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#76 2018-01-06 20:24:45

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,870

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

http://exrocketman.blogspot.com/2017/10 … ge-of.html

Unless this vehicle is refilled locally with the full 1100 metric ton propellant load,  it is stranded there!  Each launch from Mars requires 240 metric tons of locally-produced liquid methane,  and 860 metric tons of locally-produced liquid oxygen.  Launch opportunities are 26 months apart.  Required production rates are thus 9.23 tons/month methane,  and 33.08 tons/month oxygen,  at a bare minimum,  per launch.

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#77 2018-01-07 11:20:14

elderflower
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Registered: 2016-06-19
Posts: 1,261

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

Surely there is a need for a return vehicle ready and fuelled, or at least partly fuelled with the refuelling system working, before you actually send humans from LEO to land on Mars.
Maybe Musk has a Dragon style evacuation trick up his sleeve??? How much fuel would be needed to get a Dragon with stores and a crew of 5 off the Martian surface and back direct to Earth? Could be two stages or maybe three. Would such a thing fit in the load compartment of a cargo BFS?

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#78 2018-01-07 12:10:45

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 4,089
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Re: ISRU propellant production - energy requirement for the BFR?

Asking a crew to endure a 6-8 month voyage home inside a cramped capsule at zero-gee guarantees either death by insanity (a risk demonstrated as real on Gemini 7),  or death by heart failure during a 12-15 gee Earth entry with microgravity-weakened hearts.  (Plus,  there's no room for any life support supplies in any capsule plus service module plus ascent stage that might possibly fit inside a BFS.)  That is why I consider all such proposed capsule transits to or from Mars both technically infeasible and unethical in the extreme.

An alternative might be to land in one BFS with a capsule-plus-ascent stage inside,  to rendezvous quickly with a second BFS left in Mars orbit specifically for the voyage home.  That's two BFR/BFS launches to send one small crew (maybe 4-to-6 people) to Mars,  using something like a crewed Dragon (max seats 7,  but the larger the crew the bigger the ascent stage,  and very quickly it won't fit inside a BFS) plus an as-yet undesigned ascent stage as the crew ascent vehicle. 

The BFS that lands the crew plus ascent vehicle cannot be retrieved until its propellant can be manufactured on Mars.  A small crew is not going to be able to set up much of a base or manufacturing plant.  The capsule plus ascent stage eats up all the payload that could have been construction equipment.  Somehow,  I don't believe that Musk-and-company thinks like that. 

I think his real concept is both very bold and very risky:  cargo for base and propellant manufacturing gets sent ahead in a couple of unmanned BFS's that are permanently marooned there.  The big crew comes in another BFS to set up the base and start manufacturing.  They do not come home for however many years it takes to manufacture the propellant,  perhaps a decade with the solar panels on the 2 or 3 BFS's.  Crews arrive like that every 26 months,  but do not rotate home for some number of years,  not until the propellant plant can be greatly expanded in capacity.

The biggest risk I see is simple mechanical instability landing a tall ship (on narrow-span legs) on unprepared rough ground with obstacles at multiple scales,  including the size of the landing pads themselves.  Until a crew arrives with a bulldozer,  landing fields cannot be prepared. 

More than one of the early BFS's is going to tip over and explode.  That risk includes at least the very first manned one,  and any subsequent ones until they can bulldoze the landing fields very smooth and very flat,  as well as large enough.

The second biggest risk I see is the entirely-unknown effects of reduced gravity upon health,  when exposure times are on the order of a decade.  We never built the spinning space stations to explore the effects of reduced gravity.  We only have data at 1 or 0 gee,  and the 0-gee data do not look good for exposures exceeding a year.

GW

Last edited by GW Johnson (2018-01-07 12:14:46)


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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#79 2018-01-07 19:45:49

louis
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From: UK
Registered: 2008-03-24
Posts: 5,875

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

GW, I agree with you about it being madness to expect a crew to endure months in a capsule environment. I don't think in reality too many people are arguing for that now.

I do have more sympathy with the idea of landing an Apollo-style ascent vehicle with a BFR and then connecting with an LMO return  BFR.  Makes a lot of sense to me. But I don't feel I can really gainsay the Great Elon on this.  I can only assume he feels like this is going to be the architecture going forward (ie make your propellant on Mars), so let's get it right from Day One. It's bold but it is also quite simple and that has a lot of merit...not need to design and build an Apollo style ascent vehicle for one thing! smile

I think you are wrong on the propellant timeline. Previous discussion on this thread has shown that solar-powered propellant manufacture is very much doable with a total cargo landing of 450 tonnes to the Mars surface as Space X's Mission One. In fact I would say the more I have learnt from our discussion it is very comfortably within the cargo landings.  We are probably talking about around 100 tonnes of equipment being landed.



