FLIGHTS OF THE IRONIES - The Three Stooges of Space Tourism
This post aims to take a critical look at what I see as a new space race. Unlike the Soviet/American cold war space race, this one will be among private companies (with the help of a few billion dollars in government subsidies, meaning tax dollars). My primary concern is with the amount of carbon dioxide that will be produced from the combustion of rocket fuel, as rockets begin punching through the atmosphere with unprecedented frequency.
There are dozens of companies aiming to get a piece of the projected space tourism pie, but of particular note are Jeff Bezos' Blue Origin, Elon Musk's SpaceX, and Richard Branson's Virgin Galactic. I mention these three, because they appear to be making the most progress, and are certainly among the most popular among the laity.
That space tourism pie, also includes the ingredients of private, and government contracts to put satellites into orbit, as well as future moon, and Mars missions for those aimed at colonizing both. How profitable all this will be without the crutch of subsidies is debatable and beyond the scope of this blog post. I'll simply assume ferrying cargo and people into, and through space will soon be profitable.
Getting to space requires a lot of energy, proportional to the mass of the rocket (and cargo) trying to get there. As an example, SpaceX's impressive BFR fully fueled plus max payload would weigh in at about 4.55 million kg. I'm not known for my math skills, but if I plug the numbers into this kinetic energy calculator, I get over 2.85 million megajoules of energy needed for the BFR to achieve escape velocity from Earth's gravity well. Assuming a 3-mile long lightning bolt is 5 billion Joules, then a launching BFR equates to as much energy as about 570 3-mile long lightning bolts.
It takes the combustion of a lot of fuel to convert that much energy (energy isn't produced); over a million kilograms of it in the case of the BFR, and I suspect much the same for Blue Origin's Blue Glenn rocket.
Both the BFR, and New Glenn will use liquid methane, combined with liquid oxygen (LOx) as an oxidizer for their fuel. As is the case with nearly all combustion reactions, carbon dioxide gas will be produced in substantial quantities with each launch.
A few rocket launches per year I doubt would have much of an impact on our climate, or the environment at large. I could be wrong about that assumption, as I'm basing it on an unscientific gut feeling.
However, if we consider Elon Musk's plan to transport people anywhere on Earth in an hour or less via rocket, with a target frequency of 12 flights per day, and couple this with Jeff Bezos' aim to begin ferrying luxury tourists to the edge of space on a regular basis, and couple that with Richard Branson's vision of making his company's first commercial spaceflights an occurrence of "unprecedented frequency", and couple that with the necessarily-consistent resupply missions for future moon, and Mars colonies, one might be correct to assume there will be some impact on the environment (including our climate).
Musk's, Bezos', and Branson's lofty aspirations mentioned above, don't include the numerous contracts space-fairing companies (themselves included) will be awarded by private, and governmental agencies to get stuff into various orbits. There's also been plenty of talk, including from Jeff Bezos, about off-planet heavy industry. While mining asteroids, the moon, Mars or wherever spares Earth's limited resources from further plunder, these ventures will require the plundering of Earth's limited resources. If that sounds like circular logic, it's because it is. I could be wrong, but I believe the value of Bezos' idea of industrializing space to protect Earth is overestimated.
Heavy industrial equipment capable of working in a vacuum under intense radiation doesn't just build itself out there. The materials and fuel to build them, and get them there respectively have to come from Earth. Go figure.
Anyway, SpaceX has already been green-lit by the FCC to position nearly 12,000 satellites in 83 different orbital planes by the year 2020. This constellation is meant to provide internet access to all corners of the globe. They've positioned 2 so far.
If we assume the visions of Bezos, Musk, and Branson are achieved, then we can modestly expect thousands of rocket launches per year. That would be up from the 90 attempted launches in 2017; those 90 being conducted by seven different nations. The thousands hoped for by some in the years to come, would be from Blue Origin, SpaceX, and Virgin Galactic alone.
We should also recall Elon Musk's presentation at the 68th annual International Aeronatical Congress in Adelaide, where he discussed launch schedules for planned Mars colonization logistic support. This may sound a bit ironic, but a so-called self-sustaining Martian colony will "...ultimately need thousands of [rockets] and tens of thousands of refilling operations. This means you need many launches per day..." Those are the words from Elon Musk himself.
