SpaceX Rocket Emissions Similar to Large Jets Crossing the Oceans

Each flight of a SpaceX Falcon 9 or any other orbital rocket launch is about the same as a passenger jet like a 777 flying across the Atlantic.

The larger SpaceX Super Heavy Starship will use 1kg of methane for every 3.6 kg of oxygen. The Super Heavy Booster will use 3300 tons of fuel. 717 tons of methane. The Starship will use 1200 tons of fuel or 260 tons of methane. This would be 715 tons of CO2.

Sub-orbital flights should need only need about 25% of the fuel. This would reduce Starship emissions to about 200 tons of CO2 per flight.

The Super Heavy Starship would generate 8 times as much CO2 emissions as the Falcon 9. The Starship alone would be about double the CO2 emissions of the Falcon 9.

Calculations below would have about 2 days payback of the CO2 emissions (versus using coal) from the flights to launch space-based solar power using Super Heavy Starships.

The Falcon 9 rocket runs on highly refined kerosene. Each launch burns 29,600 gallons or 112,184 Kilograms, with each Kg of fuel releasing 3 Kg of CO2, so each launch releases 336,552 Kg of CO2.

A flight from London to New York City has a carbon footprint of 986 Kg, so a SpaceX launch is the equivalent of flying 341 people across the Atlantic. One 777-300 uses 45,220 gallons of fuel. One transatlantic flight of a 777 is considerably 52% more than a flight of the Falcon 9 which is about 513 tons of CO2. The Starship would have 40% more emissions. The Starship would be more equivalent to a crossing of the Pacific Ocean.

The Airbus 380 has 80,000 gallons of fuel. This would be 934 tons of CO2.

The 777 would have less emissions than a SpaceX Starship flight and the Airbus 380 would have more.

Elon Musk is planning to eventually put 1000 people into a Starship. They would ride in seating like a roller coaster and the actual flight would be less than one-hour. This means the per person emissions would be less than a 777 with three times the seating capacity but double the per flight emissions for a trans-Atlantic crossing.

The World currently has about 30,000 large passenger jets. There are 4 billion passenger trips each year and this is increasing and should double by 2035. About 10 million flights per year.

Rocket travel replacing passenger jets would be better in terms of CO2 than existing aviation.

How Much CO2 for Launching Space-Based Solar Power?

1000 tons of CO2 per gigawatt-hour of coal power.

A 1-gigawatt coal plant at 60% operating capacity would be about 5 Terawatt hours per year. 5 million tons of CO2 per year.

Space-based solar in the right orbit would have almost 100% capacity factor. Inefficiencies beaming it down. So 600MW delivered to the ground would be 5 terawatt-hours per year. If the system was 2 kilograms per kilowatt. Then 1.2 million kilograms for 600 MW. 120-ton launches will come from the SpaceX Super Heavy. 10 launches. 27000 tons of CO2). 2 days of payback for the CO2. If the weight can be cut in half then 1 day of emissions payback. Even if the weight of the space-based solar system was higher it would still be emissions efficient.

Elon Musk has talked about getting the cost per launch of the SpaceX Super Heavy Starship down to $2 million per launch. This would mean about $20 million to launch a space-based solar coal plant replacement.

SpaceX Could Revolutionize Global Travel

I believe that SpaceX could take over long-haul flights. First for package delivery to prove the 10,000X improvement in safety before flying people.

SpaceX should also exceed NASA’s budget in revenue by deploying the Starlink satellite network. Direct TV makes $40 billion a year in revenue. Direct TV shows that satellite constellations can make a lot of revenue.

Safe, rapidly reusable rockets can be used to speed up global connections with 25X the speed.

The future history of SpaceX will be as follows:
* SpaceX capture over 60% of the commercial launch market. This has already happened.
* SpaceX launches and starts operating Starlink mega constellation. 120 production Starlink satellites are already launched and the initial service will start in mid-2020. There should be 1400 Starlink satellites in orbit by the end of 2020.
* SpaceX flies Starship to orbit in 2020. In 2022 or 2023, SpaceX rolls out its ultra-rapid delivery package service.
* SpaceX annual revenue surpasses NASA’s budget by 2025
* Around 2027, SpaceX is operating over 1000 flights per day for 1 to 6-hour international deliveries.
* Around 2030, SpaceX proves the safety of rockets after millions of flights for human one-hour anywhere passenger service. There would already be over one-hundred Spaceports and thousands of Starships.

