Research Antigravitation technology and the build Air Field to perform Recon missions. Once you've done that, purchase several Recon Drones. Send Recon Drones to the other player's Sector to gather intelligence. Your Combat Advisor will inform you on your recon mission's outcome and collected information.
Recon missions allow you to get full information about the number and type of Troops in other Sectors and about the amount of Resources you can raid from that Sector. Your Recon Drones can be defeated by reconned Sector's Drones while performing the mission.
Recon missions can be performed in 3 ways: