From: bthorn64@cox.net   
      
   On 10 Dec 2004 23:42:14 -0800, ilpolagerste@jippii.fi (Ilpo   
   Lagerstedt) wrote:   
      
   >What is the difference between Delta 4 and Titan III-type launch vehicles?   
      
   Delta IV has a standard large "main" rocket stage design which burns   
   hydrogen and oxygen propellants, with a smaller hydrogen/oxygen second   
   stage on top. One of these launched is called a Delta IV-Medium.   
      
   Strap three of these puppies together in a line (with the second stage   
   on top of the middle one) and you have a Delta IV-Heavy. All three   
   ignite at liftoff.   
      
   Titan III (now IV) has a standard two-stage "core" rocket design   
   burning hypergolic propellants (which burn on contact with each   
   other). This was more or less the original Titan II ICBM design and   
   later the launch vehicle for Gemini. To each side of this are two very   
   large solid propellant boosters. Only the two boosters ignite at   
   liftoff. The core ignites when the boosters burn out at altitude.   
      
   Some, but not all Titan IV's use a third stage atop the two-stage   
   core. This can be the solid-propellant Boeing IUS (made famous on   
   Shuttle launches such as Galileo and Magellan) or the powerful   
   hydrogen/oxygen Centaur.   
      
   So Delta IV uses two basic rocket stage designs (core and second   
   stage) to replace Titan IV's two core stages, solid boosters, and IUS   
   or Centaur. It should be less complex to prepare for launch and have   
   fewer parts to break.   
      
   Atlas 5, by the way, is very much like Delta IV except that is burns   
   kerosene instead of hydrogen and uses Centaur instead of a new second   
   stage design. There are no current plans for an Atlas 5-Heavy, but the   
   capability is available should the need or customers arise.   
      
   Brian   
      
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