65 thoughts on “SpaceX Rocket Emissions Similar to Large Jets Crossing the Oceans”

  1. Airships don’t have a great future. A warming climate is a more energetic climate, and airships historically are ‘way worse than airplanes when it comes to the weather they can cope with.

  2. The paleoclimate guys use the size of fossilized leaf stomata as a proxy for the historical CO2 level. So the climate-consequences literature you haven’t read, has been up on stoma since the funding got serious around 1990. Hey, depressing-reading-R-us since 2000.

    Being mildly water-retentive isn’t much help to a plant if the Hadley cells march far enough from the equator to put the plant’s location under the descending, dry-air edge of the cell.

    You really need to google “map australia fires”. Good for net photosynthesis ? No. A place to scatter those tree seeds that Brian so loves ? Again no, because these days a burnt forest is probably in the process of being replaced by scrub.

  3. (part 2)

    One complication I’ve gleaned from that paper is that the primary source of O(1D) in the stratosphere seems to be photolysis of ozone. And there’s a few reactions that consume ozone. But production of ozone is several OoM slower. Which suggests that the oxidation capacity is limited. Put too much stuff up there, and it will saturate that capacity. Photolysis will get things eventually, but it can take longer (depending on alt). suggests that NO helps convert some of the methane to more ozone, which would increase the oxidation capacity.

    > water vs methane

    The concentration of methane in the stratosphere is around 0.7ppm (maybe closer to 1+ ppm today, and closer to 2 ppm in the atmosphere overall). It’s roughly 100 times stronger than CO2. The GH potential of water is difficult to estimate, but AFAIK it’s somewhere in between CO2 and CH4. If addition of water helps break down CH4, that should be a net win up to a point. But at some point the extra water will add the same amount of radiative forcing.

    The water does break down to OH, but there’s an equilibrium, so some will remain. Bottom line is, it’s complicated.

    One final thought: WAY more water down in the troposphere, up to 4 OoM more. So would a bit of water in the strat really matter much? I think it will primarily affect the portion of IR that’s reflected from clouds.

  4. (part 1)

    First, I just realized the stratopause is at 50 km. The strat and meso are often discussed together, so I was under the impression it was higher. says the main water breakup reaction below 60 km is with high-energy oxygen radicals. Photolysis of water dominates above 65 km, which is half way into the mesosphere.

    Also note: mesopause is at 80 km, not 60.

    > more weird carbon ions in exhaust

    Wouldn’t worry about those too much. Plenty of weird radicals up there anyway. They’ll get oxidized to CO2 (and water) eventually.

    > If methane photolyzes into water …

    Not exactly. Rather, there’s several oxidation reactions starting from high-energy oxygen (“O(1D)”). On top of that, there’s direct photolysis to CH2 + H2, faster at higher alt, followed by oxidation of the H2. Both end up producing OH and water, and the water partially breaks down to more OH. Eventually the carbon also oxidizes into CO2.

    Overall, yes, it looks like there should be an exponential feedback loop for oxidation of methane in the presence of water. But reality is likely more complex.

    (Down in the troposphere, oxidation with OH seems to be dominant, O(1D) and photolysis play a lesser role, and water is less catalytic.)

  5. Another comment (I ran out of room):

    If methane photolyzes into water and water catalyzes methane, which I think is what you’re implying, then you have a positive feedback loop that might actually be beneficial for cooling.

    I’m having trouble figuring out whether water or methane is a more potent GHG on a per-mole basis. Much more of the radiative forcing comes from H2O, but it has a mixing ratio that’s 1-4 orders of magnitude higher. I think that this means that, if you were given the choice to swap a mole of methane for a mole of water, you’d prefer the water, but I’m on really shaky ground here. Thoughts?

  6. The Raptor O2:CH4 mixture is about 3.6. Stoichiometric mixture would be 4, so the system runs fuel-rich. That’s normal for most rocket engines, because the oxidizer components have more atomic mass than the fuel components. Specific impulse is solely dependent on the average speed of the engine exhaust, so lighter is better.

    The net result is that you’re going to get more weird carbon compound ions in the exhaust.

