The total fuel required is the same in both cases, but to do it in a single trip the upper stage would have to be nearly twice as large and the lower stage exac

The total fuel required is the same in both cases, but to do it in a single trip the upper stage would have to be nearly twice as large and the lower stage exactly twice as large. This is already far larger than anything that has been done before, so making it twice the size would be a significant problem.