To move spacecraft from the Vehicle Assembly Building out to the launch pads at Kennedy Space Center, NASA has a pair of huge Crawler-Transporters. These 5.5 million pound tracked hauled 12 million pounds worth of space shuttle and launch pad around, but to handle the new Space Launch System, they'll be getting an upgrade.
The Crawler-Transporters (or CTs) have been around since the 1960s. NASA was looking for a way to assemble spacecraft launch systems safely indoors, but launch them between three and four miles away to ensure that they didn't have to rebuild the vehicle assembly building (a wonder in itself) every time. The agency considered railways, a system of canals and barges, and a land transport system, of which the land transporter was deemed to be the most feasible and cost effective. Built at a cost of about $100 million, for a while the transporters were the largest land vehicles in the world.
Each crawler-transporter weighs about 5.5 million pounds by itself, and is about the size of a major league baseball field. Top speed while carrying a load is one mph, doubling to two mph if the CT is just cruisin' around empty. Power comes from a pair of 12 cylinder diesel locomotive engines producing 2,750 HP each, which drive electrical generators to feed the electric motors that actually drive the tracks (16 of them at 375 HP each) as well as the hydraulic system. The hydraulics are how the CT gets its job done: it crawls underneath something, uses hydraulic power to lift it up, and then crawls away.
The CTs are usually tasked with hauling around spacecraft on top of a mobile launch platform. The mobile launch platform is separate from the CT itself, and it's what supports the actual launch. The CT carries the platform and vehicle out to one of the pads and drops it off (lowering onto a special set of pedestals), the CT gets the heck out of there, the launch happens, and then the CT comes back and picks up the now empty platform. Here's a time-lapse of the CT picking up a launch platform and hauling it out to the pad:
The mobile launch platform with a space shuttle on top weighed in at about 12 million pounds, of which nearly 9 million is just the launch platform itself. The new Space Launch System, however, tips the scales at 6.5 million pounds, equivalent to nearly 9 fully-loaded 747s. That puts the weight of the system as a whole at close to 16 million pounds, and to move that around, the current Crawler-Transporters need an upgrade.
To boost its lift capacity to a whopping 18 million pounds, one of the CTs (Crawler Two) is getting a major overhaul, including new engines, new exhausts, new brakes, new hydraulics, new computers, and possibly some phat new rims and a pair of fuzzy dice. This isn't going to improve fuel efficiency or anything (32 feet per gallon is still as good as you can expect from a CT), but by 2014, the work will be done and the Crawler Transporters will be all set to haul NASA's brand new Space Launch System for its first flight in 2017.
NASA, for the record, decided seven years ago not to scrap the CTs (which are listed on the National Historic Register) in favor of something new (likely with wheels). The CTs may be old technology, but they're effective and reliable, and there's no reason why they shouldn't be operating for another fifty years.
Below is a video from NASA showcasing the crawlers during the shuttle era, along with a gallery of pics.