The Space Age Heats Up
Near-earth space, brimming with satellites, is becoming ever more like Earth’s trash-strewn front yard. Now it has a driveway, too. In October workers completed the two-mile long runway at Spaceport America, near Las Cruces, New Mexico, which aims to be the nexus of the burgeoning commercial space-tourism industry. Virgin Galactic hopes to be launching two space flights a day within three years and is said to have reserved 500 seats already, at $200,000 apiece.
But if space flight is to become everyday, it soon may need something that other everyday forms of transportation already require: emissions standards. A recent study found that the sooty output from just 1,000 commercial space flights a year -- well within reason, considering that Virgin Galactic is not likely to be the only carrier ferrying passengers into space -- could be enough to alter Earth’s climate, by raising temperatures, melting sea ice, and altering ozone levels worldwide.
"It’s surreal if you think about it," says Darin Toohey, an atmospheric scientist at the University of Colorado at Boulder and one of the study’s three authors, who with his colleagues modeled the effects of just a few flights a day -- a tiny fraction of the 30,000 commercial airline flights that take off each day in the U.S. alone. "Never in my wildest dreams would I have thought that such a small amount of material would have an impact that significant."
Toohey and lead author Martin Ross, of the Aerospace Corporation, a federally-funded research and development center established to support the U.S. Air Force and government space programs, drew attention last year with a study that looked at the effect of rocket launches on the stratospheric ozone layer. (Short answer: not good. By 2050, rocket exhaust -- which is unregulated, overlooked by the Montreal Protocol, and rich in ozone-depleting chemicals -- could cause more ozone destruction than was ever realized by chlorofluorocarbons.)
To gauge the potential effects of soot on global climate, Ross and Toohey first estimated the black-carbon emissions from 1,000 rocket flights a year, then ran the numbers through the Whole Atmosphere Community Climate Model, a standard tool for modeling how earth’s climate might respond to various inputs. The results were both predictable (to an atmospheric scientist) and eye-opening.
The launches create a persistent soot cloud in the northern hemisphere above Spaceport America (the sole source of the flights in the model). The surface temperature in its shadow falls by half a degree, while the atmospheric temperature there rises. Those changes in turn alter the wind and circulation patterns in the atmosphere, redistributing ozone: ozone levels above the tropics drop by 1 percent and rise at the poles by as much as 6 percent. Meanwhile, surface temperatures at the poles rise by a full degree at certain times of year, and the area of sea ice shrinks by as much as 15 percent.
Commercial space flight is taking off, thanks in part to funding initiatives from NASA. The immediate push is into the suborbital realm, roughly 60 miles up into the stratosphere. One estimate puts the demand at more than 13,000 flights annually by the year 2021, limited mainly by the number of available spaceports on Earth. Many prospective customers are wealthy tourists, but scientists -- astronomers, microgravity researchers -- have a keen interest too.
The rise of a new, economical rocket that uses a hybrid of liquid and solid fuels is also to blame, or thank, depending on your perspective, for the rise of commercial space flight. This new rocket also spews black carbon, which absorbs sunlight and can warm the atmosphere. At low altitudes, such as those flown by commercial jetliners, black carbon settles to the ground within days or weeks. But rockets inject it directly into the stratosphere, at an altitude of more than 25 miles -- several times higher than airline altitudes -- where it can linger for years and, as space flights become more frequent, will quickly accumulate.
Toohey is quick to emphasize that their study is less a forecast than a gauge of the planet’s response. Still, the degree of sensitivity "is surprising," Mills says. "We can’t just assume that the things we worry about with surface emissions, like carbon dioxide, are the only things we’ll be worried about going forward."
The authors collectively agree that the study is a first pass. There are uncertainties to iron out, more parameters to explore. "We need actual measurements of particles in rocket plumes, that’s never been done," Ross says. "We need to get a high-altitude aircraft, load it up with instruments, fly into a plume, measure the size and shape of particles and how quickly they fall out of stratosphere. And it should be done for different kinds of hydrocarbon engines -- not just the hybrid ones but the good ol’ kerosene engines we’ve been using for half a century."
Such research requires money and will. But the concern is great enough that the Aerospace Corporation will convene a workshop -- the Rocket Emissions and Climate Workshop, unofficially -- in January to advance it. Researchers, industry leaders, and policy-makers will be encouraged to attend, "so everyone understands where we’re coming from, what the uncertainties are, and what kind of program we need to organize," Ross says.
Tourism presents us with something like the Heisenberg uncertainty principle writ large. How many visitors can enjoy a site -- a campground, a wildlife refuge, the Galapagos -- before the object of attention is altered? At what point does observation become degradation? The axiom now applies to the earth as a whole, it seems. In some corners, space exploration is considered a moral mandate: We must venture beyond earth because our own planet eventually will become uninhabitable. Alas, that may be. Please, just don’t slam the door on the way out.