    As for your question about how long a rocket stays in the upper strat, that’s hard to answer, because different rockets have different staging criteria, which changes the trajectory.

    I just looked at the most recent Falcon 9 launch to get a feel for what happened where:

    0-20 km (SL-high strat): 1st stage, 92 s.
    20-60 km (high strat-mesopause): 1st stage, 63 s
    60-164 km (meso-thermo): 2nd stage, 349 s

    So we’re expending about 40% of the 1st stage prop in our area of interest. If you did a linear scale-up to a vehicle with 1100 t of methalox (which is a bad approximation, because an SSTSO trajectory is nowhere near the same), that’d be about 440 t of methalox combustion products in the high strat.

    In general, an SSTO will probably pitch over sooner, because it has roughly the same thrust through the whole flight, making the time in the area of interest longer. But an SSTSO may need to pop up more for short targets, making the time shorter. My guess: long-haul flights may spend 30%-40% of their prop in the upper strat.

  7. Yes, what I didn’t connect is “if point-to-point rocketry replaces commercial jets, it’ll be a similar amount of water dumped in the stratosphere”.

    IF Brian is correct about it needing 260 tons of methane per flight, then that translates to 2340 tons of water. 1000 flights per year is 2.3 million tons – still negligible, but also still far from replacing all commercial jets. If we double the fuel estimate and bump it up to 10000 flights, it’s 50 million tons, which starts to become more significant. (I also overestimated the background water content, since I neglected the conversion from ppmv to ppmm; but I took the low end of the estimate range, so that can cancel out.)

    However, as I noted in the other comments:
    – The higher up you go, the faster the water will get converted to OH radicals.
    – The more OH radicals, the faster methane (at close enough altitudes) will be converted to CO2 (producing more water in the process, which is eventually broken back down to more OH radicals).

    (Also note that each water molecule produces two OH radicals, which become two water molecules after reacting with methane, which then break down to four OH radicals…)

    Btw, when you say “will likely spend a fair amount of burn time in the upper stratosphere”, which altitude range are we talking about, more specifically?

  8. HO is highly polarized, so it still has a bond stretching mode similar to water, and (I guess) at least one rotation mode around an axis not parallel the bond. But other modes are gone.

    HOO is a 3-atom radical, but the 2nd bond isn’t polarized (or almost so). It’s also a less common radical.

    I haven’t seen either of these being mentioned when GHG are discussed.

  9. 47C isn’t a record for Sydney, I remember doing a 120 km bike ride through 47 a couple of years ago.

    I remember it because it was a tad difficult to keep going.

  10. Remember that this started out as a question about whether SSTSO emissions would have climate consequences if it replaced long-haul air travel. Those are going suborbital, and will likely spend a fair amount of burn time in the upper stratosphere.

  11. From what I understand, infrared absorption is much stronger in molecules with three atoms than those with two, because there are more vibration modes, each with its own frequency. Bent molecules like water have more modes than straight ones like CO2. HO rotation about axis through the two nuclei would have negligible effect, as with O2 and N2.

  12. The people working the land don’t appreciate forty C temperatures as much as the plants might. And the plants don’t either if the soil they’re planted in is blowing away.
    Also, while photosynthesis rates might still rise with CO2, studies are showing that nutrient levels in many crops fall – 10 % reduction in protein levels in most kinds of rice, for example.

  13. Sure, but we also — oh, about 10 years ago or so — got 45°C temps in the “wine belt” of California.  My dear old car didn’t have working HVAC — who needs it, its California! — and I was driving back … with the air outside so hot that I couldn’t put my hand on the shady-side of the car, travelling down the road.  

    Yah, hot weather. 
    Its called weather, not climate.
    -= GoatGuy ✓ =-

  14. BTW, I’m extremely pleased that my posting resulted in some actual information exchange & in a (mostly) respectful manner (unfortunately a rare phenomenon these days).
    Thx & kudos to all.

  15. The reference was from me, on the assumption that more food at the bottom of the food chain will help the entire food chain.
    “The greening over the past 33 years reported in this study is equivalent to adding a green continent about two-times the size of mainland USA (18 million km2), and has the ability to fundamentally change the cycling of water and carbon in the climate system”.

