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

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?

• 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. – LocalFluff Nov 29 '14 at 19:21
• 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. – kim holder Nov 29 '14 at 19:25
• Sounds to me that the barge will not bring the rocket home, but rather refuel the rocket so that it could fly itself home. – dotancohen Nov 30 '14 at 7:06
• @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. – kim holder Dec 1 '14 at 18:14
• 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. – kim holder Dec 1 '14 at 18:18

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).

• Are you saying you feel the application will largely be used for Falcon Heavies? – kim holder Nov 30 '14 at 1:33
• @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. – geoffc Nov 30 '14 at 1:37
• @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. – ReactingToAngularVues Dec 1 '14 at 2:59
• @Antilogical I have heard that, but I really wonder if there is a subtle misunderstanding in that statement. Time will tell. – geoffc Dec 1 '14 at 3:48
• @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. – ReactingToAngularVues Dec 1 '14 at 4:54

I've got to agree with Geoffc's comment. Especially the comment "Cost has always been seen from a payload capacity view".

I've worked as an Aerospace Engineer in both commercial aircraft and space launch vehicles for years and years. I cannot wrap my head around how the Falcon 9 saves money landing on its tail like it does, using all that fuel. Yes that is an impressive feat. The control systems that can do that are amazing. But is this a practical way to launch and recover your booster?

NASA estimates that 1 pound of payload costs $10,000 to put in orbit. (https://www.nasa.gov/centers/marshall/news/background/facts/astp.html). Reducing cost savings by having a reusable launch vehicle sounds attractive, but so far hasn't been shown to work from a cost savings perspective...YET. https://www.theverge.com/2018/5/9/17254384/spacex-falcon-9-block-5-upgrade-rocket-reusability-savings That doesn't mean it can't be done, someday. The big problem is re-entry does a lot of damage and you have to refurbish your launch vehicle. There a lot of heat damage if you need to re-enter the atmosphere. However even if your booster doesn't fly that high, just the friction of flying thru the atmosphere at the necessary speeds does a lot of damage, not me mention the engine vibration and the heat to parts from the engine burn itself. T A that cuts into the "reusable" cost savings big time. NASA's Space Shuttle NEVER became cost-effective. Granted, that was a manned spacecraft and therefore more costly and for human safety, refurbishment had to be more extensive. But at least the space shuttle had a large payload capacity. Landing as an airplane would, by GLIDING! That's very fuel efficient. Even so, it never became cost-effective. If the Falcon 9 is going to be cost effective, I think it would have to be recovered some other way. All that fuel used to land on its tail by thrust alone seems awfully wasteful. The reserve fuel necessary for that, and its cost in weight could instead be useful and revenue generating payload! Parachutes do the same thing and weigh a hell of a lot less than all that fuel, even if you add in the parachute deployment system. Modern parachutes can be "flown" like a glider as well. Makes no sense to me to recover a booster that way. Even if it lands closer to the launch pad. It looks cool. But I think that's it. But I wouldn't say the Falcon 9 has no future. I think it does. I just think for it make money it can't land like that. Too much wasted weight and payload capacity for something that is unnecessary...on the Earth anyway. If you are landing it someplace with little or no atmosphere, like Mars or the Moon, then YES it does make sense, because you basically can't land any other way. Still, Nasa has landed probes on Mars with parachutes (large ones) and even by bouncing (Mars rover). You can get away with the latter because Mars gravity is only 38% of the Earth's gravity. Parachutes don't really work on the Moon. Landing the way Falcon 9 lands would make perfect sense on Mars or the Moon. In fact, the very accurate way it lands would be very useful and given the lower gravity, it would not use anywhere near the same amount of heavy fuel. But such a mission is not about recovering your vehicle, at least not that part of it. • This does not answer the question. – user2705196 Jan 28 '19 at 20:30 • This is a head scratcher of an answer. Sounds like it was written in 2014 when this question was asked, the way it ignores knowledge gained in the intervening 5 years. Fuel use for landing is irrelevant, you're looking at the wrong things. The relevant question is -- Can the rocket launch payloads the the market wants to pay for, and be reused economically? And that question has been answered by now, with public statements of reduced cost reflights and a long run of happy customers. – Saiboogu Jan 28 '19 at 20:32 • The fuel cost is negligible. Something like \$200k to fuel a Falcon 9. A pessimistic estimate of the amount of fuel needed to land is 30% of the total load, so a landing costs \$60k. Building a new first stage costs on the order of$10M, so that's the ceiling for refurbishment cost. – Hobbes Jan 28 '19 at 20:35
• Falcon 9 is already cost-effective. SpaceX charges \$62M for a recoverable mission, and profitability estimates run from 20% margin to 40% margin -- and that's if they fail to recover the booster. – Russell Borogove Jan 28 '19 at 20:57
• @RussellBorogove I did a Fermi estimate, hence "on the order of" – Hobbes Jan 29 '19 at 7:29