New Mars Forums

tahanson43206

Moderator

Registered: 2018-04-27

Posts: 17,942

Re: kbd512 Postings

For kbd512 re latest post in Vertical topic...

Awesome!  If we had a "like" feature running, I'd be wanting to increment the value.

However, YouTube uses a simple "Like" and it is possible to turn it off, which is interesting.

I just scanned your post and will return to read it carefully later.

However, it ** was ** fun to be reminded of the history of gun launch systems.

One name I didn't catch was Dr. John Hunter, whose name has not reached household name recognition level yet, so I'm just reminding you Dr. Hunter is ** out there " for consideration.  He built working guns for Star Wars, and has been trying to built a ** real ** launcher ever since.

He was planning (and may still be planning) to use hydrogen for the fluid. The reason is velocity... Unlike the Vertical Launch Assist concept, he was going for LEO, which hydrogen gas can facilitate.

(th)

tahanson43206

Moderator

Registered: 2018-04-27

Posts: 17,942

Re: kbd512 Postings

For kbd512 re latest post in SSTO topic...

Your post included a reference to the use of spark plugs for pre-burners...

For all who might be interested in kbd512's reference ...

https://space.stackexchange.com/questio … -preburner

The discussion at the link above includes a flow diagram for the Space Shuttle, in addition to attempts to answer a question about how pre-burners work.

There are probably other references for this detail of rocket system design.

(th)

tahanson43206

Moderator

Registered: 2018-04-27

Posts: 17,942

Re: kbd512 Postings

For kbd512 re post about compressed air automobile design ...

https://newmars.com/forums/viewtopic.ph … 45#p224745

Your post included mention of acceleration from/by a 12 horsepower machine.... Your solution is interesting, but the situation seems (to me at least) to offer an opportunity for a lightweight electric acceleration/braking package.

In a scenario where you run out of air (as could happen with the limited range) a small electric system to limp home might be worth the additional expense.

Under normal circumstances, it could provide the acceleration you've identified as needed, and the ability to store energy from braking might prove useful in hilly terrain.

(th)

kbd512

Administrator

Registered: 2015-01-02

Posts: 7,575

Re: kbd512 Postings

tahanson43206,

Air powered vehicles don't need any electric motors, batteries, or brakes.  Pneumatic brakes are used to stop heavy trucks and trains, but in a light vehicle power-assisted braking is largely superfluous.  All that stuff is a great way to add weight and cost, but not much else.  Regarding acceleration, I already stated that we're using a flywheel- another simple mechanical device which requires no electronics or electricity to operate.

When Teslas run out of electricity, a tow truck operator in a diesel powered truck brings a diesel powered generator to recharge the battery.  If you had a hose to transfer air between vehicles, then you don't need a heavy diesel powered generator.  Anyone else in an air powered car can stop by to recharge your vehicle's air tank with a lightweight rubberized hose, by connecting it to their vehicle's air tank and opening the valve.

GW Johnson

Member

From: McGregor, Texas USA

Registered: 2011-12-04

Posts: 5,584

Website

Re: kbd512 Postings

Kbd512 is quite right. 

There is some kind of car manufactured in India that uses a compressed air motor.  As near as I understand,  the range of the thing is quite limited,  even compared to lead-acid batteries,  much less lithium batteries.  I could be wrong,  but that is the impression I got reading about this air-powered car,  some time ago,  now.  The brand name was Tata,  or something pretty close to that.

Compressing the local atmosphere to usable pressures in such a device is way more difficult on Mars than here on Earth.  It needs something like around 3-5000 psi to be practical,  or around 200-300 standard atmospheres.  On earth from near 1 atm ambient pressure,  that's a compression pressure ratio of near 200-300:1.  You do that with multi-stage positive displacement machines,  and they are inherently heavy and power-consumptive.  We call them air compressors. 

On Mars you still need the same compressed pressure (200-300 atm) to make the air motors work the same way they do here,  but the local ambient pressure is only in the vicinity of 0.006 atm.  That makes the required compression ratio nearer 160 times higher than on Earth,  or near 32,000 to 48,000 : 1.  There is no way to do that with a positive displacement compressor.  You will need a machine more closely resembling an extreme vacuum pump, infamous for very high power consumption at very little throughput massflow indeed!

