How do jump drives really work?

[McPerth]

So water is at least seven times as efficient as hydrogen as a coolant.


Hans

Probably, but nearly 14 times heavier, if weight can be a factor. Also quite more corrosive at high temperatures.

It takes also quite longer to take, as you must either make planetfall or mine (on ice asteroids/comets). While this may not be a problem on comercial basis (as long as your ship is steamlined), what about military operations prior to a planet invasion? You must either land on an enemy ocupied planet or take a long time mining asteroids before jumping away (so taking quite longer to take reinforcements if you're depending on limited shipping (ever played Invasion Earth ?)).

 

[rancke]

I won't argue here if N2 is better coolant than H2 (probably it is), but is it economic to use it?

It's very difficult to imagine that it wouldn't be. Volume is a Really Big Factor in starship economics. Really Really Big.

Really.


Hans

 

[rancke]

Probably, but nearly 14 times heavier, if weight can be a factor.

Well, maybe. But weight appears to be so much not a factor that some of the ship design systems completely ignore it. Of course, that doesn't mean it would be ignored in "reality", but volume is a much bigger factor than weight.

Also quite more corrosive at high temperatures.

Something that also appears to be the case with hydrogen. See Wil's (Aramis') post above. And water isn't that much more difficult to get hold of than hydrogen.

It takes also quite longer to take, as you must either make planetfall or mine (on ice asteroids/comets). While this may not be a problem on comercial basis (as long as your ship is steamlined), what about military operations prior to a planet invasion? You must either land on an enemy ocupied planet or take a long time mining asteroids before jumping away (so taking quite longer to take reinforcements if you're depending on limited shipping (ever played Invasion Earth ?)).

Or you could bring it along. You don't think that being able to carry seven jumps' worth of coolant instead of one would be something the military might consider useful?

But that's really besides the point. Granted that the military might have more important concerns than economic efficiency, the salient point is that merchants don't. Even if hydrogen was the coolant of choice for the military, it wouldn't be for civilian shipping. And the various ship design systems all omit any reference to alternatives to hydrogen. If hydrogen was used as a coolant, don't you think a ship design system that was intended to produce both military AND civilian ships would provide the option of alternate coolants?

Remember, it's not as if hydrogen is only slightly less efficient. Then we might put the omission down to other factors outweighing the economic ones. But it's very much less efficient. When you're talking about that sort of economic disincentive, convenience really doesn't come into it at all.


Hans

 

[Ishmael]

canon says hydrogen is used as a coolant
real world has areas where liquid hydrogen is used as a coolant
that should be good enough

if we get into actual real thermal management, I doubt the OTU ships, etc. would survive in its present form.

 

[rancke]

canon says hydrogen is used as a coolant
real world has areas where liquid hydrogen is used as a coolant
that should be good enough

If that's an attempt to end the argument by an appeal to authority, it's highly inappropriate. Feel free to drop out of any discussion that you don't want to participate in any further, but don't attempt to get others to do the same. (If it isn't such an attempt, I'm unable to understand its purpose).

In case I'm mistaken, I'll answer your points:

Conditions in outer space differ in various ways from conditions on Earth. One of the differences results in the canon statement about hydrogen being used as a coolant being nonsensical. Unless it's a very small portion of the total amount of hydrogen that is used for coolant, in which case it is merely moot.

Canon may be good enough for you, but it's only good enough for me when it makes at least a modicum of sense.


Hans

 

[Dragoner]

Probably, but nearly 14 times heavier, if weight can be a factor. Also quite more corrosive at high temperatures.

It takes also quite longer to take, as you must either make planetfall or mine (on ice asteroids/comets). While this may not be a problem on comercial basis (as long as your ship is steamlined), what about military operations prior to a planet invasion? You must either land on an enemy ocupied planet or take a long time mining asteroids before jumping away (so taking quite longer to take reinforcements if you're depending on limited shipping (ever played Invasion Earth ?)).

Not to mention adding a mechanical liquid cooling system and tankage for how much water, say 100,000 gallons? The economics still would seem to support hydrogen, it works and makes sense and is canon.

 

[rancke]

Not to mention adding a mechanical liquid cooling system and tankage for how much water, say 100,000 gallons? The economics still would seem to support hydrogen, it works and makes sense and is canon.

