Why is there a Jump Fuel requirement?

[Tom Kalbfus]

I have an interesting question. Why do Jump Drives need jump fuel? Why are their reactionless maneuver drives that run on only power from the power plant? Why doesn't the Maneuver Drive get the fuel instead? We could call it "Maneuver Fuel". Now "Maneuver Fuel" would be separate from fuel for the power plant. Fuel for the power plant is a source of energy, a fusion reaction occurs and the power plant fuel gets turned into something else while energy is released, the power plant then channels that energy into the various ship systems including the maneuver and jump drive. Now the maneuver drive throws hydrogen out the back to push the ship forward, while the jump drive bends space so the ship can enter jump space, I don't know why the jump drive required fuel to do that and not just energy from the power plant, and why does the Maneuver drive require only an energy input, I would thing this arrangement would be the opposite. Why not?

 

[Sigtrygg]

The answer to your question is Traveller version specific.
In every other version of Traveller the jump fuel is used in three ways:
1 - to 'supercharge' the power plant to produce an enormous burst of energy that is fed to the jump capacitors
2 - to carry away fusion waste products from the power plant
3 - as coolant

Mongoose Traveller is the only version to suggest that a portion of the fuel is used to maintain a bubble of hydrogen around the jumping ship while in jump space - this is a fanon concept from years ago that has somehow been adopted and is not in T5 nor MWM's definitive Jumpspace article in JTAS 24.

For the sake of completeness I should also add the designers of T4's FF&S mentioned the jump fuel surge tank residue being used to maintain a thin hydrogen atmosphere around the ship, but not completely fill the spacetime bubble that surrounds the ship.

 

[baithammer]

The hydrogen bubble cleans up a problem with being able to super charge the power plant, namely the power plant then should be able to use the same output for other uses.

The hydrogen jump bubble can be thought of as expanding real space into a bubble creating a void with the ship inside of it ( Jump Space), the ship is moved into the center of the jump space bubble and once the bubble has reached maximum expansion collapses with the ship at a point further out in real space. ( Variation on the rubber band warp drive.)

 

[Tom Kalbfus]

Seems to me that if a reaction drive was used, similar amounts of "Fuel" would be set aside for reaction mass, as is now set aside for the Jump Drive.

The hydrogen bubble cleans up a problem with being able to super charge the power plant, namely the power plant then should be able to use the same output for other uses.


The hydrogen jump bubble can be thought of as expanding real space into a bubble creating a void with the ship inside of it ( Jump Space), the ship is moved into the center of the jump space bubble and once the bubble has reached maximum expansion collapses with the ship at a point further out in real space. ( Variation on the rubber band warp drive.)

Oh yes, as a disposable capacitor! I guess what they were afraid of was the player characters using their Jump Drive to go Jump Jump Jump, each jump takes 5 days so to go three times as far it would take 3 jumps and take three times as long. A capacitor takes time to recharge, one could play with the recharge times, so you can't Jump immediately after taking a pervious jump, and add a rule that you can't charge the capacitor in Jump space, it might not be a capacitor for electricity either but for gravitons, if the capacitor accumulates gravitons and can only accumulate them while in normal space, this would tend to limit your ability to jump multiple times.

That is the in game techno-babble explanation, but I think the real meta game explanation is that it is a fig leaf for getting rid of the reaction mass requirement for a reaction drive, with a reactionless engine, all you need is a source of energy, no reaction mass needed, having a jump fuel requirement effectively puts back the reaction mass, only this mass is used for the Jump drive instead of the maneuver drive. I believer with a reactionless Jump Drive, you would simply charge its capacitor with energy, and when the jump drive is activated, all that stored energy is released in the form of gravitational waves when the ship goes into Jump Space. You would need maneuver drive fuel to get to the point where you can Jump from and from the point the jump takes you to the planet's surface. The purpose I think is to force the starship to refuel after every jump, I have to think why the game designers did it this way as opposed to the other way.

 

[baithammer]

with a reactionless engine, all you need is a source of energy, no reaction mass needed,

Your forgetting the fusion power plant still needs fuel and the real problem with old explanation was the ability to arbitrarily expend more energy than its power plant rating would allow by shoving more fuel through it.

