There’s no such thing, I think this is in the genre of “I wish there was a solution to this problem, and I’m sure throwing billions of dollars at it will solve it, so let’s try and see what happens”.
You accelerate toward your target at 1g. Ship is built with the floors toward the engines. Halfway there, you flip the ship around and decelerate at 1g until you reach your target.
The point being, also according to Musk; “The best part is no part. The best system is no system.”