Some sort of disaster in a spaceport highport. All the players are simply in the same lounge waiting for a liner to come in to travel to somewhere either in the next system or some other planet in the system. A few might be returning from such a voyage and are simply waiting for transport down to the planet's surface.
They can be hanging around, then something happens to the highport. The best candidates for this kind of thing are either terrorists/guerillas taking over highport, a surprise attack (or even a deep penetration raid by an existing war foe), or something along those veins. The attack doesn't actually have to even hit the highport, even the announcement that there's an enemy fleet that's right now some hours away will trigger panic. The point is that situation will force the players to work together, even if they're normally not the kinds to work together.
What the actual point of the adventure is up to you, but it will fall into a few general categories:
1) During the Rebellion, or during some Frontier War, a large fleet of Lucan's Navy / Zhodani jump into the system and start burning towards the world the players are in orbit around. It's going to be an invasion or even a "black war" strike where they'll just show up, try and do as much damage as possible, then leave. Obviously, the highport isn't going to be ignored. The point of the adventure is for the players to work together to leave the station having secured passage out of the system. They'll have to work against pretty much everyone else on the station, hundreds of people want off of the station ASAP and they're just as desperate as the players. Obeying "the authorities" would simply mean being left behind - there'll always be more important nobles / starport administrators / and so on who can use rank or Imperial Warrants to commandeer ships leaving the players along with everyone else without a ride. And you don't want to be here when the enemy arrives. Obviously, if players have their own ships, you can have them either impounded somewhere (if they're lawless types), down for annual maintenance in some remote slip, or commandeered by some other group before they can get to it. Either way, there should only be one ship they figure they can get a ride on, if they can get there in time.
2) The Enemy Takes Over The Highport. The players have to work together to defeat the enemy who have taken over the highport. Some players are going to suggest simply sitting tight and waiting for outside forces to negotiate an end to the situation, however, the players realize that the enemy have no real intention of taking over the starport at all. They're simply buying enough time to get a political message transmitted before blowing up the highport along with everyone in it (including themselves) in a suicide attack.
3) Some sort of disaster. A mysterious explosion destroys a lot of the highport, leaving it as a burning wreck (it's burning its own atmosphere) in a rapidly decaying orbit. The players have to navigate through the rickety wreck to reach a ship. Some players will probably want to try using emergency rescue balls or whatever, but show they've either all launched or appear to be sabotaged in some fashion. As the players move through the wreckage, they might start to wonder why their lounge was the only one where the safety devices worked and perhaps they might realize that their lounge was sabotaged too, but for whatever reason the sabotage on their lounge didn't work...