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The Crawlers

Season 1Nov 16, 2020

A pair of behemoth machines called crawler-trans­porters have carried the load of taking rockets and spacecraft to the launchpad for more than 50 years at NASA’s Kennedy Space Center in Florida.

NASA's Curious Universe

NASA’s Curious Universe

Episode 6: “The Crawlers”

Release Date: Monday, Nov. 16

Introducing NASA’s Curious Universe

Our universe is a wild and wonderful place. Join NASA astronauts, scientists, and engineers on a new adventure each week — all you need is your curiosity. Visit the Amazon rainforest, explore faraway galaxies, and dive into our astronaut training pool. First-time space explorers welcome.

About The Episode

A pair of behemoth machines called crawler-trans­porters have carried the load of taking rockets and spacecraft to the launchpad for more than 50 years at NASA’s Kennedy Space Center in Florida. Each larger than a baseball infield and powered by locomotive en­gines, the crawler-transporters stand ready to keep up the work for the next generation of launch vehicles to lift astronauts into space. Sam Dove, John Giles, and Breanna Rohloff explain.


SAM DOVE:It dominates whatever’s around it. You can feel as it comes by, you know, it shakes the ground a little bit… it would just amaze you: the size and the complexity of it. Think of something that’s moving very slow…around .8 or .9 miles an hour… moving this big rocket down the road. It’s fun to get up every day and come out and work on the crawler.

HOST PADI BOYD: Our universe is a wild and wonderful place. I’m Padi Boyd, and in this show, NASA is your tour guide.

HOST PADI BOYD:Rockets are what launch some of our heaviest and most far reaching instruments into space. But what gets these rockets to their last destination on the ground – the launch pad?

HOST PADI BOYD:In this episode, we’re exploring some of NASA’s most powerful ground machinery: the crawlers. These one of a kind, six million pound, behemoths, are what transport rockets and their mobile launch platforms so that they can make their ascent into space.

NASA's Curious Universe

HOST PADI BOYD:And the crawlers have a long history.

JOHN: You almost have to go all the way back to the beginnings of NASA here at Kennedy space center, that’s where they assembled the launch vehicles.

HOST PADI BOYD:That’s the crawler’s senior project manager, John Giles (Jon J-eye-uls). The launch vehicles he’s referring to are the rockets that would help NASA send humans to the moon for the first time.

HOST PADI BOYD:In the early 60’s, NASA built the Saturn V rocket to carry out the Apollo missions. Saturn V was built upright and was a staggering 363 feet tall with the Apollo spacecraft on top. That’s taller than the statue of Liberty!

HOST PADI BOYD:And somehow, the rocket had to travel from the vehicle assembly building to the launch pad, four miles away. Engineers at NASA scratched their heads.

JOHN: Well, how do you get it there? Something 300 feet long is a little tough to put on some kind of a flatbed truck and roll. And you can’t really put it on a barge or float it there.

JOHN:So there were many studies done over the years and they came up with the best way to get it there was to build this machine, this crawler-type machine.

HOST PADI BOYD:NASA needed a vehicle that could pick up millions of pounds and transport it for 4 miles all while keeping it level. But NASA couldn’t just call up anycompany to make a machine of this scale.

HOST PADI BOYD:They looked to an industry making some of the most powerful machinery out there – the coal mining industry.

JOHN: When you watch on TV and you see those giant dump trucks and those giant cranes that scoop up all the rock and stuff, the company that builds that type of equipment built this crawler.

HOST PADI BOYD:The Marion Power Shovel Company worked with NASA to make two of the most specialized pieces of equipment on the planet – Crawler 1 and Crawler 2.

JOHN: I think it’s one of the most phenomenal pieces of engineering equipment ever designed.

HOST PADI BOYD:They both live at Kennedy Space Center in Florida, but Crawler 1 mostly hangs out in storage while Crawler 2 gets to do the heavy lifting. And here to give you a tour of that Crawler are two of its operators.

HOST PADI BOYD: There’s Breanne Rohloff, who just graduated with her bachelors in aerospace engineering.

JOHN: Breanne, she’s a blast to be around cause she’s young and, you know, to her, this is just so exciting, so neat.

BREANNE:This is my first job out of college.

HOST PADI BOYD: And then there’s Sam Dove.

