Specific impulse: Nike-3 195s (http://www.astronautix.com/stages/hjnnike3.htm) Ammonium perchlorate + rubber 250s (http://ed-thelen.org/missiles.html) Saturn II 421s (http://www.astronautix.com/stages/saturnii.htm) LOX + LH2 440s (http://ed-thelen.org/missiles.html) NERVA (demonstrated) 875s (http://en.wikipedia.org/wiki/Nuclear_thermal_rocket) Solid core nuclear-thermal 1000s (http://en.wikipedia.org/wiki/Nuclear_thermal_rocket) Gas core nuclear-thermal 4000s (http://en.wikipedia.org/wiki/Nuclear_thermal_rocket) Fusion (theoretical limit) 130000s (http://www.sps.aero/Key_ComSpace_Articles/TSA-005_Fusion_Propulsion_White_Paper.pdf)