Space tourism: what about the environmental balance?

By Eloise Marais for La Conversation,

The business race to get tourists to space is intensifying between Virgin Group founder Sir Richard Branson and former Amazon CEO Jeff Bezos. On Sunday, July 11, Branson traveled 80 km to reach the edge of space in his Virgin Galactic VSS Unity piloted space plane. Bezos’ Blue Origin autonomous rocket launched on July 20, coinciding with the anniversary of the Apollo 11 moon landing.

The launch demonstrated their offer to very wealthy tourists: the possibility of truly reaching outer space. Both sightseeing packages will provide passengers with a brief ten-minute weightless frenzy and glimpses of Earth from space. Not to be outdone, Elon Musk’s SpaceX will provide four to five days of orbital travel with his Crew Dragon capsule later in 2021.

What can be the environmental consequences of a space tourism industry? Bezos boasts that its Blue Origin rockets are greener than Branson’s VSS Unity.

The Blue Engine 3 (BE-3) used liquid hydrogen and liquid oxygen propellants. VSS Unity used a hybrid propellant consisting of a carbon-based solid fuel, hydroxyl-terminated polybutadiene (HTPB) and a liquid oxidant, nitrous oxide (laughing gas). The SpaceX Falcon reusable rocket series will propel the Crew Dragon into orbit using liquid kerosene and liquid oxygen.

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The combustion of these thrusters provides the energy necessary to launch rockets into space while generating greenhouse gases and air pollutants. Large amounts of water vapor are produced by burning the BE-3 propellant, while the combustion of VSS Unity and Falcon fuels produces COâ‚‚, soot and some water vapor. The nitrogen-based oxidant used by VSS Unity also generates nitrogen oxides, compounds that contribute to air pollution closer to Earth.

About two-thirds of propellant exhaust gases are released into the stratosphere (12 km-50 km) and the mesosphere (50 km-85 km), where they can persist for at least two to three years. The very high temperatures during launch and reentry (when the protective heat shields of return craft burn out) also convert stable nitrogen in the air to reactive nitrogen oxides.

These gases and particles have many negative effects on the atmosphere. In the stratosphere, nitrogen oxides and chemicals formed from the breakdown of water vapor convert ozone into oxygen, depleting the ozone layer that protects life on Earth from harmful UV rays. Water vapor also produces stratospheric clouds that provide a surface for this reaction to occur at a faster rate than it would otherwise.

Space tourism and climate change

COâ‚‚ and soot exhaust gases trap heat in the atmosphere, contributing to global warming. Cooling of the atmosphere can also occur, as clouds formed from emitted water vapor reflect incoming sunlight back to space. A depleted ozone layer would also absorb less incoming sunlight, and therefore heat the stratosphere less.

Determining the overall effect of rocket launches on the atmosphere will require detailed modeling, in order to account for these complex processes and the persistence of these pollutants in the upper atmosphere. Equally important is a clear understanding of how the space tourism industry will develop.

Virgin Galactic plans to offer 400 space flights each year to the privileged few who can afford it. Blue Origin and SpaceX have yet to announce their plans. But on a global scale, rocket launches would not need to increase much from the current hundred carried out each year to induce competitive harmful effects with other sources, such as chlorofluorocarbons (CFCs) depleting the population. ozone layer and COâ‚‚ from airplanes.

When launched, rockets can emit between four and ten times more nitrogen oxides than Drax, the UK’s largest thermal power plant, over the same period. The COâ‚‚ emissions of the four or so tourists on a space flight will be between 50 and 100 times higher than those of one to three tonnes per passenger on a long-haul flight.

In order for international regulators to keep up with this nascent industry and properly control its pollution, scientists need to better understand the effect these billionaire astronauts will have on our planet’s atmosphere.

(The author is Associate Professor in Physical Geography, UCL)

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