Author Topic: TED talk by Gwynne Shotwell (April 2018)  (Read 45665 times)

Offline Robotbeat

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Re: TED talk by Gwynne Shotwell
« Reply #160 on: 05/05/2018 05:06 pm »
Besides the usual performance improvements like <snip> and using hydrogen instead of methane. Again, if you're making the fuel electrically.

So although SpaceX has not pursued hydrogen for a while, I expect them to return to it eventually.

Long term on-orbit storage is irrelevant for point-to-point transport. Also is a solvable problem.

Hydrogen is doubtless a solvable problem. And every solution you come up with is not worth the added cost in dollars.

The entire storage - transportation - loading - storing - design - fabrication - using chain gets meaningfully more expensive as soon as you introduce hydrogen to it.

If I would expect to see that to become a near term reality I could bet a small amount of money on hydrogen never being competitive even if the cost of electrolysis and electricity goes so low electrolysed synthetic methane becomes cheaper than any and all natural gas. That in such a case your operations, safety and hardware all combined end up cheaper if you compare hydrogen against methane.

Hydrogen is a solvable problem, at a higher ticket price per passenger seat mile.
Hydrogen is terrible for cars, but if you get high enough scale, it may make sense for things that can’t be easily electrified (like rockets). When the cost of fuel becomes dominant, then it should be considered.

I like methane as a rocket fuel and it’s the best choice for BFR right now, but sorry if I’m not in the hydrogen-phobia cult.
« Last Edit: 05/05/2018 05:21 pm by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online guckyfan

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Re: TED talk by Gwynne Shotwell
« Reply #161 on: 05/05/2018 05:12 pm »
Hydrogen on earth may make sense once we have started producing fuel from regenerative power sources or nuclear. Not as long as the source are fossil fuels. On Mars hydrogen will be produced as part of methane production. It is an easier step there, going outward.

Offline Hominans Kosmos

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Re: TED talk by Gwynne Shotwell
« Reply #162 on: 05/05/2018 05:39 pm »
Hydrogen is terrible for cars, but if you get high enough scale, it may make sense for things that canít be easily electrified (like rockets). When the cost of fuel becomes dominant, then it should be considered.

I like methane as a rocket fuel and itís the best choice for BFR right now, but sorry if Iím not in the hydrogen-phobia cult.

Hydrogen on earth may make sense once we have started producing fuel from regenerative power sources or nuclear. Not as long as the source are fossil fuels. On Mars hydrogen will be produced as part of methane production. It is an easier step there, going outward.

Cost savings in generation (skipping direct conversion to methane or ammonia) are going to be eaten up and negated by cost increases in elevated energy losses in leakage and energy intensity of the distribution and storage network. As well as the cost increases in the infrastructure and utilization hardware. Hydrogen looses all of it's benefits as you zoom out from the trade question whether to bother with anything beyond electrolysis.

The only trade worth doing is how soon after electrolysis you convert hydrogen into a storage molecule.

Pure diatomic hydrogen molecule is not the superior hydrogen storage and distribution technology. It's the more expensive and less infrastructure efficient one.
« Last Edit: 05/05/2018 07:22 pm by Hominans Kosmos »

Offline Robotbeat

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Re: TED talk by Gwynne Shotwell
« Reply #163 on: 05/05/2018 06:36 pm »
That's why hydrogen doesn't make sense for cars or trucks. But if you generate and distribute very near point of use, such as major space ports, then leakage and distribution cost is small.

Hydrogen can make sense at large scale, not at small.

You can't recycle the same arguments against hydrogen fuel cell cars (billions of vehicles, with storage of like a few kilograms of hydrogen for weeks) against something orders of magnitude different in scale and requirements (hundreds of vehicles but only like a few dozen spaceports, with vehicle storage of hundreds of tons for only about an hour). The surface area to volume ratio is vastly different, and the state of matter (liquid vs gas) is also different. You have to recalculate.

It's not about hydrogen being a superior storage method, it's that it has the fewest steps and fewest losses and the disadvantages in terms of mass fraction are less important long-term due to future structural technology improvements. Capturing CO2 out of the air is non-trivial. You're not storing the hydrogen for long.
« Last Edit: 05/05/2018 06:40 pm by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Hominans Kosmos

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Re: TED talk by Gwynne Shotwell
« Reply #164 on: 05/05/2018 07:55 pm »
But if you generate and distribute very near point of use, such as major space ports, then leakage and distribution cost is small.

Hydrogen can make sense at large scale, not at small.
Here you replace transportation losses for high energy cost. Spaceport is not located based on minimum energy market prices. It's parked at a large city. Cities are rarely in locations with the cost leading energy generation locations. Saying that just in time on site energy production for a spaceport somehow arrives you at cost savings is not realistic.


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storage of hundreds of tons for only about an hour
Just in time fuel production or compression, cheap?

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The surface area to volume ratio is vastly different, and the state of matter (liquid vs gas) is also different. You have to recalculate.
Upon recalculating, liquid hydrogen does not arrive at a better energy efficiency position than liquid methane.

