Here’s what I found: https://space.stackexchange.com/questions/43840/why-did-spacex-choose-vertical-integration-for-starship https://space.stackexchange.com/que

Here’s what I found: https://space.stackexchange.com/questions/43840/why-did-spacex-choose-vertical-integration-for-starship https://space.stackexchange.com/questions/43840/why-did-spac... It appears that it means the assembly of the rocket—whether it is assembled horizontally or vertically. SpaceX rockets and payload are apparently assembled horizontally and then lifted upright.