What impact will commercial space flight have on the environment?

Scientists are concerned that the growth of space tourism will have unanticipated consequences for the Earth’s climate. Is the impact of rocket launches on the atmosphere truly insignificant?

What impact will commercial space flight have on the environment?…… Scientists are concerned that the increased number of rocket launches and the advent of space tourism would affect the Earth’s atmosphere and contribute to climate change.

When billionaires Richard Branson and Jeff Bezos flew into space this month in their firms’ suborbital tourist aircraft, the entire world applauded.

However, for some scientists, these anniversaries marked more than just a technological achievement. After years of delays and considerable obstacles, the flights signalled the potential start of a long-awaited era in which rockets would fly into the so-far relatively clean upper layers of the atmosphere significantly more frequently than they do now. In the case of SpaceShipTwo, the ship controlled by Branson’s Virgin Galactic, these trips are powered by a hybrid engine that burns rubber and emits a cloud of soot.

“Hybrid engines can use different types of fuels, but they always produce a lot of soot,” said Filippo Maggi, an associate professor of aerospace engineering at Politecnico di Milano in Italy who studies rocket propulsion technologies and was part of a team that published an extensive analysis of hybrid rocket engine emissions several years ago. “These engines burn like a candle, and their combustion process creates conditions conducive to soot generation.”

According to Dallas Kasaboski, chief analyst at space consultancy Northern Sky Research, a single Virgin Galactic suborbital space tourism flight lasting around an hour and a half may produce as much pollution as a 10-hour trans-Atlantic journey. Some scientists find this disturbing, especially in light of Virgin Galactic’s plans to transport paying visitors to the edge of space many times each day.

“Even if the suborbital tourist sector launches at a quarter of the rate of the rest of the [tourism] business, each of their trips has a far bigger contribution, which might be an issue,” Kasaboski told Space.com.

Of course, Virgin Galactic’s rockets are not the only perpetrators. According to Maggi, all rocket motors that run on hydrocarbon fuel produce soot. Solid rocket engines, such as those used in NASA’s space shuttle boosters in the past, burn metallic compounds and release aluminium oxide particles together with hydrochloric acid, both of which are harmful to the atmosphere.

The BE-3 engine, which powers Blue Origin’s New Shepard suborbital vehicle, on the other hand, generates propulsion by combining liquid hydrogen and liquid oxygen. According to experts, the BE-3 is not a major polluter when compared to other rocket engines, producing mostly water and a few minor combustion products.

Too little is known.

The biggest issue, according to Karen Rosenlof, senior scientist at the National Oceanic and Atmospheric Administration’s (NOAA) Chemical Sciences Laboratory, is that rockets pollute the higher layers of the atmosphere — the stratosphere, which begins at about 6.2 miles (10 kilometres) and the mesosphere, which begins at 31 miles (50 km).

“You’re generating contaminants in regions where you wouldn’t ordinarily transmit them,” Rosenlof told Space.com. “We must comprehend. What is the possible harm if we raise these factors?”

According to Martin Ross, an atmospheric scientist at the Aerospace Corporation who frequently collaborates with Rosenlof, the influence of rocket launches on the environment has been minor thus far. However, this is due to the fact that there haven’t been many launches.

“The quantity of fuel now consumed by the space industry is less than 1% of the fuel consumed by aviation,” Ross told Space.com. “As a result, there haven’t been a lot of studies, which makes sense. However, things are evolving in such a way that we need to understand more about this.”

Northern Sky Research expects that the number of space tourism flights would increase dramatically over the next decade, from perhaps 10 per year in the near future to 360 per year by 2030, according to Kasaboski. This forecast is still considerably below the rate of expansion that space tourism businesses such as Virgin Galactic and Blue Origin anticipate.

Kasaboski stated, “Demand for suborbital tourism is really strong.” “Because these businesses have people standing in line, they want to expand. They would eventually want to fly many times every day, exactly like short-haul planes.”

The number of rocket launches bringing satellites into orbit is also likely to increase. However, Kasaboski believes that space tourism has a greater potential for expansion.

“It’s like the difference between a cargo aircraft and a passenger flight,” Kasaboski explained. “There are a lot more passengers that want to travel.”

According to Ross, the difficulty is that the scientific community has no notion and insufficient data to predict when rocket launches will begin to have a quantifiable influence on the planet’s climate. At the same time, the stratosphere is altering as the number of rocket launches steadily increases.

“The impacts of these [rocket-generated] particles are not well known even to an order of magnitude, a factor of ten,” Ross added. “The uncertainty is tremendous, and we need to narrow it down and estimate how space can effect the atmosphere.”

ozone holes in the space shuttle

The only direct observations of the effects of rocket launches on chemical processes in the atmosphere to date are from the space shuttle era. In the 1990s, as the globe worked to repair the ozone layer, NASA, NOAA, and the U.S. The Air Force developed a programme to investigate the effects of ozone in the stratosphere caused by emissions from the space shuttle’s solid-fuel boosters.

“There were big worries about chlorine from solid rocket engines in the 1990s,” Ross added. “Chlorine is the enemy of ozone in the stratosphere, and some models predicted that ozone depletion from solid rocket motors would be severe.”

