Is there a way to put orbital units very far away from cities?

Solution 1:

Supremacy level 6 grants you orbital coverage around all Firaxite resources, which would allow you to deploy orbital units near your enemy provided that they have sources of Firaxite within a useful range (the range of the orbital unit plus one, effectively, provided this doesn't conflict with existing orbital unit deployments).

Beyond that, your best bet is to simply stretch the orbital coverage of your cities to the max, especially if one of them is on the coast nearest your target. Launch Complexes and Neoplanitariums increase orbital coverage by 3 tiles each, added to the starting range of 4. If you're able to create the Stellar Codex wonder, that grants an additional 4 tiles of orbital coverage.

There are a few quests which have the option of increasing orbital coverage as well when certain buildings are constructed:

• "Engineering the Future" (Repair Facility): +1 orbital coverage (vs. 5% military unit production)
• "Escape Velocity" (Launch Complex): +1 orbital coverage (vs. 10% orbital unit production)
• "Filling the Void" (Field Reactor): +2 orbital coverage (vs. 5% energy yield)
• "The Stars Our Destination" (Neoplanitarium): +2 obrbital coverage (vs. 10% orbital unit production*)

With all of these bonuses combined, your cities will have an orbital range of 16 tiles, and the city with the Stellar Codex will have an orbital range of 20 tiles (plus the effective range of whichever unit you're trying to launch, minus one). Whether or not this is enough to span across the ocean depends on how large the ocean is**.

I believe that if you create the Harmony unique unit the Rocktopus, it can launch into orbit from any tile, though it's painfully slow one-tile movement likely makes that a less-than-viable option for far away targets.

_{*At least according to the description text, I couldn't actually find this bonus in the perks file for some reason
**Admittedly for this reason I typically find that using naval units is the far easier approach, especially if they have increased firing range and/or move after attack.}