JOHN: So Sam’s on the complete other spectrum. Sam is a senior driver. You know, ice water runs through his veins, nothing phases him.

SAM:I grew up in West Virginia as a farm boy, did four years in the air force, went to college. Then I was fortunate enough to get a job at the space center. I spent the first ten years in design engineering, and then I became a crawler driver. So it wasn’t just something I stepped off the street and did. Hah.

HOST PADI BOYD:Breanne and Sam both maintain and drive the crawlers. It’s a truly unique job. And Breanne still vividly remembers the first time she saw a crawler.

BREANNE: I just remember looking at it and being like, this is massive. Like it really reminded me of when you kind of take off in an airplane and you start to gain altitude and you see all of these things that you normally think of as being big as buildings and houses and cars, and they kind of just shrink and that’s kind of the moment I remember thinking, “Wow, people in cars looks small compared to it.”

SAM: It’s really not something comparable to what a lot of folks see.

BREANNE: It’s kind of like you took a steel, one story building and sheared off the top of it so it’s completely flat.

SAM: A steel box basically.

HOST PADI BOYD:A steel box that’s bigger than a baseball infield. The crawler’s platform which needs to be big enough to accommodate a launcher and rocket.

HOST PADI BOYD: Inside the steel box, below where the cargo would sit, is a whole host of important things to keep the crawler going and to keep it level.

SAM: Cables, fans, motors, pumps.

HOST PADI BOYD:And the crawlers don’t move on wheels, but on tracks like a tank. There are eight total tracks.

SAM: If you think of a giant bulldozer, there’ll be one on each corner.

HOST PADI BOYD:These tracks are heavy duty.

SAM:The tracks are made up of little segments. Well, the crawler segments are called shoes and they’re big, they’re six feet long and about, uh, I think almost 18 inches wide and they weigh 2000 pounds per shoe.

HOST PADI BOYD:With 456 shoes on each crawler, the shoes alone weigh almost one million pounds. Once you add up the rest of the equipment on the crawler, the total weight comes to 6.5 million pounds. And that’s without any cargo on top.

SAM: That’s how big the crawler is.

HOST PADI BOYD:Once you add the rocket and launcher, that’s when things get really heavy…

SAM: You know, you’re looking at almost 25 million pounds.

BREANNE: I really don’t think I’d fully understand how heavy that is.

SAM:That’s a lot of weight on the ground.

HOST PADI BOYD:So you may be thinking, can a normal road withstand the pressure of a crawler?

JOHN:So when the crawlers were first built, they did try to roll them on roads out here.

HOST PADI BOYD: Needless to say, the asphalt roads did not fare so well…

SAM:We put some cracks on them.

JOHN:So we just tore it up.

HOST PADI BOYD:Once again, NASA engineers and contractors had to get creative and design something that could support the hefty vehicle. Just like the crawlers, the crawler way is one of a kind.

SAM:Everything is special about the crawler way. I mean, first of all, it’s the size of the interstate road, right? You have two lanes on one side, two on the other and the median.

HOST PADI BOYD: But what’s most special about the crawler way is what it is made of.

SAM: It’s filled with basically a crushed and compacted limestone, hydraulic fill under that. And now on top of that, about 8 to 10 inches of gravel.

HOST PADI BOYD:That gravel is actually Tennessee river rocks, that’s what the tracks make contact with.

JOHN:And the river rock becomes the, the sacrificial component because the crawler doesn’t have shock absorbers like your car does and when you are carrying a multi-million, multi-billion dollar launch vehicle on top, you don’t want to shake it to death while you’re rolling it so the crushing of this rock attenuates the vibration.

HOST PADI BOYD:As more and more rock crushes into finer pieces, it has to be replaced to make sure it can continue to be a good shock absorber for the crawler.

HOST PADI BOYD:Roll out days, or when the crawler actually makes a trip, are big affairs. The team, composed of about thirty engineers, gathers four hours before the roll, around 8PM.

HOST PADI BOYD:They go over the mission, talk safety and discuss who is in charge of each task. Then the team fires up the engines, which take 45 minutes just to heat up.

JOHN: The first thing that lets you know, we’re starting up is you use compressed air to start these large engines and it just, just goes brrrrrrrr and it just gets louder and louder. And then the second the engine starts, that noise goes away and then you’ll just hear this mmmmm and some black smoke comes out.

