Portland cement is made from limestone (primarily calcium carbonate) in a process that emits CO2, and slowly converts back over time by absorbing atmospheric CO2. If you can make cement production near-CO2-neutral with carbon capture and storage, everything built out of concrete will turn into net absorbers that suck CO2 out of the atmosphere.
Only a loaded Model 3 Performance can get that high. ASP = Average Sale Price. Model 3 RWD PUP (the only variant they were selling in Q2) starts at $49k. Q3 introduced AWD and P as options. The other numbers come from the quarterly reports. 60k is rounding.
Telsa have $1.15B due by the end of the next quarter,
False. Tesla has $157M due in December, and another $920M due in March.
which includes the Christmas slowdown
Meanwhile, production keeps rising. If you're betting on a "Christmas slowdown" to save you, keep dreaming.
This is only just starting. Fremont scales to at least 7k without new lines (confirmed not just by Tesla, but also analysts who've toured Fremont). Model 3 is designed for 25% margin at its full range of variants. I mean, what exactly did you all think would happen to margin over time? Shorts kept complaining about high scrap rates and excess labour requirements - did you think it would remain that way forever? It takes a long time to get those things down (Tesla is still slowly reducing production costs on the Model S), and reducing them equals margin. With the introduction of the MR, margin improvements will get eaten up by a lower ASP in Q4, but in Q1 you not only get further margin improvements, but also a higher ASP due to the start of high-end sales in Europe.
Seriously, what exactly did you all expect was going to happen?
1) Tesla only delivered about 2 1/2 thousand more vehicles than they produced this quarter (due to issues related to timing the tax credit expiry). Doesn't even remotely come close to the profit this quarter. Furthermore, they were lower ASP vehicles than the ones held up in delivery delays this quarter. 2) Tesla, like all companies, has had varying disputes with suppliers. The grand total in Q3 was, if I recall correctly, around $8m. I mean, stop the presses. 3) Tesla's loaner fleet is still very much intact. It periodically sells off older vehicles and replaces them with newer ones. 4) "They haven't made a profit" - Hmm, what's that river in Egypt.... 5) "They will lose money when their debt payments come due" - Yeah, they made that much free cash this quarter alone.
Tesla aftermarket is currently $316,80. 1 year ago Tesla was $320,87. You're comparing market close (aka, from before the Q3 report).
Tesla is one of the few major stocks that's doing well while the markets are getting hammered. As it should. In a recession, demand-limited companies (aka, most companies) suffer, but supply-limited companies (like Tesla) thrive. Life actually gets easier for them, as their feedstocks, parts, shipping, contractors, etc all get cheaper.
Model 3 was ranked "Average" in reliability by Consumer Reports. For a first model year vehicle, that's not bad at all. It retains a "recommended" rating from CR. S was downgraded because they switched to making air suspension standard, and there were some air suspension reliability issues (which Tesla states their supplier has fixed).
Or, ignore inventory changes and do the math. Multiply 2 1/2 thousand vehicles times a reasonable Q2 ASP - say, $55k. That's $137,5M. Compare that to the free cash flow ($881M) and profit (GAAP: $312M; non-GAAP: $516M). Notice anything?
deliberately held off shipping (and, by GAAP rules, recognizing revenue) in Q2
M3 deliveries were about 2,5k higher than production this quarter, vs. 56k deliveries. S+X was almost identical to production. Given that the automotive margin is over 25%.... no, that was not a material factor. Furthermore: Inventory in Q3: $3,31B. Inventory in Q2: $3,32B. The given the higher ASP in Q3, undelivered inventory is more valuable than undelivered inventory in Q2.
Driver assist systems (which almost everybody offers in some form or another now - AutoPilot, ProPilot, SuperCruise, etc etc) are quite different from "self driving" systems like Uber and Waymo (and this company) are working towards. The difference being that the former pester you to make sure you're paying attention, while the latter try to never need to pester the "safety driver", and seek to remove them from the equation as quickly as possible.
