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#1 2004-03-11 16:21:39

C M Edwards
Member
From: Lake Charles LA USA
Registered: 2002-04-29
Posts: 1,011

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

The Sabatier reaction, used for on site propellant production in the Mars Direct plan, releases a great deal of usable energy.  Even accounting for the energy use required to keep the process going continuously, a properly designed propellant plant based around a Sabatier reactor could produce enough power to run both itself and the ERV during the in-situ propellant production phase of a mars mission. 

That estimate does not require energy input from a full nuclear reactor (5kW, lithium cooled, etc.).  A set of RTG’s would still be required to start the Sabatier reactor and to maintain the ERV indefinitely after the Sabatier reactor shut down.  However, the mass of the RTG’s needed would be an order of magnitude less than a full nuclear reactor.  Additional hydrogen feedstock would be required, but not so much that it would outweigh a one to five ton nuclear reactor.  RTG’s have a better success record in space applications than full nuclear reactors and last longer.  (For comparison, the maximum lifetime of the longest operating RTG on a satellite – the one on the Pioneer X probe – hasn’t been determined after thirty years.  The longest lasting full nuclear reactor on a satellite didn’t make it to six months, with the average being closer to one month.)  Current RTG technology is already adequate for on site propellant production. 

In short, using the Sabatier reactor for power, employing the hydrogen fuel already along for the ride, can eliminate the need for a full nuclear reactor in an ERV.


"We go big, or we don't go."  - GCNRevenger

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#2 2004-03-11 17:42:35

Ian Flint
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From: Colorado
Registered: 2003-09-24
Posts: 437

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

I'm no chemical engineer, but some red flags just went up.
You factored in the methanation process, which is exothermic, and the start-up power.  But to produce the right ratio of oxygen to methane you need more oxygen.  Several methods are viable, but one for sure is extremely endothermic -- the direct reduction of CO2 at 1100 degrees C.  Also, you need to electrolyze the water produced from the sabatier reaction.  I believe that is also an endothermic reaction.

Please, set me straight on this.

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#3 2004-03-11 19:59:36

RobS
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From: South Bend, IN
Registered: 2002-01-15
Posts: 1,701
Website

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

And don't forget the methanation reaction looks like this:

4H2 + CO2 = CH4 + 2H2O

It makes no oxygen and half the hydrogen ends up as water. To make oxygen for the methane, you have to break down the H2O, and that needs electricity. That is still only half the oxygen you need; burning methane with it makes carbon monoxide. So you have to split carbon dioxide into carbon monoxide and oxygen to get the rest.

As a rough rule of thumb, these chemical reactions need about 4 or 5 kilowatt-hours for every kilogram of fuel you make.

         -- RobS

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#4 2004-03-11 23:32:35

GCNRevenger
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From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

Actually I AM a chemist, and the thermodynamics don't add up, the Sabatier cycle requires an input of energy if you are going to recycle the water, and Ian is quite correct that breaking down CO2 into Oxygen is a pretty intensive process.

The Sabatier reaction produces about 27 kilojoules of energy per mole, while the energy needed to electrolyze four moles of water to produce that one Sabatier mole is about 1,140kJ/mol. Don't forget the inefficency of converting heat into electricity, which will be about four or five fold best case.

In the grand scheme of things, the only reason to do Sabatier on Mars is to convert the energy produced by the nuclear reactor (which provides GOBS of power per weight) into an easier to use and handle form (Methane, maybe Methanol, Oxygen, etc) to operate rockets, fuel cells, lab gear, etc.

Furthermore, the nuclear reactor's life depends largely on its fuel loading, and if you pack a decent amount of Uranium into them, should last many years. Russia operated its RORSATs with Topaz reactors did and Nasa's Prometheous/JIMO probe's reactor should last several years. I believe Dr. Zubrin thinks the reactor weight ought to stay below 3-5 tons, which I think is quite reasonable.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#5 2004-03-12 18:03:31

C M Edwards
Member
From: Lake Charles LA USA
Registered: 2002-04-29
Posts: 1,011

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

After all the beating this idea took today, I'm not sure if I still need to say that I went back over my calculations and found out that I was off by a factor of two _before_ accounting for efficiency...

So I won't.   
tongue

The sabatier reactor makes a lot of power, but cannot provide sufficient power for the needed production of oxidizer.

(Curses, foiled again!)   :bars3:


"We go big, or we don't go."  - GCNRevenger

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#6 2018-06-20 18:24:09

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,471

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

another topic from the past

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#7 2019-11-09 12:26:40

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,471

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

This topic relates to the Louis soalr power back up plan to use fuels to create power when solar can not do so....

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#8 2019-11-09 16:27:56

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,757
Website

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

Solar doesn't work when the sun don't shine.  Period. 

It also doesn't work very well when the sun angle is low,  off of solar noon.  Unless you build big,  heavy,  expensive tracking collectors.  NOBODY does that!  Except out in space in zero gee.

There is really good solar energy collection available for a properly-oriented collector panel for about 2.5 hours either side of solar noon,  here on Earth.  The other daylight hours,  sun angles are low,  and collection is weak.  And then there's night.  Basically,  you collect about 90% of what you are going to get,  in about a 5 hour period out of every 24. 

It's only 37 minutes different on Mars,  which is no difference at all.

Mars has a problem Earth does not have: occasional planetwide dust storms.  Now,  Mars has a lot of dust storms.  I'm not talking about those.  I'm talking about the rarer ones that obscure 90+ of the light,  like the one that killed Opportunity,  and the even bigger one that Mariner 9 saw when it arrived.

That's not just like a long night,  it's months of darkness. 

