Both Farscape and Angel say that the cavemen win.  That's got to be worth something.
Now that's a scenario where I think you're making the distinct advantages of caveman v. astronaut clear.
I also don't see how astronaut = expert weapons builder.  If you put an astronaut and a caveman each in a falling-apart spacecraft, the astronaut's more likely to come back alive (by the simple fact that the caveman is unlikely to know how to read or use duct tape), but that's a different kind of expertise than building a rocket launcher from scratch.  Your scenario is essentially Caveman Vs MacGuyver.
	
 
		
		
Doesn't take a Hummer. Just a Toro.
Or a woodchipper. Or a chainsaw.
Houston, we have a chainsaw massacre.
	
 
		
		
Even a Yugo would get the job done.
	
 
		
		
Thanks sumi, but it's just me.  -Someone- forgot to log out the last time she used it, and so I accidentally posted my news under her name before fixing it...
	
 
		
		
Both Farscape and Angel say that the cavemen win.
Crichton was an astronaut! And the astronaut won!
Liquids on a Plane is great. Thanks, flea.
	
 
		
		
CaBil, go you!  Following your bliss and all.  Good luck and writing~ma!
	
 
		
		
we are soooo showing up on insane-o site of the day.
	
 
		
		
 and Angel say that the cavemen win.
Fury already put his $0.02 in.
 Your scenario is essentially Caveman Vs MacGuyver.
See, here's the real question -- does the astronaut get a space suit, or a space ship, or anything to really make him an astronaut (beyond just a job description, and a vague one at that)? Does the caveman get a club, or a rock, or a pointed stick?
I suppose this has been asked and answered, and I'm a bad skimmer. I plead distractedness.
(Edited because I have no idea what an anstronaut is.)