Re-entry is when you splash down on planets such as HOM. You can only splash down with the Atmospheric Probe, Orion Crew Capsule, Crew Module, LOK Crew Capsule, Crew Module Dockable and the Gemini Capsule.
Once re-entering, you will experience turbulence, caused by the extreme speed experienced during re-entry. This causes it to slowly spin. Be careful: if you have your heat shield turned for too long on its side, your capsule will heat up and explode.
- In real life, the capsules' center of gravity/mass is tuned so that it will always face the right direction fighting turbulence.