Prepare what you need for session 0.
Where are the players at the start of the sesssion.
Is there a hook for them to go where you want them to go? This could include staying put, or travelling to some definite location.
What do you need/want/expect them to do first session? Prep that.
Prep a disaster plan. If they suddenly decide to go to planet X and become nerf herders and skip everything, have some Mercs start a fight in the hallway and have the group have to fight their way clear.
For a session 0 that involves a post apoc world you need the base where they start. Is the starport still there? If so, why? Is it a highport or lowport? Then a library link or storyteller to relay information about the downfall. Ship records to research/access/bribe to get to discover what ships have gone missing. Have a few names of ships, tonnages, destinations etc.
Using this information the group may figure out the flight parths of the missing ships. Maybe it shows a 'Bermuda Triangle'area where ships go missing. This could be the link to where your mystery ship is, or maybe it is a pirate band, or new political faction, or secret military invasion from another system. You still have options at this point. All the players know is X marks the spot.
Prep a ship encounter with whatever you want to have them encounter. Make it political or a fight, your choice. Or have it be a trader and let them make a deal to lull them into a false sense of safety, THEN have the enemy ship attack.