HOST PADI BOYD:Then the rest of the systems get going. The pumps, the lubrication system, the hydraulics, the fans, all with their unique sounds.

SAM:it really has sounds all its own. You really need to be attuned to what their sounds sound like and if it’s not running right you can almost immediately tell you need to start looking at something.

HOST PADI BOYD: If everything is running properly, the crawler will pick up it’s freight by rolling right under the launcher. It’s usually around midnight when the crawler begins its journey to the pad.

HOST PADI BOYD:To transport a rocket to the launch pad, the team breaks out into their individual posts. There are technicians on the ground, constantly checking the position of the crawler.

JOHN: If you’re walking alongside, it’s dusty and there’s bugs flying around and, and then you just, you just hear these shoes just constantly just slapping on the ground and it’s just, it just never goes away. They just keep rolling.

HOST PADI BOYD:And then there are the people onboard.

SAM: There’s probably about at least 10 people on the crawler at any time. You’ll have 3 engineers that are actually operating something at one time, the test conductor, the leveling system operator, and a driver.

HOST PADI BOYD:And all of those people have backups – people to switch out with if they need a break. This is very important given that the journey to the pad takes 8 hours!

HOST PADI BOYD:Why does it take so long to travel only four miles? Well, the crawler rarely goes faster than one mile per hour.

SAM: The speedometer shows zero to two.

HOST PADI BOYD:Driving such an enormous vehicle is an experience few of us will ever have. But Sam tries to explain what it is like.

SAM: Driving the crawler is – it’s something like driving your car, except it’s very slow. You know, you’re constantly watching your speed because you can’t just do a, you know, drift through a curve like a NASCAR racecar can.

SAM: And with your car, any inputs you make to the steering wheel, you immediately see that, right? Because you’re moving at a much faster speed and it’s a smaller vehicle. With the crawler, you have to think ahead.

HOST PADI BOYD:Going so slowly might seem like it would be monotonous.

SAM: Oh, no no no. Boredom is not something that you have on the crawler. Right? You’re watching where you’re going, where you’ve been, where you’re at, the speed, what’s your steering, ’cause if the crawler catches you, not paying attention, it’ll remind you.

HOST PADI BOYD:Driving the crawler can be tricky as is, but the team has to be aware of other things that might obstruct roll out like forces of nature. HOST PADI BOYD: Florida, where the crawlers are located, is the number one hurricane and lightning capital in the US.

JOHN:We don’t like rolling, carrying very tall things during thunderstorms and lightning storms.

BREANNE:Lightning and a rocket are not my favorite combination.

JOHN:So the way to get around is we start rolling very early in the morning.

HOST PADI BOYD:That’s to avoid the afternoon, when storms are most likely to strike.

HOST PADI BOYD:The weather is one thing to watch out for, but another obstacle involves things on the ground… because the Kennedy Space Center rests on a wildlife reserve.

JOHN:You are constantly on the lookout for wild animals.

SAM: You know, we see bobcats.


JOHN: Snakes.

SAM: Wild hogs.

JOHN:Coyotes are starting to come in here.

BREANNE:You kind of just sit there and you’re like, “Oh, please don’t, please don’t come into the crawler way.”

HOST PADI BOYD:Sometimes, though, pleading doesn’t work. Animals can get in the path of the crawler, and that slows the team down.

SAM: There was a, there’s like a 10 or 12 foot gator that was under one of the trucks. We had to call the wildlife officer to come and pull that gator out and he was kinda like the crocodile hunter there, you know, like Steve Irwin was, he just reached under and grabbed that alligator by the tail, pulled him up, trussed him up and took him to another part of the space center. It was the darndest thing I ever saw and off we went.

HOST PADI BOYD:And then there is the tale of the tortoise and the crawler – less well known than “The Tortoise and the Hare.”

JOHN: One time we were going up the pad slope and I noticed a tortoise…they dig burrows in the ground here. And this tortoise happened to come out of his hole while we were rolling and this vibration that we’re making, kind of got him a little uneasy. So he starts walking around…

HOST PADI BOYD:The tortoise and the crawler were both heading up the ramp, side by side.

JOHN:And this is a true statement. The tortoise beat us to the top of the pad. That’s, that’s how slow we go sometimes.

HOST PADI BOYD:I guess slow and steady doesn’t win the race after all.

