Punishments that permanently disable or main (or kill) will reduce the effective survivability of the whole group. They would be the very last choice for a Dictator wanting to insure a successful mission.
Speaking with my mad dictator hat on, I'd ensure a very low requirement for such measures by simply using the right psychological selection methods for candidates in the first place. I'd pick well motivated and loyal people with my own outlook. They'd be "trained" more before the mission (i.e. really brain-washed). You'd send fanatics who needed no discipline.
So probably you'd limit punishment to the "pain-booth" type. Perhaps flogging, although this risks permanent injury. Maybe electric shock as a punishment would be better suited to the mission goals.
Psychological monitoring and perhaps psychological methods as torture would be an option. You'd be amazed (well, alarmed) by what a week in total isolation and/or the dark can do to a human.
Zero-G is, I think, an unrealistic restriction.
In practical terms any long journey in space will need to provide some emulation of gravitation forces simply to maintain body functions. It seems unlikely from current knowledge that the human body could be maintained in a healthy state for a long journey at zero G.
As your goal is colonization they would also need to be adapted to a real gravitational force before being able to carry out the mission. That requires some functionality in your ship to help maintain a "gravity-matched" body.
Some sort of centrifuge-like device is therefore a likely thing to at least provide some place for exercise. It seems a likely place for medical procedures as well, so presumably that would encompass your more grisly choices of punishment if required.
Actually carrying out such procedures in zero-G really just amounts to the same task as Earth but with some system for gathering fluids. A table with a lot of carefully designed airflow and suction pumps might do the job.
That said, does this maniac dictator actually want a tidy job. Tortures are most effective when the people you want kept in line have to endure the misery to some extent. Being forced to watch and listen in a chamber where the bodily fluids from the victim float around and can come into contact with you (and perhaps body parts too) would strike me as a pretty gruesome way to send the message to the survivors. In this scenario, the execution just needs a suit to keep him/her self clear enough of debris and fluids to see what they're doing.
1Make sure you take the cost of shipping a group large enough to colonize and the cost of losing members of this population into account. – Logan Kitchen – 2017-03-01T17:10:16.020
These types of punishments don't scale down well since all of these folks are apparently on a one way mission to nowhere. What stops the civilians from just killing the disciplinarians? Small tribes like this historically have only two punishments. The first is extra duty, the second, exile. In this case, the air-lock (then bringing the body back in 'cause we need that water and all those minerals!). – Jason K – 2017-03-01T20:28:22.833
1Just an addition: every torturer employing the techniques below should also be required to growl "I hope you appreciate the... gravity of your situation, Mr. Torturee" in a menacing way. – Xenocacia – 2017-03-02T06:23:45.130
@Xenocacia Boo for such a terrible pun, and because you thought of it before I did – Paul TIKI -Monica come Home – 2017-07-26T18:41:33.940