Here is the full list of all 12 Orbital Gear achievements.
Destroy 100 buildings in Orbital Warfare
Kill 500 Gears
Get the most kills in a match
Stop 50 projectiles with shields
Get the most assists in a match
Shoot down 10 projectiles
Kill 10 Gears with Mines
Knock an opponent out of the stage
Kill two Gears without landing
Kill the same player three times in a row
Hit two players with the same Gauntlet attack
Hit two players with the same Discharger shot