The two crawler-transporters were designed and built by Marion Power Shovel (later Caterpillar, Inc.) using components designed and built by Rockwell International at a cost of US$14 million each. Upon its construction, the crawler-transporter became the largest self-powered land vehicle in the world.
The crawler-transporter carrying the Ares I-X on its test flight
The crawler-transporter has a mass of 2,721,000 kilograms (6,000,000 lb) and has eight tracks, two on each corner. Each track has 57 shoes, and each shoe weighs 900 kg (1,984 lb). The vehicle measures 40 by 35 metres (131 by 114 ft). The height from ground level to the platform is adjustable from 6.1 to 7.9 m (20 to 26 ft), and each side can be raised and lowered independently of the other. The crawler uses a laser guidance system and a leveling system to keep the Mobile Launcher Platform level within 10 minutes of arc (about 30 cm (1 ft) at the top of the Saturn V), while moving up the 5% grade to the launch site. A separate laser docking system provides pinpoint accuracy when the crawler-transporter and Mobile Launch Platform are positioned in the VAB or at the launch pad. A team of nearly 30 engineers, technicians and drivers operate the vehicle.
A crawler-transporter carrying Discovery travels the ramp to Launch Pad 39B. The vehicle's back end can be raised, keeping the Shuttle and the MLP level.
The crawlers were overhauled in 2003 with upgrades to the Motor Control Center, which houses the switchgear and electrical controls of all of major systems on board, a new engine and pump ventilation system and new diesel engine radiators, and replacement of the two driver cabs on each vehicle (one on each end). As of 2003, each crawler had 16 traction motors, powered by four 1,000 kW (1,341 hp) generators, in turn driven by two 2,050 kW (2,750 hp) V16 Alcodiesel engines. Two 750 kW (1,006 hp) generators, driven by two 794 kW (1,065 hp) engines, were used for jacking, steering, lighting, and ventilating. Two 150 kW (201 hp) generators were also available to power the Mobile Launcher Platform. The crawler's tanks held 19,000 liters (5,000 U.S. gal) of diesel fuel, and it burned 296 liters per kilometer (125.7 U.S. gal/mi). Due to its age and the need to support the heavier Space Launch System and its launch tower, in mid-2012 one of the crawlers was undergoing an upgrade involving "new engines, new exhausts, new brakes, new hydraulics, new computers,” to increase its lifting capacity from 5,400,000 kg (12,000,000 lb) to 8,200,000 kg (18,000,000 lb).
The crawler is controlled from two control cabs located at either end of the vehicle, and travels along the 5.6 km (3.5 mi) crawlerway at a maximum speed of 1.6 km/h (1 mph) loaded, or 3.2 km/h (2 mph) unloaded. The average trip time from the VAB along the Crawlerway to Launch Complex 39 is about five hours. Each crawlerway is 2 m (7 ft) deep and covered with Alabama and Tennessee river rock for its low friction properties to reduce the possibility of sparks. In 2000, NASA unearthed and restored an Apollo-era segment of the crawlerway to provide access to a high-bay building in order to provide protection from a hurricane.
Kennedy Space Center has been using the same two crawlers, nicknamed "Hans" and "Franz" for the bodybuilding characters, since their initial delivery in 1965. In their lifetime, they have traveled more than 5,500 km (3,400 mi), about the same driving distance as from Miami to Seattle.