Fleet Tankers Or Oilers ...

If I remember correctly, the fission plants were in use for LACs and were better because they had much longer endurance than fusion plants because they didn't need bunkerage.

zuluwiz wrote:If I remember correctly, the fission plants were in use for LACs and were better because they had much longer endurance than fusion plants because they didn't need bunkerage.

That's what the books say. Kzt's point is that fusion reactions are so much more powerful that even once you factor in the higher density of fission fuel a given volume of fusion fuel holds more power than a given volume of fission fuel.
Unless the fusion reactor is hideously inefficient the hydrogen tank necessary for 18 months of operation at a given power level should be smaller than the pile of fuel rods needed for the fission reactor to do the same.

Clearly that's not the case for Honorverse LACs, so something beyond the physics of the two nuclear reactions is tipping the balance in fissions favor.

Kzt likes to assign it to authorial fiat, aka the power of plot. I like to assume the mechanism that enables that plot device is that GRAVMAK plants have problems scaling down to as low output and size as you need for a LAC. That there's some minimal efficient size (which is too big for a LAC) and by doing so small you're having to spend something like 90% of the power produced just to run the reactor itself).

Keith_w wrote:Are you speaking RL or Honor world? Nuclear fusion produces more energy than fission which is why scientists are trying to get it to work on a self-sustaining basis.

Fusing a couple of tons of hydrogen to helium produces more energy than is yielded by fissioning 20,000 tons of 100% plutonium 239. Which means that it's totally impossible to get more power out of a fission pile than a fusion reactor on a 20,000 ton ship unless you are incredibly ineffective in your fusion reactor efficiency and incredibly effective at extracting power from fission.

I noticed that they specificaly do not refer to using heavy water. They do talk about hydrogen as fuel for all sorts of things including thrusters on starships and things like air cars.
When Honor is laying the trap for the SS ships at Cerebs she takes her ships out to the hydrogen mining operation (well extraction platform- automated) in that system, crams all the hydrogen she can into the tanks of her ships and then uses that to go from being parksed in the ambush position to accelerating in behind the SS force without the use of the impeller engines.

Hydrogen, not water.
I would suspect that the military starships and probably most civilian ships would have some level of capasity to breakdown water into O2 and H should it become critical to provide either the O2 or generate hydrogen as fuel

We all know this is very important stuff. Why in a couple of thousand years the readers of this historical account of around 2000 AD will up and say that we got it correct first.

kzt wrote:

Keith_w wrote:Are you speaking RL or Honor world? Nuclear fusion produces more energy than fission which is why scientists are trying to get it to work on a self-sustaining basis.

Fusing a couple of tons of hydrogen to helium produces more energy than is yielded by fissioning 20,000 tons of 100% plutonium 239. Which means that it's totally impossible to get more power out of a fission pile than a fusion reactor on a 20,000 ton ship unless you are incredibly ineffective in your fusion reactor efficiency and incredibly effective at extracting power from fission.

I believe that I concur with Jonathan_S.

There is or has been, a minimum practical size on the gravity-based fusion plants for use onboard a ship. Pinnaces and assault shuttles are laser fired and use magnetic containment because grav-fusion plants weren't sufficiently downsizeable in a suitable manner. They still mostly aren't, because missile and recon drone microfusion plants don't have to worry about people near them while they're active.


IIRC, the minimum grav fusion reactor is such that the power requirements to sustain and contain the reaction means that a grav fusion reactor on a LAC is dumping nearly all of its power into sustaining the reaction, but if you scale up the reactor, the requirements to sustain and the power generated don't scale similarly - that is, the power needed to sustain and contain the reaction is either flat, or nearly so, whereas power generated increases exponentially.
The fission pile, while less efficient in terms of its output, requires next to nothing to contain the reaction. As a result, the fission pile is putting nearly all of its output into the ship's other systems.
In other words, if the grav fusion plant on an LAC is putting 95% of it's output back into self-containtment and sustaining the reaction, only 5% of its output is going into the ship, whereas the LAC fission pile is only putting 5% of its output into self-containment, leaving 95% of it's output for the LAC's other systems. That means 5% of the fusion plant's output for the 95% of the fission plant to replace.
Those numbers are pulled out of my ass, mind, but the point is that the comparison isn't simply "reaction mass efficiency" vs "reaction mass efficiency" in a vacuum.



It was said that Grayson pushed fission efficiency well beyond what anyone else had ever done. So there's that.

However, the key thing is that if the fusion plant sized for a LAC eats nearly all of its output to keep itself and its associated safety systems running, whereas fission doesn't - you're not comparing the reactions themselves, you're comparing how much you get after containment and sustaining the reaction, and all the safety systems are paid for. That, supposedly, is where the difference is made.

Here's an analogy - grav fusion is pushing something heavy along a high friction surface, while LAC fission is using a very low friction surface. Friction is representing the amount of power the reactor itself eats. To push the object the same distance (powering a LAC), fission has an easy time because it's not hampered as much by friction (the reactor's internal requirments).
Alternatively, LAC grav fusion is sprinting with 200 pounds of drag weights, while LAC fission is sprinting with 2 pounds of drag weights.

