Our history with risks posed by growing amounts of space debris holds valuable lessons on climate change … but only for those willing to listen and learn.
Once upon a time, new technologies built on an important science offered vast, new benefits to the world.
People everywhere marveled at the new possibilities that became available, and governments and industries rushed to develop them.
Imaginations were fired. A Cassandra somewhere, an egghead really, looked far ahead and wondered about a problem, but it was far, far away, if it ever would be.
Progress leapfrogged over progress. The Cassandra pushed a slide rule late into the nights and published in a technical journal, largely unnoticed. Everyone else was having too much fun.
Wow, the people said, astonished at their new world. A few more eggheads read the Cassandra’s paper, and worked their own slide rules.
Technology got better, as technology does. Faster. Cheaper. Ever greater wonders. But in ivory towers the scientific sleeves were being rolled up. Some scientists had been talking. Now they were calculating. Gathering data. Making models.
The technologies were perfected and standardized. Stamped out. Indispensable, routine, taken for granted. But there may be a problem here, a few scientists now said out loud, amidst the noise and haste.
The world moved on, taking for granted what once seemed like magic. The newspapers turned to the conflict. There were conferences, committees, even a congressional hearing. But they would find a solution, the world thought. The eggheads always did.
Then, unexpected, out of the blue, a catastrophe. Just as the Cassandra, now retired, had foreseen long ago in those equations and charts. A sense of shock, a ripple of fear, out like a wave. Attention was paid.
It was here, everyone whispered. The problem, bold and black. Worry and fret, the children straining to hear the whispers of their parents late at night.
Governments sprang, as governments do. Money, money — take our money, they told the eggheads. Study this. Fix this. Tell us what to do.
Catastrophe, again. A crisis now, a palpable fear.
Too late, the eggheads said. Too late now.
If only we had listened, parents whispered at night. Nothing will be the same, the newspapers said.
And somewhere, late at night, staring at a wall, a new Cassandra began to wonder …
No, the problem isn’t climate change. That problem has started down this path, but has yet to reach the final stages.
But another environmental problem has come this way. And the arc of its story does not bode well for the issue of climate.
That problem is space debris.
Simulated image of space debris (Source: NASA).
Space debris — the tens of thousands of objects now in Earth’s orbit, put there by ignorance, by neglect, by accident — was a problem dismissed for years, even decades. Meanwhile the world gaped in astonishment at the space programs, took pride in its achievements, grew reliant on its satellites.
Eventually the problem was recognized by a few experts, who modeled, and journaled and memoed up the line. Warnings were sent, but budgets were tight.
Then, one day in 2009, the catastrophe happened.
And now the space debris problem threatens to spin out of control. A collision in space can create hundreds of new pieces of debris, increasing the probability of still more collisions. The numbers threaten to cascade exponentially, which could effectively end the possibility of keeping satellites in orbit, or even of launching rockets from Earth’s surface. The world space community now is scrambling to find a solution before humans are trapped in Earth’s gravity well, and this at the very time when we have barely looked over its rim.
Space debris was a problem first considered in the 1970s, two decades after the space age began. It would have been cheaper to fix then, when the warnings first appeared, but that never seems to be our way. Now the fix is needed fast, and it will be expensive, if it can be done at all.
Sound familiar now?
The story of space debris begins with a glove.
By the mid-1960s, the United States had responded to its Sputnik-induced panic by sending several manned flights into space. On the tenth manned mission, the Gemini 4 space flight in June 1965, astronaut Ed White made the first space walk by an American, floating outside the spacecraft, while tethered, for about 20 minutes. During his walk a spare thermal glove floated away through the spacecraft’s open hatch, becoming one of the first pieces of space debris to orbit Earth.
The glove, initially in low-earth orbit at an altitude of less then 150 miles, later burned up in atmospheric reentry. But, of course, more debris followed. Like everywhere humans have traveled, the beginning of space exploration was also the beginning of space pollution.
In their book Space Elevator Survivability: Space Debris Mitigation, authors Peter and Cathy Swan and Robert “Skip” Penny divide the history of space debris into four historical phases:
The early space community saw the orbital environment as so vast that debris was not a concern. In fact, the Gemini 4 mission plan called for White to discard his bulky extravehicular suit out the hatch and into space, though when the time came Command Pilot Jim McDivitt personally decided to save it.
Early-on, NORAD, the North American Aerospace Defense Command, began tracking space debris larger than 10 centimeters. By 1970 humans had landed on the moon, and there were already 2,500 known pieces of debris orbiting Earth.
The next phase the Swans and Penny list happened as the number of objects in orbit increased, and scientists started to wonder exactly what objects were up there and where they came from. Tensions between the U.S. and the Soviet Union intrigued the military, too, and the problem gained a new respect with the launch in 1973 of the human-occupied Skylab, whose large dimensions offered a broad target to debris in other orbits (the station’s largest side spanned more than a tenth of an acre).
Though there are many tiny pieces of space debris less than a centimeter in size — such as discarded propellant, dust specks, and paint chips, now thought to number in the tens of millions — it’s the larger pieces that are of biggest concern. Damage from small objects resembles sandblasting, but bigger pieces have surprisingly large energies as a result of their enormous speeds. A sphere of aluminum just 1-cm in diameter travels in low-Earth orbit with 10 times the kinetic energy of a bullet from a high-powered deer rifle.
In 1978, Donald Kessler and Burton Cour-Palais of NASA published a seminal paper that cast the space debris problem in a new light.
