Some number crunching.

[Drakon]

Okay been doing some number crunching using T20.

Hydrogen is 99.985 percent H1 and 0.015 percent H2(deuterium) Assuming fusion reactions are:

12H1 yeilds 2He4 + 2H1 +2n + 48.825MeV of energy
6H2 yeilds 2He4 +2H1 +2n + 43.343 MeV of energy

These are per interaction.

Jump 1 requires 5 tons of fuel. Assuming all that fuel is used (100% efficiency) over the week (and not all at the beginning) that one is in Jump space, and the number of atoms in the fuel, I come up with 32,228,912 Megwatts of power used.

Or the power plant is generating 32 Terawatts of power for a solid week. That is a lot of juice!

I also looked at water for fuel and found the same volume of water actually produces 1/6.624 times less energy. Pure Hydrogen is actually a better fuel, pound for pound than water.

 

[Richard Saunders]

Hello.
Off course pure hydrogen is better than water, the oxygen in the water is a waist of time except for breathing (maybe).
I have wondered how water can run the fusion reactor and the jump drive as well as hydrogen, i assume it's a hand wave back to the start of traveler.
Not being a scientist of any kind but - maybe some of the water is run through a cracker to split the hydrogen then feed to the reactor where the temp cracks more water into hydrogen and oxy, the hydrogen fuses and the oxy dosnt so you get free oxy which you use to cool the chamber and as reaction mass.
The problem is what do you use if you have only hydrogen.
Yes i know there are problems with it but there are problems with water in a fusion reactor.
So this should start another argument.
Bye.

 

[TheDS]

Well, if so, let me proclaim my gladness to be in on such an arguement early.

Long ago, like at least when MT was out, it was discovered that fusing all the hydrogen in the jump-fuel for a jump was just plain crazy, as you have discovered. Even more recently it has been discovered that the fuel efficiency of a fusion reactor would make it nearly impossible to burn that much hydrogen. For instance, the amount of fusion energy available in a single GRAM of Deuterium would power your car for about a year. This is about 7kL of gasoline. Even the ".1kL/year" figure for the FFS reactors is obscenely wasteful. My figures show a gram of deuterium yields 240,000 Mj, btw. Per Mw, this is about 2 liters per year, not 100 or 150.

So instead, as evidenced by the SOM (Starship Operator's Manual), the majority of the fuel is used as coolant and ballast. They dump the hydrogen overboard to maintain the jump field about the ship, over the course of the jump.

This means a number of things. For one, any gaseous material can be used, even water vapor. However, I would have to suppose that "pure" hydrogen works the best, else we have no use for fuel purifiers at all. Dumping out water may also be bad because perhaps what we need is volume and not mass, so hydrogen works out that way too. (By that I mean, if you have to dump out a certain MASS per hour, you want to dump dense materials, but if youy have to dump VOLUME per hour, you want to use less dense materials, and hydrogen fits that nicely, in addition to not weighing the ship down so much.)

You don't dump water into a fusion reactor. You dump hydrogen into it (and then you really only spray it in slowly). That means running electricity through water to crack it into Hydrogen and Oxygen. The Oxygen can be used toreplenish the ship's supply, and the rest is dumped back into space, or could be sold, I guess. No sense wasting it.

Water makes for a good absorber of heat, and it's fairly safe to handle. It's not real dense either. And you can find it all over the place. So it's going to be used for a long time to come.

IIRC, FFS2 goes and tells you exactly how much energy is required to open up a jump, and probably also says how much energy is needed to keep the ship alive in it.

 

[Drakon]

The idea was not to "dump water into a fusion reactor" The idea was to crack the hydrogen out of the water, in order to run the reactor. I looked at water as a possible fuel because I figured that water, being more dense than hydrogen, and less explosive in the confines of the hull, would be a safer or better fuel source. Plus the oxygen can be used for life support.

One of the reasons I started this was because I wanted to modify the rules for Jump drive, come up with an alternative that fit well with the Traveller rules. What I am thinking is that instead of Jumping from point to point, the drive would be a Warp drive, a la Acubierre and Van Dem Broeck. The Jump number would be more of the "full speed" rating of the Warp drive.

One could travel slower, and there are interesting effects to be explored by warp bubble collapse, merging of two warp bubbles, what happens when a warp bubble runs into a massive object or a gas nebula, etc. Plus a question of how fuel rate tracks with warp speed. Would travelling at a slower speed stretch your fuel?

 

[far-trader]

Originally posted by Drakon:


<snip>

Plus a question of how fuel rate tracks with warp speed. Would travelling at a slower speed stretch your fuel?

Interesting. As for the question above I'd probably do an efficiency matched setup. For example a J4 drive would be most efficient at Warp 4 (for lack of a better term) with efficiency dropping off the slower you go. One reason a J4 ship might travel at Warp 2 (again an example) would be to travel as part of a fleet that included J2 ships (the whole moves at the rate of the slowest). And of course for tactical reasons it could once close to the endpoint pour on a little speed and arrive moments ahead of the rest for a quick scan, like a scout looking over the hill for the cavalry.

 

[Drakon]

My first thought is to use a variation on the "square cubed" law. One example comes from pump laws. To double the speed (RPM) of a pump, and double its flowrate, you need 8 times more power, (It also increases the output pressure or "head" by 4 fold) You see this same law applied to the volume of a stereo, or on a wind turbine.

Power would be directly proportional to fuel flow. How warp speed increases with power, I am still sorting out.

Tech level would have a lot to do with many aspects. It seems that as tech level goes up, warp efficiency would go up (Less power for greater speed), size and mass would go down. (smaller, lighter engines)

Also, as size of the ship goes up, you need a bigger warp bubble to contain it. If I am understanding the (proposed) physics, this is essentially based on the size of the "transision band" between the forward and after walls of the bubble, between the contracting and expanding regions of space-time.

In short, warp bubble size would go up as a square of the size increase.

There is one issue that I am kind of hesitant to mention. Part of this is because this is based on new physics that is just now being studied, and an area that has a high kook factor which could scare off serious research. But here goes:

The shape of these ships would be such as to fit inside a spherical bubble. Inside they can be oriented in any manner desired, with one exception. One must avoid the for and aft walls. And if you look at the resulting shape, you get a flatten spheroid, or flying saucer.

 

[TheDS]

As the volume of the ship goes up, the volume of the bubble goes up proportionally. (Double volume equals double bubble volume.)

As the length (longest dimension) of the ship goes up, the volume of the bubble goes up by the cube. (Double length (diameter) equals 8x bubble volume.) The surface area of the bubble goes up by the square. (Double length equals 4x the bubble surface area.)

Now, which is the important feature of the bubble: its volume or its surface area? The answer to that question will tell you whether you need to square or cube, based on the length of the ship (aka diameter of the bubble).

If instead what youwant to do is base it on the volume of the ship overall, like a conforming bubble or implant a grid in the hull (like the jump grid), then you don't care about ship length, you care about ship volume, and in that case, there's no need to square or cube. Probably you want the bubble's volume to be double or triple the ship's volume, but double the ships's ume and you still just double the bubble's volume.

 

[Uncle Bob]

Or you can use a van den Broek geometry and the inside ara of the bubble is vastly bigger than the outside, and this whole discussion is moot.

I like the idea of using the jump "fuel" as something other than fusion fodder. I always figured the uniform predictable character of protons and electrons led to predictable jump, except for random D an T nuclei. Heavier nuclei, given the same input as a proton, will move slower.
Using water, methane, or ammonia means the jump drive has to deal with not just the hydrogen but nitrogen, oxygen, and carbon of different isotopes. It is no wonder a ship misjumps so often with unrefined fuel.

 

[Drakon]

Originally posted by TheDS:
As the length (longest dimension) of the ship goes up, the volume of the bubble goes up by the cube. (Double length (diameter) equals 8x bubble volume.) The surface area of the bubble goes up by the square. (Double length equals 4x the bubble surface area.)

I am thinking that the major component of the bubble is a ring of "negative energy" that surrounds the middle. The length of this ring goes up as a square of ship's size, not cube. This ring, which is at the transition region between expanding and contracting space-time, is also the cause of the same in the other regions of the bubble.

Now, which is the important feature of the bubble: its volume or its surface area? The answer to that question will tell you whether you need to square or cube, based on the length of the ship (aka diameter of the bubble).

Hmmm... it appears that the gradients on the leading and trailing walls of the bubble is what matters, what imparts speed to the bubble itself. If I am reading this right, then it would be closer to surface area, (actually how much space-time compression/expansion is exhibited by the leading/trailing face of the bubble)

A larger surface area however does not mean a faster bubble. A stronger curvature in the walls does, and that means more juice.

Larger bubble requires more juice, faster bubble, more juice. Larger and faster are governed by ring size (how much energy is pumped into the narrow ring separating the two halves) which scales as a square of ship radius.

If instead what youwant to do is base it on the volume of the ship overall, like a conforming bubble or implant a grid in the hull (like the jump grid), then you don't care about ship length, you care about ship volume, and in that case, there's no need to square or cube. Probably you want the bubble's volume to be double or triple the ship's volume, but double the ships's ume and you still just double the bubble's volume.

Actually, you might want even more "dead space" inside the bubble, to prevent close contact with the regions of extreme tidal stress or gradients. If your bubble insides were say, 1 kilometer in radius, then scaling the ship up would not be as big a deal until you got into huge spaceship territory. Still thinking about this, still needs work.