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So the idea of refueling in space is interesting, but I am a bit confused by the practicality. if we could refuel from the Moon, yeah I 100% see the value of it

So the idea of refueling in space is interesting, but I am a bit confused by the practicality. if we could refuel from the Moon, yeah I 100% see the value of it due to less wasted fuel getting off the moon. But unless I am mistaken, the biggest problem with fuel is that it obviously costs fuel to get fuel up. It has a weight so its not like you can just say, I want 100 lbs of extra fuel, you need that amount of fuel plus the amount of fuel to carry that amount (and then the amount to carry that amount, and so on and so forth). So in reality what is the difference between say, 100lbs of fuel across 10 Starships vs 100 lbs of fuel on a single ship? Yeah you would need a bigger ship to handle all of the fuel necessary, but something about this being necessary for the moon seems off? Mars I can understand more. I just feel like I am missing something here, until reading this I did not realize that refuel in space was necessary for the Moon. Also to be clear I am not discounting the work on doing this, but I was just always under the impression that this was a thing that was necessary for Mars where now it seems like we are talking 11 launches to get too the moon?

JumpCrisscross 2y ago
> what is the difference between say, 100lbs of fuel across 10 Starships vs 100 lbs of fuel on a single ship? Exponential. > something about this being necessary for the moon seems off? Mars I can understand more It's not necessary for the Moon. The reason we're doing it is so once Artemis is done on the Moon, we have a system ready to send astronauts to Mars. [1] https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#Experiment_of_the_Boat_by_Tsiolkovsky https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#Ex...
- nerdjon 2y ago
  Maybe there is a typo in the article then that is why this seemed weird? The first paragraph: > ambitious refueling demonstration, a technical feat that will put the Moon within reach. Again here: > By the time NASA and SpaceX are ready for a lunar landing, multiple Starship tankers will take off from at least two launch pads to aggregate propellants at a depot to supply the Moon-bound Starship. Then again here: > On future Starship missions targeting destinations in deep space, like the Moon, this docking maneuver and refueling process will be repeated multiple times to give the vehicle enough gas to boost itself out of Earth orbit. Another one: > The results of this refueling demonstration will allow SpaceX and NASA engineers to calculate how many refueling tankers they will need to fill up a Starship heading for the Moon. All of this makes it seem like this is necessary just to get to the moon with Starship which really makes me wonder about the practicality of this when later it mentions the possibility of 10 refueling missions. Or am I misreading what this is saying?
  - JumpCrisscross 2y ago
    > All of this makes it seem like this is necessary just to get to the moon with Starship The Artemis architecture requires in-orbit refuelling to go anywhere interesting. (More due to the limitations of SLS and Orion than Starship, but I digress.) The Artemis architecure isn't necessary to go to the moon--Apollo had no in-orbit refuelling. We've chosen an architecture that requires in-orbit refuelling to go anywhere because it better scales to going to Mars.
gitfan86 2y ago
The only reason air travel is affordable to middle class people is due to the economies of scale. This is the same goal with SpaceX. To drive the price of ton to orbit down a lot. That is the only way a city on Mars happens.
dotnet00 2y ago
100lbs is obviously not a lot of mass for refueling to mean much. But, if Apollo needed to launch 3000t to land 16t on the Moon, a Starship with 100t of payload and say, 300t of propellant, would need a ~75000t rocket from Earth. Efficiency improvements reduce this a bit, but not meaningfully. Hopefully you can see how that's kind of unrealistic and unscalable to do in one launch. Orbital refueling is a core technology necessary for sending useful amounts of payload around the solar system because the rockets themselves can't really get much larger without becoming completely uneconomical. Congress understood that orbital refueling would make their obscenely expensive SLS program unnecessary, which is why they effectively banned NASA from using the word "depot" (until Senator Shelby retired) under threat of canceling the entire space technology program, and strongarmed ULA into not pursuing an upper stage capable of carrying Orion and performing orbital refueling (which again, would've replaced a $2B per launch rocket with a couple of launches of a ~$150M rocket). The number of launches sounds like a lot, but consider that F9 is already launching 2-3 times each week, and Starship is being designed explicitly to not have the factors that are limiting F9 cadence from increasing further. The engines are better designed for reuse, the launch infrastructure is easier to build many copies of, the boosters always come back to land, the second stage integrates onto the booster at the launch pad etc. Also, as a side note, they'll need roughly the same number of refueling flights for Mars. The fuel requirements for going to the Lunar surface and Martian surface are actually pretty similar, since on Mars you can save a lot on using the atmosphere to slow down, while you can't on the Moon.
jillesvangurp 2y ago
The amount of fuel limits how far you can go in terms of delta-v and mass. So, if you have to have all the fuel on board when you launch from the ground, there's only so far you will go and so much you can take with you. The point of going back to the moon is not only just planting a few more flags but actually taking some meaningful amount of resources there to ultimately be able to build a moon base. Same with Mars. And we might want to take some more stuff back (rocks, minerals, whatever). So, that requires fuel as well. The point of refueling is getting to orbit and then topping up all the fuel you lost getting there (i.e. most of the fuel because getting out of the atmosphere takes a lot of energy). Starship when it starts flying will be by far the largest amount of mass we can get to orbit. Like upto 150 tonnes or whatever the maximum payload is going to be. So, that amount of fuel would enable large amounts of mass to be accelerated to a path to the Moon, Mars, or wherever way beyond what would otherwise be feasible. And with a reusable launch vehicle, it actually gets doable from a price point of view as well.

