CSF Clarifies Assumptions in Scientific Paper About Space Tourism Pollution



The Commercial Spaceflight Federation and its member organizations, including five providers of commercial reusable suborbital spaceflight services, supports the kind of scientific inquiry that led to the recent Ross et al. Geophysical Research Letters paper titled, “Potential Climate Impact of Black Carbon Emitted by Rockets.” The commercial spaceflight sector aspires to good environmental stewardship.

In an attached fact sheet, the Commercial Spaceflight Federation has clarified several assumptions used by Ross et al in their model-based analysis. Ross et al may have dramatically overestimated the actual environmental impact of reusable suborbital vehicles.

The Commercial Spaceflight Federation, working with its scientific advisory panel, the Suborbital Applications Researchers Group (SARG), and its suborbital spaceflight provider members, is exploring ways the industry can provide research opportunities to document the actual levels of emissions made by suborbital launches through ground test and in-flight experiments. The Commercial Spaceflight Federation is also assembling a panel of independent experts to provide recommendations to the industry and researchers.

The suborbital vehicles now in development will significantly benefit scientific research, particularly climate science, by allowing previously unparalleled access to parts of the upper atmosphere where atmospheric phenomena concerning global change may take place. Toward this end, the Commercial Spaceflight Federation and its suborbital provider members are working with NASA and NOAA on programs to deploy these vehicles and their valuable capabilities as new platforms for scientific instruments. At industry workshops held at the American Geophysical Union annual conference and the Next Generation Suborbital Researchers conferences, the industry received an enthusiastic response from scientists eager to use these new vehicles in their research.

The commercial spaceflight industry looks forward to the coming era of commercially reusable suborbital spaceflight and research, and the Commercial Spaceflight Federation commits to a proactive stewardship of the atmosphere through which these vehicles will fly.

Bretton Alexander, President of the Commercial Spaceflight Federation, commented, “The commercial spaceflight industry is deeply committed to protecting the environment and the priceless planet that we call home. Indeed, the ‘overview effect’ of traveling to space is well-known. Those who are blessed with seeing our fragile blue marble from space always return with a reinvigorated passion to protect it.” Alexander added, “Rocket launches are critical for understanding the environment. The NASA and NOAA space programs that provide us with critical atmospheric and climate data were all launched on rockets and would not have been possible without them. Now the new commercial suborbital vehicles in development will allow access to space that the science community has never before had, including for atmospheric and climate data that was previously out of reach.”


Regarding Assumptions Used in the Geophysical Research Letters Paper
Titled “Potential Climate Impact of Black Carbon Emitted by Rockets”

  • Each of the planned commercial suborbital vehicles has differing combinations of flight profile, anticipated flight rate, and propulsion technology. This means that the specific and idealized assumptions inherent in the Ross et al. study cannot be extended to include the general class of commercial suborbital vehicles.
  • As stated in Ross et al., there are many unknowns related to the microphysical properties of the exhaust particles, including size, structure, composition, and coagulation rates. Accordingly, the range of uncertainty in the models could be large and such ambiguities could significantly change the magnitude of the results, yet the paper includes no estimate of margin of error or a range of values for their findings.
  • The Ross et al. (2010) research paper assumes 10,000 kg of propellant per launch, but this is well in excess of the propellant load for most suborbital vehicles. For example, Virgin Galactic’s SpaceShipTwo only has a 6,600 kg propellant load.
  • For liquid oxygen/kerosene engines, Ross et al. assumes that they produce 20-40 grams of soot per kilogram of propellant. The lower value of 20g/kg is derived from measurements of an obsolete launch vehicle with 1950′s engine technology. A review of the modern literature, including Rocket Exhaust Plume Phenomenology (Simmons, 2010), suggests that modern engines, which use more oxygen and less fuel, should be an order of magnitude cleaner.
  • Ross et al. reports the results of modeling of complex propulsion phenomena and the interaction and effects of propulsion systems on our complex atmosphere. While modeling can serve as a guide to potential effects, only the actual observation of such effects during ground and flight-testing can deliver definitive results regarding environmental impacts, whether large or small.
  • It is not yet clear whether Ross et al. included in their analysis the carbon particles present in the stratosphere from various sources, including natural processes such as meteorite dust. Estimates by the Intergovernmental Panel on Climate Change (IPCC), a scientific intergovernmental body of the United Nations, of the quantity of soot already in the stratosphere are many times greater than the hypothesized emissions assumed by Ross et al