Commercial space travel on private rocket ships took a major step toward reality on Oct. 25 with the dedication of a nearly two-mile-long runway at the Spaceport America "operating hub" north of Las Cruces, N.M. Each flight will take passengers 62.5 miles above the Earth into weightless space, remain there four or five minutes, and then return to Earth.
On hand was Sir Richard Branson, chairman of the Virgin Group; Bill Richardson, New Mexico's governor and the former U.S. Energy secretary; and about 30 civilian "future astronauts" planning space travel via Branson's company, Virgin Galactic.
But at a time when a half-dozen U.S. companies are vying to be the first to bring tourists to space, a report to be published in November in the journal Geophysical Research Letters warns that fuel emissions from such rocket launches may pose serious consequences for the Earth's stratosphere—causing as much as a 1-degree Centigrade rise in polar temperatures and a 5 percent to 15 percent reduction in polar ice.
The study looked at the emissions that could be expected in the stratosphere from rocket engines.
"What we've discovered from these [engineering] models is that the stratosphere is particularly sensitive to black carbon particles, commonly called 'soot,' from rocket engines," explained study co-author Martin Ross, an atmosphere scientist with The Aerospace Corporation, a Los Angeles–based, federally funded research and development nonprofit organization that provides guidance and technical advice to military and civilian space operations.
The scientists modeled their projections on commercial space industry estimates that predict 1,000 suborbital commercial space flights annually within 10 years. According to the study, a thousand flights per year could add as much as 600 tons of soot to the stratosphere, trapping more heat there.
"Once these particles are put in the stratosphere, they stay there for years," Ross said.
The potential danger from soot, or black carbon, is the journal article's key finding, because, as Ross explained, "The effect of the soot is about 100,000 times the effect of the carbon dioxide [emitted by rockets]."
While CO2 emissions from rockets is "minuscule," Ross said, the "radiative forcing," or warming, that would result from the soot emitted by these commercial rockets "would be comparable to the radiative forcing from carbon dioxide from all of aviation."
If industry estimates of commercial space flights hold true, the level of soot in the atmosphere will increase tenfold, according to the study.
Representatives Say Fledging Industry Is Being Responsible
Deron Lovaas, transportation policy director for the Natural Resources Defense Council, said these findings are of note because of the "black carbon effect at the suborbital level. That's a big concern."
Lovaas said that before the study came out he likened commercial space travel to a Bentley sports car—a plaything for the uberrich. Unlike an economy seat on a commercial airline today, at $200,000 per ticket the flights are out of reach of the vast majority of people, potentially limiting space tourism's environmental impact.
The study has made him reconsider. "I realize now that we need to take a close look and make sure the industry is developing responsibly," he said.
Industry decision-makers say they are being responsible. "Environmental impact has been part of the decision matrix that the company has considered since the beginning," George Whitesides, CEO of Virgin Galactic, told SolveClimate News. The New Mexico–based airline plans to launch suborbital flights within three years. "The issue is one we take seriously."
Said Rick Homans, executive director of Spaceport America, where Galactic is the anchor tenant: "I think that as the industry moves forward, it wants to do this in the cleanest way possible and avoid any kind of damage to the planet."
Virgin Galactic is competing with several other companies in California and the Southwest to be the first in commercial space, including XCOR in Mojave, California; Armadillo Aerospace in Rockwall, TX; Sierra Nevada Corp. in Sparks, NV; Masten Space Systems in Mojave, CA; and SPACEX in Hawthorne, CA. There's also a broker, Space Adventures, in Vienna, VA.
Galactic deliberately chose to use hybrid rocket fuel, which combines the properties of liquid and solid rocket fuel, Whitesides said. Galactic also constructed its space vehicles from an all-carbon composite because it's lighter and can take a smaller engine, requiring less propulsive force, and therefore less fuel.
"These are choices we've made that have a lower environmental impact," Whitesides said.
Criticism of Study, and a Response
Whitesides had two major criticisms of the study. "One of the things that's a little disappointing is that the authors didn't include a range of uncertainty in their model," he said. "What's the confidence around that number? I don't think we know that."
"Given the lack of detailed knowledge of the microphysical rocket black carbon and an unknown growth rate of the space transport sector, we cannot place a formal uncertainty on our model," Ross said. "There are no measurements of soot from rocket engines of any kind, whether they're 50 years old or are going to be used 10 years from now."
Whitesides also said the amount of fuel propulsion used in the simulation is twice what Virgin Galactic would use in a typical launch. Moroever, that amount—up to 20,000 pounds per launch—is a fraction of what is employed in current global rocket launches. "The [NASA] shuttle flies five times a year, so you're talking about five million pounds of solid propulsion being burned every year—which is roughly a thousand times one of our flights. And they've been doing it for 30 years.
"I don't think anyone is attributing a .4 degree change in temperature to the space shuttle program," Whitesides said.
Ross said the Space Shuttle has been the subject of a "modest amount" of scientific inquiry, which he has been involved in, since the 1990s. It focused on the impact of chlorine from solid rocket fuel on the ozone layer. "I am not aware of scientific studies of the climate impact of solid rocket motors of the type that the Space Shuttle uses," Ross said.
Both Whitesides and Homans said they may be among the industry representatives at a conference The Aerospace Corporation is planning to host in January. The details are still being developed, but the emissions issue will be front and center at that conference, according to an Aerospace Corporation spokesman.
Industry positions will be key indicators for how the emerging sector handles concerns about emissions, said NRDC's Lovaas. "It's kind of an extra burden on the leaders in this new industry to make sure they're responsible," he said. "A lot of people are going to be paying attention."
Image: Mike Miley via flckr Creative Commons license