The U.S. Missile Defense Agency (MDA) awarded Lockheed Martin Space Systems a contract worth up to $2 billion for at least of 42 Terminal High Altitude Area Defense (THAAD) missile interceptors, the Pentagon announced June 5.

The exact terms of the contract have not been defined but the award was made under the existing THAAD production contract, according to the announcement. Lockheed Martin’s performance period is from June 4 to July 31, 2018.

The MDA purchase will be combined with a $3.48 billion Foreign Military Sale of 96 THAAD interceptors to the United Arab Emirates that was announced in December, the Pentagon said. The block buy of a minimum of 138 interceptors will result in cost savings, the Pentagon said.

The THAAD system was developed to intercept short-, medium- and intermediate-range ballistic missiles for regional defense.

In a related development, the MDA awarded Lockheed Martin Mission Systems and Sensors a contract modification that will add $9.8 million to the value of the existing Aegis Ashore engineering support contract, according to a June 7 Defense Department contract announcement. This will increase the total value of the contract from $187.6 million to $197.4 million. The work associated with the contract will conclude Oct. 31, 2013.

Aegis Ashore is a land-based version of the Aegis Ballistic Missile Defense system.