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Very recently, ESA released a new video showing the proposed Ariane 6 rocket being assembled. This mostly takes place in a large 'moveable gantry' building where the payload is placed on top of the rocket and boosters are added. This moveable building also has different platforms that come in from the sides and "hug" the rocket, presumably for technicians to access it. When the rocket is ready to launch, the whole building moves away leaving the rocket on the launch pad and ready to go.

How does ESA (or Arianegroup) justify the costs of a vertical assembly system? I can't imagine that constructing a huge moving building is cheap and the Soyuz and Falcon (including heavy) are both assembled horizontally and of similar size. Is there some deal-breaking requirement for vertical assembly? Or, am I wrong in assuming that vertical assembly is more expensive?

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  • $\begingroup$ The movable gantry is also useful to protect the rocket if a storm rolls in. This was done for the Saturn I/IB at launch complexes 34 and 37. It also gives you more options to fix or scrub a launch. But I don't know enough about Ariane to know if these issues apply there. $\endgroup$ – DrSheldon Jul 25 '19 at 3:26
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Ariane 6 had one goal: to reduce cost compared to Ariane 5. To achieve this, they took several steps:

  • replace vertical integration with horizontal integration. All components of Ariane 5 are integrated vertically. Ariane 6's first and second stages, on the other hand are integrated horizontally. This makes the integration building cheaper.

  • Cost reductions in the rocket itself, mainly by simplifying construction.

  • They streamlined the organisation, reducing the number of suppliers etc.

  • they streamlined the launch campaign, making it take up less time and enabling more rockets to be processed in parallel, which increases schedule flexibility.

There are two limitations to horizontal integration:

  1. it's not feasible to install the solid boosters while the rocket is horizontal. They are too heavy to be supported by the main stage while horizontal. So the boosters are added on the launch pad when the rocket is vertical.

  2. Customers didn't want to switch to horizontal integration because that requires a redesign of their payloads. The payload will be integrated on the pad as well, after being prepared and encapsulated in the fairing in a separate building.

The horizontal integration means people can work at ground level instead of on high platforms. It also makes air conditioning of the integration building a lot cheaper (Kourou is bloody hot, and a 100 m high building is expensive to keep cool). The gantry has no AC, which they can get away with because they've minimized the amount of work that has to be done in the gantry.

Falcon and Soyuz have no solid boosters so they're much lighter (30 tons compared to ~500t for an Ariane 64).

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  • $\begingroup$ The mobile "building" is, apart of booster integration, mainly used for final inspection of the rocket as this is something you're better able to do vertically. And many payloads can only be integrated vertically as their not designed for the loads in horizontal position. So if ArianeGroup wants to meet their goal to be able to have all kinds of payloads they do need vertical integration. $\endgroup$ – GittingGud Jul 25 '19 at 7:15

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