I dont think that the transaction speed will be that different. We have seen how astronauts make live video calls to the Earth with good graphics pictures. That means that we already now have a technology to transfer heavy streaming videos from out of space. What a blockchain or regular bank (swift) transaction? Just a number of bytes. By the time technology develops so much that will allow us to fly from populated planet A to populated planet B, data transfer would be so fast, that it wont matter what you send.
But I think future payments in space a still very far. Space payment will be on when we will have a unite currency on Earth. And having one unite currency in every country looks impossible to me.
The difference is that crypto is actually digital, so when you send something like a bitcoin to someone in mars, then you are already sending it and you do not have to do anything anymore, you are done. Whereas the difference is that if you are sending money in bytes and that's it in fiat, then you are not actually having paper there at all, in the regular world we could just send money trucks in between banks and it would work and there are no issues, if one bank store is getting too much compared to what they have, they will send it to main headquarters and all that.
What are we going to do, if I send 10 billion dollars to a bank in mars, then what are we going to do? Not like people could withdraw that in mars, not like we can withdraw 10 billion here neither, but in the end we are going to be at least having the money there, with the mars one we need to send the paper version there as well. This is the slow part.
