What bladed melee weapon would be best suited for a warrior in zero-gravity?

I am currently designing a faction of spacefaring knights, who are elite professional warriors trained to defend spaceships from hostile boarding parties, board and seize enemy ships, etc. Like in real life, these knights are usually taken from the nobility and trained from a young age.

These knights specialize in 1v1 close-quarters engagements in a variety of environments (zero-g or artificial gravity, small spaces or larger spaces). To orient themselves in zero-g, they wear boots with weakly magnetized soles, and a wrist-mounted retractable grappling line with a magnetized hook.

The knights' gear includes an insulated black bodysuit and a suit of armor over it, the armor looks like this (but way less spiky): https://www.artstation.com/artwork/qQ80nR The armor also has an airtight helmet and rig to allow breathing in space and non-terraformed planets.

For this reason I assume slashing swords (like sabers) would be impractical because the zero-g would throw you off with every slash. So the weapon I’m looking for would be mainly for thrusting/stabbing, for economy of motion in zero-g. I thought about having it be a rapier, but alternately I could just go with a gladius or some similar short thrusting sword. With that in mind the knights' other main weapon would be a dagger, well suited for stabbing in very close quarters, especially in zero-g.

All that said, I'm new to this so any input is welcome.

No need to alter your weapons. Instead, train your knights

The big problem you are trying to address is balance. Yes, how do you strike with a sword in zero g (and mag boots) without losing your footing? Create a specific set of martial arts for the task.

Downward blows will be sure to disconnect your knights from the ground. Big horizontal swings are likely to make you lose your balance, but piercing strikes, especially if angled upwards will push your opponents up while creating better friction for your boots. Depending on mobility, your knight can use his outstretched leg as a counter weight for a long strike like the Fleche

You can even incorporate your grappling with attacks. Grapple the ground near your opponent and pull yourself in for a piercing strike. The skill of the knight will determine whether he can remain attached to the ground and in a good stance after delivering a blow.

Rocket-assisted slashing weapons

As you have explained, slashing will throw people off with every slash, but you seem to have forgotten that thrusting will also do the same thing.

In order for melee to work, there are two things that could be done, either anchor yourself/the enemy so that the blade strikes with full force (you did mention that they wear magnetized boots, but since you seem to be concerned that a slash will throw them off balance I am assuming that they are not strong enough to count), or give the blade some reaction mass that isn't the user's body. The former option seems very situational and the enemy will probably be thinking very hard about how to avoid being grabbed, therefore the latter is a safer bet. The second option is more or less the definition of a rocket. For simplicity I'll refer to blades designed for zero-G as space blades below.

Design Features:

1: Space blades will most likely be single-edged, as the other edge have to contain the rocket motors which might not be suited for ramming into the enemy's body.

2: Thrusting will be less emphasised, as having a rocket pointed directly at the user is necessary to carry out a thrust without any anchoring, but a rocket with it's exhaust pointed at the user may not be practical, especially if it is meant to punch through armor that a slash will not do. Therefore, space blades will likely have a greater focus on the edge, not the tip.

3: The rocket motors may have some sort of "rocket guard", much like how hand guards are meant to protect the user's hands, the rocket motors will likely require some protection to avoid an opponent trying to shave them off

4: The rocket motors have to be attached as close to the tip as possible, as distance from the pivot increases their effectiveness.

5: A space blade may have a thickness that is huge by earth standards, both to accomodate the rocket motors and to protect them, making them quite heavy. Combined with point 4 and 1 you may end up with a weapon which vaguely resembles a single-edged Zweihander in handling characteristics



what does these features mean for the user?

Implications for the user

1: As the space blade is quite heavy and have a limited amount of slashes, users may have a more passive style of fighting where they only strike when they are very certain that the target will be hit

2: Having "boots on the ground", which is to be attached to something that serves as a anchor, is of paramount importance. Being anchored (preferably by using the foot to hook onto something) allows what is effectively a unlimited amount of slashes using the user's own strength instead of the rocket motors

3: As the space blade described is both heavy and fast(thanks to the rocket motors), it has a exceptional anti-armor capability that makes evading, instead of tanking the space blade more practical for a fellow human, even when armored

4: Attempts to shave off rocket motors from an enemy's space blade may very common, as it will stop the enemy from being able to do damage unless anchored

What's the best breed of horse for propelling a tank?

There's hypothetically an objective answer to this question (and the one about horse-drawn tanks) if you sufficiently constrain the available kinds of weapons and assign them opportunity costs; and sufficiently describe the operating conditions - environment, tactical objectives, supply chain, enemy, etc. But that answer doesn't really matter, which is why I'm answering this with a frame challenge instead of asking for clarification.

If you're bringing the weapons on your rocket ship specifically to fight with... either efficacy is not a priority for you, or your setting runs on rule-of-cool and flimsy handwaved justifications and the best weapons are the cool ones your flimsy handwaved justifications say are best. (Both of these are perfectly good options that describe wildly popular sci-fi settings.)

