Here is the full list of all 15 Gearbits achievements.
Complete the final mission
Squash 1 000 bugs
Squash 2500 bugs
Squash 5 000 bugs
Shoot down 50 enemy pilots
Shoot down 250 enemy pilots
Purchase ten weapons
Purchase all weapons
Purchase five GBs
Purchase nine GBs
Unlock the final GB
Get shot down 10 times
Clear 8 or more waves with "100% bug" and "Catastrophic escalation" parameters
Clear 15 or more waves with any parameters
Complete all missions with the Mirabilis regular type