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#151 2019-10-09 16:53:02

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,653
Website

Re: ISRU propellant production - energy requirement for the BFR?

What about the waste heat radiator that makes the heat-to-electricity heat engine-drive generator work?  Where will you put that?  It cannot work inside the cargo bay of a Starship.  It MUST SEE THE SKY!! That is what it was designed to do.

Set the thing up within a berm,  remote from ships and habs.  THAT is what NASA intended. That is how the thing works best.

GW


GW Johnson
McGregor,  Texas

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

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#152 2019-10-09 20:27:37

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,181

Re: ISRU propellant production - energy requirement for the BFR?

If the door for the exit for cargo is left open and another on the oposite side is cracked we now have a heat flow wind current being created to bring cold air in and hot air will go out. The hot air will move to the path of least resistance which is to the largest opening which will create a suction on the oposite side feeding in cold martian air to keep it going.
This is the principal of the solar updraft chimney on earth which can be used to create power from turbine blades from the radiated heat....The fanned out radiator just needs the air flow through it to make the process start. If time allows create the down spout on one side and the up spout exit on the otherside. The combination creates the chimney effect.

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#153 2019-10-10 08:15:29

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,653
Website

Re: ISRU propellant production - energy requirement for the BFR?

The radiator on Kilopower is exactly that,  a surface that radiates heat away,  even in vacuum.  It is not a convection device like a car "radiator",  which usage is actually a misnomer.

GW


GW Johnson
McGregor,  Texas

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

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#154 2019-10-10 10:49:48

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,719

Re: ISRU propellant production - energy requirement for the BFR?

Just for those ignorant of the basic principles of heat transfer; 3 types of heat transfer are taught in an engineering heat transfer course: conduction, convection, and radiation. Conduction is basically heat flow from hot to cold within a fixed medium--say a bar of metal. It's all based on the "Zeroth Law" of Thermodynamics. Convection is based on the flow of a medium over a surface, a fluid; fluids are both gaseous and liquid. Radiation is loss of thermal energy by Infrared radiation from the body to the surround. Doesn't depend on any contact with a fluid.

GW-feel free to correct me on this; based on my sometimes faulty memory of my Heat Transfer course I took over 60 years ago.

Last edited by Oldfart1939 (2019-10-10 13:04:52)

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#155 2019-10-10 10:58:26

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,653
Website

Re: ISRU propellant production - energy requirement for the BFR?

You are quite correct. 

A car "radiator" is a convection device that works by transferring heat from the water within it to the air flowing through it.  It also radiates and conducts,  but these numbers are quite trivial in comparison to the convection. 

Kilopower's radiator works by radiating infrared energy to the surroundings.  The hotter the surroundings,  the more restricted this ability is.  The sky is always the coldest surrounding that you have,  excepting where the sun is.  So you point the radiator surface at the sky,  but also away from the sun.

This surface must be hot to radiate infrared radiation.  That radiance per unit area is proportional to (surface temperature^4 minus surroundings temperature^4).   You get the best effect when the surroundings effective temperature is low. 

In an atmosphere this hot surface also convects,  and there is conduction through its supports,  but these numbers are quite trivial in comparison to the infrared radiation. 

GW


GW Johnson
McGregor,  Texas

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

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#156 2019-10-10 11:20:38

louis
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From: UK
Registered: 2008-03-24
Posts: 4,924

Re: ISRU propellant production - energy requirement for the BFR?

You think Musk is going to hold up the whole of the Mars Mission while FAA bureaucrats assess the possible dangers of launching nuclear reactors into space? I don't think so. Musk doesn't entirely preclude building nuclear power stations on Mars at some stage. But I don't think it's part of his plans for the first few missions at least.

Nuclear power might come into its own when it comes to growing food, which has a huge energy demand. I don't think we know yet whether nuclear powered multi-level (or underground) farm facilities would make more sense than PV powered or natural light farms (perhaps with reflectors to boost light levels). It will probably be partly down to population size as to what makes sense. If the population gets to one million, that's a lot of area to be covered by PV. Not impossible, but might not make a lot of sense.  By that stage, however, solar power satellites capable of beaming energy down to the surface may be operational which will give us another option.


GW Johnson wrote:

PV win hands down?  No,  it does not!!! Go look at the photos from Opportunity before and during the dust storm that killed it,  using the website URL for the NASA document that I provided.  NASA's own published data says your belief system about solar-only is BS. 

I know you don't like this answer,  but your only truly practical power combination on Mars or the moon is a nuclear baseline plus a lot of solar during the day when demand is higher than baseline.  Better get used to that!  It's true,  despite how fervently you wish to disbelieve it.

As Musk gets closer to sending one of his Starships to Mars,  and actually begins contemplating what is really needed there,  he will agree with me,  not you. There simply is no other known technological answer for Mars.  Or the moon. It's even worse on the moon with that 14-day-long night.  When the sun don't shine,  there is NO solar power.

GW


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#157 2019-10-10 13:17:07

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,719

Re: ISRU propellant production - energy requirement for the BFR?

