The guys in the red shirts who beam down with the landing party are not good candidates for recurring roles.

Well they die mostly. I just meant the other bridge staff or staff in general, sometimes you see a person twice, mostly on the next episode then. But there are never recurring characters that are not on the main staff. (Edit: In Tng there is a nurse that is seen more often, that is actually what i mean, why are there not more of those "named" background characters.)

Like a person that is on the bridge now and then, or in the medical station. Those are always new people.

They keep getting into the teletransporter with Kirk, Spock, and Scotty, which is the Kiss of Death...Nobody can survive that!!

Hi. I'll try to answer.

I don't think they always change. On The Original Series there were several actors that were regularly in the background or used for playing small roles. Yes, there were even actors as redshirts that got killed more than once. And there are different types of extras. Most extras come in for a day or two on an episode by episode basis, and will just be put at whatever station that helps make the screen look like it's filled with activity. Sometimes there are a small core group of regular extras that will appear in multiple episodes throughout the season and get paid a little more. I worked a background office worker extra on a TV show for two seasons. On the show Two Broke Girls, some of the regular diner patrons pulled double duty and worked as stand-in's for the main actors during set ups.

Day players (actors with one or more lines) are different. But, like extras, day players are not under a contract, so their appearances are subject to their availability. Basically Trek has always reused actors and does put some effort into trying to retain them, though it's not always possible, and keeping them at the same stations all the time is obviously not a priority.

How sure are you that they don't do exactly this? Have you really paid close enough attention to who is in the background of every scene to know for sure that those same people don't show up in the background of other scenes down the road?

While I am not an expert on this, my understanding is there are 'background actors' who don't have lines, and 'principal performers' who do. An actor can remain background even over an extended period of time, so there's no contractual reason to churn them, but there's also probably not that much benefit to trying to ensure some concept of continuity for individuals in roles where it's not essential to the story.

No i didn't, it was just something that came to mind when i thought about always seeing new persons that i never saw before.

But why is that so important instead of the question i asked, if there is some rule or law that prohibits using extras more than a few times without upping them to cast members?

Thanks, that is more in line of what i meant. They just use new extras because no one really cares. I was just wondering about it because i read about some laws that gives more rights (money, insurance, etc.) to people that are continually employed by a specific show in one role.

Thank for the answer, sheds a little more light on what i asked about. I put too much of star trek stuff into the question i guess, what i am interested in is really only the production side for this question.

There's not a regulation or obligation for upping an extra to a semi-regular extra, or for promoting a day player to a cast member. It's all up to the producers to make those decisions. Colm Meaney is a good example of someone that started out as a day player with an unnamed character that was later given a name and promoted to full cast member. Sometimes it happens like that, but there's no official process for that to happen to every actor.

Thanks again for staying with what i really asked. Colm Meaney is probably the best example for this.

Seems it was a pretty obvious question, i just read that the Screen Actors Guild has some pretty strict rules about stuff like that. Just for example who is mentioned in the credits and where etc. Maybe, what i was thinking about, only applies to movies.

I guess i did overthink this one a bit.

I do background acting on shows and movies. Some tv show directors are very particular about background, like to hand select them and are adamant in the casting calls about "only fresh faces " meaning you had not worked on camera on that production.

I think it just helps with authenticity in their mind. In practice, it doesn't make a huge difference to the average viewer.

I can understand that, as i said in the case of Star Trek those are ships with over a 1000people on board, so it may make sense to always see new people.

Some of the Star Treks made more of an effort about. Voyager had a few extras who were around pretty much the entire series. Understandably, of course. I remember one guy even had his own wiki entry.

Ultimately as others have pointed out it's often a matter of logistics. Someone won't necessarily be available to do extra work for 6+ months of the year, for seven years. Certainly they wouldn't want to be paid the same for that entire time either.

Voyager is a good example for this as it was one isolated ship in a far away place without any crew transfers.

I still think that there were a lot of new people brought into it for extra roles instead of relying on a small pool of people.

I actually should have brought that up in my original post.

I think the various Star Treks do try to keep some sense of recurring extras. Voyager did this as much as they could due to the premise of the show. TNG tended to stick to a handful of day players for the helm position and various other background crew. DS9 had Morn. Discovery's bridge crew has more or less stayed the same since the beginning, existing in a weird state somewhere between day player and actual cast.

It's also not a fixed crew, other than Voyager and Discovery because of their unique circumstances. Realistically, most of the crew would only serve a few years at most at a single post before being transferred and/or promoted somewhere else.

Spock and Riker had the job of creating the work schedules. If it was ALWAYS the same person at the same console that credibility goes down (like Tom Paris, Harry Kim, and Tuvok on Voyager though they were in a situation where they literally couldn't pick up a new qualified Starfleet officer.)