Vacuum pyrolysis of lunar oxygen

[Bill White]

Remember, an electrolysis plant would be a big consumer of electricity. A vacuum pyrolysis plant would be a producer of electricity.

The same heat that liberated oxygen from regolith could also be used to generate electricity. 

[A_M_Swallow]

Remember, an electrolysis plant would be a big consumer of electricity. A vacuum pyrolysis plant would be a producer of electricity.

The same heat that liberated oxygen from regolith could also be used to generate electricity. 

Sounds like an integrated design is needed.

Since the pilot plant needs to fit on a single lander it has to be small - permitting testing to be performed in a vacuum chamber.

[Warren Platts]

[snip}

I respectfully disagree. We can look to Earth technologies and use that as a guide. E.g., does solar thermal on Earth have a major mass/power advantage over PV? Correct me if I'm wrong, but I don't think there is a major mass advantage. Thus, there's no need for endless technology studies. Let's get the ball moving.

This is an article about solar thermal generation of electricity on the Earth.
http://www.thegreentechnologyblog.com/2010/sterling-technology-improves-efficiency-in-solar-thermal-electricity-production

This is information on a 25 kW solar electric generator.  On Earth it averages 26% efficiency.
http://www.stirlingenergy.com/how-it-works.htm

A lunar version would need to work over a much wider temperature range, higher incoming solar energy and a day that lasts a month.

A. The green technology blog is down.

B. Interesting link, but it proves my point there is no mass advantage to solar thermal versus PV: according to the brochure, one unit (mirror plus PCU) = 7910 kg and produces 45,000 J/s, thus the Watts per kg = 5.6 Watts per kg. Meanwhile, 300 W/kg looks doable for NASA solar arrays.

Of course, that's the wattage after converting to electricity with the stirling engine (which uses the atmosphere to cool it BTW). Moreover, although SES is working on weight optimization (they already cut off 5000 kg off of each 45 KW unit), let's assume they can get it down by 90% (since gravity on Moon is 1/6 g). Thus, we're lookin' at a specific power of 170 W/kg. Since the power requirements of a vacuum pyrolysis system capable of making 10,000 mT per year are going to be on the order of 400 MW, then the total weight of the system is 400,000,000 W / 170 W/kg = ~2,300 mT.

If we use heavy 1st generation landers of the DTAL variety that can land 20 mT at a time, then that's 115 cargo flights. This doesn't take into account the equipment for the mining operation, habs, etc.

Assuming 2 cargo flights per year, it would take 57 years to deposit all the equipment for the regolith processing plant.

Clearly, water ice is the low hanging fruit.

[Warren Platts]

The same heat that liberated oxygen from regolith could also be used to generate electricity. 

You're still handwaving away the cooling cycle of your Stirling engines. On Earth they use radiators similar to automobile radiators. So you're stuck either trying to radiate the waste heat into a pure vacuum (the best insulator in the world) or geothermal, which requires a lot of pipes and trenches or else drilling equipment and lots of pipes.

[A_M_Swallow]

{snip}
If we use heavy 1st generation landers of the DTAL variety that can land 20 mT at a time, then that's 115 cargo flights. This doesn't take into account the equipment for the mining operation, habs, etc.

Assuming 2 cargo flights per year, it would take 57 years to deposit all the equipment for the regolith processing plant.

That is because you are over specifying the initial plant.  The ability to make 2 mirrors and supports in a year using local material is all that is needed.

1
1*2 + 1 = 3
3*2 + 3 = 9
9 *2 + 9 = 27
27*2 + 27 = 81
and so on

so after 5 years 81 * 25 kW = 2,025 kW

A lot can be done with 5 MW of power.

Things are even better if the Stirling engines and tracking motors can also be manufactured locally.

[Warren Platts]

{snip}
If we use heavy 1st generation landers of the DTAL variety that can land 20 mT at a time, then that's 115 cargo flights. This doesn't take into account the equipment for the mining operation, habs, etc.

Assuming 2 cargo flights per year, it would take 57 years to deposit all the equipment for the regolith processing plant.

That is because you are over specifying the initial plant.  The ability to make 2 mirrors and supports in a year using local material is all that is needed.

1
1*2 + 1 = 3
3*2 + 3 = 9
9 *2 + 9 = 27
27*2 + 27 = 81
and so on

so after 5 years 81 * 25 kW = 2,025 kW

A lot can be done with 5 MW of power.

Things are even better if the Stirling engines and tracking motors can also be manufactured locally.

OK, well if magic manufacturing is allowed, let's make a gigantic SBSP array for Earth from Lunar materials. All our energy problems will be solved!

[A_M_Swallow]

OK, well if magic manufacturing is allowed, let's make a gigantic SBSP array for Earth from Lunar materials. All our energy problems will be solved!

You are part of the problem, not part of the solution.

[douglas100]

You're still handwaving away the cooling cycle of your Stirling engines. On Earth they use radiators similar to automobile radiators. So you're stuck either trying to radiate the waste heat into a pure vacuum (the best insulator in the world) or geothermal, which requires a lot of pipes and trenches or else drilling equipment and lots of pipes.

No matter what power conversion cycle is used, large amounts of waste heat are going to have to be radiated away as a consequence of lunar industry. That means big radiators even using photovoltaic power generation. The ISS gives a feel for the area of solar panels versus the area of radiator required.

Having said that, I agree that solar panels are the way to go  for the reasons you have already given.

[Moe Grills]

   Let's see!

The Moon is rich in hydrogen at the poles (frozen water). There's your fuel.
There's plenty of oxygen on the Moon.
There's your oxidizer.

  Electrolysis is straight forward, reliable and a 200 year old technology.
I seem to recall carrying out electrolysis in high-school chemistry.

The Moon's surface receives an abundant supply of energy (1400 watts/meter^2)

If you combine solar heating with electrolysis, you can extract and isolate
a variety of elements, besides oxygen.
   

[Hop_David]

   Let's see!

The Moon is rich in hydrogen at the poles (frozen water). There's your fuel.
There's plenty of oxygen on the Moon.
There's your oxidizer.

  Electrolysis is straight forward, reliable and a 200 year old technology.
I seem to recall carrying out electrolysis in high-school chemistry.

The Moon's surface receives an abundant supply of energy (1400 watts/meter^2)

If you combine solar heating with electrolysis, you can extract and isolate
a variety of elements, besides oxygen.

The problem is that you need to send up mass to exploit this sunlight.

Present solar arrays can do around 100 watts per kilogram. If we want to crack water at a decent rate, we'd have to send an implausibly massive solar array to the moon's surface.

I've been following Bill White's thread with interest.

Bill has mentioned some processes are thermal. Using sunlight directly for thermal energy may work better than photovoltaics or converting thermal watts to electric watts.

But details remain foggy. I think we can make a ball park guess what mass solar array we'd need to produce hydrogen and oxygen from water. But I don't know what mass Bill's vacuum pyrolysis plant would be.

[Warren Platts]

OK, well if magic manufacturing is allowed, let's make a gigantic SBSP array for Earth from Lunar materials. All our energy problems will be solved!

You are part of the problem, not part of the solution.

Seriously, Bill started this thread in the hope that vacuum pyrolysis might be a simpler, cheaper, 1st generation means to obtain respectable amounts of Lunar propellant. The main problem as I see it (besides being uncool) is that the power requirements increase faster than any gains in efficiency by converting sunshine directly to heat energy rather than electrical energy.

You can't then turn around and say, well, we'll just make our own mirrors etc. out of regolith. Because that's a whole nuther layer of complexity that will require more cargo shipments from Earth to implement. The goal is to produce propellant for Mars missions. If you've got have metal manufacturing capability before you can produce much propellant, that's going to push the schedule to the right and hugely increase initial costs.

[Hop_David]

You can't then turn around and say, well, we'll just make our own mirrors etc. out of regolith.

This is a lot like saying we could make solar cell pavers from lunar materials.

But to mine and separate regolith into the various feedstocks the paver needs, you need a power source. The first power source must be brought in from earth.

Likewise with making mirrors from lunar materials. You need energy to sinter regolith into parabolic struts. You also need energy to extract the aluminum (or whatever you're using for reflective material)

I certainly hope we will reach the point where we can make power sources from ISRU materials. But at the outset we must use a power source imported from earth.

So the watts per kilogram is a very important metric.

Watts thermal is a different animal than watts electricity. However there are processes that use thermal energy. Perhaps several power sources, photovoltaic as well as mirrors will give us the most bang for our mass buck.

From eavesdropping various conversations, I believe 100 watts per kilogram solar arrays are doable and perhaps 150 watts per kilogram in the near future.

But I still have no idea how many thermal watts per kilogram the mirrors can provide.

[A_M_Swallow]

{snip}

From eavesdropping various conversations, I believe 100 watts per kilogram solar arrays are doable and perhaps 150 watts per kilogram in the near future.

But I still have no idea how many thermal watts per kilogram the mirrors can provide.

From the Wikipedia article on 'Mirror' when the reflective surface is on the front technical mirrors “achieve reflectivities of 90–95% when new”.
Using a solar constant of 1.366 kW/m˛ at the lunar equator.
Mylar is 7 gm/m2  (=0.007 kg/m²)
Tent poles 2.10 m tall 2 off mass is 2 kg
Ref: http://www.amazon.co.uk/Vango-King-Pole-Set-210cm/dp/B001T2XUN2/ref=pd_sim_sbs_lp_4

So a 2 square metre mirror with supports will mass (0.007 * 2 * 2) + 2 = 2.028 kg

Max energy produced is 1.366 * 2 * 2 * 0.9 = 4.9176 kW (or 4917 W)

Giving maximum thermal watts per kilogram 4917/2.028 = 2424 W/kg

I suspect that lighter poles can be used on the Moon.

[Warren Platts]

{snip}

From eavesdropping various conversations, I believe 100 watts per kilogram solar arrays are doable and perhaps 150 watts per kilogram in the near future.

But I still have no idea how many thermal watts per kilogram the mirrors can provide.