  16. > if a large proportion of that goes into the stratosphere, and turnover in the stratosphere is slow

    Commercial jets cruise altitude is ~30-40K feet (9-12 km), which is below the tropopause in most places. The tropopause slopes from 56K ft (17 km) at the equator to 30K ft (9 km) near the poles. So most of that water won’t end up in the stratosphere.

    Polar and sub-polar flights may end up cruising in the lower stratosphere, but that’s also the area where the lower stratosphere circulates back down into the troposphere.

    The bigger issue may be if we add a lot of water to the mid or upper stratosphere, which (as I currently understand) doesn’t convect or mix nearly as much. But the higher up you go, the more photolysis and reactive species there are, and so the faster the water will be converted to OH radicals.

    That said, the full story is complex, and I’m by far not an expert. This is just what I’ve gathered over the past couple of days.

  17. And Tsiolkovsky’s equation works in reverse, too. FORWARD:

    ΔV = G₀ ISP ln( m₀ / m₁ ) and reversed, for ISP:
    ISP = ΔV / (G₀ ln( m₀ / m₁ )), or for m₀ given m₁:
    m₀ = m₁ • exp( ΔV / (G₀ ISP) )

    As, for example, 

    m₁ = 322,000 kg (5% landing fuel still in, at apex)
    ISP = 350 … average, for surface-to-vacuum engine performance
    G₀ = 9.81 N/kg … or m/s² surface acceleration, or ISP→v constant
    ΔV = 7,000 m/s

    m₀ = 322,000 × exp( 7,000 / (9.81 × 350))
    m₀ = 2,473,000 kg. 
    m₀ – m₁ = 2,151,000 kg of FuelOx.  

    Pretty cool.

    Using that, one can see that StarChild needs 2.2x MORE FuelOx on board, compared to its Wikipedia stats.  

    In short, it ain’t doing SSTO from its stats. 
    But it can with the SuperHeavy returnable-and-reusable booster. 

    Just Saying,
    -= GoatGuy ✓ =-

  18. Yah… maybe. But also maybe not. See TheRadicalModerate’s answer, it is good. 

    Bottom line — at least for the published numbers, Tsiolovsky’s Rocket Equation (just about as good as you’re going to get, in many regards) basically limits the ΔV of the StarShip-Alone to about 4,300 m/s for a 1,000 person carrier design, 150,000 kg of people-and-supporting-stuff, and slightly better ISP on their engines.  

    4,300 m/s is WAY short of what’s needed to do a ballistic path half-way around Earth. Way short. About 7,000 m/s is required, and a apex altitude of over 200 km.  

    It is for this reason that the SuperHeavy, not-much-talked-about-in-the-rah-rah-claims-monologues … is required. The ONLY way high-speed people transport works is by jetting the people part up to 7,000 m/s or so.  

    Which requires about 25 kg of FuelOx per 1 kg of payload.  Or, $30 per kilogram of people-stuff.  I put 150 kg/person as the payload, to account for seats, luggage, vomit suits, crew, oxygen, emergency preparedness stuff, and so on. Have to have a CPR machine while in flight!  Maybe more than one.

    $30 (FuelOx cost) × 150 = $4,500 ticket price. WITHOUT profitizing things. 

    Just saying… the numbers oft quoted, don’t seem to work. 
    -= GoatGuy ✓ =-

  19. ‘ 2 ppm would be ~1 billion tons of water in the stratosphere.’
    According to this estimate, about 270 billion litres of fuel was burnt worldwide in 2017 – – about 220 million tonnes. Burning a tonne of jet fuel makes nearly 1.3 tonnes of water vapour, so if a large proportion of that goes into the stratosphere, and turnover in the stratosphere is slow, it could have a mounting effect. If tropical storms are more powerful, from hotter sea surface temperatures, that would also push more vapour up through the stratopause. Water from oxidation of CH4 is estimated to cause about 15 to 20 % of the climate forcing attributed to methane.

  20. Las Vegas – isn’t that where outside life is mostly snakes and scorpions, and the major industry is taking money off idiots in an artificially lit and cooled indoor environment ?

  21. I just can’t make those numbers work. I think it’s possible to make a SSTSO out of a Starship variant, but Starship as-is doesn’t have the thrust or the specific impulse to reach the places it would need to reach to be viable.

    Go to nine engines, mass-reduce it down to 75 t dry mass, and get vacuum Isp up to 380 s. At that point, you can get halfway around the world from most latitudes.

