Water vs Hydrogen discussion

[Dragoner]

After talking to an Israeli rocket scientist who works at Purdue University, he categorically says liquid hydrogen is far better fuel source than water as 1) cracking the water to get hydrogen takes more energy than the hydrogen supplies but the 2) carrying the weight of water far more negates the energy savings, and he has done work for/with NASA. Just thought I'd throw this out there, he even confimed that hydrogen was 14m^3 per ton and was suprised when I could quote the number.

-Robert

 

[BytePro]

Any categorical answer to a scientific question should always be questioned.

When asking a technical opinion, it also helps to provide all the context the question refers to. If you ask me which is better - liquid H or water for rocket fuel - I'd also state, without hesitation or qualification, the former. Unless you put it in the context of the assumption of a futuristic game...

He likely assumed that separation of the H2 was by electrolysis. Which is a quite reasonable assumption in the RW. However, that assumption need hardly hold true in a fictional setting. (Nor does it have to hold true in real life! Of course, a rocket scientist is also not a necessarily an industrial chemical engineer, either.)

If one assumes another (fictional) method - nano structure membrane element separation or a catalyst, then the answer may change... especially if 'feasibility' includes gravitics (i.e. negating the mass difference) and looking at safety of transporting large volumes and acquisition (fuel availability). Not to mention availability of oxygen.

Put your question in the full context of the game and seek an answer. (I.e. - Traveller specifically negates both #1 and #2 already... via 'refining' and gravitics.)

 

[Dragoner]

well traveller supports LHyd, but no matter, we also talked about deuterium and people we knew at JPL and now it makes me rather sad, I miss them all.

 

[aramis]

After talking to an Israeli rocket scientist who works at Purdue University, he categorically says liquid hydrogen is far better fuel source than water as 1) cracking the water to get hydrogen takes more energy than the hydrogen supplies but the 2) carrying the weight of water far more negates the energy savings, and he has done work for/with NASA. Just thought I'd throw this out there, he even confimed that hydrogen was 14m^3 per ton and was suprised when I could quote the number.

-Robert

For rocket fuel, he's right.

For fusion fuel, he's DEAD wrong. (We know the energy released is FAR more than the cost of cracking it out of water. We just can not, at present, capture enough of that energy to make the reactor even pay it's own operational cost, let alone crack the water, but cracking the water is only a couple percent of the power cost to run the reactor. So, it's just a matter of energy capture.

Which Traveller tech has solved.

 

[McPerth]

(...) especially if 'feasibility' includes gravitics (i.e. negating the mass difference)

I'm afraid gravitics don't negate any mass difference, only negate weight (the effect of gravity on mass).

 

[BytePro]

The difference in mass = difference in weight in the RW. With gravitics, the 'weight' can be fixed to zero, regardless of mass. Therefore, gravitics negates the mass difference in reference to weight - which is the context of the post.

 

[McPerth]

The difference in mass = difference in weight in the RW. With gravitics, the 'weight' can be fixed to zero, regardless of mass. Therefore, gravitics negates the mass difference in reference to weight - which is the context of the post.

In reference to weight, but not in other aspects (momentum, inertia, energy needs to accelerate it, etc...).

 

[Dragoner]

For rocket fuel, he's right.

For fusion fuel, he's DEAD wrong. (We know the energy released is FAR more than the cost of cracking it out of water. We just can not, at present, capture enough of that energy to make the reactor even pay it's own operational cost, let alone crack the water, but cracking the water is only a couple percent of the power cost to run the reactor. So, it's just a matter of energy capture.

Which Traveller tech has solved.

Not really, the conversation began with the current plan of sending a nuclear reactor plus large tanks of liquid hydrogen to mars and wandered off from there, there was another scientist who was more interested in what if type scenarios (I didn't want to go too Traveller geeky). We talked about fusion power, (which he replied how do you keep the astronauts alive in the craft, first) and even using heated plasma as a drive. Even without using deuterium eg getting that from the hydrogen, both agreed that hauling the water made no sense as one can get the water, oxygen and whatever one needs through simple chemical processes with LHyd, but that would be more complex with water and that hauling water is far more troublesome than LHyd. It would depend on where you were going, but even to find CO2 which is common it is easy to get O2 & CH4, just through a simple chemical reaction.