Kytheros wrote:

kzt wrote:Fusing a couple of tons of hydrogen to helium produces more energy than is yielded by fissioning 20,000 tons of 100% plutonium 239. Which means that it's totally impossible to get more power out of a fission pile than a fusion reactor on a 20,000 ton ship unless you are incredibly ineffective in your fusion reactor efficiency and incredibly effective at extracting power from fission.

I believe that I concur with Jonathan_S.

There is or has been, a minimum practical size on the gravity-based fusion plants for use onboard a ship. Pinnaces and assault shuttles are laser fired and use magnetic containment because grav-fusion plants weren't sufficiently downsizeable in a suitable manner. They still mostly aren't, because missile and recon drone microfusion plants don't have to worry about people near them while they're active.


IIRC, the minimum grav fusion reactor is such that the power requirements to sustain and contain the reaction means that a grav fusion reactor on a LAC is dumping nearly all of its power into sustaining the reaction, but if you scale up the reactor, the requirements to sustain and the power generated don't scale similarly - that is, the power needed to sustain and contain the reaction is either flat, or nearly so, whereas power generated increases exponentially.
The fission pile, while less efficient in terms of its output, requires next to nothing to contain the reaction. As a result, the fission pile is putting nearly all of its output into the ship's other systems.
In other words, if the grav fusion plant on an LAC is putting 95% of it's output back into self-containtment and sustaining the reaction, only 5% of its output is going into the ship, whereas the LAC fission pile is only putting 5% of its output into self-containment, leaving 95% of it's output for the LAC's other systems. That means 5% of the fusion plant's output for the 95% of the fission plant to replace.
Those numbers are pulled out of my ass, mind, but the point is that the comparison isn't simply "reaction mass efficiency" vs "reaction mass efficiency" in a vacuum.



It was said that Grayson pushed fission efficiency well beyond what anyone else had ever done. So there's that.

However, the key thing is that if the fusion plant sized for a LAC eats nearly all of its output to keep itself and its associated safety systems running, whereas fission doesn't - you're not comparing the reactions themselves, you're comparing how much you get after containment and sustaining the reaction, and all the safety systems are paid for. That, supposedly, is where the difference is made.

Here's an analogy - grav fusion is pushing something heavy along a high friction surface, while LAC fission is using a very low friction surface. Friction is representing the amount of power the reactor itself eats. To push the object the same distance (powering a LAC), fission has an easy time because it's not hampered as much by friction (the reactor's internal requirments).
Alternatively, LAC grav fusion is sprinting with 200 pounds of drag weights, while LAC fission is sprinting with 2 pounds of drag weights.

That reminds me of the 1970s in the US where emissions equipment was added to car engines and the laws of how horsepower was measured changed.

In the 60s, you measured horsepower as what the engine produced before you placed it in the car, by the 80's you measured how much got to the road surface after the emissions equipment, alternator, various system pumps, and AC stole engine power. So, an engine rated at 350 horsepower in 1969, may have been rated as 150 horsepower in 1980, because that was the actual "useable" power of the engine.

However, that "lost" 200 horsepower is still important - it being used to keep the car systems working, and fuel is still being burned all the time fo those lost horsepower.

According to wikipedia, The largest nuclear reactors in operation are 1,600 MW. A nuclear power station might have multiple reactors, but 1,600 MW is the largest per single reactor, and may be much smaller, with 200-500MW reactors common and research reactors avalible at less than a megawatt.

To give an idea of the power usage for starships, 1,600 MW will be enough to power a city of 400,000 to half a million people, yet is barely enough to power a 20K ton shrike.

I am under the impression that the grav fusion plant is a one size fits all. Reliant class BC Nike in SVW at 877K tons required 2 plants but had 3 for redundancy.

If everything scaled linearly, that means that one grav fusion plant would be somewhere between 36-70 gigawatts, and that is enough power to supply all the electrical power for all but the 12 largest electrical producing countries.

36.4 GW Italy
44.4 GW United Kingdom
50.9 GW South Korea
52.9 GW Brazil
65.6 GW France
72.7 GW Germany
74.3 GW Canada
94.7 GW India
118.7 GW Russia
123.5 GW Japan
394.6 GW China
498.7 GW United States

At 17,000 volts, which is the most common voltage for power lines in residential areas in the US, 1 GW would require 588,235 amps, which would be a main bus bar of 2,000 square centameters, or 44 CM (18") on a side, so now we know how spanner got his name when he dropped one.

darrell wrote:At 17,000 volts, which is the most common voltage for power lines in residential areas in the US, 1 GW would require 588,235 amps, which would be a main bus bar of 2,000 square centameters, or 44 CM (18") on a side, so now we know how spanner got his name when he dropped one.

I thought the standard distribution primary in the US was 11000 volts to ground or 13.3KV phase to phase. Homes generally have a transformer pulling from one phase and delivering 120V to ground to the house. Large buildings (e.g. 20 apartments) can have 13.3KV three phase going into a transformer in the basement. I have heard of factories who have 3-phase 33KV going into a substation in the building. I believe 33KV is the largest distribution normally seen in the US.

12.47 kV is the delivery voltage I see marked on feeder conduits and transformers around work.