The purpose I think is to force the starship to refuel after every jump

Not true, you can take shorter jumps without having to refuel, you just end up taking longer overall than the single jump.

 

[Hakkonen]

Mongoose Traveller is the only version to suggest that a portion of the fuel is used to maintain a bubble of hydrogen around the jumping ship while in jump space - this is a fanon concept from years ago that has somehow been adopted and is not in T5 nor MWM's definitive Jumpspace article in JTAS 24.

For the sake of completeness I should also add the designers of T4's FF&S mentioned the jump fuel surge tank residue being used to maintain a thin hydrogen atmosphere around the ship, but not completely fill the spacetime bubble that surrounds the ship.

The hydrogen-inflated bubble idea struck me as silly the first time I read it, and it still does.

 

[Tom Kalbfus]

Mongoose Traveller is the only version to suggest that a portion of the fuel is used to maintain a bubble of hydrogen around the jumping ship while in jump space - this is a fanon concept from years ago that has somehow been adopted and is not in T5 nor MWM's definitive Jumpspace article in JTAS 24.

For the sake of completeness I should also add the designers of T4's FF&S mentioned the jump fuel surge tank residue being used to maintain a thin hydrogen atmosphere around the ship, but not completely fill the spacetime bubble that surrounds the ship.

The hydrogen-inflated bubble idea struck me as silly the first time I read it, and it still does.

I think the propulsion systems should be kept as real and as close to real physics as possible while still meeting the FTL requirements, I would use reaction drives, and give them realistic fuel requirements and by "fuel" I am also including reaction mass, only a small part of that fuel is actually fusion fuel. If you skim a gas giant for fuel, most of it is going to be plain hydrogen and helium, only a small part of it is the easily fusible stuff, the rest is just reaction mass, processing the fuel separates it out into its components. The fusible stuff is fed into the power plant, the energy output is them fed into the maneuver drive, and plain hydrogen and helium is also fed into the maneuver drive, the energy inputs heat the rest of they hydrogen to a high temperature plasma, magnetic fields then channel that plasma out the back of the starship pushing it forward according to Newton's laws. When you get to a certain distance from the planet, the Jump drive then is used to transition to Jump Space, I would have no specific jump fuel, just energy from the power plant feeding into a capacitor to accumulate a charge, that charge is released all at once activating the jump drive and causing the ship to go into Jump Space, that is how I would do it if I were designing a traveler game.

 

[Sigtrygg]

If you are going to do that (use more realistic reaction drive fuel/reaction mass for maneuver drives) then you will need to use the jump fuel formula or the like to determine fuel/reaction mass, and even then all that fuel/reaction mass is only good for a few minutes burn, hours tops. This is pretty much what TNE tried to do with HEPlaR but still got the numbers wrong - the drive has too great an endurance.

I recommend reading up on the Tsiolkovsky rocket equation, and spending a few hours at the Atomic Rockets web site:

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

 

[Hakkonen]

I think the propulsion systems should be kept as real and as close to real physics as possible

If I disagreed with this statement any more strongly, the force of my vehemence would awaken the frost giants and bring about Ragnarok. Traveller (and, indeed, virtually all science fiction) doesn't need realism, it needs verisimilitude. It needs to be internally consistent, and to make sense according to its own rules; and, largely, it does so. Forcing the game to conform to real-world physics serves no narrative or gameplay purpose; and I guarantee that if you start rewriting the rules to bring them more in line with real life, not only will you have to rewrite the entire game, but the end product will not be fun.

 

[Reynard]

Can you imagine how many seconds Star Trek and Star Wars would have lasted if they insisted on modern realism? We'd be watching nothing but 2001 without the Monoliths.

 

[Sigtrygg]

I can not abide the ship combat in Star Wars and Star Trek. Give me the Expanse any day.

It is possible to use real world physics and only a modicum of future tech.

It's quite interesting what you can achive with known physics and the money and political will to engineer it into reality - see Isaac Arthur's youtube channel.

