From: jfindley@cinci.nospam.rr.com   
      
   In article ,   
   jfmezei.spamnot@vaxination.ca says...   
   >   
   > On 2020-11-13 13:40, Jeff Findley wrote:   
   >   
   > > SSMEs are fuel rich staged combustion cycle which required ground   
   > > support equipment to start.   
   >   
   > I know they had spark generators below engine bells, but was repeatedly   
   > tols this was to burn off any stray Hydrogen , not to ignite engines.   
      
   Yes, those external sparklers were there to burn off excess hydrogen.   
   They had nothing to do with starting the engine.   
      
   > So I am very curious how grouns equipme t intefaces with the engine to   
   > get them started.   
      
   Since the SSME is a fuel rich staged combustion engine, you have to   
   things to start: 1. The combustion chamber for the turbopump (whose   
   combustion exhaust goes into the engine).  2. The main combustion   
   chamber.  Starting all that up was a complex process, so NASA put as   
   much of the equipment and consumables to do so on the ground (since   
   that's the only place the SSME was ever started).   
      
   https://en.wikipedia.org/wiki/RS-25#Constellation   
      
   From above:   
      
      It would be expensive, time-consuming, and weight-intensive to   
      convert the ground-started RS-25D to an air-started version   
      for the Ares I second stage.   
      
   Jeff   
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