Falling space debris could increasingly affect airline traffic, research finds

A new study from researchers at the University of British Columbia (UBC) is flagging the fact that falling rocket debris will increasingly be an issue for airplane traffic, becoming a more frequent reason for airspace closures and flight delays. 

When the SpaceX Starship exploded over the Caribbean in January, people in the Turks and Caicos were treated to a spectacular fireworks display as the flaming wreckage re-entered the atmosphere over their island homes.

Thankfully, no one was injured. But the event did cause a problem for air traffic controllers who had to re-route airliners around the area to avoid collisions with the space debris, causing delays and diversions for passengers.

Delays and diversions are annoying and expensive, but necessary to avoid the small potential of space debris hitting an aircraft. The study warns that "while the probability of a strike is low, the consequences could be catastrophic" and lead to "mass casualties."

The researchers found that the chance of debris entering air space around major cities is as high as 26 per cent per year in areas such as the Northeastern U.S., Northern Europe and major cities in the Asia-Pacific region –– and this will inevitably go up as the number of rocket launches and passenger flights rise each year.

The space industry is moving toward re-usable rockets, which means the big first-stage boosters return to the launch pad. In fact, the SpaceX Starship that exploded is designed to return for reuse in future flights. Those boosters, assuming they return successfully, won't be a problem. 

But many rockets that launch satellites have upper stages — the parts that boost them up to their final orbit — and these eventually fall back to Earth. The problem is this re-entry is both uncontrolled and unpredictable.

It could take months or years depending on how high the orbit is. What's more, the satellites themselves, if they operate in lower orbits, can eventually fall out of that orbit and back down to Earth.

This has been the practice since the very beginning of the space program and is based on the assumption that most of these objects will burn up high in the atmosphere, and any material that does make it all the way down to the surface will likely fall in an ocean, since most of the Earth is covered in water, or debris will land in a remote area.

For most of our history in space this has proved to be the case. A significant exception is that large pieces of the American space station Skylab did come down in western Australia in 1979.

While the odds of an individual aircraft being hit by a piece of debris are extremely low, somewhere in the range of one in 100,000 in 2023 to an estimated seven in 10,000 by 2035, the threat of falling debris can force the closure of airspace around a city out of an abundance of caution. Any incoming flights are diverted to other airports and those on the ground cannot depart. 

It's also incredibly expensive, with fees often being shouldered by airlines and their passengers. It cost over 20 million euros (29.5 million Cdn) to close European airspace for just two hours during the uncontrolled re-entry of Russia's Phobos-Grunt spacecraft in 2012, according to researchers working with the European Union.

The biggest problem is determining exactly when and where space debris will fall. Rocket bodies are not aerodynamically shaped and often tumble end over end as they enter the atmosphere. This makes it difficult to predict how they will behave — and where they will drop. 

Much of their structure will be incinerated by the heat of air friction in the upper atmosphere, but larger pieces can make it through, crashing like cannonballs from the sky, while smaller pieces can flutter down like autumn leaves taking hours to reach the ground.

In addition, changes in solar activity can cause the Earth's atmosphere to inflate or deflate, altering the amount of drag on a spacecraft and thus the timing of its fall.

Spaceflight controllers do their best to predict where debris is likely to come down, sometimes called a footprint, that can cover hundreds of square kilometres, and that area can move depending on how the spacecraft behaves in its final moments of re-entry.

This means air traffic controllers may only have an hour or less to divert aircrafts away from the region.

Researchers point out that in 2023 alone, a record 212 rocket launches took place, leaving 128 rocket bodies to fall back to Earth on their own, uncontrolled. More than 2,300 objects from decades of launches remain in orbit, and will eventually fall from the sky.

The authors suggest that new regulations would be needed to ensure that whoever launches rockets into space takes responsibility for disposal of spent rocket bodies and defunct satellites in a safe manner.

One solution is that extra fuel could be added, then used for controlled re-entry to direct objects to fall in specific zones such as the south Pacific, where population density is low. Perhaps devices could be deployed in orbit to act as air brakes that control descent.

Delays in air travel due to weather, overcrowding or maintenance are enough to put up with, we don't need more delays because the sky is falling.