NASA's Crawler-Transporter q.

Used to transport the Saturn V and the Shuttle to the launch pad. My question is why did they make it a tracked vehicle instead of using a rail system? There’s a lot of experience with heavy rail loads and it’s what Russia and the ESA use. And since the crawlers have to run on a specially graded path, it isn’t like it’s a more flexible system than rails.

Here’s what NASA has to say about it:

Basically the cost of a rail system capable of carrying the 7700 ton stack was prohibitive. $3000 per metre of rail. Rail needed an even more carefully prepared bed than the crawler.

Nice summary here in Moonport - the definitive guide.
ETA - Ha, ninja’d :smiley:

Was the ground situation particular to Cape Canaveral that a crawler would work better there? The Soviet Energia/Buran was comparably heavy and used rail.

Given the Cape is essentially built on a swamp that is likely some contribution to the choice.

I find it hard to believe that a track system could be more cost-effective than rail, given that a track system is a rail system, with rails that you pick up and move with you. Unroll the track and lay it out flat on the ground and leave it there, and you have a rail. Yeah, the circumference of the track is shorter than the length of the full rail line, but you also avoid a lot of complexity, and have much more flexibility in the materials you can use.

The crawler system was very similar to the crawlers used on the giant surface mining shovels of the era. In fact, it was manufactured by Marion, one of the major builders of stripping shovels.
In the mining application they were used in minimally prepared conditions, supported huge weight and were capable of leveling the machine very precisely. They spread the load over a large surface area.
Seems to me it was the ideal system for the job and was pretty much perfected pre-NASA.

One of the things that **Francis **Vaughan’s link mentioned was the difficulty with curves. Both a barge canal and rail would have had tremendous problems with turning. I presume this is dictated by the geography of the cape. I wonder if the Energia/Buran launch site was built so that the stack could roll from vehicle assembly to launch pad in a straight line.

However, if you lay out a rail system you have to maintain it along its entire length. This includes periodically realigning and replacing rails, repairing and refilling the ballast and subgrade as it subsides, replacing sleepers as they rot or fracture, et cetera. Although people often assume that rails once laid down don’t require a lot of maintenance, but in fact the opposite is true; regular maintenance is required, especially on railbeds that see heavy or frequent loads or large seasonal freeze/thaw cycles. This is quite costly and is the reason that many private railroad companies went out of business in the late 1800s and early 1900s, with the remaining high value roads consolidated under a few contractors with sharing agreements and others abandoned or repurposed.

As Francis Vaughn notes, Merritt Island on which Launch Complex 39 is sited (which is technically not part of Cape Canaveral) is essentially a swamp, or more correctly, a gigantic semi-permenant sandbar which is suspended on a slurry of sand and ocean. If I recall correctly, no natural feature of the island is more than five meters above mean sea level (AMSL), and in fact the entire island is likely to subside or erode away sometime in the next few centuries. Because of the lack of foundation (bedrock or permafrost) any heavily loaded area will natural subside, and seasonal variations in altitude are common and problematic.

Another thing to consider is that the sheer mass of the Apollo/Saturn V vehicle, launch support structure, and all other associated ground support hardware would require a very specialized rail system. Even dual heavy gauge rails would not be enough to support the loads, which would increase the maintenance requirements. Even for the relatively short distance of tack you’d probably be looking at several mill runs of super heavy gauge rail, which in the marine environment of Merritt Island would have to be periodically replaced due to corrosion in the rail connections and any support structure. Maintaining a couple of vehicles, even as complex as the Crawler-Transporter, is a lot easier and likely cheaper than maintaining a railbed of comparable capacity. I’ve personally dealt with having to evaluate the requirements for refurbishing abandoned railheads for reuse at various sites, and the refurb or rebuild cost is outlandish (and where you have environmental siting considerations, such as Vandenberg Air Force Base, you can pretty much forget about doing any major construction work unless you are prepared to feed money into a furnace boiler by the shovelful). Basically, the evaluation that a rail system would be too costly is on point and likely underestimated the end cost. And really, the primary advantages of a railway are the high volume and (relatively) high speed of throughput; if you are just using it once in a blue moon for very slow transits, the cost and speed advantages are for naught.

