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Rockets first stage recovery at launch site needs a significant amount of fuel for going back. This is why SpaceX most often uses sea platform and booster back burn for re-entry. As we see on Falcon9 videos the booster needs a back burn to renter at a moment where it seems to be almost on orbit.

Wouldn't it be better in terms if fuels consumption, and hence of overall efficiency, to let the booster -- Falcon 9 or the coming Starship/Super Heavy -- realize one full rotation around the earth before gently rentering at the launch site?

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    $\begingroup$ I think the problem is, if the first stage could be enough fast to make a full orbit, no second stage would be needed. It would be an SSTO. $\endgroup$
    – peterh
    Jan 28, 2022 at 9:04
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    $\begingroup$ Also, I think it would take more fuel to reach orbit and then deorbit than it would to just not make it to orbit in the first place. $\endgroup$ Jan 28, 2022 at 11:56
  • $\begingroup$ obligatory xkcd $\endgroup$ Jan 28, 2022 at 12:47
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    $\begingroup$ The first stage of a dual stage rocket is not capable for one single orbit. $\endgroup$
    – Uwe
    Jan 28, 2022 at 17:33
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    $\begingroup$ Your chosen video is of the TESS launch...separation occurred around 75 km altitude at less than 2 km/s, nowhere near orbit: youtu.be/aY-0uBIYYKk?t=1346 $\endgroup$ Jan 28, 2022 at 18:40

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Let's look at this from the opposite direction: What does it take to go around the planet?

If you want to go around and land at the launch site you have an orbit with the apoapsis at the desired altitude and the periapsis at zero. The energy difference between this and a circular orbit at the desired altitude is small. Thus to make the booster do this you need to accelerate it to nearly orbital velocity--which is what the second stage normally does.

The booster (Block 3 and 4, I don't see the data for block 5) weighs 49,000 pounds. It's pushing 8,800 pounds of second stage, 8,200 pounds of fairing and probably (extrapolation from the block 5 data I'm finding) 16,800 pounds of payload. Note that the booster weighs more than everything above it other than fuel--which means going around the planet needs more fuel than the second stage is carrying!

And note that once it's gone around the planet it needs more fuel than it started with to do the reentry burn. The booster has no heat shield, it slows on rockets or it burns.

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  • $\begingroup$ Specifically, this is going to have the first stage do abort once around en.wikipedia.org/wiki/… which is listed as being only a couple of seconds thrust from being in orbit. $\endgroup$ Jan 29, 2022 at 8:41
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I don't think you're interpreting the first stage's use of fuel correctly. The back-burn is relatively small (and most certainly much less than the fuel required to complete a full orbit at any reasonable altitude). There's a decent amount of guided glide path on the way back down, prior to the final burn to reach zero velocity upon landing.

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