The bulk mass certainly needs to be at the bottom, for stability reasons. But the mass isn't humans, or even agriculture; it's the ascent vehicle. More specifically, the propellant in the ascent vehicle. Particularly if you're using chemical rockets (as opposed to nuclear thermal), you're looking at something like 90% of your mass in the ascent stage on the underside. Where you put everything else is pretty much irrelevant in comparison.
Gravity is simultaneously one of Venus's big advantages and curses. Advantages because it makes Venus so similar to Earth, and pretty much guarantees that people won't experience muscle and bone atrophy. But curse because, like Earth, it's hard to get off.
You can escape with chemical rockets, although they have to be recovered with balloons (there was one rocket design in the 1960s on Earth being considered for doing the exact same thing), you have to re-mate the stages while they're hanging from the underside of the habitat, and the propellant mass takes up the vast majority of your habitat's lift capacity. Far more appealing are nuclear thermal rockets, which you can launch with a single stage and a significantly lower wet mass. Some designs which incorporate compressors for air augmentation can even hover.
How do you get the raw materials to maintain the balloons?
Chapter 8.
What's the economy there? What's the draw?
Chapter 8.
How come we're not living in blimps floating above Earth?
People live in the easiest location where it is to live, near where there's economic activity to sustain their presence. See Chapter 8 re: economic activity, and if you think you have an easier location to base operations for accessing Venus's resources than an aerostat habitat, then by all means, elaborate.:)
The one thing I see is more solar gain for energy, but that's better gotten in space.
If you're skeptical about how hard it is to get physical resources at an aerostat habitat, you should be all the more skeptical about how hard it is to get physical resources at a habitat drifting in a vacuum.
Terraforming?
An unrelated topic to aerostat habitats, but... Chapter 10.
places where we can dig in for protection from radiation
In a Venus habitat, you have the equivalent mass of five meters of water over your head as shielding. No digging required.
seal up a breathable atmosphere
The very air that lofts you on Venus is breathable. And is not difficult to acquire.
and try to sustain an ecosystem.
Abundant light and space (rather than living in a cramped pressure vessel) = much easier for agriculture.
What do you mean you can't move anywhere you want on Earth? Of course you can. I could move half a kilometer away from where I'm at tomorrow if I wanted to.
On any off-world colony, where all available space is part of a man-made structure (and in this case all space not just habitable living space) it will be at a premium
It doesn't work that way, at least until you get to extremely large habitats. The amount of volume you need for lift means that the overwhelming amount of your habitat is empty space. If you tried to "fill it all up", you'd sink. The only reason that this doesn't apply to extremely large habitats is that if you confine everyone to living in a 2d plane, then the volume of the habitat (and thus lift) grows with proportion to the radius cubed but the living area only in proportion to the radius squared.
Not that you have to confine yourself to living in a 2d plane, of course.
There's much more detail about surface access and resources in much more detail in Chapter 8 here. Contrary to your assertion, Venus has all of the signs for heavy differentiation, both theoretical and observed: abnormally large melts, abnormally low viscosities, abnormally long cooling times, repeated remelting, structures associated with secondary differentiation on Earth (such as rhyolite domes, which are the most likely explanation for Venus's pancake domes), etc. Venera 8 and 13 measured U, Th and K levels that were so enriched over what's normally found in basalt that Venera 8 was initially thought to have sampled granite instead. Venus also shows signs of potential widespread carbonatite volcanism, which on Earth form some of the most valuable ores for a number of elements. Venus also has its own unique ore-forming processes, to the point that the planet literally vaporizes and plates out metals and/or semiconductors in the form of high-altitude frosts. Venus has no liquid water to assist in forming ores, but its dense, acidic atmosphere provides it with unique ore-forming properties not found anywhere else in the solar system.
