Technology question

This has probably been brought up at least once, but why, if SF technology can manipulate mass and inertia to slow down bullets can't it generate AG fields for spaceflight?<br /><br />Seems to me the only answer so far is &quot;then it wouldn't be Star Frontiers&quot;, which I think is a bit silly.<br /><br />I mean, that's the game as it exists.  I get that.  And  yes, the feel radically changes if AG gets into it, but whey then did they have inertia screens to begin with?  Or albedo screens for that matter (bending light through fields).<br /><br />Curious to see what you all think.