Higher thrust per unit fuel isn&#x27;t limited by manufacturing technique.  Per-unit cost isn&#x27;t really a limiting factor for rocket engine development.  These things cost tens of millions of dollars and they push things worth perhaps a billion.  Governments have been throwing billions, defence billions, at the technology for over a half-century.<p>The physics of ISP is well-understood and current engines are near what is physically possible, regardless of who&#x2F;what builds the engines.  3d printing could certainly make engines more affordable and&#x2F;or lighter, but it isn&#x27;t going to allow an engine to be any more fuel efficient.<p>Anyone who builds an engine with significantly increased ISP using standard fuels (ie without going nuclear) will probably win a few nobel prizes.  3d printing is about improved manufacturing, not new physics.