An illustration of debris around Earth. Credit: European Space Agency
Even if you’re not an orbital debris expert, chances are you’ve heard of the Kessler Syndrome. While opinions differ on whether this phenomenon of cascading on-orbit collisions has begun and, if so, to what extent it will impact spacecraft operations, the space community has largely embraced the general concept and the need to avoid creating additional debris.
The term’s namesake, Donald Kessler, was 38 when he pioneered the mathematical models of collision probabilities that led him to devise this scenario in which orbit could eventually be rendered unusable, and the majority of his next 18 years at NASA were spent studying the issue. His calculations and his now-famous 1978 paper — “Collision Frequency of Artificial Satellites: The Creation of a Debris Belt,” coauthored with Burton G. Cour-Palais — prompted NASA to establish an orbit debris program, which Kessler led until his retirement in 1996.
I reached Kessler at his home in Asheville, North Carolina, to discuss the arc of his career and the current debris threat, as well as what he deems an even greater risk.
Q: How did you become a NASA employee?
A: When I graduated from high school in Houston, they said, “You can go to college,” and gave me a hundred dollars. I can’t go to college on a hundred dollars. So I joined the Army and spent three years there and stepped into the University of Houston on a cooperative education program, where I could go to school for one semester and then work with NASA another semester. You start at the lowest spot and and you can work your way around and see what you might be interested in doing.
Q: How did you find your way to researching orbital debris?
A: I was learning different skills. The one that I liked the most was the Meteoroid Sciences Group, that worried about the dangers of launching where anything might land from the launch on the Earth. Other people had thought that there might be some kind of problem, but they had never gone through all the mathematics to really pinpoint exactly how bad it could get.
Their original issues were, “How many objects do we have in space that might do damage to another satellite?” They never really got to the point on their own to when you hit another satellite, it doesn’t just make it quit functioning. There’s also debris associated with it, and nobody had ever sat down to see how that debris would accumulate.
It seemed to me every time they would talk about, “Oh, that satellite’s blown up and fragments are not as bad,” they never realized they were contaminating the whole space. It seemed so obvious to me that this cascading effect has got to be important.
I knew how to write the equations in such a way to come to a conclusion about the fragment size distribution: You take certain size objects and break them up into a whole bunch of others to a distribution of sizes. What that would begin to look like is each of those fragments then can go on and hit something else. So you’ve got a process that grows with time, and you don’t turn it around until you’ve done it to all the satellites.
The thing that was motivating me mostly is I was convinced that it couldn’t not be bad. It couldn’t. It’s not a good thing to happen. And just to have those feelings is not sufficient; you’ve got to do the math to demonstrate it.
The paper I published [“Collision Frequency of Artificial Satellites”] was by Donald J. Kessler and Burton Cour-Palais. He became one of the people I just loved working with. I would talk to Burt whenever I’d run into a problem.
Q: What do you remember of the initial response to that paper?
A: I was the first person to come up with that concept, and NASA had no program like that. We had meteoroid sciences, but nothing called orbital debris. When I published the paper without permission from my management and it circulated internationally very quickly, one of the people I was working with said, “Well, it’s time to go talk to the center director, because what do we do with this concept?”
We talked with the center director at NASA Johnson, and he said we need to set up an organization called Orbital Debris. The assistant to the director said, “Go around to all the other countries that do anything in space and let them know about this concept, because everybody needs to worry about it and do what they can to keep it from getting worse.” That was extremely educational for me. It surprised me, actually, how much it has caught on.
Q: John Gabbard of NORAD coined the term “Kessler Syndrome,” putting your name on this phenomenon.
A: John Gabbard was a really good friend. There’s a thing called Gabbard plots that he put together of a breakup in space. He would plot the perigee and apogee of each satellite on a plot, and he’d come up with patterns where all the fragments would cross. Because he could identify some breakups that way, he got known for those plots. He just named that cascading effect after me, and it stuck.
Q: Today, there are differing opinions about whether the cascade has already begun, but the general agreement that this is a legitimate concern. So what can we do to prevent or minimize the Kessler Syndrome?
A: We came up with a 25-year rule where anything you put into space after you’ve quit using it has to re-enter within 25 years.
The U.S. Federal Communications Commission in 2022 shortened the period for deorbiting satellites to five years after a spacecraft’s mission concludes or it stops operating. FAA in 2023 began devising rules for the disposal of rocket upper stages within 25 years of launch, though many of the public comments advocated for a shorter duration. The final rule is to be released later this year. — JC
That would slow down the process but will not eliminate it. So every time someone says, “What can I do to change this?” the only thing I come up with is, “It’s not going to change.” The only thing that will happen over many generations of people’s lifetimes is that all of those fragments will eventually start running into each other in such a manner that they will lower their inclination. They will end up all in the same plane, so you have an Earth with a ring around it like Saturn.
We’re creating a planet like Saturn — and it’s not going to stop. So if we live long enough, we’ll see those rings. And, of course, with climate change, no one may make it to that age.
Q: You think that compared to climate change, orbital debris is a secondary concern?
A: I strongly feel that climate change is much more important than orbital debris. Once climate change does its thing, it’ll wipe out everybody on the Earth. The Earth will have a ring around it, and eventually, there’ll be some other civilization in space that says, “Oh, look at that nice planet with a ring around it. Why don’t we build a home there?”
And that’s how life may end up surviving here: migration from another planet, if Earth becomes livable again, maybe millions of years from now.
Q: So in your view, who’s responsible for cleaning up the debris?
A: NASA went to all the countries to tell them that each one of them has the responsibility to do what you can to minimize debris in space. But I don’t think it’s even slowed it down. It may be at a stalemate, but the Earth will always have this ring around it. But it’s sort of like the Boy Scout motto — if we all cleaned up after ourselves, we wouldn’t have this problem.
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