From: nospam@127.0.0.1   
      
   JF Mezei  writes:   
      
   > On 2020-11-06 13:37, David Spain wrote:   
   >   
   >> Complicated compared to throwing the stage away I meant, not more   
   >> complicated than landing an entire stage! Sorry didn't make that too   
   >> clear.   
   >   
   > How complicated would it be to make a delta IV, Arianne 5 or other   
   > "legacy" rocket land?   
      
   Not difficult at all. Most of them already do. It's mainly a question of   
   velocity. :-)   
      
   >   
   > Obviously, add legs, grid fins and software. But realistically, how   
   > difficult is it to ignite main engines in flight during descent if they   
   > don't have igniters on board?   
      
   Pretty difficult if there isn't someone on board with a match.   
      
   You'd need hypergolic propellants if you aren't using igniters.   
   Those present their own problems. Better off starting from scratch.   
   Of the legacy rockets, perhaps you could most easily retro fit a Titan   
   II. But the more I think about it, the more less it looks anything like   
   a Titan II.   
      
   >   
   > If they want to catch Vulcan engines as they fall down, doesn't that   
   > imply engine separation mechanism and likely parachutes for engines?   
   >   
   > Wouldn't it be simpler to just have it land?   
      
   Nope. Since there's no propellant for it to combust. If it it's coming   
   down on chutes it's coming down fast enough to damage itself if it were   
   to make contact. I assume it's also not buoyant so that kinda rules out a   
   water landing. Sea water is notoriously bad for rockets engines anyway.   
   See:   
      
   > https://spaceflightnow.com/2015/04/14/ula-chief-explains-reusa   
   ility-and-innovation-of-new-rocket/   
      
   Nice chart here that shows all.   
      
   Dave   
      
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