[Valgrim]

Not only that, but there are quite a few scientifically sound concepts that escape the tyranny of the rocket equation. Pre-seeded trajectories, particle beam propulsion, sails etc. Breaking the wall of light might not be possible but beating the current rockets by orders of magnitudes is enough for interstellar travel. And that is only an engineering problem.

My personal favorite these days is innumerable 'smart' pellets, bacteria sized, steering themselves using albedo-changing surfaces toward the ship's magnetic sail to transfer their momentum, allowing for constant acceleration.

[DrierCycle]

It's not an "engineering" problem, it's almost always a physics problem. If life is involved it's also an ecological and bio problem.