Louis-You're grasping at straws in a desperate attempt to support a position which is unsupportable. There seems to be come confusion about what DOES fly rather routinely in military aircraft: nuclear bombs, and Hydrogen bombs. Aircraft have crashed carrying them on training missions. The energy numbers for combined operation of a Mars base and ISRU fuel manufacture just don't add up for Solar power alone to do the job SAFELY AND RELIABLY! GW is an engineer trained to evaluate such systems as complete thermodynamic entities. You continue to make statements which are very idealistic about the engineering and scientific problems at hand. You have forgotten the landmark work of Robert Zubrin, who utilized nuclear energy as the basis of return flight to Earth ISRU. Engineers like Zubrin and GW have what you Brits call a "belts and braces" approach. They are professionally committed to making certain that nobody dies because of misplaced idealism.

Last edited by Oldfart1939 (2019-10-10 13:18:33)

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#158 2019-10-10 14:39:14

Terraformer
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From: Lancashire
Registered: 2007-08-27
Posts: 3,108
Website

Re: ISRU propellant production - energy requirement for the BFR?

The FAA have no problem with NASA launching plutonium RTGs, and those are significantly more radioactive than a reactor which has never been turned on. There won't be a problem launching kilopower units.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#159 2019-10-10 17:30:05

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,924

Re: ISRU propellant production - energy requirement for the BFR?

We'll see but ain't gonna happen...

Terraformer wrote:

The FAA have no problem with NASA launching plutonium RTGs, and those are significantly more radioactive than a reactor which has never been turned on. There won't be a problem launching kilopower units.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#160 2019-10-10 17:56:07

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,181

Re: ISRU propellant production - energy requirement for the BFR?

http://www.desertpowerinc.com/dictionary.htm

You say that its best if we point the radiator to the sky but it was tested in a building...
https://www.pro-therm.com/infrared_basics.php
https://en.wikipedia.org/wiki/Infrared_heater
https://en.wikipedia.org/wiki/Thermal_radiation
https://www.watlow.com/-/media/document … dm-89.ashx
The Theory of Radiant Heat Transfer

This is the important one Carbon Dioxide Absorbs and Re-emits Infrared Radiation but it does not lose all of what it gains
https://scied.ucar.edu/carbon-dioxide-a … -radiation

Mars does have an atmosphere but not a thick one which we have proven out multiple times to be real. So the air will be warmed even by ir heating its just not going to be a super efficient carrier of it until its moving to wick away that heat. Air when heated does expand and with the level of heat being generated it will expand to create movement as it tries to lower its pressure back to mars levels as it exits the chamber of the cargo bay. This just how the solar chimney works as via ir energy being obsorbed by the air inside the brim of the lower hat of its make up. Its rise up the chinmey creates the force to move a turbine. Thats just the air cooling which can also give us a clean source of co2 traveling as if it were pumped by air pressure.

https://blogs.scientificamerican.com/pl … ectricity/

Now waste heat capture is just what we are doing for the green capture plants here on earth to make methane from earths own co2 content. But what I would do is allow the ceiling to have a matching obsorbtion plate with any of the working fluids to obsorb the heat to cause the working fluid such as freon to boil which then can be used to turn a turbine generator from the reactors heat being obsorber. The cooling then again is via a radiator that is locate outside of the ship to make use of that radiant cooling. This is the same heating that is used to make hot water as well vai the heat exchanger tank.
These are all things that work....

adom201400103-gra-0001-m.jpg

https://en.wikipedia.org/wiki/Solar_thermal_collector
https://thesunbank.com/evacuated-tube-solar-collectors/

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#161 2019-10-10 20:36:31

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 84

Re: ISRU propellant production - energy requirement for the BFR?

louis wrote:

Nuclear power might come into its own when it comes to growing food, which has a huge energy demand. I don't think we know yet whether nuclear powered multi-level (or underground) farm facilities would make more sense than PV powered or natural light farms (perhaps with reflectors to boost light levels). It will probably be partly down to population size as to what makes sense. If the population gets to one million, that's a lot of area to be covered by PV. Not impossible, but might not make a lot of sense.  By that stage, however, solar power satellites capable of beaming energy down to the surface may be operational which will give us another option.

Solar power satellites may or may not be practicable as bulk power sources for Earth and Mars.  It depends entirely on our success in harnessing space based resources that are already at the top of planetary gravity wells.  It makes little sense trying to launch these things from Earth.  The jury is still out on whether the same is true for Mars.  One thing that is certain and was worked out quite early in development of this concept, is that solar power satellites are multi-GW powerplants.  This is determined by the fact that rectenas have a minimum practical diameter of about 10km, assuming a satellite in GEO.  Microwaves don't have enough beam coherence for rectenas to be reduced to much less than that.  The original SPS concept theorized by NASA was a 5-10GW powerplant.  I can't remember if that was at the powerplant transmitter or on the ground.  But this isn't practical on less than GW scales either way.

