[Ultra-Tech] [Spaceships] Ladderdown reactors

[acrosome]

This came up in another thread, so I figured I'd ask about it. I guess I'm particularly interested in the thoughts of David Pulver, if he's around here somewhere.

Where would Ladderdown reactors (use Ctrl-F for "ladderdown") fit into the scheme of ultra-tech power sources, and in particular spaceship drives? I'm tempted to just call them equivalent to total conversion reactors and drives... but that's not really right. They actually work a lot more like fission/fusion reactors, but much more efficiently and infinitely more cleanly. They wouldn't generate nearly as much power as a total conversion reactor- after all, after they run to completion you are left with a pile of Iron-56 (or Nickel-62), so by far most mass is conserved.

So, what would a Spaceships ladderdown power plant and drive look like?

What would power generation and lifespan be for a ladderdown power plant? I assume that lifespan is better than a fusion plant, but how much better? Uranium doesn't require the infrastructure that antimatter would, but you would need a lot more of it, so how would it compare to an AM plant?

What would acceleration and delta-V be for a ladderdown reaction drive? Would it really just be equivalent to a fusion or fission plant, only cleaner? Just how much uranium would be needed per ton of hydrogen remass, and what would it cost? Would they be explosive systems?

I can certainly make something up mid-way between an advanced fusion drive and the total conversion drive (perhaps it would look similar to an antimatter drive?) but I'm interested in the opinion of the experts that I trust, here.

Less importantly, what would other important ultra-tech equivalents look like, for instance a portable generator as on Ultra-Tech p.20?

I assume that TL would be 11^-ish somewhere?

I ask about all of this because I am in search of a ridiculously powerful and efficient torchship drive that's not complete handwavium and doesn't spew radioactive death. A ladderdown reactor is probably unobtanium rather than handwavium, and thus it interests me, because it might work well in a Traveller-esque space opera setting where one isn't worried too too much about realism, but still wants to avoid magical reactionless or subwarp drives and antigravity. If nothing else it might allow spaceships to land and take off from planets without generating a radioactive wasteland.

Finally, what secondary effects should I be aware of for this technology? Personally, I think that McCarthy dramatically over-emphasized the impact upon materials values. Sure, absolutely, there would be economic impacts (if only due to abundant clean energy) but you'd have to be burning though an awful lot of fuel metal to get to the point that streets were paved with gold just because gold is down-ladder from uranium and thus cheaper than asphalt. :)

If Pyramid were still around it might make an awesome article...

[acrosome]

I wonder if a ladderdown power plant might be modeled as a notional TL11^ fission powerplant (see Spaceships p.20), in which case it might be expected to generate 1 power point for 100 years. But it sounds much more efficient (and clean) than a standard fission plant, and you also get to ladder up all of the protons that you split off, so it has a fusion component, too. I might split the difference and give it the two power points of the fusion reactor, but the 100-year lifespan of the notional TL11 fission plant, and the option to de-rate to one power point for a doubled endurance and halved cost.

The problem there is that it compares unfavorably with the TL11 Super Fusion powerplant. Maybe I should make the ladderdown reactor TL10^? I would have a hard time justifying simply making it significantly cheaper than the (non-superscience) TL11 Super Fusion plant.

Hmm... thinking similarly a notional TL10^ NTR would have 1G acceleration and 0.75mps delta-V per fuel tank. Or would it be 0.6G? Well, either 0.6 or 1G acceleration per engine meshes very well with my setting concept, which would lack inertial compensators, but that delta-V sucks nuts. I would accept lower acceleration- and in fact might prefer 0.6G because reasons- if I can justify an awesome delta-V somehow. But since I don't really have an idea how a ladderdown drive might work I'm sort of stuck. If I can assume efficiencies akin to the Fusion Torch then at TL10^ that would be 15mps per tank, which is an awful lot more palatable, but still less than I was hoping. Or maybe assume slightly better efficiencies, in which case 30mps/tank would seem reasonable (since the Fusion Torch gets 45mps/tank at TL11).

This all makes a certain amount of sense from a game design perspective- the ladderdown is a combined fission/fusion drive, sort of, so one might assume that it is just slightly better than the fusion drive alone- but I really don't know how one would work so I'm not sure.

I guess I could also just handwave (gag!) that it is throttleable like a VASIMR or Plasma Torch. Using those as a guide this would be 1/5 acceleration at 5x efficiency in low thrust mode. So assuming high gear performance of 0.6G/engine and 30mps/tank that's 0.12G/engine and 150mps/tank in low gear. This would make it better by far than the TL10 Fusion Rocket, which gets 0.05G and 60mps per tank, and thus pretty much everyone would be using the same drive- even the cargo haulers who want cheap and efficient drives more than anything- which simplifies worldbuilding. The Ladderdown Drive would be ubiquitous. And maybe cut the cost if it is de-rated to only the lower acceleration? Basic cost might arguably be the same as the TL10^ Plasma Torch: about $1M for SM+5, half that if de-rated?

