Here is the full list of all 39 1971 Project Helios achievements worth 1,000 gamerscore.
Complete Level 1
Find the Fulgor Tank
Use Fulgor to defreeze, decrease cooldown. and reanimate (in the same combat)
Émile killed 50 enemies
Hanna killed 50 enemies
Renzo killed 50 enemies
Ame killed 50 enemies
Wilhelm killed 50 enemies
Alina killed 50 enemies
Alexei killed 50 enemies
Domi killed 50 enemies
Kill 30 Scavengers
Kill 100 Scavengers
Kill 200 Scavengers
Kill 30 Wintersöhne
Kill 100 Wintersöhne
Kill 200 Wintersöhne
Kill 30 Kaphirites
Kill 100 Kaphirites
Kill 200 Kaphirites
Use a grenade to remove stun from an ally unit
Kill 3 or more enemy units with a single grenade
Do "Overwatch + Push" combo 5 times
Shot 20 tiles away.
Kill a Blade
Kill all the Blades
Pet Ricotta in the Campfire
Wait 4 minutes without doing any action in your turn (in combat)
Finish level 7 with Wilhelm in your squad
Lose and replay the same combat 3 times
Reach Ending 1 (and complete its Epilogue)
Reach Ending 2 (and complete its Epilogue)
Reach Ending 3 (and complete its Epilogue)
Kill the Master
Read all Campfire dialogues
Finish the game for the first time
Reach the three Endings (and complete the three Epilogues)
Find all documents in the game
Unlock all other achievements