A heat shield is a part which protects shielded parts from overheating. Almost all heat shields, excluding the Heat Shield (10m), work as ablative heat shields. This means each has a certain amount of ablative material, ablator, which slowly breaks apart carrying heat away; this is represented by the ablator resource being consumed, cooling the heat shield. All four ablative heat shields have a maximum temperature of 3,400 Kelvin and an impact tolerance of 9 m/s. As a rule of thumb, it is recommended to use them on capsules which are expected to return from 55 km or higher.
Unlike the ablative heat shields, the Heat Shield (10m) is an inflatable heat shield. The part begins as a 2.5m component that inflates into a 10m diameter heat shield. As it uses no ablator, the Heat Shield (10m) has a higher maximum temperature of 3,500 Kelvin.
All heat shields can be jettisoned without the use of a decoupler.
While in the atmosphere, all parts create a "cylinder of coolness" behind them which protect other parts from heating. Any part within the cylinder of coolness will not experience aerodynamic heating. Heat shields are particularly effective in this role, as they have high temperature tolerances.
A heat shield is only able to completely protect parts which fit within this cylinder of coolness. A 2.5m heat shield will protect all 1.25m parts. In addition, conical parts (such as command pods) of equal radius will typically be protected (for example, a 1.25m heat shield will protect a Command Pod Mk1). Parts of the same general radius are sometimes protected, but any protrusions that stick out into the hot air will not be protected. For example, the Mk1 Lander Can extends beyond the 1.25m stack size, and will not be protected on reentry. Another example is the SC-9001 Science Jr.; it is protected by a 1.25m heat shield when the doors are closed, but if the doors are open, they will extend beyond the heat shield and the Science Jr. will be destroyed by heating. Even if a cylindrical part does fit behind the heat shield, the prograde or retrograde hold must be precise to ensure the part stays precisely behind the heat shield.
In addition, a small amount of heat will conduct through the heat shield to connected parts. This heat by conduction is not normally a problem, but can destroy unusually heat-sensitive parts (like most probe cores) mounted onto or very close to the heat shield.
|Image||Part||Radial size|| Cost
|Heat Shield (0.625m)||Tiny|| 150
|Heat Shield (1.25m)||Small|| 300
|Heat Shield (2.5m)||Large|| 600
|Heat Shield (3.75m)||Extra large|| 1100
|3 300||9||50||1 800|
|Heat Shield (10m)||Large / 10m||2 400||1.5|| 3 500