Heaviest self-powered vehicle

The heaviest self-powered vehicle is Crawler-Transporter 2, which is operated by NASA's Exploration Ground Systems program at the Kennedy Space Center in Florida, USA. Crawler-Transporter 2, which is designed to carry rockets from the Vehicle Assembly Building to the launch pad, weighs 3,016 tonnes (6.65 million lb). The vehicle's weight was increased as part of a round of upgrades that were completed on 23 March 2016.

Crawler-Transporter 2 is one of a pair of giant tracked vehicles built by the Marion Power Shovel Company for NASA between March 1963 and January 1966. Their original purpose was to carry the Apollo program's Saturn V rockets and their mobile Launch platforms the roughly 4 miles (6.7 km) from the Vehicle Assembly Building to either launch pad 39A or 39B. As originally built, they weighed around 2,700 tonnes (5.95 million lb).

After the last Saturn V launched in 1973, the two crawler-transporters were repurposed to support the Space Shuttle program. Then, following the shuttle's retirement in 2011, Crawler-Transporter 2 was selected for a series of upgrades that would allow it to carry the planned Space Launch System and its mobile launcher platform.

These upgrades, which included replacing the two massive locomotive engines that provide power to the four sets of caterpillar tracks and strengthening various other systems, brought the vehicle's overall weight up to what it is now.

Crawler-transporter 2 is 131 ft long and 114 ft wide (39.9 x 34.7 m; about the size of a baseball infield). Its height is variable (it has a hydrualic levelling system that can raise, lower and tilt the top deck) but maxes out at 26 feet (7.92 m). It is not designed to carry rockets directly, but rather to carry the mobile launcher platforms they are sitting on. These platforms are locked into place at the launchpad, and the Crawler-Transporter withdraws back down the crawlerway some days before the launch takes place.

There are larger land-based vehicles, most notably the takraf Bagger 293 bucket-wheel excavator, but these vehicles require an external power source to function. The Crawler-Transporters generate all their own power using a set of locomotive diesel engines. Crawler-Transporter 2 has a theoretical maximum speed of 2 mph (3.2 km/h) unloaded, but NASA engineers have never tried pushing it that hard.