 

[Dragoner]

The difference in mass = difference in weight in the RW. With gravitics, the 'weight' can be fixed to zero, regardless of mass. Therefore, gravitics negates the mass difference in reference to weight - which is the context of the post.

Logic would say that Traveller tech doesn't negate anything, it merely simplifies the situation. However, it would still be based off of real world physics, thus the onus would be to overcome the modern limitations, as far as an explanation of how it all works.

 

[aramis]

Not really, the conversation began with the current plan of sending a nuclear reactor plus large tanks of liquid hydrogen to mars and wandered off from there,

The project you're talking about isn't a fusion reaction - it's a fission reactor being sent to split the water so that the shelf-stable water can be converted to rocket fuel in order to launch a sample return mission. It's not an efficient system, but it's nothing like traveller ships.

The energy released by fusion is about billions of times higher than the energy release by combustion.

A conventional rocket is throwing stuff out the back at high speed. Burning H2+O2 is the most energetic chemical reaction we know of, and it throws water out the back.

A normal Traveller space ship (which excludes TNE) throws nothing out the back, and uses hydrogen, it fuses it into helium, and uses gravitics to throw itself around. A 100 ton starship gets around at 1G with about 1 ton of PP.

ITER's reactor is expected to produce 500MW captured, with an energy cost to operate of 10MW, for a duration of 1000 sec on 0.5g of fuel per run. It should be running in 2019. So 490GW/Sec per 0.5g of fuel. And not all of that fuel is fused. But lets expand that to the 250MW Traveller drive. One ton is 1,000,000.g which gives 980,000,000,000.MW/Sec of recaptured power potentially. A day is 3600*24=86400s, and a week is 604,800sec. Given the output of 250 MW, a ton of fuel SHOULD produce 3,920,000,000sec at ITER efficiencies... or over 6400 weeks, or 125 years.... this means that the fuel rates in HG (as rated in MW by Striker) are about 1500x less efficient than the plant being built should be.

 

[Dragoner]

The project you're talking about isn't a fusion reaction - it's a fission reactor being sent to split the water so that the shelf-stable water can be converted to rocket fuel in order to launch a sample return mission. It's not an efficient system, but it's nothing like traveller ships.

He was talking of sending LHyd, not water, to get water you just burn Hydrogen he said. His main point of water not being used is that of efficiency, that you would not carry what you did not need. It was an interesting coversation, which I thought I would relate, considering how rare (for me at least) to talk to real rocket scientist over a few pints. The fission reactor would be there to do work, so yes not as a drive or anything, iirc the only drive other than chemical discussed was an ion drive. They did talk of using CH4 (made there using LHyd and CO2) as a chemical rocket to lift a lander back into orbit, as the turn around would be that the astronauts would stay 500 days and better to do work on the ground rather than just stay in orbit.

I know the requirements of the pp are overstated, however in my mind I tend to think in that the excess is for maneuver, weapons, etc while still giving extra for a damaged duty cycle. Though I realize a damaged reactor would most likely be taken off-line, a fusion reactor while having so much more power would of course being that much more volatile if somehow compromised.

I do hand it to Traveller on the one point about Liquid Hydrogen, for being written so long ago they still got it right, or Marc or whoever had the original idea of using liquid hydrogen. Hats off to that.

 

[aramis]

Actually, a realistic fusion reactor when compromised simply fails. No "Boom!" It's such a hard reaction to get going, and it really doesn't like to sustain itself.

 

[rancke]

He was talking of sending LHyd, not water, to get water you just burn Hydrogen he said. His main point of water not being used is that of efficiency, that you would not carry what you did not need. It was an interesting coversation, which I thought I would relate, considering how rare (for me at least) to talk to real rocket scientist over a few pints.

Jump drives are not rocket science.


Hans

 

[Dragoner]

Actually, a realistic fusion reactor when compromised simply fails. No "Boom!" It's such a hard reaction to get going, and it really doesn't like to sustain itself.

If containment was breached during the reaction, not a boom per se, but a burn through at least.

Jump drives are not rocket science.


Hans

Shhhh, yes, I didn't even mention that, he would have just handwaved it away.

 

[McPerth]

The project you're talking about isn't a fusion reaction - it's a fission reactor being sent to split the water so that the shelf-stable water can be converted to rocket fuel in order to launch a sample return mission. It's not an efficient system, but it's nothing like traveller ships..