In some ways, Venus is a natural refinery, separating out different compounds into layers - there are three separate cloud decks (with a virga underlying the lowest). For example the dominant species in the upper two cloud layers is sulfuric acid, the most likely dominant species in the lower cloud layer (or at least a major species) is phosphoric. Even metals appear to be found in Venus's upper atmosphere - for example, iron has been detected, most likely in the form of iron chloride. There are some metals that we don't even know what's happened to them - for example, our models show that mercury should be common in Venus's atmosphere, yet it hasn't been detected at all; we have no clue what's happened to it.
And as for "how to harvest" materials from the surface, the simplest method is one that we can't do effectively on Earth or Mars: dredging. Venus's atmosphere is dense enough that one could dredge fines using the same fan that the lander uses for propulsion. And as for the ability to land on Venus's surface, come on - that was achieved with 1960s/1970s Soviet technology. Yes, we're talking more complex systems, but nothing remotely beyond our reach.
Oh yeah, I'm curious as to what your thoughts on sustainable ascent stages are. The early stages of HAVOC call for what's basically a gigantic Pegasus rocket... anything but sustainable, of course.
Sustainable chemical ascent vehicles look possible, but are... annoying. It basically requires two stages, which you have to recover with balloons, and re-mate while they're hanging under your habitat, and the propellant to re-fill them requires the vast majority of your habitat's lift capacity. You're also limited to low-hydrogen fuels like carbon monoxide, acetylene or cyanogen, generally meaning some combination of poor performing or hot burning (cyanogen with a small fraction of methane or hydrogen mixed in looked best in terms of balancing performance, temperature, and hydrogen content). It's... workable, but not pretty.
Nuclear thermal looked way better. You're stuck burning pure hydrogen, but don't actually need that much of it. And some nuclear thermal designs that incorporate compressors offer the potential to hover, allowing one to ditch balloon recovery. It's single stage, and allows for a significantly lower wet mass than a chemical ascent vehicle.
Have you investigated sustainable ascent stages much? What were your thoughts?
Nice to see you back, Geoffrey:) Keep up the great work!
I am curious what you think of the early-phase HAVOC approach, of having the crew slung underneath a lift envelope rather than living inside it. I have to admit, I'm not a fan (I also found some of their mass budget numbers in the initial proposal rather questionable). But it's still nice to see some work being done towards any Venus habitation concepts.:)
I guess on the upside they can be freed from the need for a transparent envelope, and thus use, say vectran or similar. Liquid crystal polymers have such nice properties for an environment like Venus. But there's still great options for (layered) transparent envelopes. When analyzing possibilities it looked like optimal layers would be along the lines of a PCTFE outer layer, an EVOH or PVDC gas barrier layer, a potential fluoropolymer coating for antifouling / anticondensation properties, and CF reinforcement, if sustainability is taken into account (PCTFE minimizes the amount of F required, since it's only found in lower ppb quantities and can be melt-bonded with other layers; it's also extremely resistant to water permeation); EVOH is simpler to produce than the more commonly considered PET and also opens up a production path for adhesives. PVDC also looks attractive, at the cost of requiring more chlorine, which isn't in huge abundance (although certainly more abundant than fluorine). As for reinforcing fibres, CF is harder to produce than UHMWPE, but its low creep, UV resistance, and wettability probably makes this worth it.
For our sample habitat, with an envelope fabric comprised of 20um PCTFE, 70um PVDC, and another 10um PCTFE, that worked out to 183g/m (not counting reinforcement) and had the following daily permeation rates w/continuous atmospheric scrubbing:
H2O: -1.44 kg O2: -0.29 kg N2: -0.22 kg HF: 2.91 ppb H2S: 19.1 ppb HCl: 23.3 ppb H2SO4: 294 ppb SO2: 92.7 ppm CO: 98.8 ppm CO2: 11.9 kg
Looks like that would (naively) require interior air scrubbing around 15 times per day to avoid reaching gas levels which would be harmful to agriculture. But probably not that bad in practice, as problematic gases like HF are hygroscopic and would be prone to being absorbed into condensation films and hydroponics channels, and with such tiny permeation rates, it might be worth considering just neutralizing them in the envelope itself. If the minor species can be dealt with, the bulk CO2 only requires about 1% of the envelope be scrubbed daily to maintain comfortable levels (and that's assuming no plant uptake). Oxygen and nitrogen losses are trivial, although the water losses are annoyingly high, even with the use of PCTFE; still, the losses are only about 5% of the water recovery rates we calculated for our scrubber.
