sierra Space's agreement has the potential to reach $798 million for its 18-satellite contribution. Those ceilings matter for board and capital planning because they frame the program’s scale and the level of commitment the primes can expect on a per-satellite basis, even if the overall $1.75 billion is the clean headline number.

Orbit mechanics are part of why this program costs what it costs, and why it is hard to “just ship later.” SDA says the 36 spacecraft will be distributed across four orbital planes as part of a hybrid missile-defense architecture designed to provide “global stereo coverage” of next-generation missile threats. The phrase “global stereo coverage” is basically the promise that sensors separated in space can see the same target from multiple angles, improving detection and tracking quality. For executives, that translates into more than engineering work. It means schedule discipline, coordination across planes, and integration into a system that has to function as a network, not as a set of one-off launches.

SDA also frames AMDT3 as an evolution, not a one-time procurement. It says AMDT3 expands upon SDA’s previous and current Tracking Layer generations, Tranches 1, 2 and 3, and it positions the award as another milestone toward “a resilient, global missile warning, missile tracking, and missile defense capability.” SDA Director G.P. Sandhoo tied this milestone to the program’s continuity, but the operational core remains the same: infrared imaging from low Earth orbit and fast data transfer into joint force operations.

Industrial planning is getting an extra push here because Sierra Space and L3Harris are not starting from blank pages. Sierra Space will base its satellites on the Horizon vehicle from the company’s Eclipse satellite series, which it also used in the design of spacecraft it provided for the Tranche 2 Tracking Layer program. Meanwhile, L3Harris says it plans to build on the success of HBTSS satellites the company developed for the Military Defense Agency. L3Harris adds that it has “more than 70 missile tracking and defense satellites on order,” including five on orbit, between MDA’s HBTSS program and SDA’s Tracking Layer across Tranche 0, 1, 2 and 3.

If you are a CFO or board member at a defense space supplier, the second-order implication is that Tranche 3 is not isolated. These 36 satellites come on top of a separate December 2025 order for 72 Tranche 3 Tracking Layer spacecraft, via contracts worth $3.5 billion that also included L3Harris, along with Lockheed Martin, Rocket Lab, and Northrop Grumman. Together, the two rounds of awards bring the planned Tranche 3 constellation to 108 satellites, worth about $5.25 billion. SDA says if everything goes to plan, all 108 satellites will be available to launch by the end of 2029, but it also describes the new contracts as “accelerated,” even though it has not established a launch timeline for the overall group.

Once the new satellites are in orbit, the Space Force assumes responsibility for their operation and integration “in support of joint force operations and delivering warfighting capabilities,” per the SDA statement. That handoff from build to operate is where programs often get messy: the integration demands do not stop at launch. For peers watching Golden Dome and SDA’s proliferated constellation approach, the takeaway is straightforward. This $1.75 billion decision signals continued scaling of the tracking layer network, and it tightens the operating window that primes and integration partners must plan around, from manufacturing and testing throughput to orbital plane deployment.

In short, SDA is adding 36 infrared-sensor satellites to the Golden Dome-aligned Tracking Layer with a defined total award and an end-2028 readiness target. For decision-makers across defense space, the real question becomes less “will it launch” and more “how quickly can the system be integrated into real-time warning and tracking workflows without breaking the network’s promised coverage.”