Here is the full list of all 16 GravNewton achievements.
Get S-rank on all Sectors
Get S-rank on 6 Sectors
Compleat Sector 12
Compleat Sector 11
Die 100 times on same sector
Compleat Sector 10
Compleat Sector 9
Compleat Sector 8
Get a S-rank on any sector
Compleat Sector 7
Compleat Sector 6
Compleat Sector 5
Compleat Sector 4
Compleat Sector 3
Compleat Sector 2
Compleat Sector 1