If you're using the weapons because something has gone terribly wrong and they're the best you've got, the best weapon is the one you have with you - whatever you're carrying already for use as a tool of some kind, or whatever your characters can make using the resources they happen to have available.

The kinetic energy goes up with a square of the velocity. Momentum goes up linearly with velocity. Kinetic energy is what does the damage.

If you're sticking to traditional medieval weapons, I would suggest (being completely uneducated here) something along the lines of a halberd. This is for a couple of reasons.

Drawbacks: Especially for the uber-long pole weapons, there is a limit before it becomes an issue for maneuverability, and the usefulness of a weapon is basically proportional to how well it fits in the space it's being used in. Maybe it could be collapsible, but this adds moving parts and probably lowers durability. Also, it's just goofy looking after a certain level. Are guns not a thing in this setting?

One interesting implication for the fighting style, which could be a drawback(?) is the number of hands used. For maneuverability, a polearm user would typically use both hands, but in zero g I'm sure there are times when only one is needed, probably just to keep the weapon on hand, because you aren't constantly fighting gravity. There could be a small range of possibilities in which one armed halberd fighting is favorable, although the vast majority of moves would probably still be two handed. The main act coming to mind is hooking an opponent and dragging them into a dagger in your other hand. Of course, if you want fewer hands to be taken up, a weapon like this is probably still impractical.

This is a Frame Challenge

The science-fiction tag still insists there's some science in there... somewhere. From this perspective there is no "best" melee weapon for zero-G combat. Why? Because to use any such weapon (even a dagger) requires both motion and the ability to bring the benefits of mass to bear and Newton's Third Law is a real honker when it comes to this.

Here's an example of the problem: When you pull back the (e.g.) sword to swing it you start moving in a spin (the mass of the sword vs. the mass of your legs) and you start moving in the direction of where you stopped pulling back (while you're spinning). Then you try to swing it at your opponent (if you can even see them at this point) and because the thrust-swing is always stronger than the pull-back-swing, you start spinning in a new direction (or perhaps on two axes). Ultimately, the force delivered to your opponent (if you hit them at all) is a mere fraction of what it should be because your body absorbed almost all of the energy in the form of Newtonian motion.

Consequently, the only way to use any melee weapon is to have a space suit (armored, naturally) that has thrusters all over it that can (and do) compensate for the action of the wearer in zero-G combat.

The armor must be backed up with a better-than-average combat computer designed for hand-to-hand analysis. This computer knows when to fire the thrusters such that the action is similar to the use of the weapon in a gravity environment.

A neural connection must exist so the computer knows within a reasonable amount of time (I'm thinking picoseconds, but you could probably get away with microseconds) such that it knows what you're trying to achieve. Not only is this important for creating all the counter-force needed to use a melee weapon, but it's really useful if you're trying to parry. In three dimensions. Honking cool! Tell me I'm wrong.

Sensors must exist in the armor to detect the natural motion of the body when using a melee weapon. This will benefit the computer greatly and they're one more thing that can go wrong for the sake of an interesting story.

The computer must also know when to lock the grip on the weapon (very useful) and when not to. If you've never used a melee weapon, having an immovable/fixed grip is sometimes useful, but not always. Use of a melee weapon is one of the better evidences that the hand and wrist are breathtakingly good examples of biological engineering.

Once you have all that, which weapon is best is only a storybuilding choice because, from the computer's point of view, it's just a block of constants fed to the computer so that it understands what the weapon is, how it's most likely to be used, and what dynamics it possesses in motion. In other words, best for zero-G is no longer a valid question as the computer can just as easily manipulate a halberd as it can a dagger. Now the choice is only due to the opponent: what are their skills, what support tech do they have, and what weapons do they have?

It's the armor, my friend

It's the armor (space suit), not the weapon, that allows any zero-G melee combat. You must have thrusters to counter Newtonian motion — and while thrusters on the weapon itself can benefit the value of the weapon, they won't have any value in real combat because (a) there's too little space to store fuel and (b) you still need to control the body.

Fair Warning: I usually vote to close "what is the best X?" questions because they're usually too story-based. What's "best" is determined by the circumstances of the story, not the facts of the world. Worldbuilding is about developing rules (a general term) that are true regardless any story. But in this case it was obvious (IMO) that you were asking the wrong question, which allowed for a non story-based answer.

For future reference, remember that best/worst/plausible/possible/realistic, etc. are almost always story-based and likely to get closed. Try to avoid superlatives.

How about variation on the mono-filament trope? Its a chain of diamond-molecule machinery, ready to cut through everything. You can accelerate it to significant speed and propell it. It wraps itself around the target and slices through the target. Energy for additional slicing, wiggling motion is generated from the impact energies.