The real problem, as always, is the hard problem of consciousness, which in practice screws all the assumptions of monkeys in tin cans. Before we discuss drive

The real problem, as always, is the hard problem of consciousness, which in practice screws all the assumptions of monkeys in tin cans. Before we discuss drive designs, we have to understand what the limitations on travel are for us. There is a very real sense in which we could send a million space ships and not care whether they make it or not, or whether our missiles are conscious and no different from space-ships and so on. The mass and propellant stuff works out the same, but the practical consequences are so different that it's hard to think seriously about any of these problems, when the actual problem is mind and not rocketry.