I’m a space systems propulsion design engineer by profession. I worked on a project which I will not name that requires on-orbit refuelling. (It’s not this one and I don’t and will never work for Elon Musk).
The technology for in-orbit refuelling doesn’t exist, and there’s a whole lot of new technology required. Remotely docking is akin to self-driving in complexity; don’t forget to factor in the signal delay if you’re in a lunar or translunar orbit. If you make this a crewed activity only, then the problem becomes one of pneumatics. A pressure system that can reliably contain and transfer pressure up to the levels of spacecraft fuel (around 300 psi for liquid, 3000 for gas) repeatedly, in both directions is very, very heavy. The valves are heavy, the tanks are heavy, the control systems are heavy. Too heavy to be considered viable for spaceflight. Even less so for a mission whose payload is “as much transfer fuel as we can possibly get up there”. A huge amount of innovation has to take place before this can become real. As of 2022, when I last worked on this, none of the technology was even being researched, that is to say it was not even at TRL 3. Typically these things take on the order of a decade or so to get to TRL 9, if they are successful and quick.
I’m not saying it’s impossible, I’m saying I’ll be fascinated to see which solutions they come up with, and that I’m sceptical that they do have current solutions which are feasible and useful, rather than something like a one-shot refueling subsystem that weighs 250kg and delivers 15 litres of hydrazine.
I’m a space systems propulsion design engineer by profession. I worked on a project which I will not name that requires on-orbit refuelling. (It’s not this one and I don’t and will never work for Elon Musk).
The technology for in-orbit refuelling doesn’t exist, and there’s a whole lot of new technology required. Remotely docking is akin to self-driving in complexity; don’t forget to factor in the signal delay if you’re in a lunar or translunar orbit. If you make this a crewed activity only, then the problem becomes one of pneumatics. A pressure system that can reliably contain and transfer pressure up to the levels of spacecraft fuel (around 300 psi for liquid, 3000 for gas) repeatedly, in both directions is very, very heavy. The valves are heavy, the tanks are heavy, the control systems are heavy. Too heavy to be considered viable for spaceflight. Even less so for a mission whose payload is “as much transfer fuel as we can possibly get up there”. A huge amount of innovation has to take place before this can become real. As of 2022, when I last worked on this, none of the technology was even being researched, that is to say it was not even at TRL 3. Typically these things take on the order of a decade or so to get to TRL 9, if they are successful and quick.
I’m not saying it’s impossible, I’m saying I’ll be fascinated to see which solutions they come up with, and that I’m sceptical that they do have current solutions which are feasible and useful, rather than something like a one-shot refueling subsystem that weighs 250kg and delivers 15 litres of hydrazine.