From: nospam@127.0.0.1   
      
   On 1/25/2021 9:39 PM, JF Mezei wrote:   
   > On 2021-01-25 09:43, David Spain wrote:   
   >   
   >> I don't think so. To get to 50km you need more propellant than to 10km.   
   >   
   > So how many engines do you need to lift a fully fueled Starship?   
   >   
      
   I do not know the exact answer to that question. I do know that Starship   
   is planned to have 6 Raptor engines in the final configuration. 3   
   configured for 'sea-level' operation and 3 for 'vacuum' operation.   
      
   I would assume the plan is to light all 6 are at staging and then once   
   fully out of the atmosphere to shut down the 3 sea-level Raptors.   
   I'm speculating here, but it also looks like the plan is for only the   
   sea-level Raptors to have gimbals. Which makes sense since their primary   
   role is to provide vectored thrust for landing operations.   
      
   For testing purposes on the single stage Starship, we will probably see   
   all sorts of combinations during the test rollouts.   
      
   >   
   >> If you are studying/testing internal tank pressure (head pressure) you   
   >> might want to profile at different propellant loads. Since the last test   
   >> at given propellant load X failed, you'd probably want to re-test with   
   >> the same load factor.   
   >   
   > Isn't the landing done using separate header tanks and those are   
   > indepedant of main tanks, so different filling of main tanks at launch   
   > shouldn't change anything at the time the engines perform final burn to   
   > land.   
      
   There might be different amounts of residual propellant left in the main   
   tanks during testing to get a profile on how well the header tanks   
   perform under different structural loads. Seems to be a relevant issue   
   based on SN8 results.   
      
   >   
   >   
   >> Doubtful. Propellant load should be able to handle whatever altitude you   
   >> are testing for. Winds aloft will be known ahead of time, so that should   
   >> provide limit bars for cross range. BTW,   
   >   
   > Can they easily change the ascent at last minute to match winds so that   
   > when it free fals the wind will push it back right over the X on the   
   > landing spot? Or would that be considered a major change to testing   
   > parameters ?   
   >   
      
   Good question. Maybe we'll get an answer to that from SpaceX someday.   
      
   >   
   >   
   >> Elon has tweeted in the past   
   >> the cross range of a typical sub-orbital Starship is on the order of   
   >> 10,000 km,   
   >   
   > I assume this is more "range" than cross-range?  10,000km is by original   
   > definition, distance between equator and north pole. That's a hell of a   
   > cross range on you launch due east and land at north pole if you turn   
   > left or south pole if you turn right :-)   
      
   Cross range was the wording Elon used. I think it has a specific meaning   
   in the context it was presented in. (Range of Starship only for surface   
   p2p flight).   
      
   >   
   > Will sub-orbital flights be ballistic, so landing is defined by how long   
   > you run engines and angle of ascent? Or would there be a "de-orbit" burn   
   > to influence where it lands?   
   >   
      
   Sub-orbital doesn't require a de-orbit burn. But an atmospheric   
   're-entry' burn can be used to change the flight profile from a strictly   
   ballistic parabola to another curve. Depends on what one wants the   
   flight path to be presumably. The ballistic trajectory would use the   
   minimum amount of fuel.   
      
   >   
   >> Doubtful, until he gets those oil rig platforms converted and presumably   
   >> placed at various spots in the Gulf of Mexico.   
   >   
   > Unless there is magic involved, those won't be ready to handle testing   
   > of Starship this year.  Wouldn't those rigs end up being landing/launch   
   > platforms ? Transportation from oil rig of a landed Starship to mainland   
   > for restaching with super heavy would be interesting. Landing superheavy   
   > on same plaform as it launched would pose challenge if the starship   
   > lands at same one a few hours later after having refueled something in   
   > orbit.   
      
   Yes I agree those platforms won't see much action during the test phase   
   which looks like it will focus on Return To Launch Site (RTLS) landings   
   only. This does minimize the amount of infrastructure needed and reduces   
   costs for SpaceX during this test phase by focusing the flight test   
   effort at Boca Chica.   
      
   Dave   
      
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