to get out of your megaship you need to have one first then you go to your back right side of your megaship while pressing shift and move forward out into space hope you have funXD

if you want to get back into your mega mothership you have to restart the game then it will bring you back into the ship however you still can build and remove blocks while in space

once you are out of the mothership you can do many things including flying anywhere in the whole universe. WARNING it takes a long time to go to a select destination in space so be understanding that it will take a long time to get to select destination