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Cont: Musk, SpaceX and future of Tesla II

Andy_Ross said:
Transfer the tank
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The fuel tanks of Starship are built into the structure of the ship. It would require a complete redesign. Furthermore, the refuelling Starship can carry at most 200 tonnes (Musk's estimate) of fuel over and above the fuel it needs to get into orbit which is about 1,500 tonnes. I don't know how much fuel will be needed to get to the Moon but people are talking about it having to be refuelled in lunar orbit, so it will probably need to be fully fuelled.

You could have removable fuel containers inside the payload bay of a Starship and it could then simply unload the containers in orbit and several of them could be strapped to the side of the HLS for the trip to the Moon. That might work.
 
it's the same problem spaceships have when travelling in low/zero-G: usually, the tanks have more fuel than needed so that enough can be pumped out, because plenty can't.
The solution is probably using some kind of solid fuel or ion drives.
 
3point14 said:
It does. More mass = less ∆V

But more than that, I think, is that the donor ship absolutely does have to worry about mass, both in terms of ∆V and thrust to weight ratio.
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Same for transferring fuel or cargo from one to the other
 
jeremyp said:
You could have removable fuel containers inside the payload bay of a Starship and it could then simply unload the containers in orbit and several of them could be strapped to the side of the HLS for the trip to the Moon. That might work.
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As I say, like a drop tank.
 
How do they do it on the ISS? I know they often use whichever craft is docked for station keeping, but it also, I think, has it's own engines. Are these refueled?
 
jeremyp said:
That's the point. Your spacecraft can be heavier and more capable if you send the fuel up separately and put it in once in orbit. Yet, they didn't do that even for the Apollo missions. Guess why not.
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Because it was a more complex, riskier solution. They were racing to get to the moon first, not best.

What I can't figure out is why NASA hasn't been pushing for orbital spacecraft assembly ever since. Larger, more capable science probes to all corners of the Solar System seems like an obvious win.
 
jeremyp said:
...snip...


That's the point. Your spacecraft can be heavier and more capable if you send the fuel up separately and put it in once in orbit. Yet, they didn't do that even for the Apollo missions. Guess why not.
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The Apollo missions were the pinnacle of what could be achieved by human craftsmanship. They did use some computers but even these were almost handcrafted, indeed they used rope memory which was literally made by hand by women who had experience of producing textiles! It's hard for us born or grew up after the computer revolution to grasp how hard some things are to achieve when computers can't be used, when you don't have access to all our IC sensors and decades of software development. Calculations that simply couldn't have been done in realtime back then can now be done in milliseconds.
 
arthwollipot said:
Based on the fact that humans have been pumping liquids against various gradients for centuries! I regret this whole conversation now!
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Pumping against a gradient isn't the problem. Pumping without a gradient is the problem.

Acceleration due to gravity ensures delivery of the fluid to a well-placed pump. Ullage motors provide acceleration in microgravity. Maybe that's the solution to bulk fuel transfers.

But honestly, if you're delivering full tanks to orbit, then probably the easiest solution is just to attach the full tanks to your spacecraft, and go from there.
 
theprestige said:
But honestly, if you're delivering full tanks to orbit, then probably the easiest solution is just to attach the full tanks to your spacecraft, and go from there.
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Unfortunately you have the rocket equation to content with in that case. The more fuel you carry, the more fuel you need to carry all the fuel.
 
arthwollipot said:
Unfortunately you have the rocket equation to content with in that case. The more fuel you carry, the more fuel you need to carry all the fuel.
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THIS IS A SOLVED PROBLEM.

The full tank is the payload. We already know all the math for getting max payload tonnage to LEO. A ton of fuel is no different from a ton of satellite or a ton of Mars rover, in terms of fuel-to-payload math.
 
theprestige said:
THIS IS A SOLVED PROBLEM.

The full tank is the payload. We already know all the math for getting max payload tonnage to LEO. A ton of fuel is no different from a ton of satellite or a ton of Mars rover, in terms of fuel-to-payload math.
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The chosen means of transferring the fuel, after consideration of all the alternatives, is the pressure differential between the source and target. I assume that means each subsequent load can only transfer less since to pressure differential gets smaller each time.
 
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I didn't realize pumping a fluid or gas in a weightless environment was all that difficult. Seems a pump and a pressure differential would all that is required.

This is what Google AI has to say.

NASA uses Lead Zirconate Titanate (PZT) mass gaging system to measure the mass of fuel and its location within a tank. Fuel is transferred actively using pumps, and sensors are used to monitor the amount of fuel remaining, tank rigidity, and defects in the tank.
 
acbytesla said:
I didn't realize pumping a fluid or gas in a weightless environment was all that difficult. Seems a pump and a pressure differential would all that is required.

This is what Google AI has to say.

NASA uses Lead Zirconate Titanate (PZT) mass gaging system to measure the mass of fuel and its location within a tank. Fuel is transferred actively using pumps, and sensors are used to monitor the amount of fuel remaining, tank rigidity, and defects in the tank.
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That's all very well when the rocket is accelerating.

The question is what to do when there's no acceleration. How do you create and maintain the pressure differential?

Personally I think it's not a serious problem, but apparently some of us are convinced that it's a major showstopper.
 
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