GW

Last edited by GW Johnson (Yesterday 15:39:31)

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GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

kbd512

Administrator

Registered: 2015-01-02

Posts: 7,575

Re: kbd512 Postings

One aspect of these "green energy" ideas that are baffling to me is why so many people believe, mostly without evidence or in direct contradiction to available evidnece, that one aspect of energy efficiency or "green-ness" translates into overall efficiency or "actually  being environmentally friendly".  Electricity flows through a conductor wire very efficiently.  That aspect of electricity is highly efficient.  Well, zippity doo-dah!  Every other aspect of generating, delivering, and consuming electricity are wildly inefficient.  50% of all the energy sunk into mining is done exclusively to mine Copper.  We extract 3,000,000,000t of Iron ore per year using 7% to 9% of all the energy sunk into mining.  We extract about 20,000,000t of Copper ore per year, and that consumes 50% of all the energy that goes into mining.

Q: Why do we sink so much energy into producing Copper ore?
A: If we tried to substitute Aluminum for Copper on a per-ampacity-limit of electrical conductor wire basis, then the energy consumption associated with making more Aluminum would be 3 times higher than the energy sunk into producing more Copper, despite the fact that Aluminum with equivalent ampacity weighs half as much as the Copper.  We already do produce a lot more Aluminum than Copper, about 3 times as much, in point of fact.  If we produced even more, that requires even more energy.

Engineers aren't dumb.  They are choosing the lowest energy / lowest cost materials, whenever those materials are available, which is why they still choose Copper over Aluminum.  When you start talking about electric motor-generators of the size installed in large hydro dams, then and only then do you see a weight and energy savings benefit by choosing Aluminum over Copper.  If you pull a stupid stunt and try to use Aluminum in an EV motor, then the motor weighs about twice as much and is significantly more expensive.  Most engineers think that's kinda dumb, and I happen to agree with them.  The major problem is that we're running short of Copper.

Since there are no "magic physics" to throw at mass, volume, and counter-electromotive force problems related to a thicker conductor further away from a magnetic field, that's a pretty fundamental technology problem.  We know how to make highly efficient and power-dense electric motors.  That is not the problem here.  The problem is that with such devices rapidly approaching 100% efficiency, there are no more efficiency improvement left to exploit.  What you're left with is high energy costs for the metals, the increasing scarcity of the metals from depletion of the best ore deposits, and not a lot of good alternatives for mass manufacture at the scale required to make everything electric.

Apart from electric motors and conductor wires, then there are the issues with electronics.

1. Electronics require specialty metals in short supply.  There is very little about solid state electronics manufacturing that is cheap, except at significant scale, energy-efficient, or environmentally friendly.

2. Recycling modern solid state electronics is mostly an exercise in futility, with the energy input beyond what is required to extract virgin ore / metal.  This is important for merely having the metals available to make newer generations of electronic devices.

3. If anything goes seriously wrong with the electronics, that happens at the speed of light.  Virtually all electrical devices more sophisticated than AC induction motors require electronic control.  Modern solid state electronics are fantastic while they work, and then they're not when they don't.  There's almost nothing that can be done to repair them, and certainly not in an economical manner, which is why we generally tell people to go out and buy a new one.

4. If solid state electronics were made from very common and low-energy materials and environmentally friendly processes, then treating them as disposable would be less of an issue.  All of the most advanced designs are made from very exotic stuff, using very exotic processes.

5. Just as there is no plan for when we run out of Copper, there is no plan for when we run out of the hydrocabon fuels that prevent every renewables grid on the planet from crashing at least once per day.  The follow-on "storage plan" to replace hydrocarbon fuels is based upon nothing more than happy talk and ignorance-based beliefs, or "let's throw more money at the problem to see what happens".  Well, we already know what happens.  That money and effort is sucked into the engineering equivalent of a black hole.  Nothing escapes from it.  It's an all-consuming endeavor that has nothing of lasting value to show for all the time and money spent.  We've arrived at a total non-solution- something which will never work at a human civilization scale, for lack of both input materials and energy.

If you're like me, and you genuinely care about both people and the environment, then you see this current state of affairs as insufferably stupid.  We're stuck on this "go out and buy the shiny new electronic gadget so then you'll be green"- whatever that's supposed to mean.  It looks like more ignorant consumerism from where I'm sitting.  If you have plenty of disposable income and are looking to blow it on something while telling everyone else that you have more money than they do, and you're better than them because you have more money, then go out and buy an EV or cell phone made with environmentally sustainable slave labor or whatever.  It's all rather meaningless.  The "greenest" thing you could possibly do with your money, short of investing into agriculture or planting trees or something similar, is probably nothing whatsoever.