If I understand well what you say, and IIRC, that seems what one small step (MT:HT) calls a nuclear teakette

(...) this means that the fuel rates in HG (as rated in MW by Striker) are about 1500x less efficient than the plant being built should be.

But yet more efficient than in MT...

In MT, one ton of PP consumes about 11.34 kl of lhyd/ week (so, about 3.36 dton/4 weeks) and has an output of 243 MW at TL15. IIRC, in HG to produce 1 EP (250 MW) at TL 15 you needed 1 ton of fuel

 

[Enoki]

For rocket fuel, he's right.

For fusion fuel, he's DEAD wrong. (We know the energy released is FAR more than the cost of cracking it out of water. We just can not, at present, capture enough of that energy to make the reactor even pay it's own operational cost, let alone crack the water, but cracking the water is only a couple percent of the power cost to run the reactor. So, it's just a matter of energy capture.

Which Traveller tech has solved.

You would still have to seperate the oxygen off from the hydrogen prior to using it for fusion fuel. Oxygen would make flourine or neon depending on whether you fused hydrogen or helium to it. Either way that is going to be tough to do even in a Traveller setting.

You can't fission the oxygen (it is a net negative energy reaction) so, you have to remove it from the hydrogen before using it as fuel.

Now, that doesn't mean that in Traveller there is some, currently unknown, method to do this efficently using a catalyst or by temperature (ie., turning the water into a disassociated plasma for example) etc. I would suspect that that would be both possible and realistic.

 

[aramis]

You would still have to seperate the oxygen off from the hydrogen prior to using it for fusion fuel. Oxygen would make flourine or neon depending on whether you fused hydrogen or helium to it. Either way that is going to be tough to do even in a Traveller setting.

You can't fission the oxygen (it is a net negative energy reaction) so, you have to remove it from the hydrogen before using it as fuel.

Now, that doesn't mean that in Traveller there is some, currently unknown, method to do this efficently using a catalyst or by temperature (ie., turning the water into a disassociated plasma for example) etc. I would suspect that that would be both possible and realistic.

No, the process produces O2 you just dump overboard.
And actually, it's not until Iron that the energy of fusion is null.

Fusion of 2O gives 1S, which does produce net energy and a net mass loss.
It's only once you get results above Fe (iron) that the fusion reaction doesn't produce energy.

electrolysis, tho, you've already separated the H2 from the O2 or NO2 (depending on what you electrolyze to get your H2). So you just vent the non-Hydrogen and fuse the hydrogen. For storage purposes, water or amonia is FAR easier to store than molecular H2.

 

[Enoki]

Iron 56 to be precise. But, trying to fusion oxygen would be extremely difficult as it only occurs in the universe in larger stars at their core and then not all the time.

My point was that you couldn't use water as is for fusion propulsion. But, on the other hand, breaking it down would give the ship oxygen it could store for things like breathing that could be important.......

You could gel the hydrogen (and likely there would be other processes too) that would make storage efficent

http://www.grc.nasa.gov/WWW/Fuels-And-Space-Propellants/GELLED.htm

 

[Dragoner]

You would not carry something you wouldn't use, nor do a process in the vehicle instead of on the ground, nor keep two separate fuel storage systems. Too much complexity - chances for something to go wrong. It is logical also that hydrogen storage tech has risen with it being a main fuel source. I'm not finding the arguments for water convincing.

Crititical failure in starships is critical, and a great adventure hook. :devil:

 

[rancke]

You would not carry something you wouldn't use, nor do a process in the vehicle instead of on the ground, nor keep two separate fuel storage systems. Too much complexity - chances for something to go wrong. It is logical also that hydrogen storage tech has risen with it being a main fuel source. I'm not finding the arguments for water convincing.

Volume is the critical resource with starships. Using water for hydrogen storage reduces the volume needed. This is a serious money-making feature. There's really no plausible reason why merchants wouldn't accept a bit more complexity (assuming for purposes of argument that it really would be noticably more complex) in order to make lots and lots and lots of money.

And let's not forget the real money-savers, the occasional astrographic locations where being able to make, say, two jump-4 in a row will save several jumps, thus making the trip much faster and much, much cheaper.

Note that I'm not saying that the canonical shipbuilding rules don't imply that there's some reason why using water for storage doesn't work. There's just no plausible reason known why this would be the case.


Hans