This is sort of a long-winded way of saying... a transparent envelope like your '93 paper called for looks perfectly workable, and sustainable.:)
Yes, please may Earth leave that system behind...;)
Note that comfortable temperatures require either lower atmospheric pressures or high latitudes, ideally a combination of both. This is amplified by the fact that, at least in a Landis habitat, you're living inside a greenhouse, with its own greenhouse effect. Higher latitudes also equate to shorter day lengths. The main limitation on high latitudes appears to be the polar vortices (although we don't yet know just how turbulent they are). High latitudes also experience less light. A reasonable balance appears to be about 70 degrees north or south at about 0,5 ATM, where there's about a 48-hour day. 70N is IMHO more interesting than 70S geologically due to passing over Ishtar Terra.
Note that when one says "0,5 ATM", that doesn't mean cutting the partial pressures of all gases in half equally. Instead you only cut the nitrogen partial pressure, leaving the oxygen partial pressure the same as on Earth. The medical studies on long-term survival in such atmospheres are limited, but appear to be very favourable in many regards (gas diffusion in the lungs is enhanced and it takes less effort to breathe), with the only apparent downside being that coughing becomes less effective at removing obstructions. Plants generally seem to love it, too (due to the enhanced gas diffusion), only suffering from falsely reacting as though experiencing drought. There are efforts underway to breed plants to not react as if experiencing drought, so that they only gain the positives of the reduced pressure environment.
Slashdot Mirror
Portland cement is made from limestone (primarily calcium carbonate) in a process that emits CO2, and slowly converts back over time by absorbing atmospheric CO2. If you can make cement production near-CO2-neutral with carbon capture and storage, everything built out of concrete will turn into net absorbers that suck CO2 out of the atmosphere.
ED: Correction, that should be $230M this quarter, not $157M.
By the way, did you ever save those children from the basement of that DC pizza restaurant?
Only a loaded Model 3 Performance can get that high. ASP = Average Sale Price. Model 3 RWD PUP (the only variant they were selling in Q2) starts at $49k. Q3 introduced AWD and P as options. The other numbers come from the quarterly reports. 60k is rounding.
False. Tesla has $157M due in December, and another $920M due in March.
Meanwhile, production keeps rising. If you're betting on a "Christmas slowdown" to save you, keep dreaming.
This is only just starting. Fremont scales to at least 7k without new lines (confirmed not just by Tesla, but also analysts who've toured Fremont). Model 3 is designed for 25% margin at its full range of variants. I mean, what exactly did you all think would happen to margin over time? Shorts kept complaining about high scrap rates and excess labour requirements - did you think it would remain that way forever? It takes a long time to get those things down (Tesla is still slowly reducing production costs on the Model S), and reducing them equals margin. With the introduction of the MR, margin improvements will get eaten up by a lower ASP in Q4, but in Q1 you not only get further margin improvements, but also a higher ASP due to the start of high-end sales in Europe.
Seriously, what exactly did you all expect was going to happen?
Standard short conspiracy theories.
1) Tesla only delivered about 2 1/2 thousand more vehicles than they produced this quarter (due to issues related to timing the tax credit expiry). Doesn't even remotely come close to the profit this quarter. Furthermore, they were lower ASP vehicles than the ones held up in delivery delays this quarter.
2) Tesla, like all companies, has had varying disputes with suppliers. The grand total in Q3 was, if I recall correctly, around $8m. I mean, stop the presses.
