I generated a new world, punched down a tree, was breaking the dirt under the tree, and i crashed before it finished breaking. Here is the log: http://pastebin.com/jvtzbVK1
I hope this helps

Looks like galactic craft can't write to a specific directory:

[14:19:54] [Client thread/INFO] [STDERR]: [micdoodle8.mods.galacticraft.core.network.PacketSimple:handleClientSide:781]: Cannot create directory %minecraftDir%/assets/temp!

Did it create a crash report with more information, maybe?

None besides the standard logs, unfortunately.

I'm not entirely sure if this is the reason of the crash, but you could try to delete the tmp directory at
C:\Users\Brooks\AppData\Roaming\.mineyourmind\instances\MyM-GalacticScience\minecraft\

I will close this for now. If it happens again feel free to reopen it.