  22. LOL… only 116°F? We get that ALL THE TIME in Las Vegas, Nevada. Almost every year. 110°F is so common that it isn’t commented on.  

    Have Aussies turned into whining woossies?

    Just asking,
    -= GoatGuy ✓ =-

  23. Sigh… numbers, numbers, numbers. 

    LEST we forget, the 1,000 passenger proposed StarShip + SuperHeavy booster (remember that part!) … working backward from a-bit-thin-on-the-details Wikipedia information, it turns out that:

    1,320,000 kg takeoff mass of STARSHIP.
    3,530,000 kg takeoff mass of SUPERHEAVY.

    4,620,000 kg together. 
    Of which FuelOx is 3,635,662 kg. 
    And the ‘people part’ is what, maybe 150,000 kg? 
    (crew, peeps, luggage, vomit-suits, chairs, oxygen, souvenier pens).  
    About a 25× to 1 ratio of FuelOx to comported peeps overhead. 
    3,600 kg/person. 

    For long haul (half-way around the world … or further to avoid traversing other nations sovereign airspace claims), this is pretty modest. For shorter-haul (transcontinental, transatlantic, transpacific), it is less optimal. 

    But no matter, the Vomit Comet is a great way to spend a few hours getting close to one’s … ermmm… bodily fluids. 


    25 kg FuelOx per kg of UPS or FEDEX packages. 
    Sounds like a winner. 
    Methane is especially cheap, and liquid oxygen isn’t much worse. 
    $1.25 per kg. $30 all-in FuelOx cost per kilogram. 

    There’s the amortization, insurance, operations, profit, research-set-aside, marketing, logistics and dividend returns to consider, of course. $30 a kilogram probably comes in closer to $100, when all that is included.  

    Still, worth it for ULTRA FAST delivery. 


    Just asking,
    -= GoatGuy ✓ =-

  24. and give some more details on the chemistry. But the paper is from 1981, so there may be new data since then.

    Apparently, high-energy oxygen radicals (“O(1D)”) and OH radicals are the main oxidizing species. When a hydrogen source such as methane reacts with O(1D), an OH radical is formed. When the hydrogen source reacts with OH, it (temporarily) forms water. But according to Table 1 of the paper, the latter process is 1-2 orders of magnitude slower.

    Eventually the water photolyzes to form H + OH radicals, or reacts with O(1D) to form 2 OH radicals. From there, I’d expect H + O2 –> OOH to be one of the common reactions, given O2’s much higher concentration than any radicals. But it seems this requires a 3rd molecule, so is one of the slowest reactions (Table 1, R14). Reaction of OH with O2 isn’t even listed. Instead, the fastest reactions seem to be formation of more OH radicals. Reactions of OH (which often form water) are 1-2 OoM slower, as noted.

    So kinetically, it seems any water will eventually be broken up primarily to OH radicals. Excess water should result in more OH radicals, which help convert methane to CO2, resulting in reduced greenhouse effect. However, some of these reaction rates may be off.

    Based on the Wikipedia link, it doesn’t seem like the OH radical is itself a GHG, but maybe they just ignore it due to low concentration.

  25. A quick google suggests the hygropause is mostly found around the tropics, where there is the most water vapor uplift from the troposphere. This is probably part of the circulation that I wrote about earlier: the air migrates north from there, and then descends back into the troposphere about 1.5 years later. However, if the hygropause is mostly found above the tropics, then it means the air must somehow dry up before it reaches further north.

    The general consensus on stratospheric water concentration seems to be ~5 ppmv, or more generally ~2-10 ppmv (based on several sources).

    (edit: 2 ppm would be ~1 billion tons of water in the stratosphere.)

    I also found there is some vertical mixing in the stratosphere and mesosphere by some sort of tidal/wave mechanism (briefly mentioned, but not much detail). It’s probably weak, but not zero.

  26. Look, that cite was just for the purpose of demonstrating that CO2 levels really did get close to the point where photosynthesis would shut down. Sure, there was some adaptation. In fact, C4 photosynthesis is pretty well adapted to current, ELEVATED levels, and is survivable under 100 ppm.

    C3 photosynthesis, OTOH, is better adapted to CO2 levels 2-3 times higher than at present, and C3 plants pretty much die below 150 ppm, so, yes, during the last ice age we came close to losing C3 plants.

