"Group B" has acquired [Plot-device] and it is able to deliver over time infinite energy of the type needed for the story to work.
They decide to place it on the most powerful space engine known to man Anno Domini 2017, place it on max thrust for 2 light years, turn the rocket around and then brake for 2 light years.
- The ship is optimized for best case scenario and does not weigh more than what is needed for the duration of the trip (size of crew compartment is depending on the travel time), the longer the travel time the more weight is needed.
- [Plot-device] weighs roughly the same amount as the motors will do.
- [Plot-device] has enough energy to deliver power to any kind of motor existing, (depending on configuration - several motors can be used)
how long time would it take to get there?