Eh, just put them outside.

As a species with a relatively impressive ability to engineer things, we can almost certainly find a way to make guillotines work without gravity. I propose the use of of rockets as a form of karmic irony.

A woodsplitter is basically a hydraulic guillotine.

Electromagnets would work nicely.

Rocket powered guillotine

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.

Someone needs to invent the rocket guillotine, ASAP