JumpCrisscross 2y ago

> what is the difference between say, 100lbs of fuel across 10 Starships vs 100 lbs of fuel on a single ship? Exponential. > something about this being necessary for the moon seems off? Mars I can understand more It's not necessary for the Moon. The reason we're doing it is so once Artemis is done on the Moon, we have a system ready to send astronauts to Mars. [1] https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#Experiment_of_the_Boat_by_Tsiolkovsky https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#Ex...

nerdjon 2y ago
Maybe there is a typo in the article then that is why this seemed weird? The first paragraph: > ambitious refueling demonstration, a technical feat that will put the Moon within reach. Again here: > By the time NASA and SpaceX are ready for a lunar landing, multiple Starship tankers will take off from at least two launch pads to aggregate propellants at a depot to supply the Moon-bound Starship. Then again here: > On future Starship missions targeting destinations in deep space, like the Moon, this docking maneuver and refueling process will be repeated multiple times to give the vehicle enough gas to boost itself out of Earth orbit. Another one: > The results of this refueling demonstration will allow SpaceX and NASA engineers to calculate how many refueling tankers they will need to fill up a Starship heading for the Moon. All of this makes it seem like this is necessary just to get to the moon with Starship which really makes me wonder about the practicality of this when later it mentions the possibility of 10 refueling missions. Or am I misreading what this is saying?
- JumpCrisscross 2y ago
  > All of this makes it seem like this is necessary just to get to the moon with Starship The Artemis architecture requires in-orbit refuelling to go anywhere interesting. (More due to the limitations of SLS and Orion than Starship, but I digress.) The Artemis architecure isn't necessary to go to the moon--Apollo had no in-orbit refuelling. We've chosen an architecture that requires in-orbit refuelling to go anywhere because it better scales to going to Mars.

gitfan86 2y ago

The only reason air travel is affordable to middle class people is due to the economies of scale. This is the same goal with SpaceX. To drive the price of ton to orbit down a lot. That is the only way a city on Mars happens.

dotnet00 2y ago

100lbs is obviously not a lot of mass for refueling to mean much. But, if Apollo needed to launch 3000t to land 16t on the Moon, a Starship with 100t of payload and say, 300t of propellant, would need a ~75000t rocket from Earth. Efficiency improvements reduce this a bit, but not meaningfully. Hopefully you can see how that's kind of unrealistic and unscalable to do in one launch. Orbital refueling is a core technology necessary for sending useful amounts of payload around the solar system because the rockets themselves can't really get much larger without becoming completely uneconomical. Congress understood that orbital refueling would make their obscenely expensive SLS program unnecessary, which is why they effectively banned NASA from using the word "depot" (until Senator Shelby retired) under threat of canceling the entire space technology program, and strongarmed ULA into not pursuing an upper stage capable of carrying Orion and performing orbital refueling (which again, would've replaced a $2B per launch rocket with a couple of launches of a ~$150M rocket). The number of launches sounds like a lot, but consider that F9 is already launching 2-3 times each week, and Starship is being designed explicitly to not have the factors that are limiting F9 cadence from increasing further. The engines are better designed for reuse, the launch infrastructure is easier to build many copies of, the boosters always come back to land, the second stage integrates onto the booster at the launch pad etc. Also, as a side note, they'll need roughly the same number of refueling flights for Mars. The fuel requirements for going to the Lunar surface and Martian surface are actually pretty similar, since on Mars you can save a lot on using the atmosphere to slow down, while you can't on the Moon.

jillesvangurp 2y ago

The amount of fuel limits how far you can go in terms of delta-v and mass. So, if you have to have all the fuel on board when you launch from the ground, there's only so far you will go and so much you can take with you. The point of going back to the moon is not only just planting a few more flags but actually taking some meaningful amount of resources there to ultimately be able to build a moon base. Same with Mars. And we might want to take some more stuff back (rocks, minerals, whatever). So, that requires fuel as well. The point of refueling is getting to orbit and then topping up all the fuel you lost getting there (i.e. most of the fuel because getting out of the atmosphere takes a lot of energy). Starship when it starts flying will be by far the largest amount of mass we can get to orbit. Like upto 150 tonnes or whatever the maximum payload is going to be. So, that amount of fuel would enable large amounts of mass to be accelerated to a path to the Moon, Mars, or wherever way beyond what would otherwise be feasible. And with a reusable launch vehicle, it actually gets doable from a price point of view as well.