From: alain245@videotron.ca   
      
   On May/24/2021 at 12:21, JF Mezei wrote :   
   > Thanks for the reality checks.   
   >   
   > Would it be correct to state that  London-Sydney can either be achieved   
   > with air breathing engines (aka: jet) flying with engines on all the   
   > time and taking forever, or with a ballistic suborbital flight that   
   > requires enough speed at MECO to be near orbital speed and thus heat   
   > shields fro re-entry?   
   >   
   > aka: Nothing in between?   
      
   You could theoretically have an aircraft with a small rocket engine that   
   would fire for an hour and do London to Sidney in an hour or two at   
   something like 40 km high. I don't think you could do it in a way that   
   would make economic sense, but I wouldn't entirely rule it out.   
      
   > I just googled altitude for re-entry interface and they state 100km. So   
   > that Virgin Galactic at 110km i sbarely above it so clearly 110km isn't   
   > enough to speed up to do ballistic trip halfway around the world.   
   >   
   > So say you drop off a Dragon at near orbital speed over London with   
   > intend to fall in Sydney harbour. From what altitude would drag be low   
   > enough that its near obrital speed would be maintained long enough to   
   > get it to Sydney?   
   >   
   > Are we talking 200km? 300? 150?   
      
   If I recall correctly, when a spacecraft de-orbits, it starts its   
   atmospheric deceleration about half an orbit from the landing point. So   
   at near orbital speed and at 100 km altitude, you would go about half   
   way around the globe.   
      
   > Since Falcon9 drops its payload at 80km, this would mean a suborbital   
   > flight to Sydney would require Dragon initiate its own burn, and then   
   > ditch the service module to re-enter only as a capsule, right?   
   >   
   >   
   > Somewhat ironic that the Shuttle may have been the best suited vehicle   
   > for suborbital flights had its launch been simpler/safer.   
      
   If its launch had been simpler/safer it wouldn't have been the Shuttle.   
      
      
   Alain Fournier   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)