From the Wikipedia article on 'Mirror' when the reflective surface is on the front technical mirrors “achieve reflectivities of 90–95% when new”.
Using a solar constant of 1.366 kW/m˛ at the lunar equator.
Mylar is 7 gm/m2  (=0.007 kg/m²)
Tent poles 2.10 m tall 2 off mass is 2 kg
Ref: http://www.amazon.co.uk/Vango-King-Pole-Set-210cm/dp/B001T2XUN2/ref=pd_sim_sbs_lp_4

So a 2 square metre mirror with supports will mass (0.007 * 2 * 2) + 2 = 2.028 kg

Max energy produced is 1.366 * 2 * 2 * 0.9 = 4.9176 kW (or 4917 W)

Giving maximum thermal watts per kilogram 4917/2.028 = 2424 W/kg

I suspect that lighter poles can be used on the Moon.

You ever fooled around with mylar? I got news for ya: you can see through it. So you're not going to get the reflectivity of a good glass mirror. Moreover, the stuff is crinkly as hell. It will not focus anywhere near as well as shaped glass mirrors. Just think of the mass they could have saved on the Hubble Space Telescope if they had only used mylar instead of glass! But there's a reason they didn't. Mylar's good for one thing in space: providing shade. That's about it.

From your own reference, they were getting a specific power of 5.6 watts  per kilogram with the Stirling engine. Remove that and assume 90% of the light is converted to heat energy (probably overoptimistic), then you're generously looking at 20 W/kg.

[A_M_Swallow]

You ever fooled around with mylar? I got news for ya: you can see through it. So you're not going to get the reflectivity of a good glass mirror. Moreover, the stuff is crinkly as hell. It will not focus anywhere near as well as shaped glass mirrors. Just think of the mass they could have saved on the Hubble Space Telescope if they had only used mylar instead of glass! But there's a reason they didn't. Mylar's good for one thing in space: providing shade. That's about it.

Thermal energy systems are not telescopes, a bit of blurring does not matter.  Providing the photons hit somewhere on the target they will heat it up.

[A_M_Swallow]

OK, well if magic manufacturing is allowed, let's make a gigantic SBSP array for Earth from Lunar materials. All our energy problems will be solved!

It is called a self-replicating machine.  Bringing everything from Earth will make Moon and Mars bases too expensive.
http://en.wikipedia.org/wiki/Self-replicating_machine

Even 80% self-replication with ISRU materials will give major benefits.

[Warren Platts]

OK, well if magic manufacturing is allowed, let's make a gigantic SBSP array for Earth from Lunar materials. All our energy problems will be solved!

It is called a self-replicating machine.  Bringing everything from Earth will make Moon and Mars bases too expensive.
http://en.wikipedia.org/wiki/Self-replicating_machine

Even 80% self-replication with ISRU materials will give major benefits.

OK fine: for the sake of the argument, let's put everything on hold until we spend enough billions to create magic Von Neuman machines. That still begs the question of whether solar thermal vacuum pyrolysis of regolith is a more advisable means of obtaining propellant than say, hydrolysis of Lunar water using PV arrays.

[A_M_Swallow]

OK fine: for the sake of the argument, let's put everything on hold until we spend enough billions to create magic Von Neuman machines. That still begs the question of whether solar thermal vacuum pyrolysis of regolith is a more advisable means of obtaining propellant than say, hydrolysis of Lunar water using PV arrays.

Do it a cheaper way build a self reproducing system consisting of smaller machines.
Regolith gatherers.
http://www.nasa.gov/offices/oct/early_stage_innovation/centennial_challenges/history/index.html
3D printers
http://en.wikipedia.org/wiki/3D_printing
Some sort of furnace.
Robotic arms to assemble the components.

If the self-replication workshop works on Earth within 4 to 5 years a space rated version can be sent to the Moon permitting production of lunar propellant in time for the Mars trips in 20 to 30 years time.

[JohnFornaro]

Max energy produced received is 1.366 * 2 * 2 * 0.9 = 4.9176 kW (or 4917 W)

Unless I misread your comment, you haven't yet produced electricity; you've received the Sun's rays.  Just sayin'.

[Hop_David]

From the Wikipedia article on 'Mirror' when the reflective surface is on the front technical mirrors “achieve reflectivities of 90–95% when new”.
Using a solar constant of 1.366 kW/m˛ at the lunar equator.
Mylar is 7 gm/m2  (=0.007 kg/m²)
Tent poles 2.10 m tall 2 off mass is 2 kg
Ref: http://www.amazon.co.uk/Vango-King-Pole-Set-210cm/dp/B001T2XUN2/ref=pd_sim_sbs_lp_4

So a 2 square metre mirror with supports will mass (0.007 * 2 * 2) + 2 = 2.028 kg

Okay, the (.007 * 2 * 2) is 4 square meters of mylar (the aluminum coating doesn't add mass to the mylar?)

2 kilograms is one tent pole. Not sufficient.

A square panel would not concentrate light. To achieve high temperatures you would need supportive struts to give the mirror a parabolic shape.

The mirror and the kiln it's aimed at would need to rotate with the sun. The turn table would have power requirements and would also have mass.

edit: following the link I saw it's two poles. Still not sufficient.