The Crawlers, on the other hand, can service both LC-39A and -39B, have proven to be a robust and flexible design which served Apollo, Space Transportation System (‘Shuttle’) and will service the Space Launch System (if and when it actually comes to fruition). Of any part of the Apollo systems the Crawler is the most enduring and has provided the greatest value. It is just about perfect for its intended role and has never suffered a major failure or launch delay (that I am aware of). It has survived through hundreds of launches with only modest amounts of periodic refurbishment, and just a handful of major rebuilds. This is not surprising given that it was designed and constructed by a mining equipment company which is used to designing equipment to withstand explosive blasts and thousands of tons of rock falling on it, so really the Crawler service is light duty by comparison, but I doubt there is any other piece of GSE in the NASA inventory which has survived the same level and duration of service. (The Russians and Ukrainians, however, are still using erector-launcher hardware left over from the original R-7 program and that stuff is built to survive a nuclear near-hit.)

All of that being said, the size, cost, and complexity of the Crawlers highlights all that is inefficient about current launch integration and launch site operation processes. There is a lot of labor involved in moving a launch vehicle onto it and securing it (including the hazardous operation of lifting and placing the vehicle), it is a slow transit from the VAB to the pad that cannot be accelerated, and if the Crawler did suffer a major breakdown in route it would be a very bad day for all involved. There is a small army of engineers and technicians who do nothing but inspect and maintain the Crawler to assure that it will absolutely function, which adds to the general overhead cost of launch operations without proportion to volume since that workforce has to be maintained regardless of the number of launches on manifest. A launch processing workflow that doesn’t require the slow and labor intensive rollout of a launch vehicle on the Crawler should be the ultimate goal of a future heavy lift launch system in order to facilitate faster, cheaper, and higher volume launches.


No, there are turns. As long as you have enough radius, turning isn’t really a problem, and if you have separate bogies for each wheel set (instead of a solid axle) you can pretty much allow for a near zero radius turn.


Russian Soyuz and Proton launchers are brought by Train in the horizontal position. I presume that was impossible for Apollo and certainly seemed to be the case for STS. I suppose that was a reason for the choice.
BTW, what brought the Redstone, Atlas, Titan and Saturn 1B (with milkstool) to the pad?

Thanks for the link, Francis.

Damn! I was such a space junkie in the 60s, and all this time I thought it was on rails! :smack: It took until now for me to realize it? :eek: Wow, thanks all! Ignorance fought!

Some special-purpose rail emplacements actually have conical wheels, to even further accommodate turns (radio telescopes, for example, where the rail bed is entirely turn).

The trade between horizontal integration (putting the stages and front section together with the vehicle lying on its side, typically on rails) versus vertical integration (stacking the sections vertically on the pad or in an assembly building and rolling it out to the launch pad) is that horizontal integration is typically easier and faster as it doesn’t require as many heavy lifting operations, but requires that the vehicle and payload assembly be able to tolerate structural loads while lying on its side (unfueled) as well as in the launch position, and there has to be a strongback and erection system. Vertical integration is slower and requires more lifts, but the vehicle can be lighter and the payload doesn’t have to be designed to tolerate the static side load and all processing considerations. Historically, the US has adapted launch vehicles from silo-based ICBMs where the vehicles were often integrated vertically, so it made sense to use the same processing flow for space launchers. The Soviets, who typically build the vehicles with greater strength and less complexity, tended to go with horizontal integration. Incidentially, this is one reason why Russian launch vehicles today have significantly lower processing costs; they essentially have an assembly line process of structurally integrating the vehicle and payload structure.

The Atlas SLV-3 was erected by an erector and then loaded with propellants shortly before launch, although I believe that upper stages such as the Burner or Agena were vertically integrated after erection. The Titan II GLV and Titan 23G was integrated vertically, with the first stage rotated using a breakover fixture and crane, and upper stage and payload transported in the vertical position and picked by crane. I am not familiar with the GSE used for Redstone, but I can redily find pictures of Redstones being erected with a crane and laucnhed at remote sites as WSMR, and given the fairly ad hoc nature of the program it is unlikely that someone would have built a dedicated transporter-erector for the test launches. I don’t know how it was assembled for use as an operational weapons system or for the Mercury Redstone flights. The Saturn I was integrated vertically on pad using a mobile and gantry crane to lift and rotate the S-I stage onto the pad.

BTW, “stool” and “milkstool” are colloqually terms that are not used in the formal literature or by people who actually design and use ground support equipment. The correct nomenclature is launch stand or launch platform (depending on construction). People will know what you mean if you say “stool” but as with calling a solid propellent rocket motor an “engine” it will identify you as not really knowing the correct jargon.