In the missionScripts, what exactly is hidden behind these?
- type: recon
- type: invasion
Would be really helpful to know the details 
And how to add new alien missions without adding them under "missionScript" ?
Each of those generates a random mission from the mission table, starting on the month defined. The mission table is composed of all the alienMissions defined in regions (example: STR_ALIEN_BASE: 20)
To add a new mission you need to define it first under alienMissions (and add the relevant entries to regions, etc.), and then use the missionScripts to define the conditions where it can be generated.
