safe aerobraking heat

[EndTraveler]

lets say I have a mk1 command piod, and I am coming in from minmus with no heat shield. lowest safe altitude for an entire stage for landing at the ksc?

[Dr. SpaceFreak]

Just now, EndTraveler said:

I am coming in from minmus

Is your orbital eccentricity <1(elliptical)? If that's the situation, you're going to fast for a safe reentry. You need to slow down while reenty, maybe using thruster, and later the chutes, or achieve a nearly circular LKO and make the reentry. If you're going to fast, depending on how fast you're going, your vessel can burn out, or you will crash on the ground cause chutes will not deploy correctly.

[EndTraveler]

2 minutes ago, Dr. SpaceFreak said:

Is your orbital eccentricity <1(elliptical)? If that's the situation, you're going to fast for a safe reentry. You need to slow down while reenty, maybe using thruster, and later the chutes, or achieve a nearly circular LKO and make the reentry. If you're going to fast, depending on how fast you're going, your vessel can burn out, or you will crash on the ground cause chutes will not deploy correctly.

i was just asking for the safe altitude if i use a little retrograde thrusting

[Dr. SpaceFreak]

Just now, EndTraveler said:

i was just asking for the safe altitude if i use a little retrograde thrusting

Usually, I crash on the ground coming back from above 250-300 km without no heat shield, but all depends on the speed you're reentring. I ignore the exact values for these situations , but about 2000-2500 m/s on reentry while in dense layer of the atmosphere will blow out your little vessel.

[Gargamel]

6 hours ago, EndTraveler said:

lets say I have a mk1 command piod, and I am coming in from minmus with no heat shield. lowest safe altitude for an entire stage for landing at the ksc?

 

5 hours ago, EndTraveler said:

i was just asking for the safe altitude if i use a little retrograde thrusting

errr.... Ummm..... From minmus....  I'd say about 75km.    Do some retorgrade thrusting until you've brought the Ap down to about 75km, and then do some more retrograde thrusting until it's about -200km, and tumble the heck out of that pod. 

[CrashyMcCrashFace]

I noticed you can stack heat shields and the ablation number grows appropriately. I didn't test it though.

Wait, I just saw you said no heat shield. Never mind on that. Engines are pretty heat resistant.

Edited May 21, 2018 by CrashyMcCrashFace

[blag]

The answer you seek is  a Kerbin Pe of 45 km. Don't go lower.

(If you're afraid of losing your ship, you can try 50Km.)

This is for a Mk1 +Mk16 chute, facing retrograde the whole time.

It'll take you two entry, the first to slow enough and the second is the real one.

Edited May 21, 2018 by blag

[EndTraveler]

5 hours ago, blag said:

 

It'll take you two entry, the first to slow enough and the second is the real one.

THANK YOU. I need two reentries to land on the ksc!

[Corona688]

For large enough craft I sometimes have to aerobrake at 55km.

[blakemw]

The complexity with command pods is they have a low internal temperature tolerance, skin temperature is basically "instantaneous", if the skin reaches that temperature even for a moment the ship explodes. Internal heating is more insidious, because heat slowly bleeds into the interior from the skin and this can lead to the pod exploding even though its skin temperature was never exceeded, the critical factor for internal heating is duration of exposure and area of skin directly exposed.

It is almost always a bad idea to have a command pod type thing directly exposed to the hot air, for Mun and Minmus return you can use random crap as a pseudo-heat shield, one example is keeping a 1.25m decoupler, flipped so it remains attached to the base. It has an internal tolerance of 2000 so it will protect the command pod. It may not matter if it burns off halfway through, because it still dramatically reduces the duration of heating for the command pod (and the command pod itself has like 2400 tolerances or something).

So the answer differs based on whether the command pod is "naked" or has something up front to prevent internal heating. Naked pods tend to have to use two (or more) passes, exiting out the atmosphere to give them a chance to cool down. A protected pod can usually dive a bit deeper and do it in one pass.

The altitude depends a lot on the draginess of the capsule, draggy capsules or those with drag enhancement (random excrements surface attached) can use an altitude of about 50km for a single pass, less draggy ones might need to use 35km or so.

[Xd the great]

I'd suggest a pe of 55km? I am not sure but do suggest quicksaving. Aerobrake a few times and should be all fine.