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How are SpaceX supposed to return the rocket's first stage to the launch pad/hangar for re-fitting after it has landed on a landing zone on land, or on a barge?

Since they aren't landing on a launch pad, they must get it back to a launchpad for the next launch? Or do they really need to do that? There seem to be a lot of equipment involved at the launchpads to keep the cooled down fuel, oxidizers and whatnot, that you don't have at landingzones or barges.

Will they fill the tanks just a little so the first stage can hover by itself, or lay it down horizontally and move it by trucks and cranes or even some russian helicopter? ;)

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    $\begingroup$ They load it on a truck trailer. Like this. (Yes, that's the one they landed.) $\endgroup$ – Ilmari Karonen Jan 7 '16 at 22:37
  • $\begingroup$ Originally spacex were talking about flying first stages back from the droneship but they don't seem to have said anything about that recently. $\endgroup$ – Peter Green Feb 7 '18 at 17:16
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SpaceX's Landing Zone 1 is just a few miles down the road from their launch sites at Cape Canaveral, so they use a crane to put it on a truck horizontally and drive it back to a hangar near the launch site (at LC-39A) for cleanup, inspection, and refurbishment. Eventually, presumably, they'll be able to prep a landed stage for reflight there and mate it with a new upper stage and payload; right now they launch out of LC-40 next door.

For barge landings, similarly, they'll bring it back to land, then drive it to the refurbishment or relaunch site by truck. (This is how they bring their rockets to the launch site to begin with.)

For safety reasons, the landing site consists of just large bare pads of concrete -- nothing to crash into. While SpaceX hit within a couple of meters of bullseye on their first LZ1 landing, that's no guarantee they can repeat it consistently. The launch sites have quite a bit of infrastructure installed, including lightning-rod towers surrounding the launch pad, so they aren't appropriate as landing sites.

We're a long way away from being able to simply land, refuel, add a new payload, and take off from the same location as we do with commercial aircraft; I don't think there's any expectation that Falcon rockets will be able to do this.

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    $\begingroup$ "We're a long way away from being able to simply land, refuel, add a new payload, and take off from the same location as we do with commercial aircraft" We will see about that! It is the commercial way to do business, and spacecrafts are becoming more like aircrafts. $\endgroup$ – LocalFluff Jan 6 '16 at 3:34
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Russell Borogove's answer is excellent, so I just want to address a small part of your question that isn't answered there:

Will they fill the tanks just a little so the first stage can hover by itself

It can't hover. Even with 8 engines shut down and the 9th throttled back to minimum, the thrust is much bigger than the weight of the (mostly) empty first stage without the second stage and payload. That's why they have to do that insane-looking "hover-slam" landing, where the rocket basically free-falls to the landing pad and then at the very last second the engine fires so that the rocket will reach a velocity of zero at exactly the same time it reaches an altitude of zero.

What they could do is "hop": fire the engine so the rocket takes off on a ballistic trajectory towards the launch pad, then do a hover-slam there. (Or do multiple "sideways hops", re-starting the engine multiple times.)

I don't know if it would make sense to put enough ballast (i.e. propellant/oxidizer) into the rocket in order to bring the thrust-to-weight-ration below 1 to make it hover-capable.

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