Say friend, did you know history is complicated?

I’m a Space Shuttle-horse butt truther.

Highlighted: A booster which is NOT the size of 2 horse butts

A copypasta/chain letter type post that dates back to at least 2001 argues the space shuttle boosters are the size of two horse butts.¹ Here’s the argument:

The Space Shuttle boosters were designed to fit through train tunnels. Train tunnels are the size of railroad tracks – 4 feet, 8 ½ inches. Railroads in the US were first made by Englishmen. English railroads were made to match tramways. Tramways were the size of wagons, which were the size of ruts in the old Roman roads, which were the size of Roman military chariots, which were the size of two horse butts. The conclusion:

“So a major design feature of what is arguably the world’s most advanced transportation system was originally determined by the width of a horse’s ass.”

This is a bad argument. The Space shuttle’s boosters were not designed to be the size of 2 horse butts. Although, the International Space Station was designed to fit on a train.

First off, the Space Shuttle had two Solid Rocket Boosters, or SRBs (the flaming white pointy sticks on the sides). They are not 4 feet, 8 1/2 inches wide, but rather 12 ft, 2 inches.² That’s about 5 horse butts.³

Space Shuttle SRB diagram, showing its width of 5.2 horse butts

Well, that seems like a slam dunk.  But then how did they fit on a train?

Train cars and the cargo they carry are often much wider than their track’s gauge (the spacing between the two rails), because the wheels aren’t at the very edge.  So trains in general are not the size of two horse butts.  But the exact words of the post are “originally determined by” two horse butts, and the maximum size of train cars is partly determined by the gauge they ride on. So for pedantry’s sake, let’s proceed.

Second, English railroad gauge was not based on the size of Roman chariots via a complex causal chain.⁴ Instead, they both come straight from the horse butts. Early horse-drawn rail carriages and Roman chariots were both pulled by horses lined up in pairs, so they were both about the same size. It’s like claiming modern shoes were built to the standards of Ancient Egyptian sandals. They’re just both the size of human feet.

Around the world, there are loads of different railroad gauges. Of the common ones, the narrowest is 1 meter (3 ft 3.37 in), used for example in Brazil. The widest is 5 ft 6 in (167.6 cm) used in South Asia, and for some reason the BART in the San Francisco Bay Area. They’re all pretty similar – that’s just a good size to build a train.

BART rails: 2.3 horse butts wide

Third, normal trains in the US are only allowed to be 10 ft 8 in wide.⁵ So the 12 ft 2 in wide SRBs were still an oversized “dimensional load”.⁶ And if they needed to be even bigger, NASA had other options than rail.

Rail was definitely convenient. The SRBs were made by Thiokol (which you might know from the Challenger disaster). Thiokol had a major factory in Brigham City, Utah. Which is literally the seat of the county where they drove in the final “Golden Spike” on the first transcontinental railroad.⁷

But if the engineers had really wanted larger solid rocket boosters, NASA could have built them somewhere else and used a barge. Exhibit 1 is that the external fuel tank (the huge orange thing) traveled by barge. Exhibit 2 is that NASA did commission a larger solid rocket motor in the Apollo era, which was more than 22 feet across.⁸ It was tested, but never flew. The parts were built by Aerojet near Philadelphia and taken on a barge to be assembled in Miami.

 

Left: External fuel tank (11.7 horse butts) on a barge

Right: Plume from the Aerojet 260 solid rocket motor (9.2 horse butts)

So the causality isn’t quite right. More likely, after they determined that the Shuttle could work with SRBs around 12 feet wide, NASA and Thiokol made sure that they’d fit through train tunnels. But that’s a pretty loose requirement.

SRB segments being hauled by normal train cars (4.6 horse butts)

What’s crazy is that the International Space Station actually is designed around railroad sizes! Just on the Russian side. The Soviets, and the Russians after them, launched primarily from Baikonur Cosmodrome in Kazakhstan, which can’t be reached by sea. The Proton rocket was first launched in 1965, and still has a few more launches scheduled before it’s retired in 2026.

According to space historian Anatoly Zak, the core of Proton’s first stage is 4.1 meters wide because that’s the absolute maximum size that could be transported by rail.⁹ The first Russian-built modules of the ISS were designed to fit on Proton, so they had to be that wide, too. Alas, Russia’s 5-foot train gauge was not directly based on horse butts. It was picked by the Tsar after an American engineer convinced him it would be cheaper to build and maintain.¹⁰

Proton rocket launching the Zvezda module (5.9 horse butts) to the ISS

Weird connections are everywhere. Even weird connections between horses and railroads, and railroads and rockets. But the truth is cool enough by itself, without extra false details. So if you see another chain of facts that’s “too cute”, beware: it may well have come out of a horse’s rear end.

Coming soon: You can just do experiments