Do you like big trucks? I’m talking about a Really Big Truck. The Biggest Truck in the World. Here it is: the Marion Power Shovel Company’s 1965 Missile Crawler Transporter Facility. It’s 131 feet (40 m) long, 114 feet (35 m) wide and 20 to 26 feet tall, and weighs 6 million pounds. Its bed is the size of a baseball infield. And like a proper CC, after an engine swap and some upgrades to increase its load capacity to 18 million pounds, it’s still in use today. You’ve certainly seen this truck before, though you may not have noticed it under its payload…
Better known as the NASA Crawler-Transporter, this truck has carried complete rocket ships from the Vehicle Assembly Building to launch pads 39A and 39B since the time of Apollo. Last weekend we saw the new Apollo 11 documentary film, which I heartily recommend to all, young and old. It’s based on a large stash of previously unscreened 70mm footage taken during the launch and recovery, and more unseen footage of the flight itself. The countdown, even though I’ve seen it a thousand times, gave me chills. Anyway, the movie starts with closeups of this massive magnificent vehicle, moving along at less than one mile per hour, carrying the Apollo 11 – Saturn V rocket ship and its launch platform and tower to the pad, as tall as a 36 story building. As huge as this truck is, you can hardly see it under that platform.
Here’s a better look at the Crawler-Transporter, carrying a Mobile Launch Platform back to the VAB. You can just see one of its two cabs at its corner. There are cabs on both ends since it goes either direction without turning around. Wheels and tires aren’t up to loads of this scale, so four pairs of tracks are used instead.
The Crawler-Transporter has a diesel-electric drivetrain, like a locomotive. As of its latest upgrade, the CT has sixteen 375 hp DC electric traction motors, powered by four 1,000 kW DC generators, driven by two 2,750 hp V16 ALCO 251C diesel engines. Two AC generators, driven by two 16-cylinder 2,220 hp Cummins engines, are used for all onboard power demands, including jacking, steering, and payload power. Its tanks hold 5,000 gallons of diesel fuel. Speed under load is 1 mph, top speed unloaded is 2 mph. Mileage? 165 gallons per mile, or put another way, 32 feet per gallon.
After the Apollo program finished, the Crawler-Transport worked in thirty years of Space Shuttle operations. The Crawlerway is a dual-lane road built for CTs. It’s 3.5 miles from the VAB to Pad 39A, 4.2 miles to Pad 39B. Each lane is 40 feet wide, separated by a 50 foot median. The top layer is Tennessee river gravel, 4 inches thick on the straight sections and 8 inches thick on curves. Tennessee river rock was chosen for its anti-spark properties. Beneath that is 4 feet of graded, crushed stone, resting on two layers of fill.
Pad 39A (seen in the back right) is now used by SpaceX, which assembles their Falcon rockets horizontally near the pad and tilts them up for launch. The Vehicle Assembly Building, Pad 39B (back left) and the Crawler-Transporters will remain in use for NASA’s Space Launch System (SLS) program, which is expected to begin flights in 2020 (maybe).
This shot shows off the Crawler-Transporter’s ability to keep its bed level while climbing a 5% grade up to the pad. If that payload fell over, it would be a Very Bad Day. So the CT has a laser guided leveling system to keep the platform level within 0.16 degrees. A team of nearly 30 engineers, technicians and drivers operates the vehicle.
Each track has 57 shoes, and each shoe weighs a full ton. With eight one-ton shoes simultaneously slapping the earth, “you get a low frequency vibration which you feel when riding on the crawler. It’s a lot like being on a ship,” said CT Project Manager John Giles in a Popular Mechanics article on the CTs.
There are two Crawler-Transporters. (“First rule in government spending: why build one when you can have two at twice the price?” — S. R. Hadden in Contact.) They were designed and built by the Marion Power Shovel Company using components from Rockwell International. Marion’s experience in massive power equipment goes back to its participation in the Panama Canal, Hoover Dam and Holland Tunnel projects.
This diagram shows the 40-inch diameter guide tubes above each pair of tracks that transmit loads from the Mobile Launch Platform which attaches to the top of the CT. Each guide tube has hydraulic cylinders for keeping the bed level. The MLP contacts the crawler at four points, arranged in a 90-foot square (same as the base line on a professional baseball field). You can also see the four electric propulsion motors on each track pair, which also has four steering cylinders, since the CT is steered like a wheeled truck would be, not by differential track speeds like a tank. Hydraulic steering pressure is up to 5,000 PSI.
One of the original diesel engines for CT and payload auxiliary AC power is being hoisted out of CT-2 during its 2012 upgrade.
Here is one of the new Cummins 16 cylinder 2,220 hp diesel engines used for auxiliary AC power before installation in CT-2.
Like any other truck, the Crawler-Transporter has a cab with driver’s seat, steering wheel, accelerator pedal and instrumentation. There’s also a windowless control room at the center of the CT for monitoring its engine, electrical and hydraulic systems.
These Crawler-Transporters are so big and so important that in 2000 they were listed in the National Register of Historic Places. A truck so big it’s a place. Here’s a picture from when it was new. There are other mobile structures which are bigger, but they have external power sources, so they’re not trucks. After over fifty years, the NASA Crawler-Transporters are still the biggest self-contained load-bearing land vehicles, i.e. trucks, in the world. And they’re ready to go for another fifty years. Who knows where its payloads will be off to in 2069?