Let's make a couple of assumptions:
the Falcon 9 block 5 and future developments like the BFR and Skylon cut the costs of getting stuff into space so that stations can be built
once the stations are built asteroids, comets and moons become resources we can develop (we will soon have to be mining asteroids for rare earths if everyone wants a tablet and smartphone)
nuclear powered spaceships are built in space
ion engines, solar sails riding laser beams, nuclear (fission) powered varaiable thrust rockets (mature and next gen Vasimir)
O'Neil habitats, colonies on the Moon and Mars, rotating habitats built inside asteroids
and then the jump drive is discovered...

 

[AnotherDilbert]

Why do Jump Drives need jump fuel?

I assume it is to make high jump ships expensive and impractical, ensuring that most starships plods along at J-1 or J-2.

 

[Condottiere]

As I recall, when you jumped, you shot your bolt: all your fuel was expended regardless of range. That was changed with the introduction of the jump governor, retrofitted to the alphabet drives.

The basic role it;s played is slowing down the player, and creating the age of sail ambiance.

 

[ShawnDriscoll]

I have an interesting question. Why do Jump Drives need jump fuel?

It's a setting thing.

 

[Tom Kalbfus]

If you are going to do that (use more realistic reaction drive fuel/reaction mass for maneuver drives) then you will need to use the jump fuel formula or the like to determine fuel/reaction mass, and even then all that fuel/reaction mass is only good for a few minutes burn, hours tops. This is pretty much what TNE tried to do with HEPlaR but still got the numbers wrong - the drive has too great an endurance.

I recommend reading up on the Tsiolkovsky rocket equation, and spending a few hours at the Atomic Rockets web site:

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

A fusion reaction is about 100 times as energetic as a chemical rocket burn. I heard it stated that a fusion rocket has the potential to reach 10% of the speed of light with slowing down. Ever hear of the Daedalus space probe?

That is a fusion rocket, I believe it was designed to reach 20% of the speed of light without slowing down, if a slow down is desired, it can reach 10% of the speed of light using the fusion reaction and 10% of the speed of light is around 30,000,000 meters per second, it would take 3,000,000 seconds of 1-g acceleration to reach 10% of the speed of light, that is 34.7222222 days to reach that speed with an acceleration of 10 meters per second squared, notice this Daedalus has two stages, each stage can go up to 10% of the speed of light without slowing down. I assume a Traveller starship can perform like one of those stages, which means it can reach a top speed of 15,000,000 meters per second and then can slow down. This is rougly equal to the four weeks of operating time I mentioned before, and that is what I'm assuming for the performance levels of your basic fusion starship. To go faster, you need something more exotic and expensive, such as antimatter. Antimatter is for small starships, for large starships, it becomes prohibitively expensive for even governments, so a black hole drive is used instead, black holes have a certain minimum mass, otherwise they get too hot and explode, a ship the size of an aircraft carrier or larger can use them, smaller ships have to use antimatter if you want to reach a speed like 97% of the speed of light.

Most of the cost of an antimatter ship is its fuel, the actual ship itself is a rounding error. No point in actually refueling such a ship, most of those are throwaways, once you expend all the antimatter onboard, you throw away the ship and build a new one with a new supply of antimatter onboard. Black hole starships are reusable, their black holes decay whether you are using them or not, they last a few years and then they must be discarded before they explode. Those black holes are safer to handle than antimatter, and for large starships they are a more economical option as well.

 

[Sigtrygg]

And how much of that ship is reaction mass...

 

[Tom Kalbfus]

And how much of that ship is reaction mass...

You can see the fuel tanks in the picture, to accelerate for a month and to reach about 10% of the speed of light requires the full fuel load of a single stage, the bottom stage has to carry the top stage, and for the purposes of the ships hull, the top stage counts as part of the Bottom stage when it is launched. the top stage is accelerated fully fueled to 10% of the speed of light and then it seperated from the bottom stage and accelerates another 10% to 20% of the speed of light.
https://en.wikipedia.org/wiki/Project_Daedalus
What I am looking at is ballpark estimates of speed, probably you need closer to 60% of its mass as reaction mass/fuel to reach 10% of the speed of light.

