Building a rocket is one thing and launching it is another but what about the bit in between, moving it to the lauchpad?
Rockets like the Saturn 5 and the new SLS for the Artemis program were and are massive. The SLS is about the same height as a 30 story building and you can’t launch it where it’s built so it has to be moved, how do you move what is a skyscraper-sized rocket and its launch tower to the launch pad in one go.
The problem was solved back in the 1960s with the Apollo missions with the crawler transporters which also transported Skylab and Apollo–Soyuz programs and then went on to be used for the Space Shuttle program from 1981 to 2011 and now the SLS rocket for the Artemis program.
When NASA commissioned the crawler transporters in 1963 they were the two largest self-propelled vehicles in the world and continued to be so until 2013 when they were pushed out by the XGC88000 Crawler Crane and they are still in use today, these are NASA’s massive crawler transporters 1 and 2.
In January 1961, just 16 days after John F Kennedy became president, three men met in a small office at Cape Kennedy to discuss new ideas for launching heavy space vehicles. They were Dr Kurt Debus, the then Marshall Space Flight Centre launch director, Theodor Poppel and Greg Von Tiesenhausen, all three had spent the last 25 years in rocket development.
They were studying new launch sites for rockets with between 5 and 10 million lbs of thrust capability and this was just three years after the launch of America’s first satellite with a rocket with just 87,000 lbs of thrust. What they had to plan for was something that had never been built before with technologies that had yet to be invented.
They had to consider how the component sections of such a massive rocket would be transferred from the contractor’s factories to the assembly building.
They also had to consider how such a rocket could be built, horizontally or vertically and then once built, how it would be transferred to a brand new launch area which at the time was either underwater or marshland.
On the 31st of March 1961, Dr. Debus outlined his proposals to the Marshall Centres board chaired by Dr. Wernher Von Braun, and on the 12th of April, the Soviet Union put the first man into space, immediately putting NASA into a flurry of activity in response to questions from the Whitehouse as to how the U.S could regain the upper hand.
The ideas for a spaceport and the massive rockets to use it, which they had been looking at only a few months earlier were now to be set into motion and on May 25th 1961 President Kennedy announced it before a special joint session of Congress.
Work was soon underway on launch complex 37 for the initial Saturn 1B followed by launch complex 39 built to send men to the moon.
It was decided that instead of having a fixed structure at the launchpad as had been used before, the rockets would be assembled vertically at the Vehicle assembly building before being attached to a Launch Umbilical Tower (LUT) and both that and the Saturn mounted to the mobile launch platform.
The launch platform alone would stand two stories high and has enough steel plates to cover half an acre. This would be picked and moved to the launchpad, once in position, a second mobile service structure would be moved into position to provide the fuel and access for technicians to perform final checks.
What type of transport would be used to transport the Saturn on the mobile launchpad from the Vehicle assembly building to the firing pad would be determined by the location and geology of Cape Kennedy as much as anything.
This wasn’t a new idea and a version of this Integrate-Transfer-Launch (ITL) system had been used with the US Airforce’s Titan III rocket before but this new version would be on a much bigger scale.
Many proposals were put forward. There was the idea of constructing a canal system and using giant floating barges to carry the combined launch assembly vertically but during tests, it was found that it would both be very difficult and very expensive to achieve.
Rail tracks were considered, these were used at other sites and by the Soviets but the size and weight of the Saturn and launchpad was much greater than anything seen before. The cost of making them capable of carrying the huge loads involved was deemed too high.
Another issue which arose from the location of the complex right on the coast. During preparation for the construction, the area was cleared and was just 1.5 feet or 0.45 meters above sea level. Due to the high water table it wasn’t possible to dig into the ground to construct the flame trench and other underground support systems.
So the launch areas would be raised to 55 feet or 16 meters with access ramps which the whole launch assembly had to be moved up onto.
Using rail tracks would run into major problems when encountering the 5 degree incline on the ramps, so that idea was also dropped.
Pneumatic tyred vehicles and even ground-effect vehicles were also looked at but were also discarded.
Eventually, a track-mounted crawler was looked at, this was the type of drive train commonly found on very large strip-mining equipment, but the difference here is that those are normally powered by an external electrical supply, the NASA crawlers had to be self-powered.
The sheer size of the load meant that the crawlers would be equally large. In fact there were built by the Marion Power Shovel Company, Ohio, who also built the worlds largest power shovel the Marion 6360 also known as the “The Captain” because it worked at the Captain mine in Southern Illinois.
The Captains drive train was similar to the NASA crawlers in that they were both delivered in 1965 and used 8 electrically driven caterpillar tracks, with diesel generators, the difference being that the captain had gross weight of 12,700 tonnes whereas, the NASA crawlers total weight carrying the Saturn 5 and launch tower was 8250 tons, although that has increased with the SLS rocket.
