TWR is only important when lifting off a planet/moon. there, the more thrust you have, the less fuel you submit to gravity. in space however, it makes no difference. you will just have to burn for a while. if you think about it, its simple. its a thrust to WEIGHT ratio. there is no weight in space (with the exception of artificial gravity designs, which have been proven to work in ksp). the thrust to weight ratio depends on the gravity of whatever planet you are on.