M Drives and Dark Energy

[Anonymous]

Too much coffee this morning Reynard?

:wink: :mrgreen:

I'm off to make the second cup...

Let's diverge a little from drives, Dragoner, how did you envisage dark matter would give us stealth in space? Some kind of cloaking generated by manipulating dark matter around the ship? Would it be one way or two?

 

[Tom Kalbfus]

I like how people compare fuel-propelled rocketships with reactionless drive ships as if they are both real things.

Antimatter is real, it is also stable absent contact with matter and can be stored, which makes it an excellent rocket fuel. Another form of fuel and part of an engine is a microscopic black hole. A microscopic black hole can convert ordinary matter into energy in the absence of antimatter. As for converting hydrogen into neutrinos, we don't even have a theory on how to do that, not all of them, though we can convert some of them into neutrinos through nuclear reactions, we can't control the direction they travel in because we have no way to contain them.

Anti-particles are real, have been detected and even produced in small quantities - not convinced that the benefits outweigh the risks of having large quantities of it in containment (even a gramme). If we had the technology to safely contain antimatter, I would suggest we would have the technology to contain and direct neutrinos as well, but still. As for black holes, the direct mass-energy conversion rate would be far too low to be useful, somewhere at the 10-20% mark - assuming the emitted energy was in a form that could be used. What has been suggested is that we could ignore the emitted energy and harness the rotational properties of the black hole to generate energy, which might be more useful. But, again, this is still pure speculation - knowing that black holes, antimatter and neutrinos exist gets us no closer to being able to use them as energy sources.

Antimatter is the only thing that gas a chance of getting a self-contained starship capable of approaching a appreciable fraction of the speed of light. As for antimatter containment, that is simple, just get a container made out of antimatter. An antimatter container won't contain a neutrino. What tends to be overlooked is you can make things out of antimatter just as you can of matter. Each element on the periodic table of elements has its antimatter counterpart. You basically make a starship where some parts are made out of antimatter, say a fuel tank for instance, and you can move this fuel tank around with magnetic fields, never letting it come in contact with matter. The tank can release some antihydrogen stored as a liquid, a laser would then ionize it and it would be channeled to react with matter using magnetic and electric fields, all this is within the current know laws of physics, the engineering details is how we make significant quantities of antimater, how we fuse antihydrogen into heavier elements we can make stuff out of, and how we fabricate the objects we need out of antimatter without bring it in contact with matter, but these are just engineering details, the physics is known.

http://www.projectrho.com/public_html/rocket/antimatterfuel.php

 

[Reynard]

Trai had too much torpedo juice during the ship's First Day holiday celebration so might be well qualified to speculate on dark matter and stealth. Since dark matter is so hard to detect even though it permeates the entire universe, using it as a fuel/reaction mass to propel a ship means the 'exhaust' would be undetectable or very difficult to detect at all but maybe very close ranges. Even neutrinos need a large quantity of dense substance to detect them including that handwavey box over in the avionics section. Still, the best stealth is the energy absorbent hull coating and a very good sensor suite. Bunnies.

"hic" What did I just say?

 

[heron61]

Neutrinos are massless. You are expelling a particle that does not push. Is that the reactionless in the formula?

More recent data (ie from the last 15 years) indicates that neutrinos have a very small mass. This isn't proven, but at this point it looks likely based on that data about neutrino oscillation (basic info here http://en.wikipedia.org/wiki/Neutrino_oscillation).

 

[Reynard]

My mistake for making a general popular claim. If neutrinos had no mass at all they would be totally intangible to all matter. I should have stated their mass is so EXTREMELY small they can pass through most matter virtually hindered. I did mention they need a very dense material to detect their passing.

As yet, no one has actually detected a material that makes up most of the universe. They're theorizing and we're speculating. As with so many things, it sounds cool as a sci fi element.

 

[heron61]

My mistake for making a general popular claim. If neutrinos had no mass at all they would be totally intangible to all matter. I should have stated their mass is so EXTREMELY small they can pass through most matter virtually hindered. I did mention they need a very dense material to detect their passing.

All true, which makes them perfect for m-drives. All you need is some process that converts matter (or matter + antimatter) into directed, highly relativistic neutrinos and you have a reaction drive that is exceptionally efficient, which also isn't an exceedingly powerful weapon, and (for those who care) doesn't violate any physical laws

 

[Anonymous]

Any theoretical issues with using such a drive in an atmosphere?

 

[Tom Kalbfus]

Any theoretical issues with using such a drive in an atmosphere?

Neutrinos work fine in an atmosphere or solid lead for that matter.

 

[Reynard]

A neutrino or dark matter drive produces no noticeable exhaust. Those 'exhaust ports' might be expelling other waste products that are less than lethal.