The scientists flew through the plumes created by the space shuttle rockets in Florida using NASA’s WB 57 high-altitude aeroplane. They were able to quantify the chemical reactions in the lower stratosphere soon after the rockets passed by, reaching altitudes of up to 60,000 feet (19 km).

“One of the main issues was how much chlorine is produced in these solid rocket engines and in what form,” David Fahey, the director of NOAA’s Chemical Sciences Laboratory, who conducted the study, told Space.com. “We measured it multiple times and then examined the findings. There were not enough space shuttle missions at the time to make a worldwide influence, but the dispersed plume [left behind by the rocket] may degrade the ozone layer locally.”

The space shuttle was retired ten years ago, but rockets emitting ozone-depleting compounds continue to deliver astronauts and satellites into space today.

In fact, the World Meteorological Organization identified rockets as a potential future issue in its latest Scientific Assessment of Ozone Depletion, which is published every four years. As the number of launches is projected to rise, the group has urged for additional study to be conducted.

Worse than geoengineering, in fact.

Using sophisticated NOAA supercomputers, Rosenlof’s team investigates the larger impacts of man-made compounds in the upper layers of the atmosphere. The work is analogous to anticipating the legendary butterfly effect, or the impact of minute changes in the chemistry of the air tens of miles above Earth on climate and weather patterns on Earth. Black carbon, or soot, created by rockets using hydrocarbon fuels is a particular source of concern for her.

“The issue with soot is that it absorbs ultraviolet light, which means it might heat up the stratosphere,” Rosenlof explained. “When the stratosphere, the layer above the troposphere [closest to the earth], is heated, the motion in the stratosphere changes. You are altering the energy transmission, which may have an effect on what is occurring on the ground.”

According to Rosenlof, many of the particles produced by some rockets have piqued the interest of scientists due to the potential effects they could have on the global climate in a different context — that of geoengineering, or the deliberate tampering with the atmosphere with the goal of stopping or mitigating global warming.

Rosenlof recently co-authored an article in which he utilised the same powerful NOAA supercomputers to simulate what scientists refer to as a climate intervention. The researchers were interested in the climate impacts of dispersing sulphur dioxide particles, which are known to reflect light away from Earth, in the lower stratosphere, in conjunction with soot (which is also part of rocket emissions). Soot absorbs solar energy and raises the height of sulphur dioxide aerosol particles by warming the surrounding air. Sulfur dioxide can begin its climate-cooling effect at a higher altitude. The experiment simulated what would happen if aeroplanes released 1.1 million tonnes of sunlight-reflecting sulphur dioxide mixed with 11,000 tonnes of black carbon into the upper troposphere during a 10-day period.

The study found no major detrimental consequences on Earth’s weather. Those findings, however, do not allay Rosenlof’s concerns about the potential hazards linked with the increasing frequency of rocket launches.

Changing the jet stream

“The black carbon in our geoengineering experiment isn’t as high as the material from these rockets,” she explained. “The issue is that when you ascend, something lasts longer. Neither is ideal since they would generate heat in regions where we do not already have heating.”

Maggi claims that the soot particles produced by hybrid rocket engines are incredibly tiny and light-weight. In fact, when he and his colleagues attempted to quantify the soot production of hybrid rocket engines in a laboratory, they were unable to do so reliably and precisely due to the particles’ small size.

Maggi explained, “We were able to detect the particle production from solid rocket engines.” “These are roughly the size of a micron, and there are a lot of them. However, due to their size, they fall to the ground more swiftly. We were unable to gather soot from the plume using hybrid rocket engines because it is so thin, only a few nanometres in size.”

Maggi is concerned that these particles will remain in the stratosphere indefinitely.

“They’re the same size as the carbon generated by planes,” Maggi explained. “And we know that there is a layer of carbon in the atmosphere at aeroplane flying levels that is permanent. Particles emitted by rocket engines are extremely likely to accomplish the same.”

The experts are concerned about the buildup of these particles over years and decades. Just as the current climate catastrophe began slowly as the quantity of carbon released into the atmosphere increased, pollution in the stratosphere may not cause harm for several years.

Injecting pollutants into the stratosphere, according to Rosenlof, might disrupt the polar jet stream, winter storm patterns, and average rainfall in the long run.

“You may go from 25 inches [64 centimetres] a year to 20 inches [51 centimetres] a year in certain locations, which might not sound like a significant issue unless you’re a farmer trying to grow your wheat right there,” Rosenlof explained. “Then a slight difference in rainfall can have an effect on agricultural output.”

Work to be done

As a result, according to Fahey, it is vital that scientific research begin immediately to assess potential hazards.

“There is this basic gap where we just don’t have the data, and that implies that the research is constrained because of this lack of knowledge,” he explained. “We believe it is part of our [NOAA] obligation to examine the impact of human activity on the stratosphere. Rockets are a major and unique source of stratospheric pollution; launch frequency are growing, and the impacts are compounding.”

Fahey proposes a larger study programme that would investigate the emissions and effects of several types of rocket engines and fuels on the stratosphere. The data might be utilised in Rosenlof’s models to better anticipate the impacts based on the predicted increase in the number of launches. Fahey, on the other hand, believes that a political decision must be made first in order to give NOAA and its partners with financing to allow them to fly the high-altitude aircraft again and collect data. The good news, he noted, is that the United States Congress appears to be aware of the issue, and things may soon begin to move.