He continues, "In terms of how many [launches] are occurring, you need to be looking at your watch, not your calendar."
In my humble opinion, this puts an old paper by Kellogg (1964) back in the spotlight. That paper concluded a doubling of atmospheric carbon dioxide (relative to the 1964 concentration of just under 320 ppm), would require 100 to 100,000 Saturn-type rockets, each ejecting 100 tons of exhaust above 100 km per year. A 100 tons of exhaust, as we'll see, is rather small compared to what will be produced by the Blue Glenn, and BFR (among others).
The threat of carbon dioxide doubling was so far-fetched back then, that the only thing most took away from that paper, was the possible loss of accurate measurements by tracer experiments in the upper atmosphere due to increased lithium concentrations from rocket launches. Tracer experiments using lithium vapor are generally used to measure neutral winds in the upper atmosphere.
At the time of this writing, average atmospheric carbon dioxide concentrations have risen to just over 411 ppm. A 91 ppm increase in about 50 years doesn't seem to alarm everyone, but should for reasons I explain in my blog, Climate Change - A Response to Dr. Lindzen's Letter to the POTUS). While even several thousand rockets per year may not double the current carbon dioxide concentration average, they would certainly increase it, and an attempt at colonizing Mars would arguably double it.
Few things are as ironic as becoming a multi-planet species in the vain of self-preservation, at the cost of habitability of our own home planet. Where's my go-to Captain Picard meme...
BFR's Raptor engines, and New Glenn's BE-4 engines, will burn liquid methane, with liquid elemental oxygen (LOx) as an oxidizer.
I was unable to find numbers on the New Glenn rocket, but it's at least comparable to the BFR if not bigger. Certainly it's more powerful, but I think SpaceX's goal has more to do with bringing down costs of spaceflight, rather than making the most powerful engine; of which Blue Origin's BE-4 is, insofar as methane-powered engines go. Since I can't find numbers on the New Glenn, we'll use numbers from the BFR to calculate just how much carbon dioxide gas is produced from a single launch.
The balanced combustion reaction is:
CH4 + 2O2 -----> CO2 + 2H2O + energy
1 molecule of methane reacts with 2 molecules of oxygen to produce 1 molecule of carbon dioxide, 2 molecules of water vapor, and energy.
The molar mass of methane is 16 g/mol, and the molar mass of oxygen is 32 g/mol. The BFR holds 240 million grams of methane, and 860 million grams of oxygen, so:
240,000,000 / 16 = 15 million moles of methane, and 860,000,000 / 32 = 26,875,000 moles of oxygen. This is a methane-to-oxygen ratio of 1 : 1.79.
26,875,000 / 1.79 = 15,013,966 g/mol is the amount of carbon dioxide. One mole of carbon dioxide is 44 g, so 44 x 15,013,966 = 660,614,504 grams of carbon dioxide are produced. This converts to about 728 tons per launch. Now this assumes 100% combustion efficiency which is impossible to achieve. But even halving that number still equates to hundreds of tons per launch. In the grand scheme of things, I doubt a few launches will equate to much in terms of climatological impact, but if Elon Musk seriously intends to launch 12 BFRs per day for his proposed (and ridiculous) international transportation system, and we couple this with the visions of others developing methane-, and kerosene-powered rockets whose ideal launch schedules would be several times a day, then we are looking at an atmospheric carbon dioxide flux in the tens of millions of tons annually.
The irony of a man who wants to promote electric cars and solar panels, yet also frequent use of massive fossil-fuel-burning rockets for international commercial travel hasn't been lost on me.
SpaceX, and Blue Origin aren't the only ones interested in methane-powered rockets. The United States Air Force (USAF), smaller private companies, and universities across the country are actively conducting research and development as I write this.
The USAF's Third-Generation Reusable Boosters (3GRBs) will be powered by liquid methane, and it appears R&D on such engines is being conducted by smaller companies like Masten, TGV, Wask, Exquadrum, and Sierra Nevada to name a few.
Universities are getting in on the action; their bright young engineering students starry eyed by the prospect of Mars colonization, and further space exploration. UTEP, and Purdue appear to be particularly active in this regard, with Purdue (that I know of) having already launched a methane-burning rocket to the edge of the troposphere.