GW Johnson wrote:

Asking a crew to endure a 6-8 month voyage home inside a cramped capsule at zero-gee guarantees either death by insanity (a risk demonstrated as real on Gemini 7),  or death by heart failure during a 12-15 gee Earth entry with microgravity-weakened hearts.  (Plus,  there's no room for any life support supplies in any capsule plus service module plus ascent stage that might possibly fit inside a BFS.)  That is why I consider all such proposed capsule transits to or from Mars both technically infeasible and unethical in the extreme.

An alternative might be to land in one BFS with a capsule-plus-ascent stage inside,  to rendezvous quickly with a second BFS left in Mars orbit specifically for the voyage home.  That's two BFR/BFS launches to send one small crew (maybe 4-to-6 people) to Mars,  using something like a crewed Dragon (max seats 7,  but the larger the crew the bigger the ascent stage,  and very quickly it won't fit inside a BFS) plus an as-yet undesigned ascent stage as the crew ascent vehicle. 

The BFS that lands the crew plus ascent vehicle cannot be retrieved until its propellant can be manufactured on Mars.  A small crew is not going to be able to set up much of a base or manufacturing plant.  The capsule plus ascent stage eats up all the payload that could have been construction equipment.  Somehow,  I don't believe that Musk-and-company thinks like that. 

I think his real concept is both very bold and very risky:  cargo for base and propellant manufacturing gets sent ahead in a couple of unmanned BFS's that are permanently marooned there.  The big crew comes in another BFS to set up the base and start manufacturing.  They do not come home for however many years it takes to manufacture the propellant,  perhaps a decade with the solar panels on the 2 or 3 BFS's.  Crews arrive like that every 26 months,  but do not rotate home for some number of years,  not until the propellant plant can be greatly expanded in capacity.

The biggest risk I see is simple mechanical instability landing a tall ship (on narrow-span legs) on unprepared rough ground with obstacles at multiple scales,  including the size of the landing pads themselves.  Until a crew arrives with a bulldozer,  landing fields cannot be prepared. 

More than one of the early BFS's is going to tip over and explode.  That risk includes at least the very first manned one,  and any subsequent ones until they can bulldoze the landing fields very smooth and very flat,  as well as large enough.

The second biggest risk I see is the entirely-unknown effects of reduced gravity upon health,  when exposure times are on the order of a decade.  We never built the spinning space stations to explore the effects of reduced gravity.  We only have data at 1 or 0 gee,  and the 0-gee data do not look good for exposures exceeding a year.

GW


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

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#80 2018-01-07 22:29:46

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,870

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

Nasa Methane versus Hydrogen question:
•LOX-Methane propellants, with their lower Specific Impulse, can only carry about 7 tons of cargo (as propellant) UP to orbit in a Ferry vs. about 20 tons for LOX-Hydrogen.
• Methane would also take more propellants to land on Mars with less payload. This means that most of the propellant mass would still have to be supplied from Earth.

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#81 2018-01-08 05:45:36

elderflower
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Registered: 2016-06-19
Posts: 1,261

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

The LOX , which is the greater part of the propellant is relatively simple on Mars so only the fuel fraction, the methane, needs to be imported for the earliest mission. Oxygen can be obtained by reducing CO2 to CO.
As I see it the availability of sufficiently pure water and power at the selected landing site are the limiting resources and these are needed in large quantities if you want to make methane. Landing sites for BFR have not been explored, unless sites already visited by rovers are used and we don't know much about water availability except at the poles, nor about the purity of that water.

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#82 2018-01-08 20:43:20

SpaceNut
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From: New Hampshire
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Posts: 19,870

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

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#83 2018-01-09 10:49:17

Oldfart1939
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Registered: 2016-11-26
Posts: 1,912

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

In the next NASA Mars lander/rover, the Moxie unit has been under consideration. It was in the early version, but seemingly has been "bumped" for some "more deserving" science experiment. We need to KNOW if the Moxie device actually works well there. It also needs to be tested on the ISS. What's the problem, NASA?

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#84 2018-01-09 12:09:12

RobertDyck
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From: Winnipeg, Canada
Registered: 2002-08-20
Posts: 6,213
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Re: ISRU propellant production - energy requirement for the BFR?

Oldfart1939 wrote:

In the next NASA Mars lander/rover, the Moxie unit has been under consideration. It was in the early version, but seemingly has been "bumped" for some "more deserving" science experiment. We need to KNOW if the Moxie device actually works well there. It also needs to be tested on the ISS. What's the problem, NASA?

Mars 2020 always was a very bad idea. The guys who built the Curiosity rover wanted to build a second one, and charge $2 billion for the mission. Literally, $2 billion. Mars Exploration Rovers A and B were finally named Spirit and Opportunity, there were two of them so the guys who built Curiosity thought they should be paid (PAID) for a second one. Mars 2020 was always about money, not science.

