The Space Development Agency, part of the ⁠U.S. Space Force, said Friday it has reached agreements with four defense suppliers to build 72 satellites, worth about $3.5 billion collectively.

The ‍agency said Lockheed Martin, L3Harris Technologies, ‍Northrop Grumman, and Rocket Lab USA have signed fixed-priced contracts for 18 ⁠space vehicles each.

The infrared satellites, which will be used for missile warning, tracking and defense ​systems, are expected to be launched into low-earth orbit in 2029.

"The addition of these satellites will ‍achieve near-continuous global coverage for missile warning and tracking, along ⁠with payloads capable of generating fire control quality tracks for missile defense," said the agency's Acting Director Gurpartap Sandhoo.

These satellites belong to Tranche-3 ⁠and support the ​space agency's objective of ⁠launching a new tranche every two years to refresh ‍its satellite architecture with updated technology.

In September, the first ‌Tranche-1 space vehicle, a SpaceX Falcon 9 rocket, was launched from Vandenberg Space Force Base, California.

The ⁠agency ​plans to include ‍a total of 154 operational space vehicles in Tranche-1, which will be ready ‍for initial warfighting capability in 2027.