Really? I'd love to see the calculations you've done to arrive at that conclusion.


Hans

 

[Dragoner]

Really? I'd love to see the calculations you've done to arrive at that conclusion.


Hans

What are the specs on your fusion plant and jump drive?

 

[rancke]

What are the specs on your fusion plant and jump drive?

Don't worry about that. Just show me your assumptions and calculations. After all, you didn't have any specs from me when you came up with your opinion. If your assumptions hold water, I'll accept them. After all, canon is on your side, so any reasonable explanation that conforms to canon must be considered valid. Or at least potentially valid, only to be challenged by other explanations that likewise conform to canon.


Hans

 

[Dragoner]

Don't worry about that. Just show me your assumptions and calculations. After all, you didn't have any specs from me when you came up with your opinion. If your assumptions hold water, I'll accept them. After all, canon is on your side, so any reasonable explanation that conforms to canon must be considered valid. Or at least potentially valid, only to be challenged by other explanations that likewise conform to canon.


Hans

The specs are the meat of the issue and note that increasing the complexity of the game will proportionally increase the margin for error. It is a bylaw of any mechanical design that an air-cooled engine is more simple than a liquid cooled engine. As much handwavium is used already the reasonble answer would be to keep it simple and go with what is there.

 

[rancke]

The specs are the meat of the issue...

If they are, surely you made a few guesstimates before you decided that the cost of using an alternate coolant would outweigh the increased earning potential of one third that I pointed out a jump-2 ship would have (And let's not even get into the between a tripling and a quadrupling of earning potential a jump-6 ship would have).

And how did you conclude that ships being able to cross the rift in half a dozen jumps instead of having to spend dozens of jumps to go around couldn't possibly be economic?

To be blunt, if you did make any calculations, I think you made a mistake. If you just pulled your opinion out of thin air, I think it's invalid.


Hans

 

[Dragoner]

If they are, surely you made a few guesstimates before you decided that the cost of using an alternate coolant would outweigh the increased earning potential of one third that I pointed out a jump-2 ship would have (And let's not even get into the between a tripling and a quadrupling of earning potential a jump-6 ship would have).

And how did you conclude that ships being able to cross the rift in half a dozen jumps instead of having to spend dozens of jumps to go around couldn't possibly be economic?

To be blunt, if you did make any calculations, I think you made a mistake. If you just pulled your opinion out of thin air, I think it's invalid.


Hans

It's all hypothetical, you are not going to get around that fact. You can't even define how the power sources even work, are they somehow turning radiant energy to power or are they using heat to do mechanical work? I don't think starships have steam turbines in their engine rooms, so it would be a safe guess that Traveller tech has moved on in the design. But adding an extra layer of complexity now deciding on some mechanical cooling system and then applying it to further changes in the vast infrastructural system of overall transportation economics is sheer folly.

It is better to find reasons and make sense of what is there, rather than to create another even more complex layer of problems.

 

[McPerth]

Well, maybe. But weight appears to be so much not a factor that some of the ship design systems completely ignore it. Of course, that doesn't mean it would be ignored in "reality", but volume is a much bigger factor than weight.


Something that also appears to be the case with hydrogen. See Wil's (Aramis') post above. And water isn't that much more difficult to get hold of than hydrogen.


Or you could bring it along. You don't think that being able to carry seven jumps' worth of coolant instead of one would be something the military might consider useful?

But that's really besides the point. Granted that the military might have more important concerns than economic efficiency, the salient point is that merchants don't. Even if hydrogen was the coolant of choice for the military, it wouldn't be for civilian shipping. And the various ship design systems all omit any reference to alternatives to hydrogen. If hydrogen was used as a coolant, don't you think a ship design system that was intended to produce both military AND civilian ships would provide the option of alternate coolants?

Remember, it's not as if hydrogen is only slightly less efficient. Then we might put the omission down to other factors outweighing the economic ones. But it's very much less efficient. When you're talking about that sort of economic disincentive, convenience really doesn't come into it at all.
Hans

I'm not sure weight may be so ignored, although you're right most of the systems ignore it, so I'd not discard it as a reason.

