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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?

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    $\begingroup$ Why? It's not about saving fuel. Fuel costs of rocket launching is negligible. It's about saving the rocket. On the barge the rocket will be refueled and then it will fly to the next site for its next launch. It is a rocket, it flies. $\endgroup$
    – LocalFluff
    Nov 29, 2014 at 19:21
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    $\begingroup$ The fuel savings is relevant to fuel margins to do the maneuver and mass available for payload or for reinforcing the structures or mechanisms of the rocket. $\endgroup$
    – kim holder
    Nov 29, 2014 at 19:25
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    $\begingroup$ Sounds to me that the barge will not bring the rocket home, but rather refuel the rocket so that it could fly itself home. $\endgroup$
    – dotancohen
    Nov 30, 2014 at 7:06
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    $\begingroup$ @dotancohen - Yes, that is what he is saying. The plan before was that the stage would fly back to the pad it launched from, which meant it would have to turn around, and that takes more fuel. By using a barge the stage can be slow passively through air friction more, and it doesn't have to change its trajectory so much. $\endgroup$
    – kim holder
    Dec 1, 2014 at 18:14
  • $\begingroup$ I had thought there would be some way to estimate this approximately based on relatively simple calculations with the numbers known for the Falcon 9. Apparently not. $\endgroup$
    – kim holder
    Dec 1, 2014 at 18:18

1 Answer 1

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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).

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  • $\begingroup$ Are you saying you feel the application will largely be used for Falcon Heavies? $\endgroup$
    – kim holder
    Nov 30, 2014 at 1:33
  • $\begingroup$ @briligg i think it opens options. If F9E can boost 30,000lbs to LEO, but F9R is reduced to 21,000lbs, then if you have a mission needing 25,000 lbs payload, what are your options? Spend more on a F9E (Expendable)? Spend more on a F-Heavy and have tons of payload to burn wasted? Having a downrange landing pad might be enough to make F9R the right call. Same basic decsions on Heavys. Recovering that center core could make a huge cost difference, so likely will be used by Heavies. But once it is available, may be cases where it makes sense for F9 itself. Possibilities become available. $\endgroup$
    – geoffc
    Nov 30, 2014 at 1:37
  • $\begingroup$ @geoffc, the 30,000 lbs figure (13,150kg) on SpaceX's website includes accounting for the payload drop due to reusability. An expendable F9 can lift greater than 16.5mT to LEO in an expendable configuration. $\endgroup$
    – marked-down
    Dec 1, 2014 at 2:59
  • $\begingroup$ @Antilogical I have heard that, but I really wonder if there is a subtle misunderstanding in that statement. Time will tell. $\endgroup$
    – geoffc
    Dec 1, 2014 at 3:48
  • $\begingroup$ @geoffc, I can understand that, and I used to be skeptical of that number, but Gwynne & Elon have repeatedly stated that it is correct. Additionally, check out NASA's Launch Vehicle Performance Calculator - F9 clearly puts 16mT to 200km LEO from Canaveral. I gave them an email and they confirmed that in expendable mode, F9 does in fact place the stated 16mT into orbit. $\endgroup$
    – marked-down
    Dec 1, 2014 at 4:54

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