    No biggy if you want to live in a world where the only plants are grasses, and we’ve lost basically all our food crops.

    Also, heat tolerance IMPROVES at higher CO2 levels for C3 plants. They get tougher, because they’ve got more energy available for the amount of water they have to expend.

    So, basically things are fine right now for C4 plants, because the CO2 levels are already elevated to the point where they’re happy. C3 plants are still suffering from a CO2 deficiency, and will be until CO2 levels double over current levels.

  27. Why, it’s like you’re not even aware that plants’ need for water actually goes down as CO2 goes up, because they lose less water out their stoma.

  28. It appears that the mixing ratio of water vapor to dry air drops with increasing altitude in the lower strat, but then there’s a “hygropause”, above which it starts (slowly) increasing. This is because CH4 dissociation increases as UV irradiation increases.

    It’s therefore a fair point that you’d need to know what your base mixing ratio was before you could decide how many launches would be required to make any discernible impact on the water vapor mixing ratio.

  29. ‘It’s still at starvation levels so far as plants are concerned.’
    That is not at all what the study you cite is saying. They say there is no evidence of plants going extinct during maximum glaciation, and that they adapted genetically to the low CO2 levels. Also that changes in response are much greater moving from glacial levels to current ones, than they are from present to projected future levels ( ~500 ppm.) Variations in conjunction with heat stress or water stress, or for C4 plants, are much more important than CO2 alone. Wheat and rice, our major food staples, are C3, corn and sugar cane C4.
    ‘A warmer Earth & more CO2 are a big win for the entire food chain!’ This is the kind of statement that makes me wonder whether the human race is getting pretty close to an extinction event, due to brain function dropping below critical levels.

  30. No, he’s not missing that, because CO2 shortage is not a factor of interest. It’s irrelevant.

    The climate science community have exerted themselves for decades, trying to estimate net primary production (AKA total planetary photosynthesis) under the various near-future scenarios. There is a literature, which I’m guessing you haven’t read. And it’s agreed that as CO2 goes up, there will be some species that are relative winners, and some that are losers, but primary production won’t change much in the near future. That’s because extra CO2 is useless if a plant doesn’t have the extra water, minerals AND sunlight needed to use that CO2. Greenhouses don’t even vaguely resemble natural ecosystems.

  31. What a cherry picker. Somehow you forget that photosynthesis takes a nose dive after 30C. Somehow you forget that the rate of change we are now undergoing is off the scale in terms of previous transitions. Unlike previous transitions animals and plants cannot migrate freely due to human constraints. Again you forget extreme weather, fire and climate feedbacks that will take us into climatic conditions similar to the Eocine, all within 200 years. Yes happy days indeed.

  32. Actually, given the above, and assuming a relatively low total hydrogen concentration, I’d expect HO and HOO (both radicals) to be the dominant hydrogen species in the upper stratosphere. There just won’t be enough hydrogen around to form a lot of doubly-hydrogenated species.

    Even if water itself isn’t photolyzed, it should react with oxygen radicals and other reactive species to form HO. But I expect that water will get photolyzed too.

    I have no idea what’s the greenhouse behavior of the HO and HOO radicals. The H-O bond is still there, so it may be similar.

  33. > it looks like CH4 and H2 get photolyzed, but H2O doesn’t.

    Based on , the bond energies of methane, H2, and water are pretty similar: 439, 436, and 497 kJ/mol, respectively. So I expect that water gets photolyzed about as much, but quickly reforms due to the high concentration of oxygen. But other HxOy species (including radicals) can also form, so there’s an equilibrium of some sort. HxNy and HxNyOz species probably form too.

    Coincidentally, the O2 bond is 498 kJ/mol, almost the same water, and ammonia is 435, about the same as methane (had to look it up elsewhere).

    N2 is more stable, at 945 kJ/mol, but it can react with other reactive species, and its concentration is higher.

    > Again, that implies that water vapor could be quite stable in the upper strat.

    On the other hand, if it is stable, that also implies there is already a background water presence in the upper statosphere, so anything we add will be relative to that.

  34. Did a quick scan of these. First thing to note: Your 1.5 year lifetime is the troposphere-stratosphere-troposphere turnover rate. That’s mostly a lower atmosphere phenomenon.

