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Comment by faitswulff | Hacker News Reader

I recently took a tour of SpaceX due to a friend and learned that their rockets, unlike most others, are constructed horizontally. This makes logistics for getting them upright an engineering feat, but it also makes construction and maintenance easier for crew - you can rotate the rocket and access almost any part of the rocket from ground level.

I'm curious to know more about the engineering constraints/trade-offs this puts the rockets under, so if anyone knows more I'd love to hear it!

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That depends on what you mean by "constructed". The individual stages of all rockets are constructed horizontally. The difference is in how the stages and payload are integrated.

With a rocket like the Atlas V, the upper stage and payload are integrated with the first stage while it is vertical. This is a common approach taken with rockets that frequently fly satellites with big mirrors in them (if the payload is never tipped on its side, it's a lot easier to secure the heavy optics inside).

SpaceX does not currently support vertical integration, they only support horizontal integration. Generally speaking customers prefer vertical integration, since it makes their payload design easier (and in some cases it's a hard requirement), so SpaceX will be adding vertical integration support at their LC-39A launch pad (mostly for government launches).

Some good discussion here: https://space.stackexchange.com/questions/3922/what-are-the-...

Essentially it boils down to what g-forces your rocket components and payload are able to withstand. Designing for zero (in orbit) and high vertical (during liftoff) is tough enough, but a rocket that's horizontally built/integrated _also_ needs to withstand ~1G laterally. It may not sound like a big deal, but when every kg counts, I believe it adds up to a bunch of additional strengthening parts, plus a lot more FEA at design time.

Space X has regularly focused on lower costs at the expense of payload. Their rockets get significantly less to orbit, but the price saving ends up being huge which more than offsets the loss.

This is the standard way the russian operate. Rockets as the Soyuz or the Proton are assembled and transported horizontally to the launching site and then erected on the launch pad. There are a lot of interesting photos of trains moving these large rockets

This is the way all rockets are built. I think the OP is confusing construction and integration.

Rockets are fabricated and transported horizontally. The distinction is whether the rocket is vertical or horizontal when the payload is attached.

"All" is taking things a little far -- the Apollo Saturn V stack was assembled vertically (as were the smaller Saturn IB rockets when launched from LC 39).

Yeah, I was a little ambiguous with the term "rocket". "Rocket stages" would have been more accurate. Most rockets that use vertical integration use it to assemble the various stages (i.e. the upper stage and payload are both mated to the booster in the vertical integration facility)

There's a really good scene in Apollo 13 that shows this. Jim Lovell is giving a tour of the VAB and in the background you've got two of the stages coming together with a thud.

Thanks, didn't know the distinction!

This must be helpful for transporting the rocket by truck for reuse (see youtu.be/qohKt8ckCS4). If the rocket remained vertical, the drone ship would have to dock very close to the launch pad.

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