What If Another Depressurization Occurs?

Let’s delve into what might transpire if another depressurization incident occurs and how the crew would manage such a critical situation. The outcome hinges on several elements, notably the location of the breach and its dimensions. For illustration, imagine a perfectly circular hole measuring 5.6 mm in diameter (similar to a .22 caliber bullet).

In this scenario, a breach in the ISS's hull would result in an air leak rate of 0.009 kg/s, roughly translating to 40 cubic meters of air every hour. Given that the ISS has an internal volume of approximately 915.5 cubic meters, this would equate to a loss of about 4.4% of its air per hour.

While this loss may seem minor, it is still significant enough to warrant immediate action. The crew would not face instant danger, but it would be crucial to address the leak quickly. The software in the Russian module would raise an alarm roughly 45 minutes after the leak starts. Should that system fail, the American module's alarm would activate 15 minutes later. Moreover, the astronauts would likely feel pressure changes as their ears pop, akin to the sensation experienced during a plane's descent.

Once the alarm is triggered, the crew must take several steps:

1. Assemble together.
2. Assess the available time.
3. Check the integrity of the capsule for potential evacuation.
4. Identify the section of the station with the leak.
5. Isolate the affected segment from the rest of the station.
6. Attempt repairs to stop the leak if feasible.

The astronauts need to ascertain the time left before the pressure drops to a critical level of 490 mmHg. When the pressure reaches this threshold, all crew members must be inside either the Soyuz or Crew Dragon, depending on which craft is docked and the safety of the route to it. Therefore, verifying the integrity of the Soyuz/Crew Dragon is the top priority for emergency evacuation.

After ensuring the capsule's safety, the crew would congregate in the Russian segment and seal the hatch between the American and Russian sections. This will help determine which side of the station is affected by the leak.

If there is sufficient time—likely several hours in the case of a minor leak—the crew can navigate through the station's modules to locate the source of the leak. This is manageable by simply closing the hatches between compartments, which are designed to prevent automatic closure if a breach is detected.

Once the problematic module is identified, astronauts will utilize an ultrasonic detector to precisely locate the leak. They will then carry out necessary repairs and apply a patch if time permits.

The ISS is equipped with several kits for both internal and external sealing of depressurizations. If it becomes necessary to isolate the affected section, external repairs may be required, which involve working in open space.

Generally, small leaks measuring a few millimeters or centimeters do not pose a major risk to the station and can be effectively managed by the crew. Only larger breaches could lead to immediate evacuation scenarios.

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