Satellites can boost unit effectiveness By providing real time information on enemy approaches.
It can also increase nuke detection and blocking by the vds.
By providing imaging capabilities, it can increase resource production as well
It can also boost spy effectiveness too.
But seeing as this project will be heavily OP, either make the cost ultra huge or make it an alliance project-one nation in an alliance has it and gets 100% of its effectiveness with all other nations in the alliance getting to use a small percentage, say 1%, of the effects, fixed to a cap of say 5% of the total effectiveness of the project.