Assembly of the International Space Station (ISS) began in 1998. Since then, it has become a giant orbital outpost the size of a football field. But while its size is impressive, it also makes the ISS a convenient target for the many chunks of space debris in orbit. Is there a way to protect yourself from it and what happens if the station collides with some space object?
Micrometeorite threat
The orbit of the Earth is a busy place, as thousands of objects, the size of which does not exceed a few centimeters, as well as millions of smaller pieces, are floating around our planet. Therefore, the ISS inevitably gets hit by micrometeorites every day, but fortunately, there are safety measures in place to ensure that nothing catastrophic happens.
One of the most notable collisions occurred in 2012, when a small meteorite hit the station's module window. The emergency shutter automatically closed the windows to prevent pressure loss in the airless space in the event of a leak. However, the damage was not serious and no leakage occurred, so the valve was later removed.
In 2013, astronauts noticed another impact on the ISS. A very small hole, about the size of a bullet, appeared in one of its solar panels. The damage was caused by an unknown piece of debris. “I am glad this object did not hit the corps,” the station commander Chris Hadfield, a Canadian, wrote later on his Twitter account.
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The station's hull is reinforced to withstand impacts. It is capable of handling micrometeorites up to 1 cm in diameter. If a larger meteorite enters the hull, there is a risk of puncture, as a result of which the station may be depressurized.
Protective zone
To prevent such incidents, the station has a protection zone to measure several kilometers of space around it. It is tracked by the United States Space Observing System. If any large debris is detected that enters this area, the station is moved using onboard gyroscopes and steering gear to get out of the danger area.
“The ISS will begin to maneuver away from the object if the probability of a collision is greater than 1 in 10,000,” said NASA's public relations officer Daniel Huot. - This usually happens about once a year (although there were no such maneuvers in 2016). Over the entire history of the station, there have been 23 cases of space debris evasion”.
However, this system cannot be said to be flawless. In some cases, the object may be seen too late to give the ISS time to maneuver. In this case, the crew must be evacuated to the Soyuz spacecraft, which acts as a lifeboat.
Collision with a large object
If the ISS collides with a large object, it will be impossible to save it. In this case, the crew will have to detach and return to Earth. Up to six people are at the station at any time. All of them will be able to evacuate on two Soyuz spacecraft, if necessary, three people each. Such evacuations have occurred several times, including in 2015, although the crew never had to be detached.
Since November 2, 2000, the ISS has been continuously manned, so this defense scenario cannot be called ideal. But the station can mostly be controlled from Earth, so astronauts will simply have to close many of the hatches before leaving to insulate the modules.
Although in the event of a collision, when evacuation is necessary, the crew will have to follow a number of procedures. If the body of the station is damaged due to impact, it will begin to lose pressure. Onboard sensors will be able to determine its difference and will give a sound signal. In addition, the crew is also able to detect pressure changes.
Necessary procedures
After the alarm is triggered, the crew will have to follow a series of procedures: Warn, Gather, Work - this is a general emergency response. Crew members will have to gather at the Russian main center, called Zvezda, as this will ensure that they can safely reach the Soyuz spacecraft and detach if necessary.
Team members will have to work until the pressure reaches dangerously low levels. If they cannot repair the leak before this time, they will have to seal the hatches in the segment that was damaged. The nature of the damage will determine whether it is worthwhile to isolate the crew in the spacecraft.
Damage to ships for evacuation
It can also happen that a pressure loss occurs in one of the Soyuz spacecraft. In this case, the crew members will act depending on which part of the ship was damaged. Each Soyuz spacecraft has three segments, but only one (descent module) is needed to return to Earth. If some other segment is damaged, such as an orbital module, the crew can still safely return home.
But if a pressure loss occurs precisely in the descent module of one Soyuz spacecraft, the crew will have to manually undock it while remaining at the station and send it to an unmanned re-entry. In this case, most likely, a new unmanned spacecraft "Soyuz" will be launched to the ISS to safely return the crew to Earth, but at a later stage.
Depressurization of the station
In addition, pressure loss can occur at the station. In this case, the team will use gateways to contain the insulation leak. Its members will gradually use the hatches to work where the leak occurred, in the Russian or American segment, and then isolate the damaged module.
After identifying the damaged module and ensuring the safety of the crew, astronauts will need to work with a team on Earth to resolve the issue. The leak rate is likely to be very slow, and when a vacuum develops in the module, the crew can start looking for a solution.
The station has equipment with which it is possible to repair the damage site, but for this, most likely, two astronauts will have to perform a spacewalk outside the station. They can also wear suits inside to repair damage, as was done earlier on the Mir space station in the late 1990s.
“The highest priority is crew safety,” Huot said. "We will never send astronauts to a leaky module unless we are 100 percent sure we have a plan to keep the crew and the rest of the ISS safe."
Threat of serious injury
If the damage cannot be repaired, the entire crew will have to leave the station and return to Earth, as previously mentioned. Of course, there are scenarios in which the damage can be much more serious, and then the depressurization will occur much faster. According to Huot, procedures have been developed, including the relocation of the station, which are designed to prevent such major emergencies.
The ISS is slated to remain in orbit until at least 2024, although possibly longer. We hope that the crew will never need to evacuate.
Anna Pismenna