Even if there are better coolants, maybe isn't economic to have diferent circuits thorug your ship, and so most shipping builders simply use hydrogen as both, fuel and coolant in order to keep it easier (as hydrogen cannot be avoided if you must use it as a PP fuel). In such scenario, any shipbuilding firm that tried to use another coolant whould find its ships less competitive just for the fact that most trarports are not ready to serve its vessels (it has happened too many times in real world than more efficient systems cannot be used for lack of support services). If hydrogen is good enough, they think, why to mess with more tanks, circuitry, etc...?

As it's said in spanish: 'a menudo lo bueno es enemigo de lo mejor' (roughly translated: often what's good is enemy of what's better)

 

[whartung]

There's not a lot wrong with "Hydrogen being good enough". It has a lot of value, particularly as a mechanic in a game. But I think we're perhaps beyond discussing simply a mechanic in a game.

The key take away is that if the bulk of LHyd is being used solely for cooling, then it's a fair leap to ask what other materials may perhaps be substituted for that role, and what their effect may be.

Maybe the casual tramp freighter is designed for LHyd, and the freighter is designed for LHyd because the infrastructure of interstellar shipping is based on LHyd. But perhaps a Mega Corps purpose build freighters are alternately cooled for their purposes, because they are also willing to invest in the infrastructure to support an alternative material.

A current example is a municipal bus fleet running their buses on natural gas instead of diesel. LNG isn't really quite practical for "go anywhere, do anything" travel. But for buses all operating out of a purpose built depot, it's perfectly viable, and offers advantages (notably air pollution) to the service.

Consider the US Navy as another alternative. As I understand it, pretty much everything on an aircraft carrier runs on Jet Fuel. The planes, the forklifts, the other vehicles. Anything that needs liquid fuel, is tuned for Jet Fuel, thereby simplifying deployment and logistics. Again, in the larger, generic world, these vehicles aren't appropriate. But for the World of the aircraft carrier, it makes complete sense.

So, if there is a potential alternative to LHyd as a coolant, what are some of the ramifications?

Well a big one (but not necessarily canon crippling) is perhaps a custom designed courier that's able to span the Rift. It carries both LHyd for it PPlant, and (say) LN2 for JDrive cooling. This change (perhaps, I haven't done the math nor have I maps in front of me) enables a courier ship to span the Rift quickly rather than going around. Yet, because of the need for wilderness support, doctrine dictates that the military ships stick with LHyd. So while a courier can get across quickly, the Fleet can't get across at all.

This concept is no different than having ships on one side of Central America communicating or moving smaller cargoes across from the Gulf of Mexico to the Pacific rather than steam around the horn.

Now a more interesting option is to consider whether a hybrid cooling system could be developed. That is, what if the military had drive systems that could be cooled by either LHyd OR LN2?

You could consider the use of LN2 as a "liquid drop tank". Drop tanks have infrastructure associated with them (they have to be built, transported to the front, installed, etc.). LN2 can be similar. Nitrogen is rarer than Hydrogen, but not THAT rare. It's not untoward to consider that military bases have LN2 infrastructure, just like they might have drop tank infrastructure.

Then, on properly equipped ships, in preparation for an assault, the ships load up with LN2 to increase range and operational ability, while still being able to rely on wilderness fueling and the ubiquitous infrastructure of LHyd for normal operations.

So, I think the LHyd as coolant is a reasonable conclusion to where Jump Fuel goes, and the opportunity for alternative cooling mediums makes for interesting, but not necessarily Canon destroying, options going forward.

 

[Cryton]

Has anyone mentioned that the most abundant element in the known universe is hydrogen?

I mean that alone makes it worth using.

 

[Dragoner]

Has anyone mentioned that the most abundant element in the known universe is hydrogen?

I mean that alone makes it worth using.

Yes, cheapness makes everything better. It also mitigates loss of efficiency to a large degree, look at the average automobile engine that runs at only 18% efficiency:

The average automobile engine is only about 35% efficient, and must also be kept idling at stoplights, wasting an additional 17% of the energy, resulting in an overall efficiency of 18%

http://en.wikipedia.org/wiki/Thermal_efficiency

Why? Because it is cheap and dependable, while you could raise the volumetric efficiency, it would be in trade against cost and reliability.