Or maybe I should only use the ladderdown system for the power plant, and use it to power some sort of electric drive? That would be pretty poor performance, though- no landing on planets.

[Anthony]

I would treat a ladderdown reactor as an exotic fission reactor, possibly with increased performance for higher TL. However, ladderdown reactors are superscience, they didn't do the math (they forgot about the binding energy of the free byproducts). The elements something like that would work for are mostly already radioactive, though there might be some edge cases where alpha particle decay is energy favored but not by enough to happen measurably.

[acrosome]

I just found the rules for Hazardous Drives and Powerplants in Spaceships 7. Since a Ladderdown drive doesn't need shielding, this makes me think that a higher acceleration is appropriate, perhaps 1G/engine, and probably still 30mps/tank. So in low gear that's 0.2G and 150mps.

Originally Posted by Anthony

The elements something like that would work for are mostly already radioactive...

Huh. Ok, I'll have to rethink. What would work? If it's something suitably rare then it might work as McGuffinite. Especially one of the edge cases you mention. But even if the fuel is radioactive, presumably the exhaust still wouldn't be, significantly. Oddly enough.

I'm also not sure that I understand why it wouldn't work. I mean, handwaving away the quantum tunneling marlarkey, yes, but in the end you are fissioning and fusioning, and the energy has to go somewhere, right? Damned near 1% of mass, in fact, and that's a metric crapton of energy.

But my other options are all at least limited superscience, too, and they all spew radioactive death. So I guess I would still take the Ladderdown technology if it can be made to work at all.

[Fred Brackin]

Originally Posted by acrosome

I
I'm also not sure that I understand why it wouldn't work. I mean, handwaving away the quantum tunneling marlarkey, yes, but in the end you are fissioning and fusioning, and the energy has to go somewhere, right? Damned near 1% of mass, in fact, and that's a metric crapton of energy.

I would add one more factoid to the discussion of thsi idea and that it while you can fission atomic nuclei down to Iron por fue them up to Iron and make "some" profit energy-wise the closer you get to Iron the less profit you make.

Burning Hydrogen into Helium typically lasts a star 90% of it's lifespan with almost all the rest coming from Helium to Carbon. Carbon to Iron (only in very large stars) typically lasts about 2 weeks. This is all because you're gettign less enerrgy out of each mass-unit of fuel and have to burn the fuel faster to keep up with the demand.

Similar principles apply to Fission and I expect that the Law of Diminishing Returns would preclude much beyond Uranium down one notch or Hydrogen to Helium.

I am also not sure there is no radiation. So you're extracting a neutron from a Uranaium nucleus and gaining energy in the process. What form does that energy take? If it comes in the form of the velocity of the neutron fast neuutrons usually constitute dangerous radiation and an inconvenient energy source at the same time.

Fast protons aren't as bad.

If it's in the form of photons you need for it to be a lot of lower energy photons instead of a few higher energy ones.

If I could manipulate atomic nuclei via anything like the quantum tunnelling process I'd use it for fusion and call it a Su[per-Fusion Reactor (as in Spaceships) and/or a Fusion Torch Drive and note that the Fusion Torch didn't emit gamma rays or neutrons but was merely a "simple" (if extreme) thermal threat.

[AlexanderHowl]

The vast majority of the energy beyond the Triple Alpha cycle is released beyond sustaining the fusion process is in neutrinos, so it is would not really add anything after you subtract the energy required for the fusion process. The process is so inefficient that massive stars only burn carbon for ~1000 years, neon for ~10 years, oxygen for ~30 days, and silicon for ~1 day.

[Anthony]

Originally Posted by acrosome

I'm also not sure that I understand why it wouldn't work.

The problem is that, while elements heavier than iron have lower binding energy per nucleon than iron, they don't have lower absolute binding energy, so you can't just subtract single protons and neutrons without it costing you energy. Instead, what you have to do is find a combination of two elements where the total binding energy is larger than the binding energy of your original material. The most common example of this is alpha decay (binding energy of helium), which in fact occurs because of exactly the process described for the ladderdown reactor (quantum tunneling), and should be expected to occur naturally if this process is significantly exothermal.

Something that changed the rate of natural radioactive decay would let you run a super-RTG, but you'd be starting with radioactive materials and ending with lead.

