How to incrase the happiness of the Dwellers that are out exploring? It will go up if they do a 'coffee break'?

That only means those dwellers are not the outgoing type. Send out different dwellers.

Assgn them to rooms based on their highest SPECIAL status, surely it will make them happier.

So I kinda have to manually make them happy

I have not had an explorer get more happy than how they left. sometimes they get a bit less happy. When they get back, send em off to date. they get happy

First post on the boards and its magically somehow a double post. Whoops.

See below for my proper post!

No, coffee breaks do not help. I have found that putting dwellers in rooms associated with any of their special stats 3 or higher increases it to a base of apparently 75%. Though I do have a triple-room radio station manned by 6 level 10 charisma dwellers, so it could actually be lower. And yes, radio stations definitely effect happiness. Seems like every time the timer rolls over for a chance at a new dweller, any of my dwellers under 75% happiness gain anywhere from 1-5% happiness from them. Be warned! Removing a person from the radio station room will decrease the happiness of EVERYONE in your vault by at least 1%. This seems to include when you move a dweller out of the radio room just to do something like fight a neighboring fire.

What I know for a FACT is that having them get baby making always brings them to 100% happiness. Also, if a dweller is in a room that can be rushed, and you rush successfully, their happiness increases by 10% for each successful rush. They lose 10% happiness plus a tiny bit more if you fail the rush. Even if the dweller has only 1 point in the Special stat of a room, they will still get 10% happiness when that room is rushed. But it will start to degrade not to oon after the rush, since the dweller i in a position they don't like.

Being on a coffee break does not effect happiness. While exploring, a dweller cannot gain or lose happiness, unless they die out in the wasteland and you revive them.

Also, I don't know if its given to you no matter what your grade, but I've always had my vaults happiness at A- or above (90%+) and when I finished getting graded for the week, I'm always given a lunchbox on the 7th day.

Hope this helps.