COLORADO SPRINGS—The U.S. Space Development Agency (SDA) is now accepting proposals for its next batch of missile tracking satellites, to be launched in early 2029.

The agency released its solicitation for the Tranche 3 Tracking Layer on April 7, with plans to purchase and deploy around 54 satellites to detect, track, identify and warn against conventional and advanced missile threats.

The spacecraft would be equipped with infrared (IR) sensors and spread across six orbital planes as part of the SDA’s nascent proliferated warfighter space architecture. The constellation is envisioned as a mesh network of hundreds of satellites positioned in low Earth orbit, performing a range of missions, primarily 24/7 global communications and persistent missile tracking.

The other transaction authority contract could ultimately include more than 54 spacecraft, according to an SDA release. The agency also is exploring the option of acquiring additional prototype satellites and sensor payloads under the same agreement to “inform requirements and constellation design,” the agency said.

Tranche 3 would build upon the previous tranches of missile warning and tracking satellites. The demonstration Tranche 0 includes eight Tracking Layer satellites, with four each built by SpaceX and L3Harris and launched in 2023-24 for on-orbit testing.

Tranche 1, which is expected to begin launching this summer, includes 28 Tracking Layer spacecraft split between L3Harris and Northrop Grumman.

Tranche 2 spacecraft are targeted to begin launching in late 2026. Sierra Space, L3Harris and Lockheed Martin are each building 18 spacecraft under that contract.

The Tranche 3 solicitation anticipates a similar vendor breakdown of three contractors providing 18 spacecraft each in two orbital planes. Bidders are invited to submit two proposals: one for satellites with missile warning/missile tracking capabilities, and/or one for space vehicles with missile warning, tracking and defense capabilities.

The Tranche 3 Tracking Layer constellation will include a mix of both mission payloads, the solicitation says, with an intent to achieve “near-continuous global stereoscopic coverage for missile warning and missile tracking.”

Proposals are due May 22. SDA anticipates an award announcement in October.