There's also the United Launch Alliance (ULA)—a joint venture between aerospace giants Lockheed Martin, and Boeing— who will be equipping their new Vulcan rocket with methane-powered BE-4 engines. ULA co-developed the BE-4 with Blue Origin, and as mentioned earlier, the BE-4 is the most powerful methane-powered engine ever built; putting out about 700 kilonewtons more thrust at sea level than SpaceX's methane-powered raptor, and the BE-4 does it at a higher specific impulse.
It seems that methane is here to stay. It's certainly abundant, not just on Earth, but all over the solar system. Currently, the primary source of methane used by various industries comes from geological deposits called natural gas fields, with coal seam gas extraction being a major source. On Earth, methane is often created from the anaerobic decay of organic matter.
As an alternative source, methane could also be sourced from biogas, where the fermentation of organic matter such as manure, wastewater sludge, municipal solid waste, or any other biodegradable feedstock subjected to anaerobic conditions.
There are enormous amounts of methane hydrate beneath the Arctic permafrost, beneath Antarctic ice, and in sedimentary deposits along continental margins worldwide. The good news is we're doing a find job as a species of extracting this stuff already via anthropogenically-accelerated global warming-fueled climate change. The bad news is...(ibid.).
And perhaps one of the best sources for methane may be belching cattle. It sounds ridiculous, but according to Miller (2007), 16% of global annual methan emission comes from cattle belching. In fact, one study suggests the number is as high as 37% if other livestock like chickens, pigs, and such are included (Food and Agriculture Organization of the United Nations, 2006).
As a greenhouse gas, methane is like carbon dioxide on steroids. On a 20-year timescale, it warms the atmosphere 86 times more efficiently than carbon dioxide, and when it's done doing that, it decays to carbon dioxide. It's wicked stuff, so capturing it from belching livestock, and melting permafrost is a good idea.
But then we have to ask ourselves, what the point of capturing methane is if all we're going to do with it is combust it with oxygen to produce carbon dioxide; another greenhouse gas that will be injected directly into the stratosphere no less. So far, I know of no serious large-scale plans to capture escaping cattle burps, or methane escape from melting permafrost. It seems the most popular ideas are to continue harvesting it from natural gas fields, and future plans to tap it from coastal waters. I'd get into the environmental impacts of these practices, but that's getting off topic here.
So it's clear that methane has become the fuel of choice for most rocketeers. But why?
I may be wrong in the following assumptions, but some of the reasons methane may have become so popular may have to do with reusability, availability both on and off planet.
Unlike highly-refined kerosene fuel (called RP-1), methane doesn't leave behind a whole hell of a lot of soot and other contaminants. The cost and time required to clean reusable boosters between launches might become prohibitive. In a burgeoning industry where competition is expected to be fierce, in an environment where Earth's gravity well wears the big gloves, time and financial efficiency will be key (I guess time is money in this regard).
Of course, it's probably worth noting at this point that cutting costs in the rocket industry is probably a particularly precarious undertaking given the pronounced inverse relationship between being cheap, and being safe. Or so I'd assume.
Another possible reason why methane may be the fuel of choice, at least for those planning to colonize Mars, is that methane can theoretically be sourced from Mars. Carbon dioxide, and a modest concentration of hydrogen can be turned into a methane-oxygen rocket fuel in situ via the Sabatier reaction.
In a generalized sense, the way it would work, is carbon dioxide would be obtained from Mars' atmosphere, while the hydrogen (I assume) would come from sub-surface water ice melted in situ. The liquid water would then be electrolyzed to yield oxygen which can be cooled to the point it liquifies, then stored as an oxidizer, and the hydrogen yielded from electrolyses can be used as part of the Sabatier reaction to produce methane.
Of course, all this will require a considerable amount of energy, which is why vocal Mars advocate, and engineer, Robert Zubrin has proposed a small nuclear reactor be used.
Being able to produce rocket fuel in situ is a big deal, and probably the single most cost-reducing aspect of any future manned missions to Mars that intend to return to Earth, or use it as a stepping stone to some further destination. But in the grand scheme of 10s of thousands of rocket-brought resupply missions from Earth, I have to question the point of in-situ-produced anything if a Martian colony isn't truly self-sustaining. I fail to see the self-sustainability of a Martian colony that continues to suck from the teet of mother Earth in the form of constant resupply missions.
