NASA and Russia’s space agency changed the course of the International Space Station (ISS) to avoid colliding with debris that was heading in the opposite direction.

The fragment was a piece of a Chinese weather satellite that was destroyed in a missile test 15 years ago, the space agency Roscosmos said in a tweet on Wednesday, around the time it changed course.

If the debris hadn’t moved by Friday, it was due to approach the space station.

It was scheduled to enter the “pizza box,” a flat, rectangular zone 2.5 miles deep and 30 miles wide around the space station where any object is “close enough to cause concern,” according to NASA. “It just makes sense to go ahead and do this burn and put this behind us so we can ensure the safety of the crew,” NASA’s space station manager Joel Montalbano said at a press conference on Tuesday.

Neither NASA nor Roscosmos specified the size of the fragment. While a small fragment may not have harmed the station significantly, large pieces of space junk have the potential to cause catastrophic damage.

Roscmoscos said in a press release Thursday that the maneuver raised the space station’s orbit by about a mile (1.2 km). According to the Conversation, the ISS fired its rockets for just over six minutes to get out of the way. It happened just a day before the arrival of Crew-3 mission astronauts Thomas Marshburn, Raja Chari, Kayla Barron, and Matthias Maurer on the station.

This is the 29th time the space station has had to avoid space debris.

According to NASA, space debris is made up of fragments of often-defunct spacecrafts that have broken apart in orbit. According to NASA, it can travel at speeds of up to 17,500 mph, or about ten times the speed of a bullet.

At this speed, even a fleck of paint from a rocket can be dangerous, such as if it collides with an observation dome. “Space debris has the potential to cripple the ISS and kill the crew,” NASA Instructor and Flight Controller Robert Frost stated in a blog post in 2019. However, he stated that the risk is “highly managed.”

Ground-based crews track the largest pieces of space junk in order to give the ISS enough time to move out of the way.

According to the ESA, anything larger than a third of an inch (1 cm) could penetrate the shields of the ISS’s crew modules. According to the ESA, anything larger than 4 inches (10 cm) could shatter the station to pieces. According to NASA, the space junk in this case came from an anti-satellite test conducted in 2007, when China launched a missile against its own weather satellite – Fengyun-1C.

According to NASA, the collision resulted in approximately 3,500 large fragments and many smaller fragments.

It wasn’t immediately clear how large the fragments expected to collide with the ISS this Friday were, but NASA says ground teams only track larger objects larger than a softball.

Collisions with smaller debris can also be harmful and unpredictable. NASA previously reported that a small fragment had punched a 0.2-inch (5-millimeter) hole in one of the ISS’s robotic arms in June. Larger fragments are also becoming more difficult to track, as an increase in space flight activity has resulted in a dramatic increase in the number of fragments orbiting the planet.

NASA relocated the ISS last year after detecting “unknown space debris” that would have flown within a mile of the space station.

On that occasion, the astronauts remained sealed in a Soyuz rocke capsule, which could serve as an escape pod in the event that the station was damaged.