About once per year, the International Space Station takes evasive action to avoid colliding with a piece of space debris.
The most recent maneuver took place last week when the ISS boosted itself into a higher orbit to avoid debris from a Russian anti-satellite missile test in 2021. It is likely that such close calls will not will only become more common as humanity continues to clutter the space lanes with old satellites and debris from missile crashes and tests. Here’s what you need to know about space debris and how to avoid it.
How does the International Space Station avoid space debris?
It’s tempting to imagine astronauts piloting the ISS as if it were the Millennium Falcon, relying on their lightning reflexes (and perhaps the Force) to maneuver around chunks of wrecked spacecraft, often with a few centimeters to spare. Reality – like many things in spaceflight – is much slower and occurs over much greater distances than the Hollywood version. But it can still be extremely tense, as lives are at stake, and if something goes wrong, help isn’t on the way.
No one sits in an ISS cockpit with a joystick, turning the entire station left or right out of the path of an oncoming piece of debris. That’s not how space maneuvers work. Instead, if you’re heading towards another object in space, you’ll either speed up, which propels you into a higher orbit, or slow down, which puts you in a lower orbit. To avoid bursts of Russian satellites last week, a Russian Progress cargo ship docked at the station and fired its thrusters for about five minutes, which propelled the ISS into an orbit just under one mile above his former.
Mission Control, a few hundred miles on Earth, plans maneuvers like the October 24 boost days in advance. It takes as long to calculate a new trajectory: what is the safety orbit that the ISS is aiming for? How much push will it take to get there? Is this orbit in the path of other satellites? Formally, this is called a pre-determined debris avoidance maneuver.
“We have a flight control post at Mission Control Houston called TOPO (for Trajectory Operations Officer) which manages the orbital trajectory of the space station,” explains a NASA spokesperson. “They work directly with US Space Command (USSPACECOM) which is responsible for tracking and cataloging satellites and debris orbiting the Earth. USSPACECOM reviews the path of the ISS against its catalog of objects several times a day, and if anything is expected to pass within a ±2 km x 25 km x 25 km area of the space station in the coming days , they send a notification to TOPO with the time of the nearest approach.
What if there isn’t enough time to plan evasive maneuvers?
This is when the crew must prepare for a possible emergency. For most ISS crew members, this means gathering the important items and closing the hatches between pressurized sections of the station so that if one module is damaged, it doesn’t depressurize the others. It’s the space version of a warship closing all its watertight hatches before launching into battle.
Minutes before possible impact, crews head to the lifeboats – in other words, to the docked spacecraft that will be their homecoming (and their only shelter) if the ISS is damaged in any way. irreparable.
In his book Endurance, Scott Kelly describes a close call with a missing Russian satellite in 2015, during which he sheltered in a Russian Soyuz capsule with cosmonauts. Gennady Padalka and Mikhail Kornienko. Kelly and her teammates found themselves staring out the windows of the Soyuz capsule in the dark, even though they all know the approaching satellite will be moving too fast to see if it hits them or not.
Mission control had calculated up to the second the satellite would pass the ISS, and as the moment of truth approached, Kelly’s attention shifted from the window to the clock.
“Once the time goes to the second, I feel tense, I start to wince. We wait. Then…nothing,” he wrote. “Thirty seconds pass. We look at each other with a last heartbeat of anticipation of disaster.Then our grimaces slowly turn into expressions of relief.
What happens if something hits the ISS?
In EnduranceKelly describes how cosmonauts Padalka and Kornienko summed up the things that awaited in the darkness of their Soyuz capsule in 2015.
“’You know,’ Gennady said, ‘it’ll be really bad if we get hit by that satellite.’
“‘Da,” Misha nods. ‘It’s gonna suck.’
According to NASA, most of the crew compartments and pressure vessels that make up the International Space Station “will normally be able to withstand impact from debris as large as 1 centimeter in diameter.” This covers about a million small pieces of floating junk: paint stains, the smallest bits of debris from orbital accidents, small bits of misplaced hardware, etc.
