The Air Force said recently it awarded Lockheed Martin [LMT] a $1.9 billion contract to produce the fifth and sixth satellites of the Advanced Extremely High Frequency (AEHF) communications constellation.

The announcement comes one month after AEHF prime contractor Lockheed Martin delivered the system module for the fourth AEHF satellite to subcontractor Northrop Grumman [NOC] for payload integration. AEHF is the Defense Department’s survivable, secure military communications satellite constellation designed to share intelligence during all threat conditions, even after a nuclear attack.

“This production contract for the fifth and sixth AEHF satellites affirms the government’s confidence in our ability to deliver these spacecraft affordably and efficiently to meet the burgeoning demand from strategic and tactical users worldwide,” Lockheed Martin Vice President of Protected Communications Mark Calassa said recently in a statement.

Calassa said Lockheed Martin shifted from cost-plus to fixed-price incentive-firm target contracting for AEHF-5 and AEHF-6, which he said would allow DoD to limit its risk while still targeting cost reduction. Calassa also said since DoD is buying the two satellites in bulk, Lockheed Martin can significantly reduce costs by achieving economies in scale.

DoD said it expects AEHF-5 and AEHF-6 work to wrap up by 2022. Lockheed Martin spokesman Michael Friedman said work on AEHF-5 and AEHF-6 will begin immediately.

Lockheed Martin is now under contract to deliver six AEHF satellites and the Mission Control Segment, according to a statement. Both AEHF-1 and AEHF-2 are on orbit. AEHF-3 is slated for a September launch and AEHF-4 is progressing on schedule with a launch date estimated for early 2017. AEHF-5 and AEHF-6 will be assembled at Lockheed Martin’s Sunnyvale, Calif., facility.

The AEHF joint program is run by the Air Force and also supports special operations, special nuclear operations, missile defense, space operations and intelligence. A single AEHF satellite provides greater total capacity than the entire legacy five-satellite Milstar constellation, according to Lockheed Martin. AEHF is a follow-on to the Milstar system, augmenting, improving and expanding DoD’s Military Satellite Communication (MILSATCOM) architecture, according to a statement.