The weakness of ground based solar power in meeting any large scale equipment load is that even under clear skies at the equator, its power output follows a half sinusoidal pattern.  That means that it can only produce more than 50% of its peak capacity at that location for about 30% of the time.  That imposes quite a huge limitation on the productivity of whatever the solar array is powering, whether it be a propellant plant or an underground food factory.  A nuclear reactor that is rated for these loads will provide steady baseload power all of the time.  Whatever its other benefits and disbenefits happen to be, this is a huge economic advantage if that equipment happens to be capital intensive and expensive to ship in from Earth.  You really dont want to see it underutilized.  It is for exactly this reason that all utility grade solar on Earth is backed up 100% by fossil fuel power plants.  Essentially, it is the FF plant that meets most of the load burden and the solar plant reduces the fuel bill somewhat when it is producing.  Obviously, that option isn't available on Mars.  So we either take the productivity hit and only run our plant a third of the time; or we do what sensible people do on Earth and build a baseload powerplant.  On Mars, that means nuclear reactors.

For a long time to come, it will make sense to import nuclear reactor pressure vessels, core, instrumentation and control systems, from Earth.  However, it is likely to be far more practical to build things like heat exchangers and Rankin cycle power generation equipment on Mars, using ISRU carbon steels.  This accounts for most of the mass of the power plant.


Interested in space science, engineering and technology.

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#162 2019-10-11 01:06:20

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,924

Re: ISRU propellant production - energy requirement for the BFR?

"It is for exactly this reason that all utility grade solar on Earth is backed up 100% by fossil fuel power plants."

Not true at all. In Europe, for instance, Scandinavian hydro plays a huge role in backing up solar and wind energy. Energy from waste, geothermal and biofuels can all play a role as well. In South Australia large Tesla battery installations (100 Mwe capacity) are being used to back up and stabilise the grid.

"For a long time to come, it will make sense to import nuclear reactor pressure vessels, core, instrumentation and control systems, from Earth."

I doubt that very much.  The case for importing nuclear on Mars is extremely weak for the early missions. I can only see it having a role to play when the population increases - and we are talking about hundreds of thousands or millions of people. Then there might be the demand there for powering agriculture.  Another potential role could be in terraformation, but that is probably several decades away. 

In terms of agriculture, there are plenty of places on Mars where levels of insolation are comparable with temperate zones on Earth. A benefit of Mars's wobbly spin is, I recall, that the differential between winter and summer in insolation levels is less extreme on Mars.
Insolation levels could be further enhanced by placement of reflectors. on hillsides to direct additional insolation on to glass dome structures.

Obviously power for heating and pressurisation is also an issue. However, that can probably be minimised in various ways. There are some plants that release heat at night. These thermogenic plants could perhaps be planted in between crops to help keep a farm dome warm. I think there are glass-like materials that allow in light but suppress infrared loss at night (but don't have any references). Pressurisation could be minimal if we have a high CO2 atmosphere within farm domes.  Some crops might be used as bio fuels, but I am not sure about the energy accounting for concentrating the oxygen produced by plants.

Of course, with natural light farming you would have to accept some failed crops when there were major dust storms. In similar fashion to ancient Egypt which also experienced v. variable harvests (owing to fluctuations in the level of the Nile), the Mars community would have to prioritise the creation of food stores to see it through lean years, or even a succession of lean years.

While ground based solar has its weaknesses, as do all energy systems, it has many strengths. One of these is low cost and low maintenance (low labour input). On Mars, I think laying flexible PV directly on the ground may also allow for low cost/low labour input on installation.  The weather on Mars is so benign (no hail, no rain, virtually no floods, no snow to speak of, no thunder and lightning, no powerful winds or tornadoes of any strength) that such an approach is perfectly feasible.

Calliban wrote:

louis wrote:

Nuclear power might come into its own when it comes to growing food, which has a huge energy demand. I don't think we know yet whether nuclear powered multi-level (or underground) farm facilities would make more sense than PV powered or natural light farms (perhaps with reflectors to boost light levels). It will probably be partly down to population size as to what makes sense. If the population gets to one million, that's a lot of area to be covered by PV. Not impossible, but might not make a lot of sense.  By that stage, however, solar power satellites capable of beaming energy down to the surface may be operational which will give us another option.

Solar power satellites may or may not be practicable as bulk power sources for Earth and Mars.  It depends entirely on our success in harnessing space based resources that are already at the top of planetary gravity wells.  It makes little sense trying to launch these
things from Earth.  The jury is still out on whether the same is true for Mars.  One thing that is certain and was worked out quite early in development of this concept, is that solar power satellites are multi-GW powerplants.  This is determined by the fact that rectenas have a minimum practical diameter of about 10km, assuming a satellite in GEO.  Microwaves don't have enough beam coherence for rectenas to be reduced to much less than that.  The original SPS concept theorized by NASA was a 5-10GW powerplant.  I can't remember if that was at the powerplant transmitter or on the ground.  But this isn't practical on less than GW scales either way.

The weakness of ground based solar power in meeting any large scale equipment load is that even under clear skies at the equator, its power output follows a half sinusoidal pattern.  That means that it can only produce more than 50% of its peak capacity at that location for about 30% of the time.  That imposes quite a huge limitation on the productivity of whatever the solar array is powering, whether it be a propellant plant or an underground food factory.  A nuclear reactor that is rated for these loads will provide steady baseload power all of the time.  Whatever its other benefits and disbenefits happen to be, this is a huge economic advantage if that equipment happens to be capital intensive and expensive to ship in from Earth.  You really dont want to see it underutilized.  It is for exactly this reason that all utility grade solar on Earth is backed up 100% by fossil fuel power plants.  Essentially, it is the FF plant that meets most of the load burden and the solar plant reduces the fuel bill somewhat when it is producing.  Obviously, that option isn't available on Mars.  So we either take the productivity hit and only run our plant a third of the time; or we do what sensible people do on Earth and build a baseload powerplant.  On Mars, that means nuclear reactors.

