How Will NASA Move Its Giant New Rocket?

NASA's Space Launch System – the rocket that will surpass the Saturn V in size and power – is still on track to launch the first unmanned Orion mission in 2017. In anticipation its next big rocket, the space agency is upgrading the only machine it's got with enough power to move something that big: the crawler. Even though the technology is nearly 50 years old, there's still no better way to move a giant rocket.

NASA's crawlers were a necessary technology spawned from the decision to assemble and launch the mammoth Saturn V rocket in Florida where the air is salty and the weather can get really nasty. In the early 1960s, history dictated that rockets were assembled vertically on the launch pad. It simplified things, but for the Saturn V it wasn't feasible because the rocket was built in pieces by a host of contractors around the country. Each sent their piece to Cape Canaveral where NASA ran preflight checks before putting everything together. With a rocket as complicated as the Saturn V, assembly was a weeks long process that would have instruments exposed for days at a time. Doing this outside would pose innumerable dangers to the systems and the crew that would ride the rocket.

So NASA built a building, the Vehicle Assembly Building, where the Saturn V could be assembled shielded from the elements. At 526 feet tall, 716 feet long, and 518 feet wide, the VAB's internal volume is a staggering 129,428,000 cubic feet. It was the perfect facility, but presented the new problem of finding a way to get the rocket out of the VAB and onto the launch pad. That was a little more complicated, and finding a solution fell to Kurt Debus.

Debus was assigned the task of setting up the Saturn launch site and facilities at Cape Canaveral by Wernher von Braun, along with Georg von Tiesenhausen and Theodor Poppel. All three had worked on the V2 program in Germany together during the Second World War, so not only did they have an idea of how to work with rocket's, they'd set up the launch site at Peenemunde with great success.

It was von Tiesenhausen who came up with the idea of using a mobile launch pad. Build the Saturn V right on its launch pad, gantry and all, then move the whole set up to the launch site when it was ready. The rocket would be stable on its own platform. The idea of a mobile launch pad wasn't new, as it was the system they'd used at Peenemunde – the rocker was vertically loaded onto a platform that traveled on a railway to the launchpad. But the V2 was only 46 feet tall; the Saturn V was 363 feet tall and it needed a perfectly smooth ride. A wobbly ride could end in disaster, an outcome made even more unacceptable with astronauts' lives on the line.

Already in 1961 NASA was looking at possible mode of transportation for the world's biggest rocket. One proposal came from the Martin Company: a barge. Float the vertical Saturn V along a canal to the launch pad. It looked like a fair idea, but when NASA looked harder they realized no one on the Martin team was a naval architect. Tests of the concept revealed that the sides of the barge created a suction effect with the canal walls making steering the impossible. Wind tunnel tests showed the rocket's gantry acted like a sail while the Saturn V had a substantial drag penalty. Working out the problems wasn't impossible, but it was out of the question. It would const too much. There was talk of building a railroad between the VAB and the launch pad, but that was dismissed pretty quickly, too. The rails would have to be totally rigid, and that just wasn't a realistic design on the spongy ground.

The solution wasn't to come up with something new but to use something old, a tried and true piece of nineteenth century coal mining technology. Marion Power Shovel (later Bucyrus-Erie) had just built a massive shovel for a strip mine in Kentucky that was moved from place to place by four crawlers each twice the size of a bulldozer. Intrigued, Debus sent a team to look at the crawler. They were a little taken aback. It was huge and looked like they'd be in for a rough ride. The NASA contingent climbed aboard, braced themselves on railings, and told the engineers guiding their visit to start the ride. The engineers smiled and told them they were already on their way. It was that smooth, and totally free of any vibrations. Scaled up, it would be perfect.The crawler-transporter's long crawl, via NASA

Three years later the six million pound machine was finished. Four crawlers rolling on treads made of a series of one-ton links supported the main deck, a platform big enough to hold a baseball diamond that looked like it was a chunk of an aircraft carrier's deck. Inside were two engine rooms each with half a dozen locomotive sized diesel engines that delivered a total of 6,000 horsepower to the motors and levelers. To keep the Saturn perfectly vertical, NASA developed a sophisticated sensing system. A pair of pipes filled with mercury ran diagonally from corner to corner under the platform in a giant X. They bent up at the ends and a wire was inserted into the tube a hair's width above the Mercury level. If the platform tilted, the wire's contact with the Mercury would short it out, sending a signal for hydraulic fluid to lift to appropriate corner to level out the platform. It worked so well the top of the escape tower, the point right on top of the 363 foot rocket, never moved more than 4-5 inches out of vertical alignment. The same hydraulic lifts were used to pick up and place the Saturn V out of the VAB and onto the launch pad. In all, the process took about five hours; the crawler's top speed is around 1.5 miles per hour.

NASA built two of these monsters, one as the primary vehicle and the other as a backup. Crawler 2 is the one getting an upgrade to increase its lifting capacity of 12 million pounds to 18 million pounds for the SLS, part of a $2 billion plan to modernize the Kennedy Space Center. But that's it. The engines are still in pristine condition. Not bad for a 50 year old vehicle.