Kessler earlier had studied the growth of asteroid belts, including how space probes such as the Pioneer and Voyager missions might traverse such density fields. Turning to the problem of objects in Earth’s orbit, he and Cour-Palais used the distribution of orbiting objects — their numbers at different altitudes and of different sizes — to calculate the odds of a collision between objects of average size.
With the average cross-section being four square-meters, their model returned an expected collision rate of 0.013 collisions per year, with uncertainties in the data placing upper and lower limits of 0.007 and 0.039 collisions per year.
They then could project the number of future collisions between objects (whether placed in orbit on purpose or by accident) under different scenarios of the future growth of trackable objects. Under a conservative assumption of growth of 320 additional objects each year, the first collision was expected around 1997. A higher growth rate predicted an earlier first collision, perhaps as soon as 1985, and an average object of half the assumed size might push it out to 2005.
No matter what, the future did not look bright in their eyes. A collision could put hundreds of new pieces into the mix, increasing the chances of the next collision even more. While some objects would fall out of orbit as a result of atmospheric drag — especially when solar storms heat the atmosphere and cause it to expand — the time between collisions could still shrink.
“The result,” Kessler and Cour-Palais wrote, “would be an exponential increase in the number of objects with time, creating a belt of debris around the Earth.” Keeping a satellite in orbit would become more and more difficult, and even sending a rocket through the debris cloud or keeping a space elevator intact could become perilous. In the latter case humans would be trapped on Earth, just when we otherwise might be getting ready to go places.
Someone dubbed the scenario the “Kessler syndrome” and “Kessler Cascade.”
Top managers at NASA “didn’t like what I was finding,” Kessler told Wired a few years ago. They accepted his results, but didn’t think there was much to be done. The cost would be huge, and cleaning up space didn’t seem worth it, even as further studies solidified the cascade idea across the space community.
Kessler’s prediction came true, if a bit late, when the IRIDIUM 33 telecommunications satellite on February 10, 2009, was struck by the dead, uncontrolled Russian satellite Cosmos 2251.*
Traveling at five miles per second each, the catastrophic collision created 2,100 new pieces of debris — a quantum jump of about 20 percent in trackable debris.
It was the first explosion, but it wasn’t the first time a satellite had suffered an impact from a piece of debris large enough to appear in NORAD’s catalog. There had been several since 1991, for both active and inactive satellites. A few of them were large enough to change the satellite’s orbit and even create small amounts of additional debris.
And it hadn’t helped when, in 2007, the Chinese government purposely destroyed its Fengyun FY-1C weather satellite with a high-velocity projectile launched from the surface. The explosion generated 2,317 pieces of trackable debris, and an estimated 150,000 smaller pieces. (To be fair, the U.S. had itself conducted anti-satellite tests earlier — the last one occurred in 1985 — and before that both the U.S. and the Soviet Union had held a cavalier attitude about space debris for decades.)
The unintentional destruction of the IRIDIUM satellite brought sharp attention to the problem of space debris. Just a month after it occurred, Donald Kessler, now retired from NASA and living in Asheville, N.C., wrote:
We are entering a new era of debris control …. an era that will be dominated by a slowly increasing number of random catastrophic collisions. These collisions will continue in the 800 km to 1,000 km altitude regions, but will eventually spread to other regions. The control of future debris requires, at a minimum, that we not leave future payloads and rocket bodies in orbit after their useful life and might require that we plan launches to return some objects already in orbit.
Since then, there has been a sense of urgency in the space community that the environmental problem of space debris is spinning out control. Conferences have been held around the world, and ideas once seemed outlandish are getting a second look, such as laser brooms and giant nets.
There are now about 22,000 catalogued pieces of space debris circling Earth. A 2010 model from NASA’s Orbital Debris Program projects that, without mitigation, the number of debris pieces just in low-earth orbit will increase by 2050 from about 13,000 to perhaps 18,000, then to as much as 30,000 by the year 2100 and to more than 80,000 by 2200.
At least three times in the past 11 years inhabitants of the International Space Station had to be warned to crawl into an attached Russian Soyuz spacecraft because a piece of space junk would be zipping through their neighborhood. And last June one piece passed by at a distance of only 1,000 feet.
“There is no solution — just don’t generate new debris,” Air Force Space Command head General William Shelton said at the time. “If you look at the problem of trying to clean up debris, the physics just don’t close. With what we know about propulsion, there’s no way to get there.”
Accordingly, new international policies are being proposed to create a space “Code of Conduct,” requiring that satellites be lowered into the atmosphere after their useful life is complete, where they will burn up on reentry. And denizens of Planet Earth have had more than one scare in the last year from reentries of chunks large enough to survive the plunge. (The saving grace is that it’s unlikely you’d ever see it coming.)
Kessler concluded his 2009 retrospective with this:
As is true for many environmental problems, the control of the orbital debris environment may initially be expensive, but failure to control leads to disaster in the long-term. Catastrophic collisions between catalogued objects in low-Earth orbit are now an important environmental issue that will dominate the debris hazard to future spacecraft.
The parallels to the climate change problem are obvious. Its story line is following much the same arc as the space debris problem, though lagging behind by a decade or two.
It’s unlikely any climate catastrophes will be as clearly delineated as the sudden collision of two high-speed satellites — at least for many years yet. Scientists now are grappling with attribution of extreme events like the recent U.S. heat wave in March, or the stifling Moscow heat wave of the summer of 2010, or the 2003 heat wave in France that claimed some 35,000 lives.
But in a decade or two, when the science advances, and when ever-faster computers allow simulations at ever-finer scales, we may look back on these days much as the space community now views the history of the Kessler Syndrome, and wonder why anyone ever thought a lost glove was a trivial thing.
* This sentence was lightly edited on April 26,2012.