For a long time to come, it will make sense to import nuclear reactor pressure vessels, core, instrumentation and control systems, from Earth.  However, it is likely to be far more practical to build things like heat exchangers and Rankin cycle power generation equipment on Mars, using ISRU carbon steels.  This accounts for most of the mass of the power plant.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#163 2019-10-11 04:04:29

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,924

Re: ISRU propellant production - energy requirement for the BFR?

You appear to be placing your hopes in a system that has not yet been demonstrated, has certainly not yet been used on Mars and which will require the small number of pioneers to undertake thousands of hours of difficult and repetitive work in extremely demanding conditions.

The belt and braces approach for Mars is of course correct - it can't be otherwise. My belt and braces approach is that solar is backed up by both methox generation and battery storage. I've exposed the nonsense that major dust storms result in zero insolation. All you can come up with in response is dramatic photos that appeal to the emotions, rather than scientific fact. 

The mass totals for a Kilopower solution are not good - at least 200 tons required (and that's not allowing for the batteries and solar power the Mission will still require) if the propellant power requirement is for 1 Mwe average constant. I think that PV power can provide a solution.

Suggesting I am a naive idealist is an appeal to the emotions - an invalid argument. Appealing to GW's superior scientific and technical knowledge is an argument from authority, also a well known invalid argument (and one I could counter by reference to Musk's undoubted expertise in the world of PV generation).

Which of the following is not true or a reasonable estimate or assumption:

1. A kg of methane can produce about 9 Kwhes.  So an initial store of 3 tons of methane could produce 27000 Kwhes of electricity, enough to power a base at a constant of 10Kwes for 110 sols without any other intervention.

2. 64 Kgs of oxygen are required to burn 16 Kgs of methane. So you will need to transport to Mars 12 tons of oxygen in addition to the 3 tons of methane. A total of 15 tons. Energy for cooling comes from the onboard solar. Add on 10% for boil off if you like and another 10% for the mass of the tanks. 18.15 tons in total - also add 1 ton for two 10 Kwe methox generators = 19.15 tons. Call it 20 tons.

3. There will be residual methane and oxygen in Starship tanks after they land. That effectively is an additional energy store since you are only taking one of the six Starships back to Earth.

4. Assume the total power requirement for the base, transport and propellant production is 1 Mwe average constant. The average power output for 1 sq metre of PV panel in Phoenix Arizona is 6.57 kilowatt hours. Let's take 40% of that for locations with the highest insolation on Mars and then halve it, to allow for a lower efficiency flexible PV = 1.314 KWhs per sq metre on Mars. The requirement is to produce 24500 Kwhs per sol. That would imply 18654 sq. metres on the basis of 1.314 Kwhs. But of course, that is not an even production level and there is no production at night. Now let's assume you use a larger propellant production facility ( I will come to that later) so you can have some variation in input (above and below the constant from a nuclear facility).  In order to provide input into the propellant facility through the whole sol, let's assume that 70% of the power goes to charging batteries at 80% efficiency. I would estimate the whole PV system needs to be about 12% larger to account for that. So it would need to be 20892 sq metres.

5.  The system needs to be able to deal with major dust storms. There is clearly a dispute about the impact of dust storms. Assuming a worst case scenario with a a prolonged deficit of let's say 50% over 9 months (this is far more extreme than any that have been properly recorded - I don't accept we know what the position was during the Mariner 9 dust storm). That would require your system to be 19% larger again.  So 20892 sq metres becomes  24861 sq. metres. Then let's add on another 10% as a margin of safety. That gives us 27347 sq. metres.

6. Total battery storage requirement at 300 w per kg would be 13720 Kwhs. Of that something like 5000 Kwhes of battery would already be available in the Starships.  So the additional requirement for a PV system would be 8720/0.3 =  about 29 tons.

7.  At 1 Kg per per sq. metre of flexible PV, the total PV system would mass nearly 21 tons. Add 30% for cabling/circuit equipment = 27.3 tons.

8.  Assume the propellant plant facility masses 10 tons for a nuclear solution. We will likely need larger capacity for a solar power solution. Let's say 50% larger - probably an overestimate of the requirement, given the amount of battery storage but let's be cautious. So an additional 5 tons.

9.  Let's add maybe 2 tons for some ATK-style fan units for early deployment. Total mass for a PV solution=

Emergency methox store -                       20.0 tons

PV sytem itself -                                    29.3 tons

Additional propellant plant infrastructure -    5.0 tons

Battery storage -                                   29.0 tons

TOTAL - 83.5 tons

10. The equivalent for the Kilopower solution (100 x 10 Kwe units) would be around a minimum of 156 tons (100 x 1.5 tons for each KP unit, plus  6 tons of electrical equipment to support the power system, same as for PV). That's without including any additional batteries or PV panels you may intend taking.

So the PV system would offer a saving in mass of 72.5 tons. 

