Here is the full list of all 12 Dragons in Space trophies - there are 11 gold and 1 platinum.
Dragons defeated
Obtain 3 stars on level 1
Obtain 3 stars on level 2
Obtain 3 stars on level 3
Obtain 3 stars on level 4
Obtain 3 stars on level 5
Obtain 3 stars on level 6
Obtain 3 stars on level 7
Obtain 3 stars on level 8
Kill 50 enemies without taking damage
Defeat final boss
Die