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It's not about hydrogen being a superior storage method,
It's entirely about which is the better storage method. Better for dollars of energy put in, converted to dollars of passenger seat mile.

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it's that it has the fewest steps
counting chemical processing steps is the wrong proxy for estimating the fuel system cost

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and fewest losses
just shifting energy losses from one part of the chain to another

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You're not storing the hydrogen for long.
operating under such a process assumes on site produced hydrogen, which assumes unfaborable energy prices. Generating your propellant on site next to metropolis X is directly contradictory to lowest possible ticket price for flights.



Apologies are in order. I have to admit it's my fault my objection has been opaque. I will have to be more clear about what I mean to say.

Cheapest hydrogen is cracking natural gas. 
Emerging new energy sources are driving minimum costs of energy down. 
Minimum cost of energy is favorable for the emerging power to gas opportunistic chemical synthesis industry. 
First entrant to power to gas is hydrogen. 
Lowest achievable energy costs are only achieved in favorable geographies.
Hydrogen gas that is cheaper than hydrogen from natural gas is generated in the most favorable locations.
Major metropolitan cities are not usually located where the lowest power cost renewable generators are being built.
Upgrading a natural gas distribution network to a hydrogen distribution network is expensive.
Upgrading a methane burning rocket to a hydrogen burning rocket with the same safety and reliability level is expensive.
Compared to upgrading your natural gas distribution pipelines to hydrogen pipelines, and operating LH2 tankers in stead of LNG tankers is very expensive.
Operating a chemical synthesis factory near your electrolysis factory using the same cheap energy you use for electrolysis, is not significantly more expensive.
Operating an electrolysis factory at your spaceport where energy is more expensive is a waste of money.

Hydrogen dies a death of a thousand paper cuts and none of those are derived from some imaginary anti hydrogen car talking point library you seem to be envisioning. It's basic physics and renewable energy economics. It's not even rocket science!

Online Chris Bergin

Re: TED talk by Gwynne Shotwell
« Reply #165 on: 05/05/2018 08:09 pm »
Per report to mods. Stay on topic of the thread title....

Offline johnfwhitesell

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Re: TED talk by Gwynne Shotwell
« Reply #166 on: 05/08/2018 09:15 pm »
When the cost of fuel becomes dominant, then it should be considered.

We still haven't even reached the point where a car costs less then it's lifetime fuel...  I do admire the forward thinking though!

Offline speedevil

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Re: TED talk by Gwynne Shotwell
« Reply #167 on: 05/08/2018 11:34 pm »
When the cost of fuel becomes dominant, then it should be considered.

We still haven't even reached the point where a car costs less then it's lifetime fuel...  I do admire the forward thinking though!

I recall a post on the highest time 747 retiring in 2009, after having flown 134000 hours.
At $.25/g of fuel at around 1g/s, that is $120M.
Pretty much spot on what it cost on introduction.

In addition, in the UK, with fuel comfortably exceeding $4/g for some time now, the average car (30mpg) only needs to go 100kmiles before fuel costs exceed purchase price.

Looking at the US, with average prices at $33K or so, and 23MPG, and gas price of $2.5, that's 330000 miles.

A substantial minority of private vehicles, and many commercial vehicles will exceed this.


Offline FutureSpaceTourist

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Re: TED talk by Gwynne Shotwell
« Reply #168 on: 05/14/2018 03:30 pm »
Now on YouTube:


Offline philw1776

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Re: TED talk by Gwynne Shotwell
« Reply #169 on: 09/12/2018 05:35 pm »
The President and Chief Operating Officer of SpaceX said 5-10km offshore.  She wouldn't have said that unless SpaceX had analyzed all aspects of the offshore pad at those distances, including sound.

In the absence of any information, speculation is fine. It's part of what makes this a great forum.

But when we have it straight from the horse's mouth, speculation otherwise seems pointless.

For example, many of us here speculated that BFR specs from horses mouth at IAC 2016 would change.  They did. 
When far off plans meet reality, especially when they are not engineering constrained, but regulatory, they have an even greater risk of change. 
SpaceX statements are not stone tablets to be worshiped without question, but current plans subject to change over the many years before possible fruition.  I had thought SpaceX was notable for its ability to change course on the fly to adapt to reality intrusions and opportunities previously unknown or not sufficiently vetted.  I doubt that BFR P2P is sufficiently vetted as of 2017.

I had speculated that P2P would be no closer than 16Km from shore because of noise, etc.
As predicted, an updated "spec" from Gwynne.
Reddit: "We'll land on our own platform that's out at sea. Largely because cities probably won't want something hovering over their billion dollar buildings. It's also very loud. (Notably sonic booms.) Will land in international waters."

International waters can't be closer than ~22Km.

« Last Edit: 09/12/2018 05:38 pm by philw1776 »
Lori, you have got to tell your friend Elon he can't do that.(FH) He's in our lane! You made us get out of low-Earth orbit, so we've given him that lane, but this is our lane!  We build the big rockets!

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