11. Each Starship is going to be capable of taking up to 100 tons to Mars. But let's assume that gets designed down to 80 - so then the total lift to Mars in six Starships would be 480 tons.  At 83.5 tons, the PV approach would take up about  17% of the total mass transfer to Mars compared to 32% for the nuclear solution. 

Rather than using appeals to emotion and authority and ad hominems (all invalid arguments), I suggest you deal with the above...challenge the figures I put forward if you can.

Oldfart1939 wrote:

Louis-You're grasping at straws in a desperate attempt to support a position which is unsupportable. There seems to be come confusion about what DOES fly rather routinely in military aircraft: nuclear bombs, and Hydrogen bombs. Aircraft have crashed carrying them on training missions. The energy numbers for combined operation of a Mars base and ISRU fuel manufacture just don't add up for Solar power alone to do the job SAFELY AND RELIABLY! GW is an engineer trained to evaluate such systems as complete thermodynamic entities. You continue to make statements which are very idealistic about the engineering and scientific problems at hand. You have forgotten the landmark work of Robert Zubrin, who utilized nuclear energy as the basis of return flight to Earth ISRU. Engineers like Zubrin and GW have what you Brits call a "belts and braces" approach. They are professionally committed to making certain that nobody dies because of misplaced idealism.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#164 2019-10-11 05:46:45

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 84

Re: ISRU propellant production - energy requirement for the BFR?

Louis, you keep trying to deny the consequences of the second law of thermodynamics!  Part of me admires you for trying, frustrating as it is to watch.  Essentially, you are trying to argue the case that a system running on low density and intermittent ambient energy; can outperform a system running on concentrated and controllable stored energy with much lower entropy.  And you seem determined not to take no for an answer.  People keep trying to do the same thing here on Earth and it is already starting to cost us a lot of prosperity.  And expensive projects like space flight require a lot of prosperity, which is really a function of surplus energy.

The economy is an energy system.  Fossil fuel EROI continues to decline and nothing with comparable surplus energy is presently available to replace fossil fuels, thanks to all attempts to block it by idealistically minded 'green' people.  Ironically, these people are doing nothing to help humanity reach a more sustainable way of living.  The sort of energy solutions they have in mind require enormously greater inputs of refined materials, like steel, concrete and silicon, that must all be extracted from the environment and processed – all at high environmental cost.  The end result of all this will be much lower energy use, which will result in a proportional decline in human wealth and (quite probably) human numbers as well.  My concern is that these idealists may end up permanently costing humanity its rightful place as an interplanetary species and they will certainly cost a lot of people their quality of life and probably life expectancy, as this folly continues to unfold.  Becoming a multiplanet species is the most ambitious, expensive and energy intensive endeavour that humanity has ever undertaken.  It is very difficult to see how it can happen in an environment where the surplus energy available to the human economy is contracting.

Regarding early Mars missions, we certainly can make them work at a functional level with solar power alone.  But that comes at a price in terms of mission mass, reliability and flexibility; as GW, Oldfart1939, Kbd and many others here keep telling you.  Basically, it means a more costly mission with lower capabilities.  We can talk around various options and discuss the relative pros and cons, but ultimately there is no point deluding ourselves into imagining things are different to what they are.  If we end up relying on solar power for bulk power production on Mars, it will be because politicians, lawyers and deluded idealists, have removed the option for nuclear power or made it so impractical that we cannot use it.

Entropy gets no respect :-)


Interested in space science, engineering and technology.

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#165 2019-10-11 09:01:58

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,719

Re: ISRU propellant production - energy requirement for the BFR?

Calliban-

Thank you for such a well-written but clearly stated rebuttal to the attempts at repealing the Laws of Thermodynamics. In his books, Robert Zubrin addresses the planetary energy consumption as a measure of global prosperity. In particular, his book "Merchants of Despair," he point out that moving towards increased utilization of Nuclear power is inevitable and absolutely necessary, as is advance to thermonuclear utilization. He decries the efforts of the Green Movement as slowing the progress of society towards becoming interplanetary and finally interstellar. Utilization of the supply of He3 in the atmospheres of the Gas Giant planets will enable human society to prosper beyond the imaginations of those alive today. As you have so correctly pointed out, it all starts with energy availability.

I too, am an idealist. I enjoy the glorious vistas of Earth--the mountains, deserts, and seashores--that I DON'T want to see covered with acres and hectares of endless solar panels. Neither do I want to journey to Mars and see nothing but solar panels stretching as far as my eye can see.


Calliban wrote:

Louis, you keep trying to deny the consequences of the second law of thermodynamics!  Part of me admires you for trying, frustrating as it is to watch.  Essentially, you are trying to argue the case that a system running on low density and intermittent ambient energy; can outperform a system running on concentrated and controllable stored energy with much lower entropy.  And you seem determined not to take no for an answer.  People keep trying to do the same thing here on Earth and it is already starting to cost us a lot of prosperity.  And expensive projects like space flight require a lot of prosperity, which is really a function of surplus energy.

