[patchwork]

In terms of creating a billet where PCs are sometimes obligated to be with the ship but sometimes off doing their own thing, I'm reminded of a campaign taking Australian colonization as its model, where the expedition includes a few somewhat rich entrepreneurs outside the formal chain of command who are going along because they've secured a contract that lets them use convict labor; I'm going to assume you don't want a penal colony full of convict labor as your campaign premise, but the basic framework can still work depending on how you've set up the politics and economics back home. If we imagine a military or government that controls the bleeding edge tech - wormhole drives, AGI, swarm robotics - but for cultural or economic reasons has a very hard time attracting good human talent, you could wind up with a situation where people enter into employment contracts with the exploration corps in order to get access to that sweet tech, but are technically independent vendors, not crew members. When I served on a US aircraft carrier, we definitely had employees of Northrup-Grumman and similar companies on board as technical representatives; that too can serve as a model. As can the "embedded journalist" sometimes accompanying modern military units into warzones. They have a contract with the military which significantly limits their actions, but also they can't be ordered around the way a servicemember can. I'd dial that up to 11 - the regime has to bend over backwards to find technically skilled people so the techreps get a lot of private time and vacations in their contracts (and the service cannot function without techreps). Depending on the size of ship and length of mission, they can also be family members or counselors of crew rather than crew themselves. Although that may automatically make you part of the reserves.