Using neutrino flux *and* gravity to limit drive discharge?
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Author:  EDG [ Mon Jul 22, 2013 4:08 am ]
Post subject:  Using neutrino flux *and* gravity to limit drive discharge?

Here's an idea that I'm still investigating. I've never really been happy with needing to discharge stutterwarp drive coils in a gravity well - it seems like taking two seemingly unconnected things (radiation and gravity) and mashing them together. Also, we have the "problem" of pesky brown dwarfs being discovered that "mess up the Arms".

But... what if we could kill two birds with one stone? What if you have to discharge the drives not only where the gravity is higher than a certain value (0.11G), but it also has to be in a volume of space where the neutrino flux is higher than a certain value? We could say that the neutrino flux is actually what encourage the drive to discharge its radiation - if they're not present in high enough numbers then it can't happen even if the local gravitational field strength is high enough. This would mean that you have to be close to a star - not a brown dwarf - in order to discharge the drive, which means that solitary Brown Dwarfs and their systems can't be used as stopping points for spaceships (they don't fuse hydrogen, so they don't produce neutrinos).

If this is the case, then you would have to be a certain distance from an actual star to be able to discharge the drive. We could set this distance to be something on an interplanetary scale so that we can go to most places in a star's planetary system, but not in interstellar space.

Neutrino flux is written as "neutrinos per square metre per second". We'll give this unit a name - the "Nu", since nu is the greek letter for neutrino. Sol produces a neutrino flux of 7e14 Nu at earth's orbit (yes, that's how many neutrinos are zipping through you every second!). Since this decreases with the inverse square of distance, that drops to 7e10 Nu at a distance of 100 AU, and 7e8 Nu at a distance of 1000 AU. So if we say the critical neutrino flux for discharge is 1e9 Nu, that means that any ship within 836 AU of a solar mass main sequence star is able to discharge its drive, so long as it is within a gravitational field strength of 0.11G.

This critical Nu distance would be calculated by: D = SQRT(neutrino flux at 1 AU/1e9)

However, it seems that the neutrino flux emitted by a main sequence star is proportional to its luminosity, at least if it's less massive than Sol. More massive stars use the CNO cycle in their cores more than the proton-proton chain of less massive stars, which means that they produce a different number of neutrinos (I'm not sure if it's more or less at this stage, still researching that). And Giant stars (RGB giants, HB giants, AGB giants, and supergiants) also have different fusion reactions going on in their cores with different neutrino production rates.

But the neutrino flux for less massive stars seems to be directly proportional to their luminosities. So the dimmest M9 V star will have a neutrino flux of about a millionth that of Sol (since it would be a million times less luminous). That means we knock off 1e6 from the Nu value, so at 1 AU from this M9 V star, the neutrino flux is only 7e8 Nu instead of 7e14 Nu. That means that the critical Nu distance for the dimmest actual star would be 0.836 AU... which is pretty close, but still actually outside its habitable zone anyway so it's not going to make life too difficult.

For brighter stars and Giants, presumably the neutrino flux would be much higher than Sol, so their critical Nu distances would be even further than 836 AU. So unless the ship wants to go somewhere in interstellar space then it's not likely to be a problem.

But this does mean that those new solo/binary brown dwarfs that keep getting discovered can't be used as stopping points to discharge the drives. That said, neither can white dwarfs, neutron stars, or black holes - so that might make things interesting since a few white dwarfs are on the map too.

The only problems I see with this are twofold:
1) It's another calculation to do that varies on the stars. But that can be simplified by a table, and in most cases the critical Nu distance is going to be far beyond wherever ships may be going in a system.

2) The fusion (or fission) reactors on ships may actually produce a high enough neutrino flux to make this approach unusable. Yes, they are much smaller than stellar cores, but the stutterwarp drive is much closer to the reactor too. If the flux from the reactor is higher than 1e9 at typical distances between the reactor and drive then we'd have to increase the critical Nu so that the drives can't just use the neutrino flux from the reactor to stimulate discharge, which means that the critical Nu distance would have to move closer to the star. I'm still investigating that though.

Anyway... thoughts?

Author:  EDG [ Mon Jul 22, 2013 4:40 am ]
Post subject:  Re: Using neutrino flux *and* gravity to limit drive dischar

According to this: ... ry/027.pdf , a 1GW nuclear fission reactor would produce a whopping 1.5e20 neutrinos per second! That seems to scale with power output (so assuming that fusion is similar output), a Kennedy (with a 150MW reactor, according to GDW 2300AD) would produce 2.25e19 neutrinos per second.

At a distance of 1 metre that drops to about 1e19 neutrinos per m² per second. At 100m that would drop to 2.25e15 Nu... still way too high for the limit I propose. Even at 1000m, it'd be 2.25e13 Nu, and that would be a really huge spaceship with the drive and reactor at opposite ends! And I don't think the Kennedy is that big... (I can't actually find a length measurement for it... anyone know where that could be located?)

But the idea isn't quite blown out of the water. I notice that a lot of the civilian ships in GDW 2300AD have much smaller MHD Turbine plants, which presumably don't emit neutrinos. So this limit could work for them, while giving bigger (military?) ships an advantage since they wouldn't be affected by the neutrino flux limit (their drives are always going to be operating close enough to their fusion reactors to be able to discharge, so all they'll need is the gravitational field to discharge into. Oooo, which means that they COULD use brown dwarfs to get to places that other ships can't). Additionally, any ships close to these vessels would also be able to use the neutrino flux from the reactors to initiate their own drive discharge, which is kinda handy. Hrm... that makes things kinda interesting.

Author:  EDG [ Mon Jul 22, 2013 6:20 am ]
Post subject:  Re: Using neutrino flux *and* gravity to limit drive dischar

Turns out it's even more interesting... nuclear fission reactors would swamp the drives because they produce a ridiculous amount of neutrinos - but nuclear *fusion* reactors might not, depending on what reaction they use. Apparently the D-T (Deuterium-Tritium) and D-He3 (Deuterium-Helium3) fusion reactions doesn't produce *any* neutrinos (or at least very very few, and only from side-reactions), while the P-P (hydrogen-hydrogen) reaction used in stars produces a lot - about 33% more apparently than a fission reactor generating the same power.

P-P reactors are incredibly unlikely though since they require vastly higher pressures and temperatures than the other fusion chains, so they're probably impractical for this Tech Level. But... D-T and D-He3 reactors may be possible - D-He3 reactors would require higher energies than D-T reactors and would be more cutting edge. Neither reaction seem to produce neutrinos, but D-T reactions produce damaging neutrons that have to be dealt with and that limit the lifespan of the reactor, while D-He3 reactions produce protons that can themselves be used to generate electricity too. (see ... actor.html )

So if ships have D-T or D-He3 reactors, then they'll be restricted by the Critical Nu limit. If they have nuclear fission or P-P reactors, they won't. So maybe military ships could be fitted with fission reactors (even though they're larger), and civilian ships could have D-T or D-He3 fusion reactors?

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