The economy is an energy system.  Fossil fuel EROI continues to decline and nothing with comparable surplus energy is presently available to replace fossil fuels, thanks to all attempts to block it by idealistically minded 'green' people.  Ironically, these people are doing nothing to help humanity reach a more sustainable way of living.  The sort of energy solutions they have in mind require enormously greater inputs of refined materials, like steel, concrete and silicon, that must all be extracted from the environment and processed – all at high environmental cost.  The end result of all this will be much lower energy use, which will result in a proportional decline in human wealth and (quite probably) human numbers as well.  My concern is that these idealists may end up permanently costing humanity its rightful place as an interplanetary species and they will certainly cost a lot of people their quality of life and probably life expectancy, as this folly continues to unfold.  Becoming a multiplanet species is the most ambitious, expensive and energy intensive endeavour that humanity has ever undertaken.  It is very difficult to see how it can happen in an environment where the surplus energy available to the human economy is contracting.

Regarding early Mars missions, we certainly can make them work at a functional level with solar power alone.  But that comes at a price in terms of mission mass, reliability and flexibility; as GW, Oldfart1939, Kbd and many others here keep telling you.  Basically, it means a more costly mission with lower capabilities.  We can talk around various options and discuss the relative pros and cons, but ultimately there is no point deluding ourselves into imagining things are different to what they are.  If we end up relying on solar power for bulk power production on Mars, it will be because politicians, lawyers and deluded idealists, have removed the option for nuclear power or made it so impractical that we cannot use it.

Entropy gets no respect :-)

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#166 2019-10-11 09:51:21

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,924

Re: ISRU propellant production - energy requirement for the BFR?

Absurd! Nothing to do with entropy. And the effect on prosperity?  These are some of the most prosperous countries in the world (the percentages in brackets are how much they generate electricity from renewables): Denmark (60.5%), Iceland (100%) and Norway (97%). 
Fossil fuels or nuclear are not necessary for prosperity - that much is clear.

I'm not taking no for an answer when you refuse to state which of my 11 points is untrue or unreasonable and instead indulge in ad hominems and vague claims.

In terms of what happens on Earth the key issue is (unsubsidised) cost, because cost reflects the full range of inputs. While fossil fuels have served us well they are now being overtaken by wind energy, and in some parts of the world by solar. It doesn't matter if a nuclear reactor is built around something with stupendous energy density if it is such a highly complex operation that you have to deploy so many materials and so much  human labour to exploit that energy density. That's  why in the UK, nuclear power has to be guaranteed at over 9 pence per Kwh and why recent auctions have seen wind energy bidding way below that.

Just as people said 30 years ago that wind and solar will never compete with fossil fuels and nuclear, so now you say in effect the storage problem will never be overcome.  Well wait and see.  The cost of batteries has already fallen about 90% in ten years. Most analysts believe solar plus storage will beat everything else on price within the next 10-20 years.

As for Mars, the key issues are mass, reliablity and low labour input.

When are you going to be honest about the mass issue? How much mass do you think 100 Kilopower Units at 10 Kwe will have? We are talking about 150 tons. Far more than will be necessary with a solar-based mission.


Calliban wrote:

Louis, you keep trying to deny the consequences of the second law of thermodynamics!  Part of me admires you for trying, frustrating as it is to watch.  Essentially, you are trying to argue the case that a system running on low density and intermittent ambient energy; can outperform a system running on concentrated and controllable stored energy with much lower entropy.  And you seem determined not to take no for an answer.  People keep trying to do the same thing here on Earth and it is already starting to cost us a lot of prosperity.  And expensive projects like space flight require a lot of prosperity, which is really a function of surplus energy.

The economy is an energy system.  Fossil fuel EROI continues to decline and nothing with comparable surplus energy is presently available to replace fossil fuels, thanks to all attempts to block it by idealistically minded 'green' people.  Ironically, these people are doing nothing to help humanity reach a more sustainable way of living.  The sort of energy solutions they have in mind require enormously greater inputs of refined materials, like steel, concrete and silicon, that must all be extracted from the environment and processed – all at high environmental cost.  The end result of all this will be much lower energy use, which will result in a proportional decline in human wealth and (quite probably) human numbers as well.  My concern is that these idealists may end up permanently costing humanity its rightful place as an interplanetary species and they will certainly cost a lot of people their quality of life and probably life expectancy, as this folly continues to unfold.  Becoming a multiplanet species is the most ambitious, expensive and energy intensive endeavour that humanity has ever undertaken.  It is very difficult to see how it can happen in an environment where the surplus energy available to the human economy is contracting.

Regarding early Mars missions, we certainly can make them work at a functional level with solar power alone.  But that comes at a price in terms of mission mass, reliability and flexibility; as GW, Oldfart1939, Kbd and many others here keep telling you.  Basically, it means a more costly mission with lower capabilities.  We can talk around various options and discuss the relative pros and cons, but ultimately there is no point deluding ourselves into imagining things are different to what they are.  If we end up relying on solar power for bulk power production on Mars, it will be because politicians, lawyers and deluded idealists, have removed the option for nuclear power or made it so impractical that we cannot use it.

Entropy gets no respect :-)


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#167 2019-10-11 11:09:39

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,719

Re: ISRU propellant production - energy requirement for the BFR?

