How much fuel can SpaceX save by landing the Falcon 9 booster on a barge?

Question

It sounds from the text of this tweet like Elon Musk plans to continue to do barge landings over the long term:

"Base is 300 ft by 100 ft, with wings that extend width to 170 ft. Will allow refuel & rocket flyback in future."

If so, presumably that is because they can save on launch mass because that requires less fuel. That weight savings can then be used to reinforce the structures of the rocket, give a bit more delta-v to the following stage, have a bigger payload, or maybe just have more fuel margin for maneuvering. It also implies they are confident they can make the barge sufficiently stable for landing in all sea conditions.

Thus the long-range plan would seem to be to launch from Brownsville TX and perhaps land in the Atlantic, in order to have the best distance in which to use air drag to slow the stage.

Can the fuel they would save by doing this be calculated?

Answer 1

When a Falcon 9 first stage launches, it appears there will be two basic modes available. Reusable and expendable. We have seen mostly expendable launches so far.

In reusable mode, there is a fuel cost to brake the forward thrust, slow down for reentry through the atmosphere, and then finally for landing. While it is not an attempt to save fuel, rather that fuel must be reserved for recovery cannot be used for thrust to orbit and therefore the functional payload is reduced.

The burn to control reentry into the atmosphere and landing cannot be easily obviated, but the burn to slow down forward flight might possibly be minimized or removed if there is a target downrange to land on.

Landing back at the launch site is known as RTLS - Return to Launch Site. That is most fuel intensive and thus most payload reducing.

Secondarily, the center core of a Falcon Heavy will be firing longer and thus faster/higher at MECO. The question becomes, can that be recovered? Well RTLS in that case would likely mean a huge payload reduction so probably not worth it. But if there is a downrange target to land on, (an island, a barge, a continent) that is appropriate the cost of recovering the stage could be largely reduced. (Cost as always being seen from a payload capacity view).

Once the booster is on the barge, what do you do next? Well maybe tilt it horizontal, transfer to a faster ship and sail it back to base? Maybe refuel and fly it back? It is after all a reusable rocket stage. (Probably need a cap, since the open top end of a second stage-lacking first stage is probably very un-aerodynamic).