> Also conservation of energy. Thrust can't vary by velocity because there's no such thing as absolute velocity. So your velocity (relative to whatever) keeps i

> Also conservation of energy. Thrust can't vary by velocity because there's no such thing as absolute velocity. So your velocity (relative to whatever) keeps increasing linearly, while kinetic energy increases quadratically. At some point you start getting more energy out than you put in. Can you explain why photonic rockets are not breaking conservation of energy using this reasoning? They have the same property you describe, but are considered feasible as far as I understand (if unpractical to implement).