1 week = 604,800 second, cruise velocity equals 3,024,000 m/sec = 1% of the speed of light, fuel requirement = 15% of hull volume
2 weeks = 1,209,600 seconds, cruise velocity equals 6,048,000 m/sec = 2% of the speed of light, fuel requirement = 30% of hull volume
3 weeks = 1,814,400 seconds, cruise velocity equals 9,072,000 m/sec = 3% of the speed of light, fuel requirement = 45% of hull volume
4 weeks = 2,419,200 seconds, cruise velocity equals 12,096,000 m/sec = 4% of the speed of light, fuel requirement = 60% of hull volume

This is roughly in the ballpark with fusion, but what if we used something slightly better than fusion, there is a concept called a "Nebula drive" it is used stricly for slowing down a starship using magnetic fields, an ionization laser and the interstellar medium, with that we could use 10% of hull volume in fuel to accelerate to 1% of the speed of light, the time spent accelerating would still be 1 week, about 3.5 days accelerating and 3.5 days slowing down, using magnetic breaking saves on the fuel requirements for slowing down, so we can use a greater fraction of it to speed up. By extending this relation ship, that means 6% of light speed can ultimately be achieved using 60% of hull volume for fuel/reaction mass.

A Nebula Drive is more commonly known as a magnetic sail.
https://en.wikipedia.org/wiki/Magnetic_sail

 

[Reynard]

If I really need slower than light interstellar travel I'll use the simplicity of T5's Not As Fast As Light Drive. At least time between adventure will take weeks rather than years.

 

[Tom Kalbfus]

If I really need slower than light interstellar travel I'll use the simplicity of T5's Not As Fast As Light Drive. At least time between adventure will take weeks rather than years.

Well, I'm using it in conjunction with my wormhole campaign, the faster than light travel is with the wormholes, not the starships.

Since these ships do not carry their own FTL drives, they have some extra cargo space, such as this one with 22 tons of cargo instead of 12.
I decided to make it simple, their operating durations are the same, they just consume their Jump fuel as reaction mass. This sheet doesn't distinguish power plant fuel from maneuver drive reaction mass. Since this model had the same number jump drive as maneuver drive, I just left the fuel tankage the same as in the Jump model with the reactionless drive.
I am getting higher performance than I should with a fusion power reaction drive, but in the interest of simplicity, I just make this one small alteration and eliminate the Jump drive. I haven't adjusted the cost at all, since I don't know the cost breakdown of this ship. The performance is somewhere between a reactionless drive and a reaction drive, closer to the reaction drive, as I don't want to eliminate the fuel tankage for the jump drive as this would make this starship ridiculously empty.

Maybe some other form of fusion is used here, such as quark fusion for example. if you heat matter to a high enough temperature the atoms will simply melt into a quark-gluon plasma, and some quarks will be converted into photons in this process, the main draw back is that really high temperatures are required for this and a huge energy input is required to achieve such high temperatures to initiate quark fusion, a lot of this heart leaks out and their are losses in efficiency, so the result is that their is a slight amount more energy released than the energy needed to sustain this reaction, the result is something maybe twice as efficient as fusion, falling way short of matter antimatter annihilation, but still yielding better results than conventional fusion.

This is a real thing, I did not just make it up. Here is an article:
https://futurism.com/quark-fusion-produces-eight-times-energy-nuclear-fusion/
Maybe a quark fusion reactor, an inefficient one perhaps, could explain the performance of this starship.

 

[middenface]

Tom,
While I appreciate the free advertising, I don't appreciate the fact you have posted the image of the Type S with no acknowledgement of me as the artist.
I generally don't mind people using my work in this fashion. But I appreciate a link or a mention of where you got the art from.
From time to time people even ask me, can they use X. How radical is that>?

The image is linked from Deviant art, I can see this. Likewise no mention of where you got the ship image from, on there.
https://www.deviantart.com/art/Scout-Courier-Wormhole-Campaign-745157866

This is not the first time you have done this. And you have been pulled up on it before.