Note the bright yellow-white exhaust from the solid rocket boosters (SRBs).  The Shuttle main engines (LH2 = liquid hydrogen & LOX = liquid oxygen) are liquid fuel rocket engines.  Liquid hydrogen-oxygen rockets have the highest specific impulse of any other chemical energy rocket engines.


Hyper X-1:  Small scale, rocket launched scramjet testbed.

Image shows actual working ion engine used on Deep Space 1 probe.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

VASIMR Concept