Louis-

You are allowing YOUR PREJUDICES against nuclear power, and to some extent, so-called Fossil Fuels, to color your ability to clearly read and UNDERSTAND what GW, kbd512, Calliban, and I have presented to you. As examples of countries which you claim are among the "most prosperous," they are all tiny in comparison to USA, Russia, Canada, and other major European nations. You do NOT make your case as a result.

"My mind is already made up. Don't confuse me with facts." Louis.

You claim that wind power and solar power are king and queen of energy production. When the sun is covered by clouds, there is no solar power; when the wind doesn't blow, there is no wind power. They are merely support energy sources which can only occasionally be exploited in the fullest manner. A coal fired plant produces power 24/7; so does a nuclear reactor and does not contribute to atmospheric CO2 hated by Green Freaks.

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#168 2019-10-11 14:12:28

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,962

Re: ISRU propellant production - energy requirement for the BFR?

All,

Even if all the world's religions that tout the omnipotence of their various sky wizards fall by the wayside, it's clear to me that religious ideology is alive and well in the 21st century.  While I will never fault anyone for choosing to believe what they wish to believe in, I draw the line at them expecting me to partake in their religion or pay my tax money to perpetuate their ideology.  These "green energy" people have chosen to perpetuate a religion to their liking in lieu of math and science.  In the same way the scientology has virtually nothing to do with science, "greentology" has nothing to do with better forms of energy with less waste and pollution.

I'm here to tell everyone that at a fundamental level, all economies run on energy, not the ideology of the faithful.  Faith didn't produce models of how the forces that government the universe actually work.  Faith certainly didn't produce rocket engines.  Faith sure as hell won't lead to greater human prosperity.  Human brain constructs regarding what someone likes or dislikes have little to nothing to do with how well any given idea will work in practice.

We're no closer to "energy without emissions" today than we were a century years ago.  We're no closer to that lofty goal because we have religious faithful that evil people, using power they should never have been given, can easily manipulate ignorant people by using the articles of their religious faiths against them.  They manipulate these people into believing things that are mathematically verifiably false, not to mention empirically false from casual observation.

We have not mastered nuclear power.

We have not mastered solar power.

We have not mastered wind power.

We have not mastered geothermal power.

We do know how to use all of those aforementioned forms of power and we've made use of them to varying degrees and with varying levels of success, but we are not masters of those forms of power generation.

We use gas and oil on a massive planet-wide scale because it's the highest form of energy generation that we've actually mastered.

We haven't expanded the use of those other power generation technologies because the technology is either beyond our capabilities, as a species, not what one person or a small group of people may be capable of, or beyond our ability to produce and maintain at the scale required.

That's all there is to it in plain, simple, and empirically / observationally verifiable terms.

We should all strive for a better tomorrow, but we should also take stock of where we've been, where we're at right now, and where we're likely to be in the near future.  There's also nothing wrong at all with dreaming about a fantastically better future, but you'd better make sure you know where your dreams end and where current reality begins.

Does anybody else come here to discuss practical technical solutions to significant challenges to human space flight?

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#169 2019-10-11 14:41:50

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,962

Re: ISRU propellant production - energy requirement for the BFR?

It occurs to me that we've been trying like mad to advance all forms of energy technology except nuclear power, without much to show for all of our efforts, if the totality of our efforts at a planet-wide scale is taken into account.  We keep talking about the world of tomorrow, as if what we do in the here and now has no effect on what that world will look like.

Why can't we expend an equal amount of effort on an energy technology as promising as nuclear power?

We can't just wave a magic wand and make our existing nuclear reactors and materials go away, so why aren't we trying to get every last Watt of energy out of those largely unused materials?

At the very least, we could get rid of our existing stockpiles of nuclear fuels and use the energy created to build those fantastic new batteries and solar panels if that's what our "green energy" people really intend to do.  However, we'd actually have to use those materials to do that.  I think we need to actually try something fundamentally new.  Since we can obtain a surplus of cheap, reliable, and clean energy from nuclear power, should we decide to use it at scale, then we can easily afford to explore the various ideas that the solar and wind advocates have put forward, even if some of those ideas don't pan out.  As it stands, we're going to need a lot more energy to feed / clothe / house / fuel our burgeoning population, along with more efficient means of using the energy.

Nobody here is talking about putting nuclear reactors in cars or airplanes, just building new reactors at the sites where we already have nuclear reactors built.  For various reasons, those sites are highly unlikely to actually be completely shut down or dismantled and probably never turned into "sustainable agriculture" farms for food or cattle grazing.  We're not likely to build new shopping malls in the remote locations where most reactors are sited, either.  That said, the land still has value for using it for what we decided a long time ago to use it for.

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#170 2019-10-11 16:38:58

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,719

Re: ISRU propellant production - energy requirement for the BFR?

kbd512-
One aspect of the "nuclear waste problem," that hasn't been properly addressed is the fact that much of the highly radioactive "waste" is still loaded with fissionable material which could be reclaimed through robotic processing, and hence utilized further instead of filling up space in hazardous material waste sites. It's economics at play again. It's considerably cheaper to call it waste and use fresh Uranium!

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#171 2019-10-11 17:17:21

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,181

Re: ISRU propellant production - energy requirement for the BFR?