Methane may also be preferred by some in that it may be economically advantageous for Earth-to-orbit rockets due to its combination of high density, and specific impulse. Specific impulse is basically the amount of thrust you get per unit volume of fuel; the more thrust per unit, the higher the specific impulse.
I'm sure there are other advantages to using methane, but this doesn't change the fact that methane (and kerosene fuel), produce tons of carbon dioxide. Why preserve our species on a dead planetary embryo (Mars) at the expense of our home planet's climate and environment at large? Am I missing something here?
It's been well established for over 100 years that carbon dioxide is a primary driver of climate change (Arrhenius, 1896), (Callendar, 1937), (Plass, 1955), (Keeling, 1969), (Sawyer, 1972) etc. If this is news to anyone reading this, please check out my explanation of why in my blog post, Climate Change - A Response to Dr. Lindzen's Letter to the POTUS. I'm not the best at explaining things, but hope that post does an ok job.
At any rate, knowing carbon dioxide has been a primary driver through geologic time, and given the fact we are naive to what level might trigger a positive feedback loop, then we might be wise to consider the prospect of injecting tens, and hundreds of millions of additional tonnage of carbon dioxide into the atmosphere on a regular-and-accelerating basis to be a rather short-sighted one.
And while the other exhaust product of methane combustion (water vapor) may seem "green", and harmless, I have to wonder what adding millions of tons of it directly to the stratosphere will do for average global temperatures.
This seems far-fetched, but if we're to believe the just the visions of Bezos, Musk, and Branson alone, then we can expect water vapor exhaust will also be quite significant in the coming decades. Now I could be wrong, so take this with a grain of salt, but this may be something worth considering as well, because much of this water vapor would be directly deposited in the stratosphere.
The stratosphere is very dry by nature. This has a lot to do with the fact the tropopause (the boundary between the part of the atmosphere we live in, and the stratosphere) is very cold. Any water vapor coming up from the weather we experience in our bit of the atmosphere, tends to "freeze out" at the tropopause, preventing it from making it into the stratosphere.
Generally speaking, there are a couple ways the stratosphere gets any water vapor at all. One is from infrequent volcanic eruptions (not wimpy basaltic eruptions like Hawaii, but powerful andesitic, and ryholitic eruptions like Mt. St. Helens, or Yellowstone as examples). Another is from supercells that penetrate the tropopause through to the lower stratosphere.
Other than that, the stratosphere remains markedly dry, and this is a good thing too. Scientists have learned in recent years that stratospheric water vapor concentrations have a pronounced effect on global average surface temperatures.
Consider a study that found from 2000-2009, stratospheric water vapor decreased on average by about 10% from previous decades (Solomon et al., 2010). The authors concluded that this acted to slow the rate of increase in average global surface temperatures during that same period by about 25%, versus that which would have occurred due to carbon dioxide, and other greenhouse gases.
From 1980-2000, stratospheric water vapor increased, and this enhanced the decadal rate of surface warming during the 1990s by about 30% as compared to estimates neglecting this change (Ibid.). This demonstrates stratospheric water vapor is an important driver of decadal global surface climate change. So altering this delicate system by injecting tens of millions of tons of water vapor gradatim ferociter, may not be in our best interest.
Does this mean water vapor from tens of thousands of rockets blasting through the stratosphere will enhance average global surface temperatures? I don't know, and am not claiming such here. I'm just putting it out there. Perhaps someone reading this with the know how can plug the numbers into some climate model and see what the ol' supercomputer spits out.
I'm not trying to save the planet. The planet will be fine. It's the life on this planet I'm worried about; that includes us ironical humans.
Now before I jump to ozone talk, I want to add that something which might give my remote concern some more oomph, are the studies that show warming temperatures in the tropics is projected to increase stratospheric water vapor concentrations due to a combination of warmer tropical tropopause temperatures, and powerful convective activity. Warmer tropopause temperatures is a pseudo-nerdy way of saying less-effective water trap preventing water vapor from getting into the delicately balanced stratosphere, which is a wordy way of saying "ahh shit".
One thing we all know is the stratosphere is home to our ozone "layer". I use scare quotes around "layer" since it's generally 1 to 10 parts of ozone per million parts of 'air', which I'd hardly consider layer like. It's far more delicate than the concept of a layer portrays.