3) Tesla's loaner fleet is still very much intact. It periodically sells off older vehicles and replaces them with newer ones.
4) "They haven't made a profit" - Hmm, what's that river in Egypt....
5) "They will lose money when their debt payments come due" - Yeah, they made that much free cash this quarter alone.
Tesla aftermarket is currently $316,80. 1 year ago Tesla was $320,87. You're comparing market close (aka, from before the Q3 report).
Tesla is one of the few major stocks that's doing well while the markets are getting hammered. As it should. In a recession, demand-limited companies (aka, most companies) suffer, but supply-limited companies (like Tesla) thrive. Life actually gets easier for them, as their feedstocks, parts, shipping, contractors, etc all get cheaper.
Lol, only on Slashdot can linking the official Q3 report be called "pump and dump".
Sorry you feel bad about losing money. Here, maybe this will cheer you up.
THE BELLS! THE BELLS!!!
Model 3 was ranked "Average" in reliability by Consumer Reports. For a first model year vehicle, that's not bad at all. It retains a "recommended" rating from CR. S was downgraded because they switched to making air suspension standard, and there were some air suspension reliability issues (which Tesla states their supplier has fixed).
Completely contradicted by the report (whether you want to talk gross profits or net profits), but hey, thanks for playing.
Or, ignore inventory changes and do the math. Multiply 2 1/2 thousand vehicles times a reasonable Q2 ASP - say, $55k. That's $137,5M. Compare that to the free cash flow ($881M) and profit (GAAP: $312M; non-GAAP: $516M). Notice anything?
M3 deliveries were about 2,5k higher than production this quarter, vs. 56k deliveries. S+X was almost identical to production. Given that the automotive margin is over 25%.... no, that was not a material factor. Furthermore: Inventory in Q3: $3,31B. Inventory in Q2: $3,32B. The given the higher ASP in Q3, undelivered inventory is more valuable than undelivered inventory in Q2.
No matter how kind you think you are, German children are kinder.
Driver assist systems (which almost everybody offers in some form or another now - AutoPilot, ProPilot, SuperCruise, etc etc) are quite different from "self driving" systems like Uber and Waymo (and this company) are working towards. The difference being that the former pester you to make sure you're paying attention, while the latter try to never need to pester the "safety driver", and seek to remove them from the equation as quickly as possible.
Yes. Yes it is.
The bulk mass certainly needs to be at the bottom, for stability reasons. But the mass isn't humans, or even agriculture; it's the ascent vehicle. More specifically, the propellant in the ascent vehicle. Particularly if you're using chemical rockets (as opposed to nuclear thermal), you're looking at something like 90% of your mass in the ascent stage on the underside. Where you put everything else is pretty much irrelevant in comparison.
Gravity is simultaneously one of Venus's big advantages and curses. Advantages because it makes Venus so similar to Earth, and pretty much guarantees that people won't experience muscle and bone atrophy. But curse because, like Earth, it's hard to get off.
You can escape with chemical rockets, although they have to be recovered with balloons (there was one rocket design in the 1960s on Earth being considered for doing the exact same thing), you have to re-mate the stages while they're hanging from the underside of the habitat, and the propellant mass takes up the vast majority of your habitat's lift capacity. Far more appealing are nuclear thermal rockets, which you can launch with a single stage and a significantly lower wet mass. Some designs which incorporate compressors for air augmentation can even hover.
Chapter 5
Chapter 8.
Chapter 8.
People live in the easiest location where it is to live, near where there's economic activity to sustain their presence. See Chapter 8 re: economic activity, and if you think you have an easier location to base operations for accessing Venus's resources than an aerostat habitat, then by all means, elaborate. :)
If you're skeptical about how hard it is to get physical resources at an aerostat habitat, you should be all the more skeptical about how hard it is to get physical resources at a habitat drifting in a vacuum.
An unrelated topic to aerostat habitats, but... Chapter 10.
