[Space/Spaceships] Getting the velocity/Delta V I want with the tech I want

[malloyd]

Originally Posted by johndallman

Those were carrying goods (such as spices) that were both lightweight and extremely valuable, rather than more general trade. Also, sailing ships were a technology that was quite economical to run, didn't have to carry their propulsive energy with them and provided a very low standard of living for their crews. Spaceships don't usually meet those criteria.

Actually spaceships on a freight run 4 years long probably should meet the second of those, since there's no good reason to have any crew at all.

And the freight *better* be high value for its weight. Even at perfect efficiency, getting your ship up to 300 mps and back down uses energy thtn has never been cheaper than on the order of $1000 per pound. So if you can't charge $1000 per pound for it, your freight run is a money loser even if the other operating costs are zero and cargo (and ships!) are free at the point of origin.

It's next to impossible to make interstellar trade make sense in a realistic setting, since any civilization that can actually build a starship is going to be able to make anything at home more cheaply than they could ship it back. Even if they have to assemble it atom by atom. And you can send the atomic scale blueprint without a starship.