The part of the space junk problem that might be fixable

The problems with junk still orbiting Earth are talked about occasionally; we've done dedicated stories on it over the years, like this one in Dec. '22, but for the most part it's a tough problem.  The prospect of thousands of small objects, such that collisions could cascade, becoming unmanageable or unsurvivable, is awful.  

Some recent work on the problem has used different approaches, predictably giving different results.  The International Astronautical Conference has focused on the pieces of debris that could trigger the biggest problems.  

They've concluded that the worst of the debris is over 25 years old, and largely emptied boosters that were never de-orbited.  

"The things left before 2000 are still the majority of the problem," said Darren McKnight, lead author of a paper presented Friday at the International Astronautical Congress in Sydney. "Seventy-six percent of the objects in the top 50 were deposited last century, and 88 percent of the objects are rocket bodies. That's important to note, especially with some disturbing trends right now."

The 50 objects identified by McKnight and his coauthors are the ones most likely to drive the creation of more space junk in low-Earth orbit (LEO) through collisions with other debris fragments. The objects are whizzing around the Earth at nearly 5 miles per second, flying in a heavily trafficked part of LEO between 700 and 1,000 kilometers (435 to 621 miles) above the Earth.

Hey, it's 2025, and by now everyone remotely interested in a story like the Sandra Bullock, George Clooney movie from 2013, Gravity, has seen enough of it to know the story is about a chain reaction of space junk collisions taking out the Space Station and most of everything in orbit, a phenomenon called the Kessler Syndrome. This is what everyone is most concerned about.

The IAC analysts considered how close objects are to other space traffic, their altitude, and their mass.  For example, large debris at high altitudes pose a bigger long-term risk because they could create more debris that could remain in orbit for centuries or longer.

Russia and the Soviet Union lead the pack with 34 objects listed in McKnight's Top 50, followed by China with 10, the United States with three, Europe with two, and Japan with one. Russia's SL-16 and SL-8 rockets are the worst offenders, combining to take 30 of the Top 50 slots. Here's the Top 10:

1. A Russian SL-16 rocket launched in 2004
2. Europe's Envisat satellite launched in 2002
3. A Japanese H-II rocket launched in 1996
4. A Chinese CZ-2C rocket launched in 2013
5. A Soviet SL-8 rocket launched in 1985
6. A Soviet SL-16 rocket launched in 1988
7. Russia's Kosmos 2237 satellite launched in 1993
8. Russia's Kosmos 2334 satellite launched in 1996
9. A Soviet SL-16 rocket launched in 1988
10. A Chinese CZ-2D rocket launched in 2019

In an update to this list published back in 2020, McKnight's team's simulations showed that if these 50 most dangerous pieces of rocket debris were removed the overall debris-generating potential in low-Earth orbit would be reduced by 50 percent. If just that Top 10 list were removed, the risk would be cut by 30 percent.

The European Space Agency's Envisat satellite launched in 2002 and failed in 2012. It is the second-most hazardous object in the Top 50 list. Image credit: European Space Agency.

On the other hand, "the bad news is, since January 1, 2024, we've had 26 rocket bodies abandoned in low-Earth orbit that will stay in orbit for more than 25 years," McKnight said. 

The 25-year discriminator is important because that is the guideline promulgated by the Inter-Agency Space Debris Coordination Committee, an international group that includes representatives from all of the major space powers: the United States, China, Russia, Europe, India, and Japan. If a piece of space junk is left in low enough of an orbit, aerodynamic resistance will drag it back into the atmosphere in less than 25 years.

US and European governments have policies requiring launch companies to deposit their spent upper stages to altitudes low enough to naturally reenter the atmosphere within 25 years, or deorbit their rockets altogether.

If you've been following SpaceX and their operations, you'll know that they pay a lot of attention to junk.  The biggest example of that is they routinely deorbit the upper stage of a Falcon 9, usually driving them back into the atmosphere over the open ocean.  The Starlink system was designed to be at lower than typical orbit heights to minimize delays in the internet service they're providing.  That has led to the loss of more than a few satellites. 

China, on the other hand, frequently abandons upper stages in orbit. China launched 21 of the 26 hazardous new rocket bodies over the last 21 months, each averaging more than 4 metric tons (8,800 pounds). Two more came from US launchers, one from Russia, one from India, and one from Iran.

This has led to continued concern about China from McKnight and the IAC team.  China is in the first stages of creating two new megaconstellations - Guowang and Thousand Sails - with thousands of communications satellites each in low-Earth orbit. 

However, most of the rockets used for Guowang and Thousand Sails launches have left their upper stages in orbit. McKnight said nine upper stages China has abandoned after launching Guowang and Thousand Sails satellites will stay in orbit for more than 25 years, violating the international guidelines.

A concept that appears toward the end of the source article is one that anyone familiar with military uses for any real hardware will recognize.  Any hardware that a space-faring civilization could develop to clean up after themselves can be seen by a second space-faring civilization as the first group intending to take out the second group's payloads.  Another example of how any defensive weapon can be viewed as an offensive weapon.