From: someguy@somewhere.se.retro.com   
      
   Ilpo Lagerstedt wrote:   
   > Why not any first stage with LH2/LOX before Delta IV?   
   >   
   Depends on what you mean with first stage. The Shuttle main engines burn   
   H2/O2 since many years, Ariane5 does as well, but both these vehicles   
   use/need solid fuel boosters to do a proper lift-off. Note also that the   
   main engines ignite some seconds before the boosters are ignited in   
   order to give full thrust at lift-off.   
      
   How does the Delta IV work in this respect? Is there any specific   
   ignition order and how quickly do the engines give full thrust from   
   ignition?   
      
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