The Worst Collision of Orbiting Satellites and Space Debris So Far

The Worst Collision of Orbiting Satellites and Space Debris So Far
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Has a spacecraft ever been disabled or destroyed by a collision with space debris? originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.

Answer by Thomas Ulrich, Electrical engineering grad student at Stanford University, on Quora:

Iridium 33 was destroyed in 2009 by a collision with a defunct Russian satellite.

Back in 1993, low Earth orbit was a lot less crowded than it is today. And just two years after the breakup of the Soviet Union, the new Russian government was not exactly suffering from an excess of funds. So when the Russian military launched the 900 kg communications satellite Kosmos-2251 into a highly inclined orbit passing over the country’s remote northern regions, the decision to cut costs by not installing a propulsion system was hardly controversial. The military did not anticipate that it would ever need to change the satellite’s orbit — certainly not to avoid a highly unlikely satellite collision — and the expensive extra weight could be put to better use.

Four years later, on the other side of the world, bankruptcy loomed for cash-strapped Iridium SSC. The company had already spent billions of dollars on a new constellation of telecommunications satellites designed to offer phone service anywhere in the world. But until the constellation was complete, Iridium could not guarantee 24-hour coverage, and the 32 satellites already in orbit were essentially worthless. Under pressure from investors, Iridium engineers worked hard to finish the last batch of satellites quickly so that the phone service could finally go online. In September 1997, satellite number 33 — halfway to the planned total of 66 — was launched successfully into a high polar orbit.

On November 1, 1998, the Iridium constellation was finally complete. US vice president Al Gore made the symbolic first phone call. But just nine months later, the company was bankrupt. The market for satellite phone service wasn’t as large as Iridium had hoped, and the initial cost of the satellites could not be recovered.

That left 66 Iridium satellites unattended in low Earth orbit. In 2001, a new group of investors bought the constellation for a bargain price and began offering satellite phone coverage again under the name Iridium Communications. However, while the satellites did have hydrazine monopropellant thrusters and could change their orbits as needed, the company was still not especially profitable and there was not enough money to seriously investigate the possibility of a collision. The engineers were already busy enough keeping the phone service running.

Space is big. In principle, there’s enough room in low Earth orbit for millions of satellites to operate simultaneously without crossing paths. But this requires careful coordination, and it only takes a few satellites with slightly incorrect eccentric trajectories to cause a disaster. And the unmonitored Iridium 33 and the helpless Kosmos-2251 were on intersecting orbits. Drawn inexorably together by the iron laws of physics, the two satellites circled closer and closer to their demise.

Late at night on February 10, 2009, 789 km above the Taymyr Peninsula in Siberia, they collided at about 12 kilometers per second.

Both satellites were destroyed instantly. Kosmos was no longer functional anyway, but Iridium phones began experiencing service outages in a predictable daily pattern. The company quickly realized that the 33rd Iridium satellite was no longer operational.

Meanwhile, debris began to spread.

NASA estimated that the crash created about 1000 fragments larger than 10 cm, and there were many smaller pieces as well. The world’s space agencies worked together to find and catalog the largest and most dangerous chunks. Fortunately, it was soon clear that the International Space Station and other major satellites were not at risk. However, the station did execute a collision avoidance maneuver in 2011 to ensure it kept a safe distance.[1]

Today, most of the debris from the 2009 collision has already burned up in the atmosphere or is on track to do so within the next few years. But could something like this happen again with even more serious consequences?

If history is any indicator, the answer is yes. There are already hundreds or thousands of close approaches (within a few km) every day between satellites in low Earth orbit. Since we don’t have perfect information on satellite orbits, all we can say is that there is some probability of a collision for each of these events. Indeed, there have already been eight known collisions between satellites and pieces of space debris [2]. Furthermore, the danger is only going to increase as we launch more and more satellites.

There are no easy solutions to the problem. It’s tempting to suggest that satellite operators should just move their satellites to avoid collisions, but accurately tracking satellite orbits is very difficult, and an incorrect maneuver might just make matters worse. Ultimately, we probably need to require operators to de-orbit satellites or send them to a graveyard orbit after a certain period of time.


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