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