Attacking Darius:

cthia wrote:There will always be at least one long vein of highly combustible hydrogen coursing through the ship. Which brings us right back around to my notion of the one long fuse leading to a stick of dynamite. Which leads right back to the reactor.

You do realise that ship has 2 or more nuclear reactors going at any time, with core temperatures measured in the millions of kelvins, right?

I'd say that hitting the reactor is a far bigger problem for the ship than the cold hydrogen lines after water has been separated but before it's been compressed for fusion.

The point of carrying water all around your ship is that it serves multiple purposes in one:

1) you have to carry a lot of it anyway. As many including you have argued, it's better to carry water than molecular hydrogen, even if it weighs 9x more per mole.

2) having plenty of water would allow crew comforts, like no water rationing for showers, for cooking, etc.

3) it's a good heat sink

4) it's a good radiation shield and possibly a good laser shield too (attenuation)

Because of all of those, it makes sense to carry them all around your ship and have plenty of pipes and pumps to distribute it. The water can be used to keep the ship just warm enough too.

What's more, water is very easy to find in the Universe (unlike what all the invasion Sci-Fi movies have told us). A ship in distress could simply snag the closest comet or drive through a water spewed into space by a moon's underground ocean into space and use that as a fuel source.

Water is not the best for any of the options above aside from cooking, but it's good enough for all of them.

ThinksMarkedly wrote:

cthia wrote:There will always be at least one long vein of highly combustible hydrogen coursing through the ship. Which brings us right back around to my notion of the one long fuse leading to a stick of dynamite. Which leads right back to the reactor.

You do realise that ship has 2 or more nuclear reactors going at any time, with core temperatures measured in the millions of kelvins, right?

I'd say that hitting the reactor is a far bigger problem for the ship than the cold hydrogen lines after water has been separated but before it's been compressed for fusion.

The point of carrying water all around your ship is that it serves multiple purposes in one:

1) you have to carry a lot of it anyway. As many including you have argued, it's better to carry water than molecular hydrogen, even if it weighs 9x more per mole.

2) having plenty of water would allow crew comforts, like no water rationing for showers, for cooking, etc.

3) it's a good heat sink

4) it's a good radiation shield and possibly a good laser shield too (attenuation)

Because of all of those, it makes sense to carry them all around your ship and have plenty of pipes and pumps to distribute it. The water can be used to keep the ship just warm enough too.

What's more, water is very easy to find in the Universe (unlike what all the invasion Sci-Fi movies have told us). A ship in distress could simply snag the closest comet or drive through a water spewed into space by a moon's underground ocean into space and use that as a fuel source.

Water is not the best for any of the options above aside from cooking, but it's good enough for all of them.

But the reactors are deep in the bowels of most ships while the thrusters are on the hull.

cthia wrote:But the reactors are deep in the bowels of most ships while the thrusters are on the hull.

Yet another reason for the fuel for the thrusters to also be near the hull.

cthia wrote:There will always be at least one long vein of highly combustible hydrogen coursing through the ship. Which brings us right back around to my notion of the one long fuse leading to a stick of dynamite. Which leads right back to the reactor.

Does there actually need to be? What happens if you feed the fusion reactor with water? The oxygen wouldn't participate but would it be a problem?

Loren Pechtel wrote:

cthia wrote:There will always be at least one long vein of highly combustible hydrogen coursing through the ship. Which brings us right back around to my notion of the one long fuse leading to a stick of dynamite. Which leads right back to the reactor.

Does there actually need to be? What happens if you feed the fusion reactor with water? The oxygen wouldn't participate but would it be a problem?

Feed the reactor which is located in the bowels of the ship with water to produce the hydrogen? Then that hydrogen has to travel in a vein thru the ship back out to the thrusters.

Unless everyone is positing that the fusion thrusters have their own built-in reactor.

Loren Pechtel wrote:Does there actually need to be? What happens if you feed the fusion reactor with water? The oxygen wouldn't participate but would it be a problem?

At a minimum it would be incredibly less efficient. The oxygen atoms won't participate in the fusion reaction at the energy levels required for fusing hydrogen, deuterium or helium-3, but will absorb energy, both created by that fusion and by the means by which the energy levels of the reactants is brought up. We don't know how a gravity reactor works, but in a plasma reactor like a tokamak, you inject energy into the system by huge electromagnets so the protons accelerate around the torus. If you have these huge blobs with 16x the mass of a proton in the way, they will absorb energy too. And they may have different trajectories than the hydrogen and helium nuclei, which means they could impact the walls of the reactor.

No, electrolysis is very simple. It's expensive to us only because it takes energy to do it. But if you have a nuclear reactor producing an excess of energy, it's actually cheap. You separate out the hydrogen and deuterium atoms from the oxygen ones before the reactor. What you do with that oxygen, is up to you.

In a star, the heavier elements sink to the bottom, and as gravity isn't enough to make them fuse, they stay inert in that core for a long time. For a star like our Sun, that's upwards of 10 billion years in that state. That starts with helium, then heavier elements including oxygen, all the way up to iron. Our Sun will eventually fuse the helium, once the supply of hydrogen runs low and the outward pressure of the fusion slacks off: then it contracts and ignites helium fusion for some millions of years. It'll do the same to oxygen too at a later time, for an even shorter period. And once it gets to iron, game over.

cthia wrote:Feed the reactor which is located in the bowels of the ship with water to produce the hydrogen? Then that hydrogen has to travel in a vein thru the ship back out to the thrusters.

Unless everyone is positing that the fusion thrusters have their own built-in reactor.

