Download and extract to a new folder. Name the folder "ZZZ_SSSPatches"
Put into KSP Folder -> Gamedata
Do NOT put into KSP RP1/RO Folder.

This adds all the payloads for the Space Shuttle System for Realistic Progression 1 (RP1).
All pieces require the Space Shuttles tech tree node to obtain.

Ku-band antennas are under "Communication" category
Spacelab, both Spacehabs and science tunnel under "Science" category
The rest of the parts are under "Structural" tab

Ku-band cost 1000, other parts cost 200. 0 Entry cost.
If needed, you may adjust the cost for the parts in the .cfg file.

For reference, here is some background for the Space Shuttle's Extended Duration Orbiter Program and the Spacehab/Spacelab program.
EDO: https://en.wikipedia.org/wiki/Extended_Duration_Orbiter
Spacelab: https://en.wikipedia.org/wiki/Spacelab
Spacehab: https://en.wikipedia.org/wiki/Astrotech_Corporation#Spacehab

Small note, the Pallet didn't fly on just Spacelab missions, it also flew on HST Servicing missions and ISS missions to carry modules and experiments. It also has some electric charge.
Some images have been added for a perspective into what the modules looked like in the real orbiter's cargo bays.

Enjoy, Thank you!