Ah so that's where they came from! 
I've got a few of those plastic armoured soldiers kicking around, mostly from EM4 miniatures, I did wonder what game system they were originally for.
The old Grenadier Space Rangers minis, you mean? Much like the modular robots EM4 sells, they didn't have a parent system when they were produced. The story I always heard was that both those kits were meant to be used in a never-released boarding action game set in ICE's Silent Death universe. What little teaser stuff I remember hearing about said it was going be vaguely like Space Hulk, with the warbots and rangers against Night Brood bioweapons - the things delivered by their "worm pod" assault craft. That was supposed to be their answer to larger human ships, who were vulnerable to boarding actions.
Nothing came of any of it as far as I know, but maybe Black Widow Pilot/Leland Erickson knows more. Did get us a few nice sets of minis, and the rangers were pretty popular locally as alternatives to the original plastic 40K marines despite their lack of psoe variety. The real draw was the sheer number of heavy weapon bits you got in a box, something GW wasn't very generous with - very few missile launcher frames in one of their boxes and nothing else in terms of heavies, where the ranger kits had enough varied heavy weapon choices to outfit everyone but the sergeants if you wanted to go ga-ga for devastator proxies.