HOST PADI BOYD:The whole ride down the crawler way is leading up to the most crucial and technical moment, when the crawler approaches the launch site.

HOST PADI BOYD:It has to go up a ramp, called the pad slope, and place the rocket with its launcher precisely onto its mounts.

BREANNE: And that’s when things get really exciting but also things get really focused.

JOHN:By far the most stressful part of any roll is going up the pad. Everything’s gotta be perfect. We got to do this right. Everybody’s got to work as a team. Can’t get anything wrong.

BREANNE:The first time I was on the crawler, when, you know, we pulled up the pad slope and I like, I wasn’t even driving. I was just observing, but seeing other engineers, the more experienced ones pull up, I felt nervous just being in there for them. I was like, Oh my gosh.

JOHN:When we go up the slope, it’s all hands on deck. Everybody is stationed in a certain area. All of our engines have to be running at their peak performance. There’ll be technicians standing by them watching every gauge and every fluid level on them as we’re rolling.

JOHN:If we were to go up that ramp and then lose power for some reason, we could roll backwards…

HOST PADI BOYD:The crawler is on a 5 degree slope, but the rocket needs to stay completely level, so the jacking and equalization equipment kick into high gear. By that time, the crawler is going even slower than normal.

SAM: Then once you get up close, we Jack up to the proper height to go over the mounts and then you get yourself straight and we use a laser to do that. And then once everything is leveled. And then you set the whole thing down on the mounts and it fits within a quarter inch.

HOST PADI BOYD:After a successful roll out, everyone on the team can breathe a sigh of relief and take a moment to celebrate. They’ve just taken a rocket on its last Earth-bound leg of its journey before it launches into space.

SAM:We have a tradition when we complete roll out. We pop open a bag of, uh, chips and somebody breaks out of a jar of salsa. Gosh everybody comes in off the pad into the crawler to get chips and salsa.

JOHN: it’s just something you need to experience.

HOST PADI BOYD:When NASA first conceived of the crawlers, it wasn’t clear how long they would stay in use. By now, the crawlers have long outlived the lifespan of most vehicles. And that’s because the crawler operators spend most of their time maintaining and upgrading them.

JOHN: It’s over 55 years old now. And she was not designed to last this long. So the reason it has lasted this long is because it’s, it’s so well maintained.

HOST PADI BOYD:The crawlers have been there almost since the beginning of NASA, starting with the Apollo days.

HOST PADI BOYD:Now, the crawler team is getting ready for another mission to bring humans back to the Moon – the Artemis 1 Mission. For this mission, the crawler will need to move some of the heaviest loads it ever has.

HOST PADI BOYD:To prepare, the team has had to update the crawler. New, more powerful generators and cooling systems, bigger bearings. There’s a lot at stake because without the crawler, there is no launch.

SAM:It’s a big responsibility, but it’s really great because if there’s something going on in the space center, you know, that’s really important, well the crawler is usually right in the middle of it.

SAM:What we’re doing here is just, it’s so important for the country, I believe. And you gonna have to have this machinery to be able to launch that rocket. And, um, it’s just great to be a part of it.

HOST PADI BOYD:Engineers like Sam and John have maintained the crawlers throughout the Space Shuttle program and we’ll need them again when we return to the Moon and go on to Mars as part of the Artemis era.

HOST PADI BOYD:And young engineers like Breanne will keep the crawlers functioning for whereverNASA goes next.

HOST PADI BOYD:As long as there are rockets that need to get from point A to point B, the crawlers will keep rolling.

HOST PADI BOYD: This is NASA’s Curious Universe. This episode was written and produced by Margot Wohl. The Curious Universe team includes Maddie Arnold, Micheala Sosby and Vicky Woodburn. Our executive producer is Katie Atkinson.

HOST PADI BOYD:Special thanks to Laura Aguiar, Ryland Heagy, Lorne Mathre, Derrol Nail, Madison Tuttle, Tracy Yates, and the Kennedy Space Center.

HOST PADI BOYD: If you liked this episode, please let us know by leaving us a review, tweeting about the show @ NASA, and sharing this episode with a friend.

HOST PADI BOYD:Still curious about NASA? You can send us questions about this episode or a previous one and we’ll try to track down the answers. You can email a voice recording or send a written note to Go to for more information.