Photos: Inside the world's largest wind tunnel

As a matter of national security, 20 percent of the staff at Moffett Field in California are not allowed inside this building. Operated by the United States Air Force, the 80x120-foot wind tunnel is accessible to U.S. citizens only, as the flight vehicle research conducted inside has implications for national security.

This week, CNET's cameras were allowed inside for a special look at this tech research facility.

Originally built in the 1940s, the gigantic wind tunnel is the largest in the world and conducts advanced helicopter research. Although the site is not operated by NASA, it has tested one-third scale models of the space shuttle to learn how crosswinds effect shuttle landings and examined the parachutes for NASA's Spirit and Opportunity rovers. After testing here, it was determined the parachutes were insufficient and had to be redesigned. The unique capacity and perfomance of this wind tunnel gives researchers an opportunity to test equipment in conditions nearly identical to their intended real-world uses.

Security is tight at the National Full-Scale Aerodynamics Complex, operated by the Arnold Engineering Development Center of the U.S. Air Force. We had to go through multiple layers of security checkpoints to access the wind tunnel.

William Warmbrodt, branch chief of the Aeromechanics Branch Flight Vehicle Research and Technology Division, talks about some of the advanced helicopter research that takes place in the wind tunnel. The room, big enough to house a Boeing 737, is wider than it is tall to accommodate the wingspan of large aircraft.

At its full capacity of wind generation of 100 knots, the tunnel uses 100 megawatts of power. The highly controllable environment paired with an array of cameras and diagnostic equipment give researchers the information they need to improve safety, efficiency, and reliability of aerospace technology.

When you run six 15-bladed fans, each with a diameter equal to the height of a four-story building powered by six 22,500-horsepower motors, a lot of noise is generated. The walls of the facility are carpeted with 8 to 12 inches of acoustic liner to prevent excessive noise pollution seeping out into the surrounding communities.

Testing for NASA's next mission to Mars passed flight-qualification testing at the Moffett Field wind tunnel in March and April. The Mars Science Laboratory mission, which is to be launched in 2011 and plans to land on Mars in 2012, will use the largest parachute ever built to fly on an extraterrestrial mission.