Aegolius13

Ablator on Soviet-Style Command Pods

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Has anyone else noticed that the Onion/Pea/Pomegranite pods use next to no ablator on reentry?  I've come in hot a few times from the Mun and Minmus without engine-braking, and only use up like 2 units of ablator during reentry.  If I remember right, you use well over 10 times that much on a Mk 1 command pod with heat shield.  Wondering if this is a bug, has something to do with the spherical design, or just if not all ablator is created equal.

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Posted (edited)
13 hours ago, Aegolius13 said:

Has anyone else noticed that the Onion/Pea/Pomegranite pods use next to no ablator on reentry?  I've come in hot a few times from the Mun and Minmus without engine-braking, and only use up like 2 units of ablator during reentry.  If I remember right, you use well over 10 times that much on a Mk 1 command pod with heat shield.  Wondering if this is a bug, has something to do with the spherical design, or just if not all ablator is created equal.

IRL, the Vostok had no RCS thrusters once it decoupled from its equipment module, so it had to be equally protected from re-entry heat on all sides, necessitating the spherical design.

AFAIK, the spherical design had no other effects on re-entry, and I don’t know if either the USA or the USSR had better ablative materials than the other.

Mods, I hope I answered the question without starting a Mercury vs. Vostok thread for Science and Spaceflight.

A similar thread:

 

Edited by ErinBensen
Further clarification

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Yes, I've noticed even at the hottest part of reentry, it's only using up like 0.01/sec of ablator, vs normal heatshields that are more like 0.5 - 0.75/sec at peak reentry heating.   I think it's been like that since 1.7, or at least that's when I started to notice it.  Prior to that, I think they used up ablator more like normal.

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Is it that they are just fatter and less aerodynamic so slow down quicker? 

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It still seems like a bug to use ablator at only 2% of the rate of a conventional heat shield.   And I'm going fast enough (usually Mun or Minmus returns) that the whole pod is visibly heating up to a nice bright red, but the ablator isn't being lost.  When I do have a reentry from LKO, it doesn't even nudge the ablator off the full 20 units.

It's not a big deal - if I was going much faster than I already am, I'm pretty sure the pod wouldn't survive the heat regardless of how much ablator is left.  Therefore, IMO it isn't unbalancing the game to favor the Soviet-style pods, its just curious that their ablator barely ablates

12 hours ago, Foxster said:

Is it that they are just fatter and less aerodynamic so slow down quicker

I don't think they slow down all that much quicker, but that's more my perception than any measurement.  Now you have me wanting to do a test of a Mk 1 pod + heatsheild vs the equivalent Soviet-style.   Use alt-F12 to set identical orbits, do a deorbit burn to a 30km Pe, then don't touch anything & see what the distance from KSC is on recovery.  I may try this tonight if I get a chance

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I got to run a test sooner than I thought.  Initial conditions for both:  100km circular orbit w/ 0* inclination, single deorbit burn as close as possible to the dessert launch pad (I set a target vessel there) lowered Pe to 30km, then staged off the engine & fuel tank.

Test 1:  Mk 1 Pod + parachute + heat shield (set to 60 units of ablator):  

Spoiler

Even at 48km, it's burning off 0.1/sec of ablator

M67My9N.png?1

Splashed down, 610.5km from KSC.  34.18 units ablator remaining, 25.82 units used.

eV8NLy8.png?1

 

Test 2: Onion pod + parachute.  

Spoiler

At 46 km, it is not losing any ablator yet

Uv9OiMF.png?1

Splashed down 460.2 km from KSC with 19.98 units of ablator remaining, only 0.02 used

xUVPrLq.png?1

So my perception was wrong, at least for the Onion - it decelerates quite a bit faster than the Mk 1.  Yet it uses almost no ablator while doing it.

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Hang on. Are you were talking about stock capsules with heatshields attached? Stock capsules have no ablator themselves. 

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On 6/11/2019 at 6:46 PM, Cavscout74 said:

I got to run a test sooner than I thought.  Initial conditions for both:  100km circular orbit w/ 0* inclination, single deorbit burn as close as possible to the dessert launch pad (I set a target vessel there) lowered Pe to 30km, then staged off the engine & fuel tank.

Test 1:  Mk 1 Pod + parachute + heat shield (set to 60 units of ablator):  

  Reveal hidden contents

Even at 48km, it's burning off 0.1/sec of ablator

M67My9N.png?1

Splashed down, 610.5km from KSC.  34.18 units ablator remaining, 25.82 units used.

eV8NLy8.png?1

 

Test 2: Onion pod + parachute.  

  Reveal hidden contents

At 46 km, it is not losing any ablator yet

Uv9OiMF.png?1

Splashed down 460.2 km from KSC with 19.98 units of ablator remaining, only 0.02 used

xUVPrLq.png?1

So my perception was wrong, at least for the Onion - it decelerates quite a bit faster than the Mk 1.  Yet it uses almost no ablator while doing it.

Yes, the stock pod had a heat shield.

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