 

[Anonymous]

At what point would you have atmospheric vehicles crossover between a neutrino based drive and grav plates for thrust?

I'm asking in pursuit of the long running debate on the difference between small craft and grav vehicles and to try to clarify how the drives and anti grav systems work in Traveller.

Of course, Dragoner could just tell me to hush and leave his thread alone but it's kinda related...

:mrgreen:

 

[Reynard]

Not to get too off track but I still believe the difference between vehicles and space craft is the maneuver drive which is more powerful for long flight. Both use anti-grav for planetary lift but small vehicle AG is too small and inefficient for long term/long distance flight.

 

[dragoner]

Let's diverge a little from drives, Dragoner, how did you envisage dark matter would give us stealth in space? Some kind of cloaking generated by manipulating dark matter around the ship? Would it be one way or two?

Someone on fb mentioned having to turn your ship into a haze of WIMPs, which I didn't think so, at first I was thinking of the modern coatings that damp EMR, such as on Aircraft and ships. However, your question, made me thinking of destroyers laying a smoke screen (or any vehicle) http://en.wikipedia.org/wiki/Smoke_screen a rather Traveller-ish solution. What the screen would be composed of (or coating), however one could emulate the natural property of dark matter which makes it hard to detect, whatever it is; materials engineering handles this all the time. There is a military maxim: "if you can see he enemy then the enemy can see you"; so one way for the most part. That also would give reason for the fighter screens, drones, and Type S scouts; to ride outside the screen and broadcast back data.

 

[dragoner]

Neutrinos are massless. You are expelling a particle that does not push. Is that the reactionless in the formula?

A certain female aslan engineer hugs her ship's maneuver drive. "There, there. You work just fine and get us where we want to go very well. Do not listen to their insanity! Anti-matter! Dark matter! Do they think you are one of Grandfather's toys?!"

Anti-Matter and Fusion "rockets" - motors, still share the same problem of the orion or bomb engine; there isn't a material to make the combustion chamber from. Then there is the radiation factor which would kill the crew, then, yes, it would be like strapping a .50 Cal BMG to a bicycle and riding the recoil. Possible, but most local authorities would frown on the practice. In TNE, they upped the specific impulse by an order of another magnitude to FTL exhaust, in order to get the velocity in the range where a ship would move; not that anybody would want to be around that much heated plasma anyways.

Thinking on Dark Energy propulsion, the article did mention the expansion of space driving the universe outwards. That could be it with the M drive, micro-expansion of space, it could even be visible in a similar manner to heat distortions in the air, except as spatial distortion.

 

[heron61]

At what point would you have atmospheric vehicles crossover between a neutrino based drive and grav plates for thrust?

I'm asking in pursuit of the long running debate on the difference between small craft and grav vehicles and to try to clarify how the drives and anti grav systems work in Traveller.

We've seen published info that grav drives become less powerful away from gravity wells. I like the idea of this being true in a fairly significant manner - just as gravity decreases as the square of distance, so does my preference for grav drives, so at 10 diameters, reduce the thrust of grav drives by a factor of 100. This would allow any grav drive of more than 1 G* to be used for station-keeping and basic maneuvering in orbit around most planets, and would allow the ship to easily take off and land, but would make the drive useless for interplanetary travel.

So any craft used solely for travel on a planet or going to orbit could use a grav drive - you could even use on for a journey between the Earth and Luna, since your initial acceleration could still get you there fairly rapidly. However, for long trips, like gas giant refueling and then traveling to a habitable planet in the same system would use neutrino thrusters.

This also allows for an intermediate sort of starship that is designed solely for use with a support network, but still has some maneuvering capability - a mildly improved X-boat would be a good example, as would some large corporate cargo ships and liners. These ships would have jump drives and grav drives (which presumably require very tonnage or energy than standard thrusters), but lack maneuver drives, so they can move around in orbit around a planet, like heading from their jump point to the high port or even to landing, but are useless for interplanetary travel except in emergencies.

* I'd also change the rules very slightly so that the G-rating of a grav drive refers solely to how much better it is than the strength of the gravity well it's in, so a 2-G grav drive could generation 2 Gs of thrust on Earth's surface, and 0.333 Gs (1/6th G x 2) on Luna's surface. This isn't a change that would make any real difference, but I like it.

 

[heron61]

Anti-Matter and Fusion "rockets" - motors, still share the same problem of the orion or bomb engine; there isn't a material to make the combustion chamber from. Then there is the radiation factor which would kill the crew, then, yes, it would be like strapping a .50 Cal BMG to a bicycle and riding the recoil. Possible, but most local authorities would frown on the practice. In TNE, they upped the specific impulse by an order of another magnitude to FTL exhaust, in order to get the velocity in the range where a ship would move; not that anybody would want to be around that much heated plasma anyways.

