A meteorite impact, the kind that forced Russia to plan a space station recovery mission, is nearly impossible to avoid, but the bigger threat to spacecraft is actually man-made debris in orbit, experts say.
Russia announced Wednesday that it is on a mission to retrieve crew members stranded after a strike to the International Space Station in February damaged the capsule that would take them home.
Didier Schmitt, head of human and robotic exploration at the European Space Agency, said it’s not uncommon for small meteorites to hit the space station.
Micrometeorites can travel at speeds of 10 to 30 kilometers (6-18 miles) per second — “much faster than a shotgun bullet,” Schmitt said.
Therefore, when the space station’s large observation window is not used, it is covered with “very, very thick layers of protective material,” he said.
Small meteorites are coming from so far away and at such high speeds in the distant universe that they cannot be tracked realistically, he said.
But space agencies are monitoring the known meteor showers as expected in early August.
NASA had previously said that December’s Geminid meteor shower was unlikely to hit the Soyuz capsule as the fuselage punctured from a different direction.
– What about space junk? –
While meteors may sound scary, the biggest threat to spacecraft is believed to be from orbital debris – disused satellites and other man-made objects orbiting Earth known as “space junk.”
That’s because colliding space junk creates even more debris, causing a “runaway chain reaction” of cascading collisions filled with small, dangerous objects into orbit, NASA says.
The UN Office of Outer Space Affairs said last month that there are half a million pieces of debris the size of a marble and 100 million pieces of debris about the size of a millimeter in orbit.
“Millimetre-sized orbital debris represents the highest end-of-mission risk for most robotic spacecraft operating in low Earth orbit,” said Stefania Soldini, an aerospace engineering lecturer at the University of Liverpool in England.
Soldini said the ISS is “the most heavily shielded spacecraft” against such debris.
The space station has orbital shields to protect it from debris smaller than 1.5 centimeters.
But the space is only getting more crowded.
The UN office said about 35 percent of the 14,000 satellites launched so far have entered orbit in the past three years alone, with potentially 100,000 more satellites to be added in the next decade.
– Missiles in space? –
Countries that use missiles to shoot down their satellites for weapons tests have also significantly increased their space junk pile.
Russia drew criticism from NASA in 2021 when Moscow destroyed one of its satellites during a missile test, creating more than 1,500 pieces of debris and forcing those on the ISS to seek shelter.
According to NASA, China created more than 3,500 large, traceable debris when it downed one of its weather satellites in 2007.
Incidental conflicts have also increased in recent years. More than 2,300 new debris was also launched into orbit when a disused Russian military satellite crashed into the US’s Iridium communications satellite in 2009.
The US Department of Defense tracks objects in Earth orbit, mostly larger than 10 centimeters (about four inches).
If a larger chunk of debris is seen heading towards the ISS, its thrusters will pull the football field-sized space station out of the way.
In 2021, the ISS was tuned to avoid debris known to originate from China’s 2007 anti-satellite test.
– The biggest threat to astronauts? –
Schmitt said the “big problem” for now is that without the Soyuz MS-22 capsule, about half of the seven crew members on board couldn’t make it home.
Normally, if a critical event occurred at the station, the crew could return to Earth within three hours, hypothetically.
“But now there is a risky period where we can’t get everyone back in the event of a major threat,” Schmitt said.
Russia’s space agency Roscosmos said a new spacecraft will be sent to the ISS on February 20 to pick up two cosmonauts and an astronaut, who originally planned to take the Soyuz MS-22 capsule home.
“You can’t open the windows,” said Schmitt, who said that in normal times the biggest threat to astronauts on the ISS is probably fire.
He called solar flares another danger—not to mention the myriad of dangers that await those planning to fly on upcoming missions to the Moon and Mars.
“Human space exploration is risky,” he said.
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