[acrosome]

I think I stumbled upon the idea of the ladderdown reactor being equivalent to an advanced fusion reactor last night, while thinking upon it as I went to sleep. In fact that's exactly what I said to myself, though my logic wasn't the same (and probably wrong).

First, yes, looking at the graph of binding energies it is obvious that you don't get as much per step when laddering down as when laddering up. That makes sense to me, as a layman.

However, every time you ladder down a step you release a proton, which is then laddered up. And as just mentioned you get an awful lot more energy from laddering up.

So, anyway, I understand why as you say it probably is most like an advanced fusion reactor. Most of the energy comes from fusion. In which case why not just start with hydrogen? The stuff is everywhere.

My logic last night was different, and probably not a very sound product of my sleep-addled brain. For every one step laddered down you release a proton, which is then laddered up 55 steps. So, 27:1 fusion:fission, according to my poor understanding. But looking at the graph of binding energies it looked like there was a trap at helium, so it may have been less, and thus both iron and helium might be the end products. (And maybe some nickel.) Though in retrospect it just takes a bit more energy in to fuse helium to lithium, so you don't get energy out of a few steps until you hit carbon, probably. Thus the known helium fusing to carbon reaction.
Again, just my my poor layman's take on it, at the time. :)

As I said, really what I want is a (relatively) powerful and (more importantly) efficient torch drive that doesn't spew radioactive death- and ideally a setup where a particularly fast ship might manage three or four Gs. And I would prefer that it be unobtanium rather than handwavium. I should have known better. :) But if I can just say that the Fusion Torch doesn't spew radioactive death, well, that's probably a victory for me. And after all, it is described as "limited superscience"...

It would have been really nice to get delta-V/tank into triple digits, like with the antimatter plasma torch, but as I understand it there is no way to make antimatter not be radioactive death.

[Fred Brackin]

Originally Posted by acrosome

as I understand it there is no way to make antimatter not be radioactive death.

<makes waggling hand gesture> Eh, that depends on what you call "radioactive death".

A straight matter-antimatter drive makes gamma rays and pions and then the pions decay into more gamma rays and you don't want to be following it too closely.

The antimatter plasma drive howeer is using the plasma part to absorb the antimatter annihilation products and the better it absorbs those the more efficient it is. The result will be a hot and fast moving mass of charged particles but the particle speed will be much less than c and the photons produced by blackbody radiation will be much lower energy than gamma rays.

It would still be a massive thermal hazard and you don't want to be in its' wake but until you're close enough that your hull heats up excerssively it's not an exceptional hazard by space standards.

Without superscience radiation shielding your spacepeople need the DNA Repair nano seen in Bio-tech (and/or Transhuman Space) just to deal with the cosmic rays so a spaceperson's standards about "radioactive death" might be somewhat relaxed anyway.

[acrosome]

But aren't a significant fraction of the pions uncharged, and thus they scatter off in random directions uncontrollably (and uselessly) before they decay into gamma rays? For that matter, gamma rays are pretty damned energetic, too. :)

So I guess I'm asking, what manner of antimatter drive are you referring to, that manages to control these energetic little suckers so well? Are you saying that the antimatter plasma drive (which IIRC is a superscience drive) isn't really a radiation hazard unless you're stupid enough to walk up behind one while it's running? I really don't know the notional physics that underpins such drives, so I have no idea.

Because that's the first thing I thought of- using properly constructed Visser wormholes to make antimatter on demand for the drive. (To keep costs down- the wormhole generator and short term containment are part of the drive's cost, so you just buy remass.) And I was trying to figure out exactly what sort of matter-antimatter annihilation might not qualify as radioactive death, since basically any sort of particle beam you fire through a Visser wormhole can be made to produce it's antiparticle. I struck upon proton-antineutron or antiproton-neutron interactions, which I thought might be a bit more "clean", but that turned out not to be so. Lord knows that proton-antiproton annihilation is dirty as hell. Electron-positron is better, but still frighteningly dirty.

But for the record, "not radioactive death" to a first order approximation means "it's reasonable to land it on an inhabited world". I don't think that any conceivable antimatter drive would qualify.

Mind you, I'm already positing a technology that uses Alcubierre drives and microscopic Visser wormholes, so if you can come up with a reasonably unobtanium* (as opposed to handwavium*) way to clean up an antimatter drive by using such things, I'm all ears.

* Handwavium is totally made up blafflegarb, like on Star Trek. Dilithium crystals are handwavium. Unobtanium is something where we can conceive of how it might actually work, even if we really have no idea how to do it at this point. Wormholes and Alcubierre drives are unobtanium, at least ostensibly.