This story is part of a special PopularScience.com series on the future of energy.
Virgin Galactic proudly touts the fact that each of the passengers who will fly into sub-orbital space on its SpaceShip2 will emit less carbon dioxide than a typical air passenger on a flight from New York to London. But some scientists say carbon dioxide emissions are irrelevant to measuring the greenhouse gas footprint of the nascent space tourism industry. The big threat from the scaling-up of space travel, they say, comes from something called black carbon—a type of particulate matter that, when hurled into the stratosphere, builds up for years, absorbing visible light from the sun. According to one study, black carbon emitted into the stratosphere by rockets would absorb 100,000 times as much energy as the CO2 emitted by those rockets.
"There's one issue and it's simple: you don't want to put black carbon in the stratosphere. Period," says Darin Toohey, a professor of atmospheric and oceanic sciences at the University of Colorado, Boulder. Industry insiders say otherwise. Who's right?
Black carbon should be familiar to anyone who's ever idled behind a diesel truck or sat by a wood stove: it's what makes soot black. Formed from the incomplete combustion of fossil fuel, biofuel, and biomass, it is emitted directly into the atmosphere and absorbs about a million times more energy than CO2. According to one study, it is Earth's second largest contributor to climate change, after carbon dioxide. The reason black carbon doesn't wreak more havoc on the environment is that it has a short lifetime in the lower atmosphere—precipitation washes away black carbon emissions from planes and other sources within a matter of weeks.
Not so in the stratosphere, which begins as low as 5 miles above the Earth and rises up to about 31 miles. Rockets need to scream through the stratosphere to the point 62 miles above the sea level, where space is conventionally said to begin. They are also the only direct source of human-created compounds above 12 miles. Because there is no rain or other atmospheric factors to wash out the black carbon in the stratosphere, black carbon would linger for 5 to 10 years or more. Moroever, rockets produce over 1,000 times more black carbon per unit of fuel than standard aircraft.
So in 2010, Toohey and Martin Ross, the head of the Center for Launch Emissions Analysis and Research at Aerospace Corporation, and Michael Mills of the National Center for Atmospheric Research,crunched the numbers to estimate the black carbon effects of a hypothetical 1,000 flight-per-year industry. They measured the black carbon's "radiative forcing" – a metric for how much extra energy the Earth and its atmosphere absorb from a given manmade or natural phenomena. The radiative forcing from the black carbon that rockets placed in the stratosphere was up to 100,000 times greater than that of the CO2 released by the rockets. (In contrast, the radiative forcing of the black carbon placed for just a few weeks into the atmosphere by jets is less than 1/10 of that of its carbon dioxide).
Here's where space tourism comes into play: The number of space launches annually around the world numbers around 70 today, but that figure could rise drastically, as private companies jockey to turn space tourism into routine adventure travel. The aerospace research firm Futron forecasts that by 2021 the space tourism market will consist of 13,000 potential customers, with possible revenues of roughly $650 million per year. Assuming the business is successful, commercial space travel might very well reach 1,000 launches per year some time in the next decade – XCOR alone plans to ramp up to four launches per day, as part of its "Southwest airlines" model. That creates 1,000 opportunities to shoot black carbon directly into the stratosphere. The amount of black carbon emitted during combustion on Earth, or in the trophosphere, where airlines fly, tends to be low, because of the relatively rich supply of oxygen. Once you get into the stratosphere, where low pressure leads to less oxygen, black carbon can amount to as much as 5% of the products of combustion.
The Federal Aviation Administration (F.A.A.), the organization responsible for assessing environmental impacts and deciding whether to grant licenses to launch vehicles into space, says the effects of black carbon in the stratosphere are unclear. "Although black carbon is known to be a short-term climate forcer, research on the potential climate change impacts of black carbon from rockets is in a very early stage, and any projections of impacts are speculative," writes George Nield, the F.A.A.'s associate administrator for commercial space transportation, in an email.
The space-tourism industry has downplayed black carbon's potential harm. Virgin Galactic declined repeated inquiries to comment. Andrew Nelson, the chief operating officer of XCOR Aerospace, which is currently selling $95,000 tickets for sub-orbital flights, says that the blend of kerosene and liquid oxygen in his XR-5K18 rocket engine powering its Lynx suborbital spaceplane will emit much less in the way of "aromatic" hydrocarbons than traditional kerosene-based rocket fuel. And he says the XR-5K18 will burn much more cleanly than the solid rocket boosters used in the Space Shuttle or "hybrid" rocket engines, which burn both solid and liquid propellant.
