From Outscape Wiki
As of Alpha 3 A planetary assault is an attack to conquer a planet from another player. Also see Raid if you are merely attempting to steal some resources.
To succeed in a Planetary attack of this kind you will need to defeat any defending troops with troops carried by the specialised Assault Troop Carriers built into at least some of the attacking ships
As every planet at least has its Home guard to defend it don't even consider an attack unless you can muster in a single invasion fleet at least 5% of the planets population as troops.
All troops in an invasion attempt currently have to be delivered in one go, which means from a single fleet. At present only Ships from the Frigate tech tree and one or two [Corvette | others ]] can carry troops you will have to use the Ship Design rules to make up specialised ships for this purpose.
Once your fleet(s) are ready you can make the attempt.
For an assault to proceed you will have to clear the planets orbit of any and all foreign ships. You can not launch an attack until you control Orbital space.
- Orbital Guns will deliver their damage to the attacking fleet(s) to enter orbit after the last defending ship is destroyed. If a fleet with troops on board survives this. You have a time period while the Orbital guns recharge. See Orbit Defense System for full details on their operation.
- Even if they are recharging one or more Orbit Defense System will destroy a proportion of any troops you send to the planet. This is a flat percentage of the total you send 25%/50%/75% depending on the best Orbital Gun remaining on the planet. Multiple Guns should not combine their defence ratings (But some have a reported that they do - please Bug report if you discover this)
If you discover the defending planet has these guns or an overwhelming number of troops you will need to consider using Orbital Bombers to reduce numbers or stand a chance of destroying one of the Guns.
Select the fleet with troops (or the first one if you have more than one) now click on the planet. A New options will appear alongside "Enter Orbit" or "Colonise" : Assault planet, & steal resources.