When you have landed in your escape pod you want to exit the pod.

After you exited the pod you want to move away from your little Base that has built itself

just wait about 80 seconds without connecting to you base and essentially you will DIE

There are plenty of other way to die in Astroneer :
1. Just jump of something very high
2. Just click esc go to the red symbol and klick Respawn
3. Get hit by a dangerous enemy like an angry plant