Anything over a centimeter wide is potentially much more dangerous. We imagine space junk — and the ISS itself, often — as floating lazily through space, but it’s actually moving very quickly, at around 25,000 to 50,000 kilometers per hour. At that speed, a centimeter-sized object would hit the ISS with about ten times the force of a similarly sized bullet fired from a gun here on Earth.
And something even bigger – any of the 25,000 pieces of known debris over 10 centimeters wide, which include things like the defunct satellite passed by Kelly’s crew in 2015 – would be devastating. If the satellite had hit the ISS in 2015, it likely would have vaporized most of the station on impact, according to Kelly, who found closing the station’s hatches an exercise in futility in the face of that possibility.
This is why ISS crews and their mission controllers on Earth avoid space debris so much, keeping several miles between the station and possible collisions.
“The ISS will normally move away from the object if the risk of collision exceeds 1 in 10,000,” NASA explains.
How often should the ISS dodge space debris?
Counting the maneuver on October 24, the ISS moved its orbit 32 times to dodge a piece of space debris or a dead satellite. That’s about 1.5 evasive actions a year since 2000 on average, but a NASA spokesperson says the actual frequency varies.
“For example, we had to do 9 maneuvers in calendar years 2014-2015, then we had zero until 2020,” they say. Two of those maneuvers — one on Oct. 24 and one in June 2021 — dodged chunks of Cosmos 1408, the satellite Russia blew up during its 2021 missile test.
Currently, the station’s biggest orbital debris problem is a link between the scattered remains of a Pegasus upper stage rocket (the same type of rocket that launched NASA’s NuSTAR telescope) and those of a Chinese satellite, Fengyun 1C, which China blew up in an anti-satellite missile test in 2007. NASA says Reverse that the ISS had to dodge pieces of each of these spacecraft three times.
The 2015 shelter-in-place episode portrayed by Kelly in Endurance was the fifth such incident since 2000.
Is the space debris problem getting worse?
Right now, there’s about 9,000 metric tons of trash orbiting our planet, ranging from paint specks to entire satellites that have run out of fuel or stopped working – and we keep adding more. . This happens when space agencies or private companies fail to ensure that their satellites fall back into the Earth’s atmosphere at the end of their life, when a rocket stage or an entire spacecraft explodes, when two satellites come into collision (as an Iridium communications satellite and a Russian Cosmos satellite did in 2009), or when a country blows up one of its own satellites in order to demonstrate that it has the power to blow up the satellites of someone else.
It’s exactly the kind of test that destroyed Cosmos 1408, forcing the ISS to continue dodging bits of its debris for at least several more years. Weeks before the station’s last evasive action on October 24, the UK became the latest country to ban such anti-satellite missile tests – joining Canada, Germany, Japan, New Zealand, South Korea and the United States. Russia and China are notably absent from this list.
An Indian anti-satellite missile test in 2019 also created a huge cloud of debris, but most of it had burned up in Earth’s atmosphere about a month after the test. Debris in lower orbit (below about 600 kilometers, according to NASA) tends to fall back into Earth’s atmosphere within months or years because the weak upper remnants of Earth’s atmosphere create just enough drag to slow it down. things, breaking down their orbits, so they succumb to gravity.
But while they last, these fragments potentially remain a huge problem, especially in the aftermath of a missile test, collision or rocket accident.
“During the first days after the event, you still have a dark risk because you know you are surrounded by fragments and you don’t know where they are,” said Holger Krag of ESA’s Space Debris Office. in 2019.
But even without deliberately tossing old satellites into thousands of space junk, the few hundred miles of space around our planet are becoming increasingly crowded. New space missions add about 40-50 objects a year to the ever-growing cloud of wreckage and jetsam in Earth orbit, usually in the form of metallic slag from solid rocket engines or new satellites that will continue to orbit the planet once their fuel runs out or their communication systems make them unmanageable.
And each of those unwanted satellites is a thousand or more little pieces of debris just waiting to arrive. Currently, the biggest source of space debris remains a collision in 2009 between the Iridium-33 satellite and the Cosmos-2251 satellite, which the ISS has already had to avoid three times.
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