Apollo defense possibilities

kzt wrote:We've already gone over this. Fusing H to He yields far more power by mass. Like 100 liters is equal to thousands of tons of refined plutonium.

SWM wrote:The question right now isn't energy per mass, but energy per second.

That, too, has been discussed, and Duckk is right that ship fusion generators give more power than LAC fission generators.

What I can't recall is whether the old LACs before Cimeterre and Shrike also used ship-sized fusion generators, or the smaller fusion generators used on pinnaces (which give less power than LAC fission generators).

Jonathan_S wrote:I recall they used ship style GRAVMAKs.

But for the fission breakthrough to work there pretty much had to be some horrifically bad scaling issues cramming those fusion plants down into a LAC.
(Like way over half the power output getting eaten as overhead just to run the GRAVMAKs -- something like that)

It's been said somewhere that the smallest fusion bottle it's possible to build with that technology would power an old-style destroyer, while the small-scale fusion plants used in pinnaces and assault shuttles have horrible problems scaling up to LAC size. The fission piles fit in the middle. Trying to build something like a LAC around a destroyer-size fusion bottle produces something a bit ... unbalanced ... shall we say. The imbalance isn't quite as bad with a dispatch boat or a frigate since it's got to have a hyper generator and two rings of nodes, including alpha nodes. This is why the Nat Turner frigates have a fusion bottle instead of the fission piles the Shrikes in their ancestry might suggest.

kzt wrote:

Weird Harold wrote: but the big advantage of the Fission-powered LACs is the space saved in bunkerage (fuel storage) and the increase in endurance not having to refuel every day permits.

Which is where physics says "not so much". If you are refueling your fusion reactor every week you'd be refueling a fission reactor every hour.

IIRC, Cimmeterre endurance is on the order of 96 hours while a Shrike-A was given as 24 months (incorrectly given as years in early editions) Honorverse physics would seem to deviate from Real World(tm) physics.

Weird Harold wrote:IIRC, Cimmeterre endurance is on the order of 96 hours while a Shrike-A was given as 24 months (incorrectly given as years in early editions) Honorverse physics would seem to deviate from Real World(tm) physics.

Minor nit: I think it was originally 18 years, which should have been 18 months.

kzt wrote:

Weird Harold wrote: but the big advantage of the Fission-powered LACs is the space saved in bunkerage (fuel storage) and the increase in endurance not having to refuel every day permits.

Which is where physics says "not so much". If you are refueling your fusion reactor every week you'd be refueling a fission reactor every hour.

One thing you seem to be forgetting is how much of the fuel is used to keep the fusion bottle powered in the first place. If, at the scale of a LAC, you need to feed 90% (percentage randomly picked, of course) of the generated power back into the system just to keep it running, and this is only 5% for the fission pile, the differences probably start to be a bit different than you think.

MaxxQ wrote:

Weird Harold wrote:IIRC, Cimmeterre endurance is on the order of 96 hours while a Shrike-A was given as 24 months (incorrectly given as years in early editions) Honorverse physics would seem to deviate from Real World(tm) physics.

Minor nit: I think it was originally 18 years, which should have been 18 months.

I believe that is correct, now that you mention it. Still hours vs months between refueling.

mark wrote:

kzt wrote:Which is where physics says "not so much". If you are refueling your fusion reactor every week you'd be refueling a fission reactor every hour.

One thing you seem to be forgetting is how much of the fuel is used to keep the fusion bottle powered in the first place. If, at the scale of a LAC, you need to feed 90% (percentage randomly picked, of course) of the generated power back into the system just to keep it running, and this is only 5% for the fission pile, the differences probably start to be a bit different than you think.

If I remember the math correctly, the energy of fissioning 20,000 tons of 100% plutonium 239 is roughly equal to the energy of 100 liters of Hydrogen being fused to Helium. (Given that the critical mass of Pu239 is 11 kg I'd tend to wonder how you could run a reactor with 20,000 tons of Pu239, but that's besides the point.)

Anyhow the overhead would have to be so absurd that a destroyer couldn't actually finish an interstellar voyage to a nearby star without running out of fuel, much less traveling for weeks.

kzt wrote:

mark wrote:One thing you seem to be forgetting is how much of the fuel is used to keep the fusion bottle powered in the first place. If, at the scale of a LAC, you need to feed 90% (percentage randomly picked, of course) of the generated power back into the system just to keep it running, and this is only 5% for the fission pile, the differences probably start to be a bit different than you think.

If I remember the math correctly, the energy of fissioning 20,000 tons of 100% plutonium 239 is roughly equal to the energy of 100 liters of Hydrogen being fused to Helium. (Given that the critical mass of Pu239 is 11 kg I'd tend to wonder how you could run a reactor with 20,000 tons of Pu239, but that's besides the point.)

Anyhow the overhead would have to be so absurd that a destroyer couldn't actually finish an interstellar voyage to a nearby star without running out of fuel, much less traveling for weeks.

But now you're talking about a destroyer, which is a bit larger than a LAC. (And, yes, I do understand that real world physics won't add up however you look at it)

Anyway, the overhead argument really makes only a very limited amount of sense, since if it works, why would anybody build a LAC in the first place, instead of simply building a DD and not installing a hyper generator. (and why wouldn't you install that hyper generator?)