The two crawlers were ordered from Marion in 1963 and delivered in 1965, at a cost of $14 million each about $130 Million today, so they also got the nickname of the “Golden Slippers”.
In 1987 a recurring sketch on Saturday night live show about two Austrian bodybuilders called Hans and Franz led to the crawlers also being nicknamed Hans and Franz for their ability to “Pump Iron”.
Although the overall size of the crawlers are 131 feet long, 114 feet wide or 40 meters by 34 meters the actual contact area that connects with the mobile launch tower and service tower is 90 feet square or 27.4 meters square with four locating posts at the corners. To distribute the huge weight to the ground, each of the 8 tracks are 12 meters long by 3 meters high by 2.2 meters wide and made up of 57 shoes, each weighing 907kg.
The tracks are driven by 16 electric traction motors. Power is generated by four 1-MW generators which in turn are powered by two 2,750 horsepower ALCO V16 diesel locomotive engines. Each crawler carries about the 19,000 litres of diesel fuel and it travels about 2.5 meters per litre of diesel or about 0.007 MPG.
Two more 750kW generators are driven by a further two 1,065-horsepower diesels to power the systems for levelling, jacking and steering.
The crawlers top speed is 1mph or 1.6km/h when fully loaded and 2 mph or 3.2km/h unloaded.
One of the issues created by having the raised launch pads was that getting a 30+ story rocket and tower up a 5-degree incline could cause serious stability issues, so the platform of the crawlers had to tilt to allow for the incline and keep the assembly as vertical as possible.
The crawlers were fitted with a levelling system that raises the back of the vehicle and can keep the top of the rocket within 30cm of vertical or 0.16 arc seconds. This was achieved with two hydraulic servo systems which were feed by error data from manometers connected to a 130 ft long horizontal pipe that acted like a giant spirit level. This controlled variable speed pumps to adjust the corners to bring it back to level.
Having massive tracks might well distribute the huge load but the roadway it runs on had to specially constructed to withstand the weight of upto 8250 tons without subsiding considering that the ground before was marsh land.
The road ways are 2 meters deep and made up of Hydraulically packed sand to a density of 96% almost that of solid rock for the basis of the roadway, which then has a layer of hard packed limestone then another layer of crushed Alabama and Tennessee river rock which was used for its low friction properties and reduce the possibility of sparks incase of fuel leaks.
One of the biggest natural hazards to face the Spaceport is that of hurricanes, even though the 445 ft high Vehicle Assembly building is built to withstand them a fully loaded rocket and tower could be potentially blown over, although that would be unlikely it would far more likely to be damaged by flying debris and rockets only have relatively thin skins.
This was at the root of Dr. Debus’s idea to only move the rocket to the launchpad when everything was finalized and ready for flight. Earlier smaller rockets once at the launch pad would have been taken down or disassembled if a hurricane warning was issued, with the mobile launch pad it could be quickly moved back to the VAB and once the storm was over rolled back again ready to go.
Luckily, hurricane warnings normally have a 24 hour window and the transit time from VAB to pad or back again was about 12 hours including disconnecting the various supply cables and pipes, the actual transit time was about 5 hours.
On June 8th 1966 hurricane Amla came into view and Debus used it to test his theory. On a one hour notice he ordered the Saturn 5 back the VAB in driving rain and winds gusting at 65 mph or 105km/h. They did it in 10 hours proving it could be done with a usual 24 hour notice.
After the Space shuttle era had come to an end in 2012-2014, both crawlers were upgraded with new engines, exhausts, brakes, hydraulics and new computers.
Crawler 2 was further upgraded in 2014–2016 to increase its lifting capacity from 5,400 to 8,200 tonnes to handle the new SLS rocket and its greater weight.
Crawler 1 was intended to be used for commercial flights for Orbital ATK, now Northrop Grumman Innovation Systems but the loss of the contract for the National Security Space Launch to United Launch Alliance and SpaceX left just Crawler 2 to do the work for SLS and Artemis program.
Although they only travel at 1-2 mph they have clocked up 3400 miles or 5500 km in their 50+ year of use.
The method of moving the whole rocket and tower when everything is ready has worked well for NASA but with the SpaceX Starship super heavy, it’s using a more traditional method of transporting to a fixed launch tower and lifting into position.
Now just as I was finishing the script for this video, the SpaceX Starship Superheavy made it’s first flight, and it did look like the launchpad did take a bit of a hammering from the 30 out of 33 engines that fired, and although the flight ended in an autodestruct when it deviated from its flight path, it was just a test and this these happened on many occasions when NASA was testing their new rockets but it will be interesting to see which will be the best method getting to the rocket to the pad and launching as we move forward again into a new era of very large rockets.
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