Honor Harrington's Impeller Wedge -- conundrums

I’ve just started reading David Weber’s Honor Harrington book series. I’m in the middle of the 3rd book (The Short, Victorious War) at the moment.

I can live with the fact that the Impeller drive blatantly violates the Conservation of Momentum. (Hah! Take that, Sir Isaac Newton!)

But the indestructible dorsal and belly wedges created by the impeller drive … well …

Missiles use their own miniature impeller drives, which generate their own top and bottom impeller bands. I read somewhere that a countermissiles destroys a missile by intersecting the target missile’s impeller bands with its own impeller bands. This overloads and shorts out the drive rings on both the missile and the countermissile.
So … why can’t a missile’s impeller bands do the same thing to the impeller wedge of a ship?

It would certainly make warships less invincible when they roll to face their belly wedge toward their attackers.

It’s a matter of scale. Anti-ship missiles are larger than countermissiles, but only by something like a factor of 10 or so, and countermissiles have disproportionately large wedge nodes anyway. An actual ship, however, is so much larger than any missile that the fluctuations induced by a missile’s wedge are lost in the noise. Presumably, a ship could ram another ship, but that’d be both suicidal and insanely expensive. Alternately, a ship could be designed to produce an extended wedge that would protrude far enough out to attack another ship, without damaging the attacker: That’s what the gravlance Honor used in the first book was. It’s still not enough to actually kill an enemy’s wedge, but it is enough to instantly take down sidewalls.

While we’re at it, the restrictions on wedges and sidewalls: A wedge can only be produced on two sides of a ship. A sidewall can be produced on two more sides without sacrificing thrust: This is how warships are usually configured. Additionally, you can also protect the front or back (but not both) with sidewalls, but doing so prevents the ship so protected from using its wedge to accelerate. Or, you can completely surround a ship (or more likely, stationary space station) with sidewalls on all sides, again with no acceleration.

Agreed. Tonnage given in this webpage Missile | Honorverse | Fandom state that a capital ship missile masses 80 tons. A destroyer class ship weighs 1000 times that.

Weber also has his own website and discussion forum. I don’t know how fast conversations move there…

Spoilered for tech that comes in later books.

Weber did come up with “bow walls” on the graser armed LAC’s.

Is this why fixed installations (e.g. space stations) use onmidirectional sidewalls, instead of projecting the much-tougher top-and-bottom impeller bands around themselves for protection? Because they’d have to leave one side completely open?

EDIT: And I just had a thought – wouldn’t an impenetrable impeller band make an EXCELLENT shield for a ground-based installation on a planet? Why haven’t I seen anything like that yet? Just 'cause it can’t move doesn’t mean it couldn’t have its own impeller rings installed.

Oh, and I just thought of yet ANOTHER conundrum:


There’s no way the fusion power plants on a starship are generating anywhere near as much power as the Kinetic Energy gains their starships are undergoing when they’re accelerating at 500 g. 0.3 c? That’s an enormous amount of kinetic energy per unit mass. I mean, enormous. The starship would have to burn several times its own mass in fusion fuel to expend that much energy-per-unit-mass.

This means you could put an impeller drive on an electric generator turbine, run it off of a tiny bit of fusion fuel, and use the resulting impeller-propelled generator to power a small city. Or even better, instead of powering the impeller drive on your generator with fusion, power it with a smaller impeller-powered electric generator!

Voila. Something for nothing. Bottle it and sell it!

That part, I think we’re supposed to just politely ignore.

Because it would have spectacular effects on the atmosphere, and because the opposite wedge would stick into the ground and that would be even messier. They don’t seem to use wedges in-atmosphere for anything bigger than missiles.

Yes, they draw energy from hyperspace; most of the energy for moving the ship doesn’t come from the fusion plant, it comes from the wedge. He’s called it a primitive version of the Core Tap from his Dahak books.

For the curious, the5thImperium.com has a bunch of collected ‘infodumps’ from Weber about the Honorverse and his other settings here.

Hell, it’s the inertial compensator that seems more like magic to me than the wedges. I can see using extreme gravity wedges to propel a ship, assuming you could generate the field. And, assuming you could do it, I could see how they could be impenetrable. But how do they keep the crews from turning into paste with every maneuver? Well, with inertial compensators of course. But how would those work?? How do you dampen inertia at all, let alone dampen it when you pulling 500 gravities and making radical turns and such?? Squish like grape.

It’s the same thing in most sci-fi stories involving star ship combat. They all use the same thing to get around the fact that making any sort of radical maneuver in space when going at high speeds would kill the crew.


Well, in the Honorverse at least the inertial compensator works by dumping inertial effects into the wedge somehow. Which is one reason why the missiles accelerate at tens of thousands of gs and the ships only a few hundred; compensators can’t handle that kind of acceleration and the crew are squishier than missiles.

Like I said, I could see how, if you could control gravity and produce a high gravity field (which is what a wedge is IIRC), you could push a ship or whatever else at high velocity. I could see how such a wedge would act as a shield (be like trying to fire something into a neutron star or even a black hole). I can’t see how you could dump inertia into such a sump, though as you say that’s how it works in the books.

Hell, I just love the books and simply suspend belief when I’m reading them, going with the flow. Sort of like the Lost Fleet series…it’s pretty cool, but at a certain point you just have to nod and accept if you want to get into the story.


Actually, I find it more contrived that dumping inertia is a problem at all; with most gravity based drives in SF it isn’t an issue because the field pulls on everything equally. You don’t feel any inertial force for the same reason you don’t feel any while in free fall.

I don’t think you’d move in that case. Basically, if you have a field that can generate high levels of gravity (or, I suppose, anti-gravity) then it needs to be directional in order to move the ship. Inertia though is inertia…it’s not about the gravity driving the ship, it’s about making radical turns at high velocity. I can’t wrap my head around how you could do that no matter what fantasy tech you had. How do you ‘dump’ that into anything? You are making a radical right turn at 500 gravities…what do you do? What do you do??


Squish happens when the vessel is accelerating at a different rate than the human inside.

If you could generate a gravity field, gravity would act on the vessel and the human and accelerate them at the same rate. Ergo, no squish.

I think the idea is that the technology is mastery of gravity and gravitic theory. They even use gravitic lenses to achieve fusion in their reactors.

They rotate the ship, and continue accelerating forward. (In a new direction.) You would only have to cushion the effects in generally one direction.

Edit: Actually, I like Tabby’s explanation better.

And since we already KNOW they can generate gravity fields – it’s why the crew can walk around on board a docked starship, instead of floating through the hallways – all a starship accelerating at 450g needs to do is generate a 450g field directed toward the front of the ship.

I think the U.S.S. Enterprise uses something similar when they engage their Impulse Drive.

That’s not correct, tracer.

That’s explicitly stated to happen when they’re “under sail” in a gravwave, but it’s never mentioned for normal space, or even for quiet hyperspace. It’s as good a fanwank as any, though.

And any technology that can manipulate gravity like they do can also, inherently, manipulate inertia, so that’s not a problem (or at least, not a new problem: Gravity control is an indistinguishable-from-magic tech as it is).

I didn’t mean the Impulse Drive used gravity-control technology to acheive propulsion – I meant that the starship had to engage an internal counter-gravity field in the opposite direction to keep the tremendous thrust of the Impulse Drive from turning everyone on board into crepes. (I believe they referred to it as the Inertial Dampener.)

Still doesn’t explain why, if they can violate the Conservation of Energy like that, they don’t built impeller-powered Power Plants.