The Air Force is on schedule to conduct a preliminary design review in the coming months of Lockheed Martin's solution for the future Ground Based Strategic Deterrent's Mk21A reentry vehicle. The Mk21A program seeks to modify the legacy Minuteman III system's Mk21 reentry vehicles so they can deliver the W87-1 warheads the National Nuclear Security Administration is building for GBSD's intercontinental ballistic missiles, which the Air Force will begin fielding in the late 2020s. Lockheed won a $108 million contract...