Crawler - Transporter are gigantic machines used to transport rockets and spacecrafts from the Vehicle Assembly Building (VAB) to Launch Complex 39 at NASA's Kennedy Space Center in Florida. The largest vehicle ever built, Crawler-transport 1(CT) and 2 (CT-2) were constructed in 1965 and used during the Apollo, Skylab, Apollo-Soyuz, and Space Shuttle programs.
Traveling 1 mph, the crawler carries the launch vehicle with its mobile launcher platform to the launch pad using a laser guidance system and lowers them both onto the pad pedestals. After the launch, the crawler re-lifts the mobile launcher and returns it. Each transporter travels on eight tracked tread belts containing 57 tread belt "shoes."
One crawler houses 16 traction motors, two AC and two DC generators, and two control cabs that drive the vehicle forward and backward. The jacking, equalizing, and leveling (JEL) system keeps the upper deck and pickup points level at all times, even when traveling at an incline, to prevent the payload from toppling.
NASA's Ground System Development and Operations Program (GSDO) has been refurbishing the crawlers since the last space shuttle launch in 2011. CT-1 is being strengthened to carry commercially operated launch vehicles, while CT-2 is being modified to support NASA's Space Launch System (SLS) and the Orion spacecraft.
The JEL system is being upgraded to increase how much weight the crawlers can carry from the previous 12 million pounds to the needed 18 million pounds.