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Re-entry for planes


rcp27

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Normally I'm mostly a straight rockets person but have recently taken an interest in spaceplanes. Re-entry is a balance between spending enough time in flight to slow down and not crash but getting down quick enough not to overheat. With long thin rockets with heat shields, a shallow entry from LKO seems to work, but with planes this seems a recipe for firey death. If I have s space plane, say a Mk2 based SSTO, how should I attempt re-entry? What's a good height for PE after a de-orbit burn? Should I fly with a nose up attitude for maximum drag or a more straight on approach to get down to the high drag/high lift thicker atmosphere quicker to minimize time spent getting hot? Do radiator panels make a difference to survivability? Help greatly received

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Nose-first concentrates heat on just a few parts and will incinerate your craft. Come in with the belly of the plane facing prograde to maximize braking drag and distribute heat. Radiators don't help much because they draw most strongly from the parts they are connected to, but would be destroyed if you put them on the parts getting hot during a re-entry. As for a periapsis to aim for, I don't think it matters that much as long as you don't to come down too radically fast. I generally put mine between 32kms and 50kms. 

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You want something that can pull a 40 degree+ AoA (and then pull out of the stall once the thermal loading drops enough (1.5km/s orbital) that you can just glide...). Aim for your CoL to be at your CoM during reentry and maybe run some RCS to help out. All-moving stabilizers (i.e. the standard canard) give you the most aerodynamic variability and can help you keep pure-aero control, too.

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I use Pe between 50 and 60k (1.2), 45 and 55k (1.1), hold 90 degree AoA as long as I can, then 45 degree AoA, and straighten out to level flight at around 25-30k altitude and around 900 m/s surface speed. To do this I pump fuel between the fore and aft tanks to keep the craft stable -- it has to be very nearly balanced to hold that steep AoA that long, but absolutely not under any circumstances tail-heavy as that'll cause it to spin out of control. If it's too nose-heavy it'll flatten out too early and you'll burn up.

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This is how I do it, when I want a pinpoint landing at KSC.

First I aerobrake at 40-50 km until I can establish an equatorial orbit at 80 km.

ZfYbYnN.png

  1. 80 km orbit. In Map mode, focus Kerbin and turn camera so KSC is facing towards you right above the Navball.
  2. Time warp until your spaceplane is right behind Kerbin.
  3. Put a maneuver node right where you orbit appears from behind Kerbin on the left side.
  4. Pull the retrograde handle until the maneuver is ~100 m/s dV.
  5. Move the maneuver node until the planned orbit intersects the surface through KSC.
  6. Pull the prograde handle until the maneuver is ~80 m/s dV.
  7. Perform the maneuver.
  8. Turn Prograde and time warp till you enter atmosphere.
  9. Keep nose ~30° above horizon. (May need to move fuel around to keep stable)
  10. At 36 km altitude pitch down to 10° above the horizon.
  11. When you pass over the coast of the landmass where KSC is pitch down 5°-10° below horizon.
  12. Adjust pitch to pass the mountains at 10 km, at 650-750 m/s.
  13. When you’ve passed the mountains aim for a point about half the runway length in front of the runway.
  14. At 200 m, flare and aim for the runway.
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Steep re entries are my favorite with space planes.  You have much more drag than a rocket so you don't need to spend much time slowing down.  The method above is about what I use, but I wouldn't be so straight forward.  Your aoa will depend on design and mass.  The key thing I look for is getting below 1400 m/s before dropping below 30km.  At that point I'm not worried about burning up anymore and will adjust aoa to bring me down at ksc.  One thing to help with over shooting, turn belly up and pull up so your angled down.  You will come down faster, but you're still generating high drag and hopefully will still slow down.  I usually only need this after getting through the worst of the re entry heat.

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This is how I do it.

  • From any orbit,
  • Set pe to 67km
  • At pe burn retrograde to bring the AP down to just below 70, or skip out of the atmosphere and try again, but leave 100km/s dv
  • Turn prograde again and keep the PE above 65km until you get to the last bit of desert before KSC
  • Turn retrograde and burn PE down to 40km
  • Turn prograde and pitch up to 45 degrees
  • When you have slowed down enough you should be over the "Too short Mountains"
  • From there it's an easy glide to the runway, powered if needed using the remaining fuel. 

GE

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