When you run the numbers, the ISP of TNE's HEPlaR drive is 4 million, which gives an exhaust velocity of 40,000 km/sec or 13.3% of the speed of light, which is way to high for any fusion drive we can imagine, but given the existence of nuclear dampers, gravity control, and all of the other wonders of Traveller tech isn't outright impossible, but I also wouldn't expect to see that sort of drive below TL 11 or 12. Also, as you mention, it would make any ship equipped with that sort of drive into an exceptionally deadly plasma weapon.

Any sort of direct conversion or matter-antimatter drive (including the neutrino drive I discuss above) would have an ISP of 30 million (meaning it as an exhaust velocity of C). if you want to allow for a bit of inefficiency, you could give it an ISP of 24 million, allowing it to use 1/6 the fuel+reaction mass of a HEPlaR drive, giving it an operating range more like what we see for maneuver drives in both CT & MongT. Making the drive into one that emits neutrinos also entirely de-weaponizes the drive.

 

[dragoner]

If you hand-wave the combustion chamber issue, then it becomes problematic in raising the question of why aren't ship's hulls armored with same material?

High ISP, doesn't necessarily translate to high thrust, a Hall thruster is a good example of high ISP and low thrust due to the mass of the propellant. In that vein I did once envisage a super ion thruster pushing through a gravitational field as a sort of m drive. I think I like the micro expansion of space now, or taking advantage of another quantum field, space is supposedly filled with them and they are full of energy.

Antimatter annihilation might not generate as much energy as we once thought, according to a CERN paper I read. Then there is the question of the gamma rays as well, making the rocket extremely hazardous.

 

[heron61]

If you hand-wave the combustion chamber issue, then it becomes problematic in raising the question of why aren't ship's hulls armored with same material?

For the neutrino m-drive, all you need (which is admittedly a pretty big, but not physically impossible "all") is a process that converts matter into highly relativistic directed neutrinos, at that point, you don't need much of a combustion chamber, or (depending on the exact specifics of the drive), all you need is a combustion chamber that reflects say 80+% of neutrinos. You could have this effect produced by a field that's some variant of nuclear damper tech (or maybe the tech used to enhanced the molecular bonding in Bonded Superdense armor). The best part is that this field need not be any more impervious to other forms of matter & energy than any other material.

High ISP, doesn't necessarily translate to high thrust, a Hall thruster is a good example of high ISP and low thrust due to the mass of the propellant. In that vein I did once envisage a super ion thruster pushing through a gravitational field as a sort of m drive. I think I like the micro expansion of space now, or taking advantage of another quantum field, space is supposedly filled with them and they are full of energy.

Absolutely, but often the reasons for this are either high energy requirements (like the VASIMR drive) or limitations of the durability of the combustion chamber (as with a matter anti-matter drive or in fact many proposed fusion drives. If 99+% of the energy produced from the neutrino m-drive is neutrinos and the process requires lots of clever tech, but no more energy than a typical ship's fusion reactor can produce, then neither of these is a factor and you can get 1+ G thrusts & a 20 million+ ISP. Sure, there's a lot of handwaving, but considerably less than for a reactionless drive, and it has (at least from my PoV) more interesting limitations, that are also more game-useful (like making it considerably more difficult to accelerate a weapon to 99.9999% C, since doing so requires lots of fuel+reaction mass (unlike thrusters, which merely require sufficient fuel to the fusion reactor to run them for a year or two at 4+ Gs).

 

[dragoner]

You are going to have a massive amount of neutrinos in the exhaust to get the mass you need, esp once you get into large ships.

Thinking more on micro expansion, there could be advertising: "With a Ling Standard M Drive, every time you fly your ship, the universe gets a little bigger." The downside of this is Space Expansion Pollution, or SEP; and worlds will manage traffic in order to keep SEP down. So that makes things like beanstalks much more viable, esp on high traffic worlds.

 

[Tom Kalbfus]

A neutrino or dark matter drive produces no noticeable exhaust. Those 'exhaust ports' might be expelling other waste products that are less than lethal.

Why is that an advantage?

 

[heron61]

A neutrino or dark matter drive produces no noticeable exhaust. Those 'exhaust ports' might be expelling other waste products that are less than lethal.

Why is that an advantage?

From a game perspective, it makes turrets and bay weapons useful, since they aren't completely outclassed by the ship's maneuver drive, and from a setting perspective, it allows ships to use their m-drive near planets w/o risk of vaporizing other ships, space stations, or portions of cities. A fusion drive would be fairly dangerous, while a matter-antimatter drive on a 100 Ton Scout would outclass the weapons of a 50,000 ton warship.