You don't always have to pair up an electrolysis reactor to separate hydrogen from oxygen to a nuclear fusion reactor. You can have 2 to 6 nuclear reactors aboard the ship with their dedicated electrolysis chambers, however many are required to ensure they don't become the bottleneck in case of battle damage, inside the armoured reactor assembly.

And you can have electrolysis chambers spread over the ship's inner hull area, taking in water and separating oxygen and hydrogen. The hydrogen is then accelerated using the technology available (for us, an ion engine) out of the ship in the direction opposite that which you want to go. The oxygen I'm going to guess is simply expelled out at low velocity, because I think the ship will have more oxygen surplus in the reactors than it actually needs.

This is energy-intensive, sure. So my calculation a few pages back of just how much energy a reactor needs to produce to accelerate a ship at 50 gravities for one hour using just thrusters would be way off. The mass consumption would be off too: I calculated 30 tons/hour of hydrogen, but if the input is water, than the mass consumption is actually 9x bigger (you have to add one ₁₆O for every two ₁H), to the tune of 270 t/h, but is also within the realm of feasible as this ship masses over half a million tonnes. It can have that much bunkerage volume.

The problem is only Thermodynamics: expelling the heat produced. There's no current known way to get rid of that much heat. And given that spider drive ships still have a problem with heat exhaust, the problem is not completely solved in the HV and Thermodynamics has not been wholly circumvented.

cthia wrote:Feed the reactor which is located in the bowels of the ship with water to produce the hydrogen? Then that hydrogen has to travel in a vein thru the ship back out to the thrusters.

Unless everyone is positing that the fusion thrusters have their own built-in reactor.

Cthia, the whole ship is plumbed with Plasma conduits - it's how Honorverse ships transfer power. The capacitors are Plasma Capacitors. Each weapon, drive system, sidewall generator, etc, etc is run off live Plasma.

It came to me about 3 years ago, the plasma system is analogous to Late 19th century steam systems. A ship's screws are turned by steam, the turrets are turned by steam, the guns are elevated by steam. Steam lines are plumbed all over the ship. The steam pressure from the boilers isn't enough on their own so there are steam accumulators (ie capacitors) all over the ship to add more pressure where it is needed.

So hydrogen storage tanks are no biggie, because Hydrogen/Helium plasma at >30,000K is plumbed all over the ship, and every capacitor (one at every weapons system, in every missile, and spread over the ship to add redundancy and power the wedge) is full of live hydrogen/Helium plasma.

cthia wrote:Feed the reactor which is located in the bowels of the ship with water to produce the hydrogen? Then that hydrogen has to travel in a vein thru the ship back out to the thrusters.

Unless everyone is positing that the fusion thrusters have their own built-in reactor.

Theemile wrote:Cthia, the whole ship is plumbed with Plasma conduits - it's how Honorverse ships transfer power. The capacitors are Plasma Capacitors. Each weapon, drive system, sidewall generator, etc, etc is run off live Plasma.

It came to me about 3 years ago, the plasma system is analogous to Late 19th century steam systems. A ship's screws are turned by steam, the turrets are turned by steam, the guns are elevated by steam. Steam lines are plumbed all over the ship. The steam pressure from the boilers isn't enough on their own so there are steam accumulators (ie capacitors) all over the ship to add more pressure where it is needed.

So hydrogen storage tanks are no biggie, because Hydrogen/Helium plasma at >30,000K is plumbed all over the ship, and every capacitor (one at every weapons system, in every missile, and spread over the ship to add redundancy and power the wedge) is full of live hydrogen/Helium plasma.

There are at least two steps in there that we do not understand; because it involves millennia in the future technology, that is akin to magic for us.

First is how the plasma is confined to the tubes. We can only speculate that it uses the artificial gravity generators in repulsion or pressor beams (that also seem magical). We expect that most of those tubes only contain plasma on demand, with automatic shutoff in case of rupture. Note that the method of confinement probably will not stop radiative heating of those tubes (another source of waste heat).

Second is how that plasma is converted into what we would consider usable energy, such as electricity. We expect that they have something better than magneto-hydrodynamics (or at least a very much improved version of MHD).

Which causes me to wonder:
If they could use gravity to contain plasma in the tubes; then why couldn't they use gravity induced fusion, instead of laser initiated fusion, in the shuttle reactors?

tlb wrote:Which causes me to wonder:
If they could use gravity to contain plasma in the tubes; then why couldn't they use gravity induced fusion, instead of laser initiated fusion, in the shuttle reactors?

My assumption would be that the plasma in the tubes would be below the temperature/pressure levels necessary for fusion. (Because otherwise you've got a distributed fusion reactor running throughout your ship; and YIKES!!)

So if they use gravity to confine plasma into the tubes then presumably it'd require less gravity to do so that it would to hold hydrogen at the fusion point as the heat and energy of that fusion tries to drive it apart. The gravity you'd need to generate for the fusion reactor is probably many times what you'd need to confine non-fusing plasma. We know that ships use gravitically/electro-magnetically compressed (aka GRAVMAKs) fusion plants -- but it appears those have significant issues scaling down (hence, apparently, why destroyers and many cruisers have to make due with just 2 reactors instead of being able to carry 3 smaller ones -- and why fusion LACs have such crap endurance despite fusion providing much more power per lbs or per volume than fission)

Presumably the minimum viable scale for the grav generators necessary to achieve GRAVMAK fusion are just too large for a shuttle or pinnace -- any I can only assume that's because they'd need to be vastly more powerful than grav generators that need only to contain non-fusing plasma.