Heat exploding question

[Tiaga]

I don't understand why a smaller vessel with batteries and solar panels on the exterior will not explode during descent but a larger vessel with exterior batteries and solar panels will explode due to heat.

Example: Put a small vessel and a large vessel with solar panels in orbit of eve and try to land it. The solar panels on the small vessel will survive but the larger vessel will not.

[Mahnarch]

Collected heat? Larger area? Faster speed?

Just spit balling.

[AbacusWizard]

Without further information, my first guess would be that the larger vessel is more massive and therefore takes more time to slow down, so the exterior parts are exposed to the high temperature for a longer period of time and thus heat up more.

[Hydrazine_Soup]

KSP thermo model works in misterious ways.

Edited March 5, 2020 by Hydrazine_Soup

[Tiaga]

I'm trying to work out the physics of collected heat, area, and speed in my brain but its not going well.

[michaelsteele3]

Heavier the object is, the more momentum it has, thus the harder it collides with the atmosphere.

[MarvinKitFox]

I don't understand why a smaller vessel with batteries and solar panels on the exterior will not explode during descent but a larger vessel with exterior batteries and solar panels will explode due to heat.

Take a Twinkie, throw it at the floor. Note the very little impact damage.

Now take a twinkie, and glue it to the face of a brick. Throw at floor again.

More damage? Why!?!? They hit the floor equally fast!

The universe is obviously badly coded, debug it now!

- - - Updated - - -

I'm trying to work out the physics of collected heat, area, and speed in my brain but its not going well.

Ok, in physics..

The small and large vessel will reenter as basically the same speed, so that is constant.

Lets say the small vessel is a 3 meter sphere, the large one is a 10 meter sphere. Similar construction.

The small one has surface area proportional to 3^2 = 9

The large one has a surface area proportional to 10^2 = 100, so it presents 11 times the surface.

The small one has a mass proportional to 3^3 = 27

the large one has a mass proportional to 10^3 = 1000, so it masses 37 times as much.

Similar speed, 37 times the mass, distributed over 11 times the surface. = 3.36 times the energy flux (heating) imposed on the object.

Expect its surface to be much hotter. Not quite 3.36 times as hot, but easily 1.2 or 1.3 times the temperature.

[-Velocity-]

Not sure if this is what is going on in KSP- I'm having no problems with exploding spacecraft yet in this post-1.0.0 career- but if it's based on real physics then it's like Marvin says.

Basically, the amount of an object that is subjected to heating is related to the radius squared. The surface area, effectively.

However, the amount of kinetic energy that an object is carrying is proportional to radius cubed- the volume.

Thus small objects have larger surface areas and lower masses, since r^2 (r == radius) gets larger in proportion to r^3 when r is small. However, as r grows bigger and bigger, then r^3 grows much more quickly than r^2.

This is known as a "scaling law". The behavior of the physical world is HIGHLY dependent on scale. You can't arbitrarily shrink things or enlarge things and expect them to work the same.