"XCOR will have di minimus impact on our environment," Nelson says. "Our fuels are almost completely free of particulate matter. [They have ] 20-40 times less aromatics than traditional rocket fuels, and hundreds, if not thousands of times less particulate matter than hybrids or solids. So the concern about carbon or other particles is moot for us."
Toohey still wants to see peer-reviewed studies of the actual interaction of XCOR and other engines with the stratosphere. "I have not seen any publications that confirm (or refute) the claims of particle-free emissions from combustion of any fuel in the upper atmosphere," Toohey says. "So I think it is fair to say that we need studies to benchmark the emissions of all rocket types in order to be able to assess their impacts."
Seriously? How many tourists do these scientists think we are talking about here? Unless we fly them into orbit one by one for twenty years I don't see pollution being a big problem.
Whatever happened to LOX and liquid hydrogen?
Haha, rockets... so last millennium. What we need is some electromagnetic propulsion. That's the only way space tourism will ever kick off. Rocket propelled anything will soon be nothing more than bright, loud, and noxious memories.
We need electromagnetic RAIL launch and once the craft is high enough and escapes into space, launch the ion nuclear engines!
If black carbon is such a problem, why didn't they mention it during NASA flights? Answer: they are only worried about private companies not the government.
There's no satisfying climate scientists... We will never succeed in doing anything without a little risk or harm. There are so many solutions to Earth's problems outside of our atmosphere. If we need to do a little harm to do a lot of good I think we should! Otherwise we can sit here and complain about everything from water bottles to refrigerators.
Looeiwu...my thoughts exactly on reading this article.
Even if the above mentioned transportation systems are not designed for using hydrogen as a fuel, I am happy that the Skylon spaceplane that Reaction Engines is developing is.
@killert and dagwood52
Space tourism companies are striving to become a regular thing in society's vacation plans. Current space flight, government and private, is too intermittent to be too much of and issue. These scientists are just pointing out the potential problems before the space tourism industry is large enough to cause large scale problems. Its easier to grow around the need to minimize pollution than to completely overhaul the industry when it becomes a problem.
Electromagnetic rail launching is not a feasible option for space launches. You simply cannot launch anything fast enough from the earth without ongoing thrust to get it into orbit. It would take speeds and acceleration that would destroy the vehicle long before it left the end of the rail. You have to have continuous force on the spacecraft if you want a realistic shot at getting it into orbit.
Ion engines just don't have the needed thrust to leave earth. They are great for long-distance travel in space, but don't have enough thrust to even consider as launch vehicles.
The only real and feasible option for satisfying the long-term requirements of drastically cutting the price to put anything into space, deal with environmental issues, and minimize space junk, is a space elevator. The technologies needed for such an endeavor are just now getting to the point where it could be technically feasible in the next decade. It would be a large up-front cost, but would easily pay for itself over time.
I say we divert all funding from projects that are "too far forward" as I like to call them and divert most our space funding to building a space elevator. We would enlist other partner countries in this as well, but mostly on the funding and technical expertise side (no need to have a manufacturing debacle). Once deployed the space elevator could then be used by the member countries and also (for a fee) by private organizations/companies.
It is doable with the same kind of effort that we put into the moon shot. And it would be just as big an accomplishment. And the doors that would then be open for bases/colonies/mines on the moon, Mars, and asteroids/comets would be tremendous. I really believe that we could be exploring/colonizing nearby moons/planets much faster than we realize, and that by far the best way to do so is by starting with the construction of a space elevator.
Well then, lets go to the moon and begin lowering the cable for the space elevator asap!
Besides, the moon is gently leaving the Earth in orbit anyways. We can use this to our advantage to pull the cable on Earth and create energy as well, thereby paying for the elevator or more once established.
After the elevator is clearly establish, we can then send back to Earth helium3 for more energy production. Say maybe we generate electricity right on the moon and beam it back to Earth by the cable.
Yes, we need this moon elevator asap!
Rockets need to clean up their act. Well, this puts the screws to most of the smaller outfits now that they've spent years and much treasure. Sure does make for an inviting business climate, too. What's it gonna be next time you need to get all the benefit of public approval for space, but want to squash all competition as well?
