Here is the full list of all 31 Headlander achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Took Methuselah offline
100% Headlander
Popped your head into every room to have a look-see
Defeated the Methuselah titan
Found all mid-range zap locations
Used Overcharge Boost to take out 25 enemies
Kill Mappy without taking his Data
Found the entrance to Methuselah's Core
Found all alpha, beta and gamma terminals
Played a game of H.O.R.S.E.
Found a power gem charging Shepherd and returned it to Rhea-6
Unlocked all upgrades
Found your body and witnessed ERL's sacrifice
Drained all of the Energy S.A.C.s
Found all the bodies for Athena-7
Used the long range zap to Luna Citadel
Defeated the Kill Queen
Uploaded the Archive Data to Earl
Shut down the power stations in the Power Dome to gain access to the Archives
Destroyed 25 enemies using melee attacks
Eradicated the Spectrum Shepherds
Executed 50 headshots
Aligned the Satellite Chalet dishes to gain access to the Archives
Found Frank the Dog and return him to Eudora-5
Thrusted through the Pleasure Port to find the Satellite Chalet
Used explosions to kill 5 enemies
Escaped the Starcophagus to crash land on the Pleasure Port
Execute all possible dance subroutines
Boosted for 5.2155e-13 parsecs (10 miles)
Used Auto Sentries to take out 10 enemies
Docked with every body type