In a Venus habitat, you have the equivalent mass of five meters of water over your head as shielding. No digging required.
The very air that lofts you on Venus is breathable. And is not difficult to acquire.
Abundant light and space (rather than living in a cramped pressure vessel) = much easier for agriculture.
I'm not much of an advocate for self-driving cars. If plan to stalk me, please do a better job at it in the future.
What do you mean you can't move anywhere you want on Earth? Of course you can. I could move half a kilometer away from where I'm at tomorrow if I wanted to.
It doesn't work that way, at least until you get to extremely large habitats. The amount of volume you need for lift means that the overwhelming amount of your habitat is empty space. If you tried to "fill it all up", you'd sink. The only reason that this doesn't apply to extremely large habitats is that if you confine everyone to living in a 2d plane, then the volume of the habitat (and thus lift) grows with proportion to the radius cubed but the living area only in proportion to the radius squared.
Not that you have to confine yourself to living in a 2d plane, of course.
There's much more detail about surface access and resources in much more detail in Chapter 8 here. Contrary to your assertion, Venus has all of the signs for heavy differentiation, both theoretical and observed: abnormally large melts, abnormally low viscosities, abnormally long cooling times, repeated remelting, structures associated with secondary differentiation on Earth (such as rhyolite domes, which are the most likely explanation for Venus's pancake domes), etc. Venera 8 and 13 measured U, Th and K levels that were so enriched over what's normally found in basalt that Venera 8 was initially thought to have sampled granite instead. Venus also shows signs of potential widespread carbonatite volcanism, which on Earth form some of the most valuable ores for a number of elements. Venus also has its own unique ore-forming processes, to the point that the planet literally vaporizes and plates out metals and/or semiconductors in the form of high-altitude frosts. Venus has no liquid water to assist in forming ores, but its dense, acidic atmosphere provides it with unique ore-forming properties not found anywhere else in the solar system.
In some ways, Venus is a natural refinery, separating out different compounds into layers - there are three separate cloud decks (with a virga underlying the lowest). For example the dominant species in the upper two cloud layers is sulfuric acid, the most likely dominant species in the lower cloud layer (or at least a major species) is phosphoric. Even metals appear to be found in Venus's upper atmosphere - for example, iron has been detected, most likely in the form of iron chloride. There are some metals that we don't even know what's happened to them - for example, our models show that mercury should be common in Venus's atmosphere, yet it hasn't been detected at all; we have no clue what's happened to it.
And as for "how to harvest" materials from the surface, the simplest method is one that we can't do effectively on Earth or Mars: dredging. Venus's atmosphere is dense enough that one could dredge fines using the same fan that the lander uses for propulsion. And as for the ability to land on Venus's surface, come on - that was achieved with 1960s/1970s Soviet technology. Yes, we're talking more complex systems, but nothing remotely beyond our reach.
Oh yeah, I'm curious as to what your thoughts on sustainable ascent stages are. The early stages of HAVOC call for what's basically a gigantic Pegasus rocket... anything but sustainable, of course.
Sustainable chemical ascent vehicles look possible, but are... annoying. It basically requires two stages, which you have to recover with balloons, and re-mate while they're hanging under your habitat, and the propellant to re-fill them requires the vast majority of your habitat's lift capacity. You're also limited to low-hydrogen fuels like carbon monoxide, acetylene or cyanogen, generally meaning some combination of poor performing or hot burning (cyanogen with a small fraction of methane or hydrogen mixed in looked best in terms of balancing performance, temperature, and hydrogen content). It's... workable, but not pretty.
Nuclear thermal looked way better. You're stuck burning pure hydrogen, but don't actually need that much of it. And some nuclear thermal designs that incorporate compressors offer the potential to hover, allowing one to ditch balloon recovery. It's single stage, and allows for a significantly lower wet mass than a chemical ascent vehicle.
Have you investigated sustainable ascent stages much? What were your thoughts?
Nice to see you back, Geoffrey :) Keep up the great work!
