NASA designated a four-person space capsule built by Lockheed Martin Corp. as its likely premier exploration vehicle to take future astronauts beyond earth orbit.

The decision, announced Tuesday, is anticipated to lock in billions of dollars in revenue for Lockheed Martin over the next few years, and reinvigorate a program that has been struggling due to budget cuts and uncertainty about NASA's long-term manned exploration goals. It also comes in the wake of stepped-up congressional complaints that NASA is improperly withholding...