Generally speaking, interstellar travel outside the stargate network is uncommon, many systems go years without seeing a starship. Still, a small minority of people make their living voyaging from star to star. These nomads generally fall under one of three categories: traders, explorers/researchers, and military. The third category probably has the largest population at a given time but also the highest turnover rate.
The Federal Guard is the only governmental military with interstellar reach, though they tend to act more like a police force than military, lacking enemies with even close to comparable power. The few outworlds with space navies are usually no match for even a civilian Federation freighter, and the Destroyers are so dreaded that the Guard’s standing orders in case of an encounter are to evacuate as many civilians as possible before retreating at full throttle. It’s common for restless citizens to sign up for a 50-year term of duty (up to 80% of the time spent in stasis) with the Guard, then transition back to civilian life almost seamlessly. Those who find that they enjoy the interstellar life may sign up for another term or seek employment as a trader or explorer. Others may have been expecting more “action” when they signed up, or actually were in combat once or twice and found they enjoyed it a bit too much. Those parahumans might end up going private.
Private Military Contractors have only three legal roles in Federation space: claim protection, colony security, and training, and a company with a long-term contract may end up filling all three in sequence. Before a colony is established there is a lot of preparatory work to do, and with the spotty nature of interstellar communications more than once has a planetary claim been grabbed by another group before the one who cirst filed the claim even had the chance to launch. While there’s usually enough room on a planet for multiple colonies these “misunderstandings” tend to result in a lot of friction, and so settlement companies might hire mercenaries to land first and enforce their claim. These mercenaries will typically receive the job notice on the stargate’s laser network and the company stationed closest to the destination system will generally get the job, most colonists come from the more densely populated core worlds while PMCs tend to find the most employment out on the frontier, it’s convenient. Upon arriving the mercenary company will deploy orbital sensor and weapons platforms and nanofab an air-droppable forward base from an asteroid or two. Most of the company will remain in stasis until another ship arrives though a few will remain awake in shifts to watch for intruders or suppress hostile fauna if the planet is inhabitable without terraforming. If a ship that doesn’t belong to their clients arrives after them the interlopers can usually be turned back, disappointed but unharmed. Still, there’s little to no oversight out there on the edges of the frontier and more than once the would-be claimjumpers have have tried taking the planet by force. There are also rumors of mercenary companies that arrived to find claimjumpers already entrenched in the system, with messy but unconfirmed results.
After the colony has been established the PMCs can act as the colony’s home guard, defending the settlement from bandits or pirates, occasionally helping settle disputes within the colony or with rivals. When the colony gets around to founding their own home guard the mercenaries help to train them. Once that final phase is complete the mercenary company will typically collect their pay, with all the interest accumulated, and leave. Most of the time they’ll work with agents in the core worlds who will forward them job contracts via a quantum link and will have a new contract waiting before they finish their last one.
Outside the Federation’s borders, however, all bets are off. The Federal Guard maintains a small patrol in any outworld system, often just a single cruiser/AKV carrier, but so long as no one brings non-implanted nanotech down to the planet’s surface they usually won’t take notice. For long-term campaigns mercenary companies will plant a nanofab seed in the system’s asteroid belt and use it to manufacture their supplies and armory, air-dropping when needed, similar to how most traders sell physical products to primitive worlds.
In the outworlds there are far fewer restrictions on what mercenaries can and can’t do, missions range from securing sites for trade enclaves to outright conquest. Some outworld governments may have limited access to the Federation’s communications network and use it to hire mercs for wars with other powers on the same planet. Unscrupulous traders may find a given outworld nation’s policies “troublesome” and want them “persuaded”. Or a Crusader sect of the Noospherists could see an opportunity to “civilize” some “ignorant savages”, in fact Crusaders frequently form mercenary companies for this very purpose.
When fighting outworlders mercenaries usually find themselves highly outnumbered but much better armed as even the least regressed outworlds lack access to nanofabbed materiel or medical microbots. However, there’s always the risk of a lucky bullet scrambling the brainpan beyond the ability of microbots to repair or worse, the enemy also hiring mercenaries. For those reasons many mercs call it quits after their first mission in the outworlds, taking only Federation-space contracts or quitting the soldier-of-fortune life altogether and returning to civilian life, assuming that they have access to a ship going back into Federation-space that is.