Eh, just put them outside.

Rocket powered guillotine

Electromagnets would work nicely.

Put their head into the hydraulic press from the YouTube channel. I bet Elon's head would get billions of likes overnight.

Guess we're just gonna have sharpen fan blades then.

Something kinda in the same vein, in the book series Red Rising, hanging people on Mars is ineffective because of the low gravity (not enough force to snap the neck), so someone has to go up and pull on the legs of the executed person to kill them.