OK so that was a little long and ridiculous but if done MY way, it's 100% possible!
For day 6 send 50 BLUE pikmin after that bridge leading to the Sagittarius provided that you already built the other bridge (if you didn't you're totally screwed), and send 50 blue pikmin after that partially submerged wall leading to the Nova Blaster.
Then send 30 blue pikmin after the Sagittarius itself and send 70 blue pikmin after the dark dirt wall leading to the Armored Cannon Beetle and the Radiation Canopy.
Then get the Armored Cannon Beetle (and send its carcass back to an Onion), the Radiation Canopy and get the Geiger Counter any way you want with the blue pikmin (and 3 yellow pikmin, if you didn't get the light rock wall earlier).
If you need more help, we've got more Pikmin cheats and also check out all of the answers for this game
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