For the first session of the campaign, I want to start the PCs in media res, pretty much right at the beginning of their first action scene. But, being the first session of the campaign, I'm concerned the setup of the scene will take away from the feel of beginning it in the action.

The background of the scene: the PCs have been hired by a scout to serve as his crew on his mission to survey a planet whose coordinates he wants to sell for big money. The PCs are to make a cut of that price.

The setup of the scene: the ship is parked in a savannah next to a lazy river, and the scout has wandered off to check something out. The PCs are back at the ship, doing whatever, waiting for his return.

The scene: the PCs begin hearing distant shouts of "run!" coming from the direction the scout went off in. Very soon, they see him cresting over a low rise, running toward the ship and gesturing wildly at them. It quickly becomes evident as he comes into view he is being chased by a fistful of gundarks. Roll initiative.

Simple enough, right? I'm stealing the beginning of Raiders of the Lost Ark, but from Jock's point of view.

My concern is needing/wanting to know what their characters are doing when the scene begins, but not wanting the moment of action ruined by a round table discussion of minutiae and arguments of "I would totally be on guard at all times!"

Do I, more or less, dictate what each of them is doing at that moment based on what their role or skills are?

Do I ask them ahead of time, like during Session 0 or character creation, for 3 or 4 or 5 activities of what they might do on the ship when they're relaxing in between scenes and then randomly roll one for each? (That could be a useful chart for future encounters as well.)

Something else?

My concern is needing/wanting to know what their characters are doing when the scene begins, but not wanting the moment of action ruined by a round table discussion of minutiae and arguments of "I would totally be on guard at all times!"

Do I, more or less, dictate what each of them is doing at that moment based on what their role or skills are?

Do I ask them ahead of time, like during Session 0 or character creation, for 3 or 4 or 5 activities of what they might do on the ship when they're relaxing in between scenes and then randomly roll one for each? (That could be a useful chart for future encounters as well.)

Something else?

If anyone wants to say they're on guard all the time, that can easily be proven with a Vigilance check. Even the most alert fightin' type might be seduced into relaxing in such bucolic beauty.

You could certainly set the scene in Session Zero, but that might ruin the surprise. I don't think it impinges player agency to set the scene including what their characters are doing right at that moment.

Have you thought about them landing near the ruins of what appears to be a settlement?

So parked by a river mention there are fish, it looks like what a river would be here and it appears idyllic.

If they investigate the settlement let them stumble into the basement discovering this was once a thriving Republic settlement until they were forcibly relocated by Imperial stormtroopers for reasons unknown.

Then as they're still down there have your scout start running back to the ship announcing over their come he's being pursued by Gundarks and they need to lift off as soon as he gets back to the ship... THEN ask them to roll initiative and let their reaction decide where you go from there!

I do like to use in media res from time to time. Sometimes, I'll give a tiny bit of detail to allow some preparation for what they can reasonably expect. For example, GM: You're going to a jungle world this time. Player 1: OK, I want to have adverse environment gear for that climate and some bogfly repellent.

In one adventure, I started them off in a bad spot with little time to prepare, so I flipped a Destiny point in their favor at the beginning, so that they could either have fortune on their side in solving the problem, or introduce a fact later on. GM: The bogflies are swarming around you, for one setback on all skill checks. Player flipping the extra Destiny: Good thing we brought repellent!

The players can absolutely describe what the characters would be doing, but as TheMensch pointed out (as I was typing the above) how successful they are at those things is defined by their scores.

Character creation is a good time to point out that some skills reflect personality traits.

Brave/Unflinching=Discipline or Cool

Always on his guard=Vigilance

Intimidating= Coercion (and a Talent)

Would making an opening crawl help take some of that scene-setting burden off of you? Or, use a basic map and/or a general picture resembling the area to decrease setting description time.

You could always go the old school WEG route and write up a short script. Say about one or two lines for each player that establishes the situation and then dumps them right into combat.

Player one: Pass me that hydrospanner, the antenna on this scanning unit is stuck again.
Player two: More of those river flies stuck in the extension motor probably... when it's not the heat, its the flies, when it's not the flies it's those critters with the teeth and stripes... I hate these scout jobs, I never know what to call these creatures and I don't even want to think about the horrible diseases we'll probably discover...
Player three: So think about the money. Dr. Spaalderston promised us each half a percent of the planets market sale price. That's.....ummm... well it's a lot.... Hey Doc! Doc? Where'd he go?
Player four: He went to go check out a hill nearby...oh look, there he is coming over the ridge now! Man he is really running. I know I grill a mean whatever this is, but I didn't think it was that good.
Player five: It's not. Look, he's got company!
Player six: I've got a bad feeling about this...

Players 1-3 start Engaged with each other around a field scanning unit. 4-6 Are engaged with each other around a field kitchen. Both groups are Short to each other Extreme to the Doc, and Medium to the scoutship.

Go.

"In media res" doesn't have to be right when the action starts. You can start the adventure as the group lands on the mysterious, yet peaceful and quiet planet or even as they're in hyperspace on the way to the planet.

Then once they land you can give them a chance to perhaps set up camp or just explore the nearby surrounding area. After a bit of exposition, you can throw the gundarks on them.

Some very good ideas here. Thanks!

An opening crawl would help set up the scene without having to actually say a lot. And it lends very well to the feel of Star Wars of course.

I think I'll have them roll Vigilance checks for initiative, but have it be an Easy roll instead of Simple. I'll flip a Destiny point to make it a Challenge die. Then we can determine in the story what each character was/is up to by what they rolled.