You can't "believe" valid engineering solutions into existence.  That's not how valid math, science, or engineering actually works.  For the most part, we get major technological advancements within some category of technology about once per human lifetime, maybe twice if you're lucky.

That takes us back to air powered vehicles.  If we truly want a practical motor vehicle that consumes less or has less environmentally-destructive consumption, then you can't continually demand an-ever increasing amount of input energy and materials while still accomplishing those objectives.  They're opposing engineering requirements.  They are not compatible with each other.  That's why I call EVs, photovoltaics, and Lithium-ion electro-chemical batteries, "entropy machines".  In order to make those devices do what they do, highly disordered matter and/or energy has to be converted into the highest ordering we're capable of imparting to the materials or energy sources that make these machines function.  Doing that is very consequential, with respect to the amount of input energy required.  The science that we have and know how to reduce to repeatable engineering practices or processes makes that unavoidable.

I think we "know enough" at this point to state with a high degree of certainty that demanding more order / less entropy from our energy generating or consuming machines can only have one result- more energy and materials consumption, at rates we cannot sustain using what we have and what we know.  The most obvious solution to that problem is to back-track in the opposite direction when the result produces machines which last longer, require less energy-intensive materials inputs, and less energy and technology to maintain.

Do you know what practical aspect of transportation that a car provides, regardless of what powers it?

A machine capable of transporting people and cargo far faster, and thus more efficiently with regard to time, than human muscle power alone could reasonably accomplish.  That is why we rode horses, and eventually invented self-powered cars.

A car that runs on compressed air is less impactful to the environment, relative to internal combustion engines or electro-chemical batteries and the machines required to recharge them, as we presently use them.  Air goes into the car, and then air comes out of the car as it's driven.  After we're done "using" the air, it goes right back to where it came from.  We briefly take the air from the Earth's atmosphere, and then we give it right back.  The "battery" is the enormous supply of air surrounding us no matter where on the surface of the planet we happen to be.  That means the supply of "fuel" to power an air powered car, is not limited to what we can dig or drill out of the Earth.  Until something truly cataclysmic happens, that fuel supply will remain available for our use, forever.

How does this differ from hydrocarbon fuels or electro-chemical batteries?

A number of energy-intensive transformative processes are required to create both of those energy stores.  Additionally, both what we take and what we put back are very different to each other.  Often times, the byproducts or other consumables are toxic and have various undesirable environmental effects.  Using air as our energy store, we don't need to dig nearly so many giant holes in the Earth to obtain the gases, liquids, or metals.  We don't even need electricity to compress the air that powers the cars.  We can connect a sCO2 gas turbine powered by a solar thermal array, directly to the air compressor, and then use the waste heat from air compression to transform liquid water into steam, recapturing at least some of the energy from compression or producing a byproduct that humans consume in enormous quantities- fresh water or hot fresh water required for cooking / cleaning / bathing / industrial processes.  That is how you work with physics, rather than against it.  You use the available resources, rather than what you wished you had more of.

Even by using compressed air and steam and steel vs polysilicon, it's not all sunshine and rainbows, but it most certainly will be far less environmentally impactful than the non-viable alternatives.  Beyond what is obvious about which energy sources and conversion methods are most viable to scale-up to the degree required, I also want our next generation of mechanics and engineers to tinker with these emergent natural energy technologies, so they can figure out how to make them more efficient.

I've heard mechanics and engineers assert that electronic fuel injection can do a better job of fuel economy than a carburetor.  Why should it be the case that we cannot make a mechanical device that can accurately meter fuel to within some fraction of a percentage point of the efficiency of electronic fuel injection?  Have we ever really tried to build such a carburetor, or have we simply "asserted" that it cannot be done without taking all of our modern materials and machining tolerances into account?  I think that's likely to be more of an assertion than an inability.  Since we haven't actually tried, we don't actually know.  You make things as simple or as complex as they need to be, but no simpler and no more complex.  If there is no practical way to make something work without electronics, then use electronics.  If there's no way it would work without being electrical, then make it electrical.  If it works just fine as a mechanical device and sees very little practical benefit from being powered by electricity or combustion, then use natural energy.  It really is that simple.