Hey guys, great stuff above. I had just made an account to suggest some more to this, maybe a bit more detail to the already existing framework you've laid out:
Whilst playing Astroneer I had the issue with going out on long expeditions or having a friend of mine go out, and of course we would become lost somewhere on the other side of the planet. Now you could come up with a network of beacons but then you have to remember which one is the next one and not the previous one, it's a mess in the end. So when this happened to me recently, all I could think of was having some sort of satellite that you could send up with a GPS module and it would slowly (over the course of maybe 2 in-game weeks) make maneuvers and map the planet.
This got me thinking, what if you could have more than just GPS modules? What if you have a scanner that you can use to seek out precious materials both above and below the surface? Or what if you have (as mentioned by others above^) base attachments like those you have on the surface, but for space? You could have 2 different connector pieces, a Probe and a Station. The Probe is a 3 sided triangular prism that holds 2x2 on each side, has a engine on the bottom and a 2x1 on the top. The Station is a bigger rectangular prism that holds 2x4 on each side, an engine on bottom, and a 2x2 on top. You could even use engines that you find already on the surface to construct these as well.
I could imagine the player would simply build and launch these the same way they do the Shuttle and the Spaceship. However, I might suggest it works more like the Trade Platform. A Launchpad perhaps? A place where you build Probes and Station sections onto an existing small rocket engine and launch them into orbit. Once its in orbit it will perform what ever duties it has based on the modules it is equipped with.
As for docking parts together to make a station, you may need a Docking Port module on what ever sides it will be connecting to other pieces. If your satellite has these ports then you can choose to connect them using the Launchpad's interface. This could be displayed as a hologram with points showing each orbital you can send your satellite too.
Eh, I'm just spitballing here, but being a game developer myself, I think something like this would fit very well into the existing game mechanics.
There's my 2 cents!