I am against some model where one size fits all, maybe there are liquid cooled jump drives in more settled core worlds. Maybe the Traveller starship rules represent ships with "off road" ability, where dependability is key,while in the core million ton freighters ply the lanes and any idea of gas giant refueling is absurd.

I kind of like the idea of some frontier starships cooling with LH2, opening vents and blasting it out into space, like a signal: "look out, she's gonna jump!" Similar to some old steam locomotive and it's open lubrication and expansion piston and valve sytem. Maybe these ships wouldn't even be licensed to operate in the core: "get that junk out of the space lanes!"

I re-read Annic Nova, whatever wonder tech it may have, it's a pig: one TENTH of a G acceleration? I'd take my 200 MCr and go looking for a Suleiman, gimmie two used, at least you know what you are getting. Annic Nova gives you funky non-standard tech and a virus to boot.

If someone asks to put extra capacitors in the hold, just tell them no, they have to go in a remodeled engineering section, plus you would need heavier gauge wiring, larger conduits (remodeling the interior of the ship), larger fuse blocks, more Quantam Diodes and recalibrated Casimir Plates. So after a couple of hundred megacredits and 20 months in a custom shop that would hotrod a starship, it may or may not work, no guarantee.

 

[shadowcat20]

If you were to use more exotic coolants they MIGHT only be avalible at Class A starports. No Skimming or Ice cracking.

Also How much harder/more expensive is it to get and hold Nitrogen vs Hydrogen today?

It may be better, and it might work, But is it really more economical? Ships using this system would be stuck going from Starport A to Starport A. Pinning them down to higher Tech older developed routes. Not likely to be as profitable due to large volumes of traffic.

If ships were to ply these routes saving money due to coolant savings then prices would also drop due to lower shipping costs. Carriers would drop prices trying to force out all non Nitro equipped carriers and that would become standard. At this point ONLY certain carriers could afford to deal in these systems and the system would suffer from the monopoly.

 

[rancke]

It's all hypothetical, you are not going to get around that fact.

And I guess you're not going to come up with any support for your opinion. That being the case, I stand by my original statement.

It is better to find reasons and make sense of what is there, rather than to create another even more complex layer of problems.

That's very true. I agree 100% with that sentiment. That's why I think it's a bad idea to add the complexities that establishing that any significant part of the hydrogen is used as coolant.


Hans

 

[Dragoner]

And I guess you're not going to come up with any support for your opinion.

This applies to you more then me, what have you added to the discussion? C'est la vie.

That's very true. I agree 100% with that sentiment. That's why I think it's a bad idea to add the complexities that establishing that any significant part of the hydrogen is used as coolant.

Except it looks like it already is canon:

A significant amount of the fuel consumed during charge to jump is actually used to supercool the reactor while it is in overload mode; more than normal is used as fuel itself, as overload mode is less efficent than normal mode in fuel use, and ship plants are less efficent than stationary power systems to begin with.

http://traveller.wikia.com/wiki/Jump_drive

 

[rancke]

Even if there are better coolants, maybe isn't economic to have diferent circuits thorough your ship, and so most shipping builders simply use hydrogen as both, fuel and coolant in order to keep it easier (as hydrogen cannot be avoided if you must use it as a PP fuel).

I've already addressed this argument. Volume is so important to starship construction, especially the economics of interstellar transport capacity, that it simply won't work. Especially since heat management is not exactly starship science. Such an alternate heat management system would have to cost multiple megacredits to offset the advantages, and we already have a pretty fair idea about what such a system would cost at TL 7. I see no reason to suppose that it would become more expensive at higher TLs.

In such scenario, any shipbuilding firm that tried to use another coolant whould find its ships less competitive just for the fact that most trarports are not ready to serve its vessels (it has happened too many times in real world than more efficient systems cannot be used for lack of support services). If hydrogen is good enough, they think, why to mess with more tanks, circuitry, etc...?

This assumes that a tradition of using hydrogen for coolant would become established in the first place if a much more economical alternative existed. It wouldn't. Being able to carry a substantially larger amount of goods for roughly the same cost would ensure that hydrogen would never be used in the first place.


Hans