I believe you will find the tech to research it directly a little bit later on. I'm currenly in 2380 and can make them but can't remember how far back it was when I researched it. Just keep going for a bit. Cheers!

you can build deep space stations when you unlock the unity perk ,then go to empty system where you want to place one right click a emty planet and you get the option to build megastructure, mind though you can only have 3, they are very usefull for frontline duty repair ships etc.

I didn't realize it was with unity perks.

Thanks!

Yeah, it's very misleading as the research tree almost forces you to research deep-space related techs even when you can't / will never build them. Frankly, it's a bit of a weird mechanic, especially for the federation that should be the first and foremost user of those stations.

What I mean is that due to the very multi-species nature of the Federation, they have access to way more colonisable planets which are way better than deep space stations. Yet, in canon, they have a lot of "Starbases" which are in fact deep space stations. This just doesn't work in Stellaris, having both is overkill and those stations should supplement a lack of colonisable planets.

In the end, you end up with a situation where you never build deep-space stations as the federation but you could really use them as another species... but don't because those species profit very little of the expensionist unity tree. Ugh.