And,  as I said,  solar don't work when the sun don't shine.

PERIOD.

GW

Last edited by GW Johnson (2019-11-09 16:28:43)


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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#9 2019-11-09 16:42:00

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,471

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

The other part of earth versus mars is on earth orbit its about 1300 with a mer 1000 getting to the surface for the panels to change into electricity but on mars its around 480 w on orbit with the amount on a clear day being 430 w. its the starting point that makes mars such a challenge. Even though the atmosphere does spread the light out by difusive effects by the dust in the air its still only slightly longer in day changing with a lower starting point due to the dust level drop. Where pointing the panels in winter become critical for getting the most out of what can be recieved.
Of course the real possibility is if we find a Methane vent or underground gas pocket to tap into we are still only half way there for making it a viable backup. Since there is no useable free oxygen on mars.

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#10 2019-11-09 17:50:11

louis
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From: UK
Registered: 2008-03-24
Posts: 5,368

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

Mars may have global dust storms but on the other hand its seasonal fluctuations are less extreme, which means that solar power is more evenly distributed over the equatorial and temperate zones than on Earth.

"...like the one that killed Opportunity" - let me complete that sentence for you "...after 14 years"! smile

The measurements for Mariner 9 were very crude. No one knows it was the worst on record.

A global dust storm does not, most definitely NOT, mean "months of darkness". It means months of reduced solar radiation...between probably 20% and 60%.

GW Johnson wrote:

Solar doesn't work when the sun don't shine.  Period. 

It also doesn't work very well when the sun angle is low,  off of solar noon.  Unless you build big,  heavy,  expensive tracking collectors.  NOBODY does that!  Except out in space in zero gee.

There is really good solar energy collection available for a properly-oriented collector panel for about 2.5 hours either side of solar noon,  here on Earth.  The other daylight hours,  sun angles are low,  and collection is weak.  And then there's night.  Basically,  you collect about 90% of what you are going to get,  in about a 5 hour period out of every 24. 

It's only 37 minutes different on Mars,  which is no difference at all.

Mars has a problem Earth does not have: occasional planetwide dust storms.  Now,  Mars has a lot of dust storms.  I'm not talking about those.  I'm talking about the rarer ones that obscure 90+ of the light,  like the one that killed Opportunity,  and the even bigger one that Mariner 9 saw when it arrived.

That's not just like a long night,  it's months of darkness. 

And,  as I said,  solar don't work when the sun don't shine.

PERIOD.

GW


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

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#11 2019-11-09 19:32:19

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 17,471

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

To make it work you need to know how much oxygen for the fuel to burn rate to how much energy must be expended to gain the oxygen...sure saving the exhaust for later recycling for fuel is a must to aid in the rate of enegry needed as you will be at a higher pressure for the recycled versus the original mars atmospheric capture which is going to be higher in consumed power to gain.

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#12 2019-11-10 12:25:47

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,757
Website

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

Louis:

Your "20-to-60%" figure is NOT true.  NASA's own publicly-released images and data refute that.  I posted them at "exrocketman".  Go look for yourself.  Their data,  from Opportunity itself,  say 10%-or-less,  nobody knows for sure,  except that it was 10% or less.

As for Mariner-9 data:  its crudity has NOTHING to do with its truth!  Crudity (and lack of surface data) is NOT a valid argument to ignore that data!  No giant dust storm since has obscured the 3 tall volcanoes on Tharsis Mons.  That one did,  for about 6+ months.  And 9 months to clear generally.

When you compare that Mariner observation to the 5-10% insolation levels that killed Opportunity,  you realize that you are talking about something fuzzy but inherently very near 0% insolation,  for many months.  Just because we cannot pin the numbers down with ground data (because Mariner-9 was only an orbiter) doesn't make the observation any less true!

It happened.  One or two not quite as bad have happened since.  It WILL happen again.  No one can predict when.  THAT is what we know!

You CANNOT hand-wave that truth away,  or try to discredit it with selective source-quoting.  A piece of real data,  fuzzy or not,  outweighs any academic paper ever published.  Sorry to disappoint you with my distrust of academic citations,  but academics only get embarrassed when they are wrong,  while people die if engineers get it wrong.  (I'm an engineer,  if you cannot tell.)

A Mariner-9-class dust storm (near-0% insolation for several months) is a real threat.  And the dust storm class that killed Opportunity reduced insolation to 10%-or-lower levels for a few months,  demonstrably.  And THAT is what you have to deal with,  when you select a mix of power supplies for a settlement on Mars!  Or else you will kill them all when it happens.

GW

Last edited by GW Johnson (2019-11-10 12:36:38)


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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#13 2019-11-10 15:39:31

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 244

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

I don't understand Louis' desperate need to avoid the deployment of nuclear energy, on a planet where it is clearly needed.  Everything that humans do on Mars will be more energy intensive than it is on Earth.  Even breathing, and especially eating.  Water on Mars, has the same embodied energy as concrete on Earth.  And we need lots of it for just about every human function and industrial process.  All these energy needs in a place with half the sunlight intensity of Earth.  To live in the place at any reasonable standard of living, will require bucket loads of energy, delivered very cheaply.


Interested in space science, engineering and technology.

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#14 2019-11-10 16:12:18

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,757
Website

Re: The Sabatier Reactor as Powerplant - Forget Nuclear, Go Chemical

Calliban:

Well,  sad to say,  Louis is infected with the same irrational fear of anything nuclear that so many others are.  That attitude is not based in fact,  but in fear-mongering. 

Which is not to say that big improvements are not needed in all forms of nuclear,  because they so very clearly are.  But even what we currently have is "good enough" to use where we really need it.  Like on Mars.

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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