Mars 2001 Lander was cancelled after failure of Mars Polar Lander. It was the same model chassis. They found and solved the problem, but Mars 2001 Lander was never launched. Then someone discovered it sitting in storage in a clean room, removed all engineering experiments to add more science, and renamed it Phoenix. The first version of MOXIE (with a different name) was on it. That was removed. Now they want to remove MOXIE. If they do that, then cancel Mars 2020 entirely!

I spoke with Robert Zubrin at a Mars Society convention when Mars 2020 was first announced. I said we could send a mission the size of Phoenix with a rover the size of Sojourner. This much smaller mission could have a return rocket, fuelled with ISPP, and return a capsule to Earth the same as Stardust or Genesis. A single mission, entirely self contained. Since then Dr. Zubrin has said we could send a larger mission, as he put it a mission the same size as Curiosity with a rover the size of Spirit or Opportunity. It could still return a sample to Earth, using ISPP and a return capsule like Stardust or Genesis. Still self contained, but larger; as large as Curiosity.

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#85 2018-01-09 13:07:14

louis
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From: UK
Registered: 2008-03-24
Posts: 5,875

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

We all know that NASA could have done 100 interesting things pertaining to Mars exploration and preparing for a human mission with the available money. But at every turn they get seduced into what appears to them as science gains...but this is a very short termist view. The amount of Mars-related science we could do in 10 years' time if we had a human base would be exponentially greater than all we can do now, robotically and remotely.

RobertDyck wrote:
Oldfart1939 wrote:

In the next NASA Mars lander/rover, the Moxie unit has been under consideration. It was in the early version, but seemingly has been "bumped" for some "more deserving" science experiment. We need to KNOW if the Moxie device actually works well there. It also needs to be tested on the ISS. What's the problem, NASA?

Mars 2020 always was a very bad idea. The guys who built the Curiosity rover wanted to build a second one, and charge $2 billion for the mission. Literally, $2 billion. Mars Exploration Rovers A and B were finally named Spirit and Opportunity, there were two of them so the guys who built Curiosity thought they should be paid (PAID) for a second one. Mars 2020 was always about money, not science.

Mars 2001 Lander was cancelled after failure of Mars Polar Lander. It was the same model chassis. They found and solved the problem, but Mars 2001 Lander was never launched. Then someone discovered it sitting in storage in a clean room, removed all engineering experiments to add more science, and renamed it Phoenix. The first version of MOXIE (with a different name) was on it. That was removed. Now they want to remove MOXIE. If they do that, then cancel Mars 2020 entirely!

I spoke with Robert Zubrin at a Mars Society convention when Mars 2020 was first announced. I said we could send a mission the size of Phoenix with a rover the size of Sojourner. This much smaller mission could have a return rocket, fuelled with ISPP, and return a capsule to Earth the same as Stardust or Genesis. A single mission, entirely self contained. Since then Dr. Zubrin has said we could send a larger mission, as he put it a mission the same size as Curiosity with a rover the size of Spirit or Opportunity. It could still return a sample to Earth, using ISPP and a return capsule like Stardust or Genesis. Still self contained, but larger; as large as Curiosity.


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

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#86 2018-01-09 13:32:22

Oldfart1939
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Registered: 2016-11-26
Posts: 1,912

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

I suspect the only way we'll find out about performance of the Moxie system is if (when) SpaceX resurrects the Red Dragon missions. They are absolutely necessary for what they (SpaceX) hopes to accomplish. I think a 2020 Red Dragon is well within the realm of possibility at this juncture. A lot more has to happen before BFR.

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#87 2018-01-09 14:22:47

RobertDyck
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From: Winnipeg, Canada
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Re: ISRU propellant production - energy requirement for the BFR?

Where did you hear about cancelling MOXIE? I still see MOXIE included on several NASA web pages.

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#88 2018-01-09 17:43:58

Oldfart1939
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Registered: 2016-11-26
Posts: 1,912

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

There were some representations made earlier on spaceflightinsider.com; I'll try to find the reference and post the link (presuming I find it before I forget about it).

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#89 2018-01-09 20:29:07

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,870

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

http://spacecraft.ssl.umd.edu/design_li … DRM_v3.pdf

pg 23 Table A3-2  ISRU System Breakdown for Version 3.0 labeled 13 on the bottom of the page

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#90 2018-01-10 03:52:18

elderflower
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Registered: 2016-06-19
Posts: 1,261

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

If we want to do Mars science, we need scientists and the most effective way to do it is to ship them to Mars. In much the same way that Cook took Banks along on his voyage to Australia.