    Because of the temperature inversion in the strat (i.e., it gets hotter the higher you go, due to increased UV flux), the higher areas don’t convect. That means that if there’s water vapor deposited in it, it’ll likely stay put.

    Based on one of the photchemistry blurbs in your second link, it looks like CH4 and H2 get photolyzed, but H2O doesn’t. Again, that implies that water vapor could be quite stable in the upper strat.

  35. Couldn’t find your reply to Marcel. Can you republish the links?

    I’d be more interested in water vapor near the stratopause than vapor down in the lower stratosphere. It’s cold enough and high enough pressure in the lower strat for water to condense, freeze, and eventually fall. Up near the stratopause, the pressure is low enough that it’s vapor, and the temperature inversion should keep it buoyed. However, mean free path is getting so long up there that maybe “buoyancy” isn’t a great concept.

    Rockets spend a fair amount of time in the upper strat: at that altitude, they’re mostly going downrange, so altitude rises fairly slowly in that part of the trajectory.

    I’m not even pretending to know whether this is a serious problem or not. However, it did seem to me that Brian’s focus on CO2 was pretty naive. I’d be surprised if CO2 were even the dominant effect.

  36. London to New York is 5600 km. To do that in 12 hours is 470 km/h. On average. Say a cruising speed of 500 km/h.

    The fastest airship (according to my 10 second google search) is 115 km/h. That gets you to NY in 50 hours. Not really overnight.

  37. The fully fleshed out plan is having offshore space ports a few 10s of km out from the (coastal) cities.

    Of course that adds a bunch of travel time to these estimates.

  38. That’s true, but what you’re missing is that basically all plants are currently suffering under a CO2 shortage relative to the levels they find optimum. Before the CO2 levels started back up, we were getting pretty close to the level at which there would have been an extinction event due to most plant species not being able to sustain photosynthesis, CO2 was so low.

    It’s still at starvation levels so far as plants are concerned.

  39. no, you got it wrong. Every organism evolved in a specific set of environmental conditions and tolerates only a certain level of variation for what is its optimal environment:
    -all plants need light, but certain plants that evolved in the underwood, low light (like ferns) do not tolerate intense direct light. They just die.
    -all plants need water and minerals, but most root systems will rot if constantly submerged in wet soils. Only specific plants thrive in swamp and ponds.
    -the same is true for variation in CO2 levels which also changes the acidity of the waters.

  40. You nailed the issue. The noise will limit the implementation of this idea to existing spaceports and sparsely settled coastal areas which will greatly reduce the market potential earth-side. Things will develop differently off-planet.

  41. What about the noise factor? These things launch LOUD. A 777 on takeoff probably sounds like a large desk fan compared to a Starship’s boost phase. Who will want these spaceports anywhere near even a few miles of where they live?

  42. The article is focusing mostly on the next generation Starship, and compares the passenger numbers:

    Elon Musk is planning to eventually put 1000 people into a Starship. They would ride in seating like a roller coaster and the actual flight would be less than one-hour. This means the per person emissions would be less than a 777 with three times the seating capacity but double the per flight emissions for a trans-Atlantic crossing.

    (That refers to suborbital point-to-point flights.) Falcon 9 will carry 6 people at a time, but only to orbit (primarily to the ISS). It is less relavent to this disscusdion.

  43. 1) Supposedly, startospheric air stays up there for about 1.5 years at a time. Not sure about the mesosphere. In the upper stratosphere there is also natural(?) water resulting from photolysis and oxidation of methane. See my reply to Marcel.

    2) The higher up you go, there more photochemistry there is. The 2nd link in that reply suggests that the upper stratosphere has plenty of reactive species anyway. Nitrogen oxides are a way of life there. (Full disclosure: I didn’t read it fully, only skimmed it.)

    Of course, all of this is a matter of scale. Too many lauches could have a noticeable effect. But that may take a very big “many”.

  44. The 9 day lifetime of water in the atmosphere is likely an average for the troposphere, which is where almost all atmospheric water and weather are found. Its lifetime in the stratosphere is likely longer, since there is almost no weather there.

    There is circulation in the stratosphere, but it’s difficult to measure. Google brings up a result from 2017, which suggests that the cycle (or rather the half-cycle from up to down) takes 1.5 years. Which is still not very long, but longer than 9 days.