I am curious what you think of the early-phase HAVOC approach, of having the crew slung underneath a lift envelope rather than living inside it. I have to admit, I'm not a fan (I also found some of their mass budget numbers in the initial proposal rather questionable). But it's still nice to see some work being done towards any Venus habitation concepts. :)
I guess on the upside they can be freed from the need for a transparent envelope, and thus use, say vectran or similar. Liquid crystal polymers have such nice properties for an environment like Venus. But there's still great options for (layered) transparent envelopes. When analyzing possibilities it looked like optimal layers would be along the lines of a PCTFE outer layer, an EVOH or PVDC gas barrier layer, a potential fluoropolymer coating for antifouling / anticondensation properties, and CF reinforcement, if sustainability is taken into account (PCTFE minimizes the amount of F required, since it's only found in lower ppb quantities and can be melt-bonded with other layers; it's also extremely resistant to water permeation); EVOH is simpler to produce than the more commonly considered PET and also opens up a production path for adhesives. PVDC also looks attractive, at the cost of requiring more chlorine, which isn't in huge abundance (although certainly more abundant than fluorine). As for reinforcing fibres, CF is harder to produce than UHMWPE, but its low creep, UV resistance, and wettability probably makes this worth it.
For our sample habitat, with an envelope fabric comprised of 20um PCTFE, 70um PVDC, and another 10um PCTFE, that worked out to 183g/m (not counting reinforcement) and had the following daily permeation rates w/continuous atmospheric scrubbing:
H2O: -1.44 kg
O2: -0.29 kg
N2: -0.22 kg
HF: 2.91 ppb
H2S: 19.1 ppb
HCl: 23.3 ppb
H2SO4: 294 ppb
SO2: 92.7 ppm
CO: 98.8 ppm
CO2: 11.9 kg
Looks like that would (naively) require interior air scrubbing around 15 times per day to avoid reaching gas levels which would be harmful to agriculture. But probably not that bad in practice, as problematic gases like HF are hygroscopic and would be prone to being absorbed into condensation films and hydroponics channels, and with such tiny permeation rates, it might be worth considering just neutralizing them in the envelope itself. If the minor species can be dealt with, the bulk CO2 only requires about 1% of the envelope be scrubbed daily to maintain comfortable levels (and that's assuming no plant uptake). Oxygen and nitrogen losses are trivial, although the water losses are annoyingly high, even with the use of PCTFE; still, the losses are only about 5% of the water recovery rates we calculated for our scrubber.
This is sort of a long-winded way of saying... a transparent envelope like your '93 paper called for looks perfectly workable, and sustainable. :)
Yes, please may Earth leave that system behind... ;)
Note that comfortable temperatures require either lower atmospheric pressures or high latitudes, ideally a combination of both. This is amplified by the fact that, at least in a Landis habitat, you're living inside a greenhouse, with its own greenhouse effect. Higher latitudes also equate to shorter day lengths. The main limitation on high latitudes appears to be the polar vortices (although we don't yet know just how turbulent they are). High latitudes also experience less light. A reasonable balance appears to be about 70 degrees north or south at about 0,5 ATM, where there's about a 48-hour day. 70N is IMHO more interesting than 70S geologically due to passing over Ishtar Terra.
Note that when one says "0,5 ATM", that doesn't mean cutting the partial pressures of all gases in half equally. Instead you only cut the nitrogen partial pressure, leaving the oxygen partial pressure the same as on Earth. The medical studies on long-term survival in such atmospheres are limited, but appear to be very favourable in many regards (gas diffusion in the lungs is enhanced and it takes less effort to breathe), with the only apparent downside being that coughing becomes less effective at removing obstructions. Plants generally seem to love it, too (due to the enhanced gas diffusion), only suffering from falsely reacting as though experiencing drought. There are efforts underway to breed plants to not react as if experiencing drought, so that they only gain the positives of the reduced pressure environment.