I have come to some conclusions as well having bought 2 simular off the shelf LED with times light levels, Solar thin film plastic encapsulated, Lithium ion with motion detection.
1. Flaws in the designs start with what level of energy that is always possible from the solar cells to charge the battery for the light to work for the period of time being all night as motion detected activated. The panels are 2 to 3 times to small for surface area to garentee we get a full battery even when aligned on semi cloudy days. Simular to the dust effect.

2. the battery capacity on whrs is incorrect as well since they appeared to use full charge to calculate the time for the use as they were not even close. To figure the hours you need to average low voltage and high voltage for power levels to get the mid value that is the constant power which can be drawn. Since we know that we should factor a reduced value for what to use for calculating the time we would lower that by 5% before pluging into the equation the power for the LED to light as its a constant power device when turned on.

So to fix the alignment issue for earth and for mars we would use collecting lense to gather the light and cuminate it to the panel so that its concentrated. The lense does work for diffused light in both cases.

Scaling Up The Production Of Highly Efficient Solar Modules

scaling-up-the-production-of-highly-efficient-solar-modules-hg.jpg

The technology developed by Swiss startup Insolight, tested under concentrator standard test conditions (CSTC) in the pre-production phase, achieves 29% efficiency. This is well above the efficiency levels of standard photovoltaic (PV) panels, which typically reach 18-20%.

https://insolight.ch/

This is the thin film flexible cells DGIST achieves the highest efficiency of flexible CZTSSe thin-film solar cell

Energy Technology achieved 11.4% for the photoelectric conversion1 efficiency of flexible CZTSSe thin-film solar cell. This achievement is drawing more attention because its mass production is much easier with the use of low-cost, ecofriendly materials such as copper(Cu), zinc(Zn), tin(Sn) than the existing thin-film solar cell (CIGS, CdTe, perovskite2), which uses high-cost heavy metal materials such as indium, lead, and cadmium.

http://dx.doi.org/10.1038/s41467-019-10890-x

Opportunity and Spirit are in Mars' southern hemisphere, where the Sun appears in the northern sky during fall and winter, so solar-array output is enhanced by tilting the rover northward.
Notice that the rovers park on a slope to point the panels.
639pxOpportunity_in_Endurance_Crater.jpg?mw=600
A perfect storm of dust build up, with no ability to move to help angle the panels meant a slow death as the batteries froze.

When men are on mars for the set of panels that we have we will need to tilt them to be able to get the most out of the winter sun.
http://www.planetary.org/explore/space- … pdate.html

The rover's bad wheel does slow it down though and it took Spirit most of this month to find and get to its current position off the northern edge of Home Plate, where it will hunker down for its third Martian winter. During the week before Christmas though, the rover deftly descended over the edge of Home Plate North and parked at a 13-degree tilt, to take in as much sunlight "fuel" as possible.

Spirit will continue to inch farther down as winter sets in, angling its solar arrays to follow the Sun, eventually reaching a 25 to 30-degree tilt. Even if it hibernates and goes to low power for a while in the New Year, which is part of the plan, this rover is going to need all the power it can glean to survive this winter, because the dust that has accumulated on its solar arrays from the summer’s global dust storm is blocking a lot of the sunlight and the depths of the season in the planet’s southern hemisphere won't pass until next July.

It did not wake up...

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#172 2019-10-11 22:08:05

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 84

Re: ISRU propellant production - energy requirement for the BFR?

Good replies all.  For those interested, here is a link to a MIT study on the relative mass of thin film solar, RTG and nuclear fission based systems in support of Mars missions.

http://systemarchitect.mit.edu/docs/cooper10.pdf

Solar PV in broadly competitive with the baseline fission solution at latitudes between the equator and 30 degrees north.  Outside of this area, system mass will be greater.

There are other complications that need to be addressed.  The PV panels need assembling and weighting down, which is estimated to be about 30 man-hours work.  The assessment does not seem overly concerned with the potential for damage to the panels assembled over a rubble strewn surface, or the inefficiency that this would impose by bending the panels into random orientation.  Dust would need to be periodically removed, maybe using compressed CO2.  Obviously, the array needs to be positioned on a flat or slightly southerly facing surface outside of shadow.  Undulating of the surface due to rubble and other surface imperfections could be problematic.  Overall the system can be made to work.  It is more complicated and generally less mass competitive than a 100KWe fission reactor would be.

The reason we see so little innovation and development in small fission technologies is the difficulty imposed by licensing and regulations.  And this all gets even more difficult if designs use highly enriched uranium.  For this reason, it is very expensive to develop fission reactors.  The plants themselves probably aren't that expensive if we produce them in series production.  A lot of cost and BS that make nuclear power development so expensive on Earth, can presumably be dropped by an independent Mars base.  Once a base reaches a population level of tens of thousands, it could begin building small, carbon moderated natural uranium reactors, without interference from Earth.

Last edited by Calliban (2019-10-11 22:32:19)


Interested in space science, engineering and technology.

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#173 2019-10-11 22:57:12

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,181

Re: ISRU propellant production - energy requirement for the BFR?

Thanks for the document but

The structural overhead is based on ISS. Also, multi-axis tracking was assumed to achieve perpendicular solar flux incidence throughout the Martian day.

Not laying on the ground and support for panels have quite a bit of mass plus.

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