I'd imagine it was something along those lines that Virgin Galactic would have talked about if they were as crude as me.
I just gotta say that this is so RUDIMENTARY. If we ain't been thinkin on this previously, we got NO BUSINESS inviting private enterprise to start this push. GROUND THEM ALL.
Apparently, my previous wonderings about who was in charge of regulating this push and what are The Regs were things to wonder about, indeed. I know that it's been assigned, but I don't think this came from them, but rather from people from the climate crowd watching Virgin's launch.
So why is the only response from Xcor? Spaceship 2 uses a hybrid motor with the solid fuel being rubber. You can practically see the carbon output on that thing, so much so the photo almost looks fake with the black shadows within the plume.
Xcor, you're not the problem. you're also not even near the only source.
"Black carbon" in the upper atmosphere absorbs light from the sun. Said heated black carbon does not have any heating affects on the surface as heat rises. If anything It would be counter to the global warming they warn about. It would directly work against CO2, which is only considered a greenhouse gas because it sinks low in the atmosphere and warms the ground level. Warming in the upper atmosphere would seriously not be an issue.
On top of what others have said, LOX and Hydrogen propulsion are better anyway so what's the big deal?
Sulfur back in the fuel reflects the sun back into space. Sulfur was in our gas and fuel. It protected us from global warming, but created acid rain. Up this hi it will be even more effective and last even longer while at the same time create little contribution to acid rain. If Global warming really is an issue controlled targeted sulfur emission is part of the solution because it buys us time for other solutions to reach viability.
The people of Babel had the best-est solutions and ever since those pesky interfering aliens keep holding us humans back....... sigh.
@ Mike13323 Your comment is so nonsensical as to be laughable. It defies logic and common sense. I'm saying it has no place on a website dedicated to science, "There are so many solutions to Earth's problems outside of our atmosphere. If we need to do a little harm to do a lot of good I think we should!"
I'm certain you can not document one feasible solution to Earth's problems outside our atmosphere any more than you can validate "a little harm".
Beyond that you sentiment to do a lot of good is more than welcome.
There are all sorts of solutions to Earth's problems outside of our atmosphere. Not to mention the technologies we will discover to get there.
Nearly every resource humans covet can be found in numerous forms within our solar system. Water, precious metals and gases, room and more. We can solve over population problems and stop exploiting our planet's resources and start exploiting that of asteroids, planetoids and other planets.
Also, space travel has led to numerous inventions that have bettered our lives. Check out this little article:
These are only a few benefits of seeking solutions outside of our atmosphere. The most prominent benefit that has come about in small doses is sustainability. The International Space Station has made some significant steps forward in sustainability, after all, you have to be sustainable to live in such a harsh environment.
I would rather add a little bit of pollution to our atmosphere if it means we can stop drilling, mining and destroying our planet.
I don't believe the regulatory authority of the US government extends into low earth orbit.
@ riff_raff; Go out halfway between Earth and the moon and advertise that you built a nuke. We'll figure out who the regulating bodies are and just what they regulate once and for all.
Seriously, this is my point. ALL of the UN Security Council nations and many others are hellbent for leather with a commercial space push-but no one has The Regs. How is that supposed to work? Virgin is finding out.
Is everyone that goes up required to carry a passport with visas for EARTH? How's dat work? And who gets to appoint who can do legal marriages in space? If an American woman gave birth to a baby in space; that baby would be American. Correct? So if she gave birth on Mars, is the child American? As things are now, that child could never hope to hold an address within the U.S.. Can't vote, correct? Can't hold office? Is some part of Mars or any other world American soil, then? Citizens that get to shut the hell up and take it, as rules are rammed through with no representation?
Just what are required emergency trauma intervention certifications for these spacetaxi drivers? Will they be required to be bilingual? What fuels are legal in Earth Airspace? What will the crash test of SpaceShip2... be required to prove? How many of em do we get to make em each smash for our entertainment? Will those all be broadcast live in 3-D interactive so people can ride them in just for fun? What is the space equivalent of a 5 Star safety Rating? Are they required to have a 5 mph bumper? What are The Limits going to be for these craft regarding radio emissions? Lasers? How much in flight time under power will be required as reserve capability? What kind of rocket motor is required in Earth airspace? What kind of guidelines should all of these people be looking at as they continue pouring in the money on platforms because governments say it's time?
Who cares about the problem? Like really?!