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#91 2018-01-10 04:44:06

louis
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From: UK
Registered: 2008-03-24
Posts: 5,875

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

Absolutely - this is what I can't understand about NASA's attitude. It's very short termist...it says effectively lets spend $20 billion over 40 years accumulating a very small pile of science facts about Mars rather than spending $20billion over 10 years to establish a base on Mars and then accumulate an absolute mountain of scientific knowledge about the planet and that neck of the solar system. Well, I can understand how it has come about but it still doesn't make sense.

elderflower wrote:

If we want to do Mars science, we need scientists and the most effective way to do it is to ship them to Mars. In much the same way that Cook took Banks along on his voyage to Australia.


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

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#92 2018-01-10 09:47:20

Oldfart1939
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Registered: 2016-11-26
Posts: 1,912

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

Louis-

I can't understand the NASA attitude either. We're reaching the end of what additional robotic missions can hope to accomplish. On top of it all, they continue ignoring the microgravity issues which have PROFOUND effects on human physiology. Major problem is risk aversion after killing 3 different batches of astronauts--first in Apollo, and then 2 different shuttle disasters.

Having human boots on Mars will in a single mission of 500 days, answer nearly ALL  the remaining basic questions about water and the potential for life past and present.

I'm VERY negative about this Deep Space Gateway using the Rocket to Nowhere to get there.

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#93 2018-01-11 14:29:37

EldenC
Member
From: Tucson, Arizona
Registered: 2018-01-09
Posts: 7

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

(Newbie alert!)

Thermal Isolation:  When the BFS (the top part of BFR) lands on Mars,  slide a concentric ring (lightGreen) out of the door such that it is like the ring on a finger at the door level.  Then inflate each layer to 110Pa, 120Pa, 130Pa.... 
FluxBB bbcode test

Question:
BFS Mars Grasshopper (M2M?):  I would like to know, how far could BFS (85 Tonne, dry) jump from location to location on Mars if it is fueled to perhaps 5% capacity (55 Tonne) while carrying 50 Tonne Payload; probably leaving 0.5% fuel in the fuel system as reserve.

Any good pointers as to where to look to get the reasonable equations and 'rules-of-thumb' for calculating this?

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#94 2018-01-11 21:07:02

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,870

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

Welcome to NewMars EldenC,

The near vaccum of mars atmosphere is better than pressurized zones that would slowly pass the energy to and from the tanks for boiloff a sun shade would need to be used.

I would think that the equation would be simular to the one used for the falcon 9 first stage as that is about the same.

Flight Mechanics of Manned Sub-Orbital Reusable Launch Vehicles with Recommendations for Launch and Recovery

https://en.wikipedia.org/wiki/Sub-orbital_spaceflight

US08678321-20140325-D00000.png

http://orbitalaspirations.blogspot.com/ … ckets.html

https://www.reddit.com/r/KerbalSpacePro … el_thrust/

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#95 2018-01-11 23:19:12

EldenC
Member
From: Tucson, Arizona
Registered: 2018-01-09
Posts: 7

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

Thanks!

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#96 2018-01-20 23:50:23

EldenC
Member
From: Tucson, Arizona
Registered: 2018-01-09
Posts: 7

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

The sun shade would be provided by the Mylar balloons since Mylar is highly reflective.  Not too sure how well fit the balloon would be around the [not :-) ] delta wings.  Mr. Musk insisted that those are not delta wings....but man they look like delta wings......

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#97 2018-01-21 10:25:49

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,912

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

Robert-Just following up on the Moxie unit; apparently it's still a "go" for the 2020 mission. We discussed this at the last RMMS (Rocky Mountain Mars Society) meeting in Boulder, and one of the engineers present said it was still planned.

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#98 2018-01-21 13:22:49

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,870

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

Ah EldenC what you are talking about is a thermal blanket made from the Balloons, which have a metalized reflective sprayed coating onto the mylar material.  https://en.wikipedia.org/wiki/Space_blanket 

coated with a metallic reflecting agent, making it metallized polyethylene terephthalate (MPET), usually gold or silver in colour, which reflects up to 97% of radiated heat. Space blankets are made by vacuum depositing a very precise amount of pure aluminum vapor onto a very thin, durable film substrate.

http://usa.dupontteijinfilms.com/wp-con … erties.pdf

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#99 2018-01-22 05:38:20

elderflower
Member
Registered: 2016-06-19
Posts: 1,261

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

It cant be too thin/light as this film has to withstand Mars winds and dust storms. This makes the gas pressure supported film attractive provided one hole only deflates a little bit of it. You might have to consider the effect on permafrost beneath it, though.

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#100 2018-01-22 17:17:22

EldenC
Member
From: Tucson, Arizona
Registered: 2018-01-09
Posts: 7

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

Yes Spacenut exactly.
elderflower the pin whole problem should probably be solved the way that bouncing castles solve it.... expect small wholes in it and just keep blowing in air...if its not too hot use the exhaust from the Sabatier processing plant. 

Does a rip stop version of Mylar exist?  Rip stop is the plastic/cloth stuff used for hanggliders and I think most parashoots.

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