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SpaceX's original plan was landing the 1st stage to a landing ship, that waits far away from the launch site, and it was like this:

initial plan

But tonight, the rocket's first stage landed at Cape Canaveral. Looking at this original plan slowing down and coming back to launch site seems not possible. So how did it made all the way back? Was it a different maneuver than landing on a ship.

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  • $\begingroup$ I don't know whether it actually doubled-back on itself, but the landing site was still a considerable distance from the launch site $\endgroup$ – Kaz Dec 22 '15 at 4:08
  • $\begingroup$ Possible duplicate of How are SpaceX going to land their Falcon first stage? $\endgroup$ – oefe Dec 22 '15 at 14:30
  • $\begingroup$ I read some more information about this and clearly the 1st stage cut of happened much closer to the launch site than the original plan I posted above. @Zak 's flight plan shows the updated trajectory. $\endgroup$ – dvdmn Dec 22 '15 at 16:48
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The "return to launch site" flight profile flown on December 21, 2015, requires that the first stage re-light three of its engines after separation, turn around, cancel out all its speed, and accelerate back towards the launch site. To do this, it has to keep a lot of fuel in reserve after the separation -- less than you might think, though, because the first stage is quite light once the ascent fuel, second stage, and payload are gone.

In this launch, there were three significant factors that allowed them to do this:

  • They "supercooled" the fuel and oxidizer to much lower temperatures than before, which makes them denser, allowing them to carry more fuel in the same volume of tankage on the first stage;
  • They lengthened the second stage, allowing more tankage there, so the second stage could provide more of the necessary speed to get the payload to orbit (meaning the stage separation could occur at a shorter distance from the launch site and at lower speed);
  • The payload was relatively small, consisting of 11 functional and 1 dummy satellite of about 175kg each -- with mounting and ejection hardware and so on, probably less than 4 tons of payload, compared to the 13 ton payload Falcon 9 is normally capable of launching to LEO.

For full-payload missions, the first stage will have to do more work to push towards orbit, so return-to-launch-site may not be possible, so I believe those missions will use the Florida-to-Atlantic-barge or Texas-to-Florida flight profiles, which require much less fuel in reserve after separation.

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    $\begingroup$ Looks like SpaceX also considering launching from Texas and landing the 1st stage to Florida. I read it on another discussion. $\endgroup$ – dvdmn Dec 22 '15 at 15:32
  • $\begingroup$ Ah, right -- added that. $\endgroup$ – Russell Borogove Dec 22 '15 at 16:06
  • $\begingroup$ Can someone source these Tx-Fl claims? It's a thousand miles distance, the F9 doesn't go more than a few hundred miles to the ASDS typically. And if the distance wasn't unrealistic, it would involve overflying populated areas, not likely to get approval for a non-gliding propulsively landed rocket. $\endgroup$ – Saiboogu Jan 15 '18 at 18:54
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I think this is pretty self-explanatory:

enter image description here

(Thanks to @TildalWave for finding an updated graphic)

It's important to note that the landing pad was a different site to the launch pad (6 miles away), so it didn't return *exactly* to its' original point of take-off, as can be seen here:

enter image description here

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    $\begingroup$ The picture you attached also shows the drone ship. $\endgroup$ – dvdmn Dec 22 '15 at 4:36
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    $\begingroup$ Drone ship is just a floating landing pad. Exact same process applies. $\endgroup$ – Kaz Dec 22 '15 at 5:01
  • $\begingroup$ This article from last night discusses some of the figures where a barge landing may still be used in the future - essentially where the upper stage needs to be travelling faster at separation, so it would use a lot more fuel to get back to land. $\endgroup$ – James Thorpe Dec 22 '15 at 8:49

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