System ||| Void is a rule supplement adaptation of Marc Miller/Steve Jackson Games' Triplanetary for the universe of The Expanse.
This adaptation is not stand-alone. The standard ruleset is required for this to be usable.
SJG's 2018 edition of the game rules is available in PDF form here:
Steve Jackson Games' TRIPLANETARY This webpage also links to a bunch of additional maps, scenarios, alternative rules, and reviews for the classic TRIPLANETARY game.