    Another result suggests that the lifetime of methane in the stratosphere ranges from over 100 years to just a few months, depending on altitude. Higher altitude has more active photochemistry. The methane is broken down, and the hydrogen is oxidized to water.
    (under “Stratospheric Photochemistry”)

  45. Instead of super or hypersonic flight from London to New York, or the current 6 hour flight, how about a hydrid lifting body and variable bouyancy airship that gets you there in 11-12 hours? You fly overnight and because airships can carry much more weight economically it is like a luxury sleeper train with your own little cabin and bed, bar, restaurant. Maybe even onboard customs proceedures? Get into NY at 8am on a dock peer in the central city and go about your day.

  46. And somehow I almost forgot catastrophic fire as well. Shouldn’t be forgetting this when the smoke here is so bad you cannot bare to be outside and can’t see more than a couple of hundred yards. Emissions equal to half our total annual output released in just a couple of weeks as we lose our native forests and wildlife.

  47. Plant food until the plant dies from an extreme weather event. New records of over 47C coming this week here in Sydney ahead of 50C regularly in the summer within 20 years. Have you ever experienced 50C? The fact that anyone can call mass extinctions, mass migrations and catastrophic weather a big win shows just how idiotic some people have become over this.

  48. Actually, it is important as far as global warming is concerned since some greenhouse gasses remain in the atmosphere a lot longer than others. Water vapor may be a more effective greenhouse gas but its lifetime in the atmosphere is only about 9 days.

    The CO2 produced from a methane/oxygen rocket could remain in the atmosphere for nearly a century.

    Significant methane leakage into the atmosphere before the rocket is launched might also be a greenhouse problem. Methane can remain in the atmosphere for 12 years but is a much more effective greenhouse gas.

  49. As Radical Moderate says, where the methane comes from isn’t as important as where it goes to, and what it turns into. Mostly water vapour in the stratosphere, which has about three times the warming effect of the CO2, plus unknown effects on the ozone layer and noctilucent clouds.

  50. Starship 120 tons per launch is for LEO, but SBSP on LEO makes it difficult to beam microwave power to earth as the satellite moves fast relative to earth.
    there is a good presentation of Japan’s project for SBSP in
    Their plans call for a geostationary plant of 10000 tons plant for 1GW power. Starship geostationary payload is 40 tons, so we are talking 250 flights here, not 10…

  51. Several things about this:

    1) Water vapor is a bigger greenhouse gas than CO2, and a rocket launch puts much more of it into the upper stratosphere and lower mesosphere than a typical aircraft does. I don’t know how long water vapor stays up there, but mesospheric heating will likely keep it in vapor form, so it could be a while.

    2) Rocket exhaust isn’t just CO2 and H2O. It’s every possible species of stuff you can imagine, from atomic hydrogen and oxygen ions to carbon monoxide and hydrogen peroxide. There are enough reactive ions emitted that it’ll make all kinds of nice nitrogen compounds, too. Figuring out what large amounts of that stuff will do in the upper atmosphere is non-trivial, and the second-order effects could be large.

    3) While I’m still rooting for SBSP, the carbon footprint isn’t the limiting factor; the launch cadence is. It requires a ridiculous number of launches. Even if they’re very cheap, there’s an air traffic control limit hiding out there somewhere.

    Instead, the proper way to look at SBSP is to figure out how much stuff you need to launch to the Moon to set up the industrial base to toss SBSP components into GEO. From that standpoint, the number of launches is almost trivial.

    Edit: Temperature actually peaks at the stratopause, the boundary between the stratosphere and mesosphere. Temperature and pressure are -15℃ and about 100 Pa, respectively, which makes water a vapor there. This is well higher than aircraft fly.

  52. The methane fuel that Space X will use for the Starship can easily be produced from renewable energy resources:

    1. pyrolyis of urban hydrocarbon waste (garbage and sewage),
    2. pyrolysis of agricultural biowaste,
    3. the pyrolysis of forest biowaste (dead trees and fire hazardous forest materials) or
    4. through the synthesis of CO2 extracted from the atmosphere and hydrogen extracted from water.
  53. Since neither plants nor the animals that eat them can speak (or type), I’ll stand up for them & welcome the massive influx of a primary plant food ingredient (CO2) into the biosphere with thousands of SpaceX launches. A warmer Earth & more CO2 are a big win for the entire food chain!

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