Heat shield isnt working

[apoptosis]

i am trying to reenter kerbin at 5500 m/s with a mk2 lander can and the heat shield that fits it size, entering straight at retrogade and have 2 reaction wheels, including the can,the heat shields absorbs for a few seconds then then mk2 suddenly explodes with a full red bar that comes out of nowhere, it has full ablator, tried many different saves and tried different heights, same thing happens, why?
Edit: The problem was the lander can is too heat sensitive and the slightest exposure on reentry will instantly blow it up, I managed to orbit kerbin after hours and had to do a rescue mission

[Chibbity]

A screenie might help us help you.

[FourGreenFields]

What Ap and Pe are 5.5km/s? Sounds like quite a lot, even heat shields are not 100% effective.

[apoptosis]

Originally posted by Chibbity:

A screenie might help us help you.

https://steamcommunity.com/sharedfiles/filedetails/?id=2248057529

[apoptosis]

Originally posted by FourGreenFields:

What Ap and Pe are 5.5km/s? Sounds like quite a lot, even heat shields are not 100% effective.

coming from deep space, trying to aerobrake or land

[1.10e+25 Worms]

Originally posted by Apoptosis:

Originally posted by Chibbity:

A screenie might help us help you.

https://steamcommunity.com/sharedfiles/filedetails/?id=2248057529

Uh I think you put your heat shield upside down... I don't know how much this affects it but it probably does.

[Noobly]

Heatshield placed wrong, the smooth brown texture need to be exposed to the planet when reentry

[apoptosis]

Originally posted by Noobly:

Heatshield placed wrong, the smooth brown texture need to be exposed to the planet when reentry

thats my second lander i retried the mission,first one had it with brown side down and same issue, also no mods installed

[FourGreenFields]

5km/s at less than 40km. I suspect it's just too much.
At that kind of speed I probably wouldn't go below 50km (then again, I play at max reentry heating, and rarely use heatshields).

[apoptosis]

Originally posted by FourGreenFields:

5km/s at less than 40km. I suspect it's just too much.
At that kind of speed I probably wouldn't go below 50km (then again, I play at max reentry heating, and rarely use heatshields).

ablator heat shields are meant to burn up and protect anything behind them until ablator is gone, i entered eve at 8km/sec and nothing happens to the ship, i did enter kerbin once at 7km/s so i dont know what is going on now :(

[FourGreenFields]

Maybe the lander can is heat-sensitive enough that even <0.1° off the retrograde is enough to expose it to the airflow and have it burn up?

[apoptosis]

Originally posted by FourGreenFields:

Maybe the lander can is heat-sensitive enough that even <0.1° off the retrograde is enough to expose it to the airflow and have it burn up?

i think that is the most likely thing because when i spin it, it takes longer to explode which means there is 100% a part that is exposed althrough it doesnt look like it, but spinning makes the gee force take it out of control at lower altitude, right now i am trying to aerobrake higher so i can spin and not loose control

[Quizzical]

If you tilt slightly, other parts besides the heat shield get blasted by the atmosphere and explode. Remember that the dominant term of the rate of temperature increase is proportional to your velocity cubed times the density of the air. At 5500 m/s in Kerbin's mid atmosphere, that's going to be very, very fast.

The proper way to use heat shields is:
1) make sure that your heat shield(s) protect a cross-sectional area considerably wider than the portions of your ship that they need to protect so that tilting slightly doesn't cause explosions, and
2) design your ship such that the aerodynamics will force you to stay retrograde, rather than trying to flip you over.

I'd usually advise against using heat shields on Kerbin. It's much easier to just do a retrograde burn. The same is true on Laythe and Duna. Heat shields are really only good for landing on Eve or reaching Jool's lower atmosphere, as the retrograde burns required would be enormous. Well, you might also want heat shields if trying to get unreasonably close to the Sun, but that's a different matter.

[Quizzical]

Here's an example of heat shields used properly:

https://steamcommunity.com/sharedfiles/filedetails/?id=2248250911

Note that while there is one inflatable heat shield at the bottom to protect the rest of the components, there are four at the top for the sake of aerodynamics. If you start to flip, aerodynamic forces on the bottom heat shields will try to push you further in the direction you're turning. Aerodynamic forces on the top heat shields will try to push you back toward retrograde. The latter torque is much stronger than the former, so you don't even need reaction wheels to keep you pointed toward retrograde, at least so long as you're pointed retrograde when you enter the atmosphere. If you're not, you may explode before the heat shields can turn you.

That allows the probe to enter Jool's atmosphere at about 9700 m/s relative to orbit (8600 m/s relative to the surface), stay retrograde, slow down, and survive. I didn't even need a retrograde burn to slow down, but only some side burns to adjust the periapsis to a suitable latitude (near the equator) and altitude.

When trying to use heat shields, always make sure you're doing everything relative to the surface, not relative to orbit. Air moves with the surface, and velocities relative to the surface are what matters. You also want to stay pointed retrograde relative to the surface, as if you're retrograde relative to orbit, the angle is off a little.

Also make sure that you're aiming your orbit such that the periapsis is at a suitable altitude as you approach. You typically want to target the mid-atmosphere. If you aim straight at the center of a planet, you may still explode because the heat shields don't have long enough to slow you down. On the vehicle linked above, if you aim for a periapsis in the 130-160 km range, everything works. If you aim it far below Jool's surface, you'll still be going too fast when you reach denser atmosphere, and the high g-forces tear off the top heat shields. At that point, the aerodynamics are all wrong, so the vehicle flips and then quickly explodes.

[funkynutz]

Too fast. Do a retrograde burn to lock yourself into an orbit of Kerbin first.

Lower your PE to somewhere between 70km and 100km.

Lower your AP to anywhere between 100km and 1Mkm (the lower the better).

No lower your PE again, to around 55km for aerobreaking. You should be going less than 3km/s at the lowest point of your orbit (preferably around 2km/s). This will further degrade your AP. Depending on the height of your AP and your speed, you may go back out into space a few times (I call it skipping) as your velocity and orbital height drops.

[Quizzical]

I'd question why you're going 5500 m/s relative to Kerbin. If you do it right, returning from any planet or moon in the game should only get you to about 4000 m/s (or less for the nearer ones) as you approach Kerbin's atmosphere, and that's readily handled by a retrograde burn. Maybe returning if you were trying to get near the Sun gets you that fast. But I suspect that you botched your return from wherever you were.