Here is the full list of all 12 ORBIT achievements worth 1,000 gamerscore. It takes around 6-8 hours to unlock all of the achievements on Xbox One.
Play mayhem and tournament
Observe all orbitals
Play a map created in forge
Max out all ability tech trees
Play all mayhem modes
Destroy 1000 enemy ships
Annihilate a player in Annihilate after you have been annihilated
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Play 50 tournaments
Kill a player through a wormhole
Keep a rocket intact for more than one minute
Win a round of Survive without dying