It's well know that stratospheric ozone protects us from ionizing UV-C radiation from the Sun. Radiation that would certainly kill all terrestrial life on Earth if it were to get through to Earth's surface.
Ozone is generated when diatomic oxygen absorbs long ultraviolet-c (UV-C) causing it to dissociate. The oxygen atom then combines with another diatomic oxygen to form ozone. Ozone absorbs the shortest wavelength of UV-C, and breaks it down to diatomic oxygen and atomic oxygen. The diatomic oxygen absorbs another long wavelength of UV-C, and the process repeats over and over again.
In other words, ozone lost, ozone gained; to be lost again, gained again, ad infinitum. Ozone, therefore, exists in the stratosphere in dynamic equilibrium; This is a delicate balance that can be destroyed by simple short-term, seemingly harmless human activity. I'm referring, of course, to the days when everything from air conditioners to hair sprays used chlorofluorocarbons (CFCs) as if it were candy.
There are two basic types of rocket fuels: solid, and liquid. While it's been shown that solid rocket fuel is more destructive to stratospheric ozone than liquid fuels (Ross et al., 2004), both fuel types nonetheless contribute to ozone depletion (Ross et al., 2009).
As it turns out, Virgin Galactic will be using hybrid rocket engines in its SpaceShipTwo. A hybrid engine encorporates both liquid and solid fuel, and the purpose for this is so the engines can be shut off in the case of an emergency. This isn't possible with liquid fuels.
The engines will burn Hydroxyl-terminated polybutadiene (HTPB) and liquid nitrous oxide. HTPB is the same stuff used by the Delta II rockets. It was shown that Delta II rockets destroyed up to 40% of the ozone in the presence of their wake by the expanding rocket plumes (Ross et al., 1997). While global stratospheric ozone isn't generally threatened by the current rate of rocket launches using solid fuels, the potential increase of launches may begin to have a negative effect. For instance, according to their website, Virgin Galactic aims to be flying their SpaceShipTwo with "high frequency".
The combustion of solid rocket fuel spawns chlroine in the exhaust that originates from the ammonium perchlorate present in the fuel (Ko et al., 1994). Another chlorine source comes from afterburning, which can lead to a reaction that converts hydrochloric acid (a primary volatile created by combustion in solid rocket motor plumes) to pure chlorine molecules (Martin, 1994).
Chlorine combines with ozone after exposure to sunlight (photolysis) to form a hypochlorite (a chlorine-bearing molecule), and diatomic oxygen (O2). The hypochlorite combines with another hypochlorite which is quite harmful to ozone because it's able to be recycled, and therefore available to destroy another ozone molecule again and again and again (Lohn and Wong, 1996). On average, 5 to 10 molecules of ozone are consumed by every chlorine atom deposited in a rocket's plume. It has been established that chlorine is the biggest contributor to ozone destruction resulting from rocket plumes (Ibid.).
Fortunately most, including the U.S. Department of Defense, have begun getting away from the use of HTPB. Let's hope Virgin Galactic's does too, or at least hope their idea of "high frequency", isn't on the order of Elon Musk's idea of high frequency resupply missions to Mars.
Anyway, I think we have to prioritize our future goals as a species, and do so with future generations in mind. We ought to look to the future through the sometimes harsh, but thoughtful lens of critical thinking before we leap forward, or become indiscriminately awed, and blindly supportive of ideas that could ultimately subvert us all.
Opening space up to tourism, commercialization, industrialization, colonization, or whatever else kind of 'ation there is, may have the same detrimental effects on our climate and terrestrial environment, that tourism, commercialization, industrialization, and colonization have had on... well, our climate and environment.
It seems we've been here before.
Ah, but historical recurrence has practically become an axiom of human nature over the centuries. I hope I'm wrong about that.
Our hopes and aspirations for a better tomorrow, in whatever capacity we think that ought to be, should be approached mindfully so that those dreams can be fine tuned if need be.
This careful progress will help ensure we truly do achieve a better tomorrow. And a better tomorrow for us, should invariably include a better tomorrow for every other living thing on this planet. If we continue to take leaps and bounds forward with reckless abandon, as appears to be the case insofar as I can see, then I'm afraid our continued blind technological optimism will ultimately be stomped out by the many elephants standing in the room right before us.
As always, thanks for reading.