Good Day 
Team i read that you can only use 1 mod but these mods work together as 1
Version : 1.12.2
mods
Galacticraft
: https://micdoodle8.com/mods/galacticraft/downloads
Extra planets
: http://www.9minecraft.net/extra-planets-mod/
mjrlegendslib(Required for Extra planets as Galacticraft has needed mods)
: https://minecraft.curseforge.com/projects/mjrlegendslib
extra planets is an addon to the great world of galacticraft which expands the gameplay with tons of more features and adds tier 4 to 10 rockets and dungeons aswell as atleast 1 planet for each rocket
Thankyou Team