Millennium Space Systems will build six more satellites in the first phase of an effort to develop a constellation of missile-tracking satellites in medium Earth orbit, the Space Force announced Wednesday. The firm, a Boeing subsidiary, was already on contract to deliver six spacecraft for the Missile Track Custody, or MTC, program, and the new order deal brings its total contribution to 12. The $386 million contract is less than the $509 million deal the company was awarded for the first six satellites.

The first batch of satellites is on track for delivery in 2026 and the company plans to deliver the second batch of satellites in late 2027, Lindsay Dewald, Millennium’s program manager for the effort, told Defense News. The new order follows Space Systems Command’s decision in May to oust RTX from the program. The MTC program is one piece of the Space Force’s plan to make its on-orbit missile warning and tracking capabilities more resilient against growing threats from China and Russia.

Through MTC, the service plans to launch warning and tracking satellites to medium Earth orbit, located between 1,200 and 2,200 miles above Earth, where space sensors can observe a larger area. Millennium’s first 12 MTC satellites, part of Epoch 1, will carry an electro-optical infrared payload built by Boeing that uses advanced sensors to detect and track heat signatures from missile threats. Dewald noted that Millennium is working closely with its suppliers to ensure they can continue to deliver on schedule despite an increased buy from the Space Force.