# What are the different forms of FTL travel and how do they interact?

The Honorverse includes several different forms of FTL travel, and I must admit I'm confused about the differences.

There's 'hyper', which has different 'bands', each with a different relative speed compared to n-space. This is the most common form of travel I've seen referenced.

Then there's grav waves, which exist in hyper (but not in n-space?) and kill ships under impeller drive (which is still used in hyper) but you can ride them with grav sails.

Then there's wormholes, which allow nearly instantaneous transit between two points, under grav sails (essentially super grav waves).

But in many books they mention ambushes between grav waves (notably in Honor Among Enemies climax).

Essentially, I'm just confused about the different forms and how they interact. Can someone tell me if the above is correct, or explain why not?

• I would not say they are different forms. All of them use travel through hyperspace, although in the case of wormholes the amount of time in hyperspace is very very small. Commented Feb 4, 2011 at 16:40
• And there's the new drive invented by the bad guys. I'm still fuzzy on that one, though it appears to be faster than anything except a wormhole. Commented Nov 19, 2014 at 16:21
• @Donald.McLean: Two new drives, now: spider and streak, although the latter seems just a more efficient version of hyperdrive travel -- but the spider drive has no hyperspace transition at all (which is the primary event sensed by the early warning systems). Commented Jul 27, 2015 at 15:51
• @BenVoigt: Actually, it has no impeller drive (without that, though, you can't go to hyper). The spider drive seems to instead do something similar to tractor beams latching onto the alpha wall...
– Jeff
Commented Jul 27, 2015 at 17:07

There's an additional dimension that's neither space nor time. Under normal circumstances, we do not move in either direction along it. A hyperdrive allows for movement along that dimension.

This hyper dimension is broken into bands. Normal space is a 4 dimensional hyperplane through the 5 dimensional hyperspace. The hyperspace bands are 5 dimensional 'slabs' parallel to normal space with 'gaps' in between. The gaps are the hyper walls. The alpha wall separates the alpha band from normal space, the beta wall separates the alpha band from the beta band, and so on. There's some ambiguity whether there are a finite number of discrete 4 dimensional hyperplanes within each level or whether it consists of a continuous 5d hypervolume with infinitely many 4d hyperplanes.

Within a band a hyperdrive can move you up and down the hyper dimension, and it can jump you over the gaps. There's a notion of a velocity along the hyper dimension and this seems to apply to the jumps over the gaps as well.

Impeller drives and reaction drives (and presumably spider drives as well) all work the same in most of hyperspace as they do in normal space. The exception is Gravity Waves which cause impeller drives to blow up, and can even damage ships without any gravitic systems if navigated incorrectly. I don't think there's been any suggestion of how they might interact with spider drives.

Gravity waves are distortions of spacetime that occur in the portions of hyperspace other than normal space. They are generally linear structures with a defined 'width' and portions of that width are flowing on one direction or the other along it. These streams within the wave carry charge particles and by using a hyper sail within a stream moving the right direction, and ship can move along it can achieve much higher acceleration than under impeller outside the wave.

So generally speaking, ships move into hyperspace using their hyperdrive, move to the nearest gravity wave under impeller, switch to hyper sail and find a current int he wave going the direction they want, and move along it. If they need to change to another wave, they have to move out of it, switch to impellers, and then traverse the intervening space.

Wormholes are special gravity waves that intersect normal space rather than being confined to hyperspace. The result is that if you go to the right location in normal space, turn on the hyper sails, point in the right direction, and turn on your hyperdrive, you don't move into hyperspace like normal, but instead jump to a distant point in normal space without passing through the intervening space.

• Graphcis, a better description of bands, and touching on the spider drive - this is the better answer now. Commented Jan 15, 2015 at 17:12
• For what it's worth, I think the ambiguity is because they don't actually know in-universe. But it's been a while since I read them. Commented Jul 27, 2015 at 15:17
• What is the source for the image and the data (specifically, the discreet "bands" for each of the letters)? Commented Apr 6, 2021 at 16:28
• @DVK-on-Ahch-To Image is my own. The idea of the multiple bands is based on instances of David Weber using the plural when referring to them: "Alpha bands", "iota bands" etc.That implies more than one band for each level. Commented Apr 12, 2021 at 23:20

Sounds like you have it essentially correct.

The basic impression I got -- hyper is a different dimension, with different relationships between time and space than normal or "n-space." Conventional impeller drive generally works in hyper - its just that the different time-space relationship means you're covering more ground. The bands definitely have an influence on increasing n-space speed but I don't think the books are ever clear on what they are exactly - further dimensions they are transitioning too, likely.

Gravity waves are stretches of turbulence; I get the impression of a very powerful, fast moving current in the fabric of hyperspace. Grav sails allow the ships to safely be pulled along by the waves at greater speeds than they could normally obtain, while regular impeller drive clashes violently with the wave. The waves are naturally occurring and don't go to all destinations, so there are times when a ship must leave the waves and navigate a calm area to reach the destination (or another wave). The lower speeds during these maneuvers make ambushes more effective, plus ships can sit idle in these areas without active drives.

Another interesting point I picked up from the stories - it seems no drive power is needed to simply be in hyper -- only for transitioning to or from it, or movement on impeller drive between waves. So a ship could suffer drive damage that would leave it trapped in hyper. However, it also sounds like search and rescue, EVA, and other normal operations can be performed - a bit unlike the sense of being in a vague "nothing place" with no interaction with others that some other stories give.

• Actually, I believe that no power is required when you're using sails, as the grav wave provides the power.
– Jeff
Commented Feb 4, 2011 at 18:23
• Thanks, I forgot that. I would assume power is needed to initially enter the wave, but after that they can harvest from it. I also forgot to mention power needed to travel on impeller drive in hyper, so corrected both points. Commented Feb 4, 2011 at 18:32
• I think of the bands as compressed realities. Each band is a more compressed layer of space. The ship is still traveling at 0.3 times the speed of light whether it is in normal space or one of the hyperspace bands. Its just that you get more bang for your buck the higher you go. I tend to think of it as a triangle with the base being normal space and as you go higher up the triangle the width with respect to the base becomes narrower. Commented Jul 11, 2011 at 2:06

The part about ambushes between the gravity waves refers to two points: 1) Within a grave wave you can only use the sails. You can't have sidewalls up, you can't fire a missile. (The impellar drive of the missile would be instantly destroyed by the much more powerful grav wave around it.) 2) Between grav ways, normal impellar rules apply in hyper. So if you are outside a wave you could sit undetected (no impellar signature to give yourself away.) This would allow you to attack ships exiting the grav wave with missiles.