Was the recent ISS leak imminently dangerous?

[Tom Hammer]

The ISS suffered a leak apparently caused by a 1/8 inch hole left during manufacture and never repaired. On Quora, the claim has been made that such a hole with one atm of pressure difference would only cause 324 cu ft of air to rush out per hour. I don't think this is close to correct, but I am lacking data re pressure differences, nozzle size, and air flow. Does anyone have a good table of references to help out?

 

[Cutter Ketch]

The relevant formula is conductance of a tube. I am familiar with it from John H Moore’s brilliant and essential “Building Scientific Apparatus”, but it appears many places. There are two formulae for two different conditions. Here the viscous flow condition applies and the conductance of air through an orifice D cm in diameter and L cm long is

12.1 D^3 / L liters/sec

Lets say the wall is 2 mm thick and you mentioned the hole was the hole was 3 mm in diameter giving a conductance of ~2 l/s

The flow rate is the the conductance times the pressure differential. Here that is 1 atmosphere, so the hole leaks something like 2 l-atm / s or 7200 l - atm / hour. 1 cu ft is 28 l so that is 260 cu ft / hour. Given the precision of my estimates, I think that is close enough to make 320 plausible as the correct number.

 

[fresh_42]

Has anyone references whether they really run the station on 1 atm?

 

[Cutter Ketch]

Has anyone references whether they really run the station on 1 atm?

Ah, yes. Forgot about that. A quick Google search indicates they do actually pressurize to 1 atmosphere, but, that didn’t have to be the case. Actually, why do they? Important for long duration?

 

[fresh_42]

Ah, yes. Forgot about that. A quick Google search indicates they do actually pressurize to 1 atmosphere, but, that didn’t have to be the case. Actually, why do they? Important for long duration?

I meant it as an interesting question, rather than a criticism. I guess they also lose a bit of pressure while outside missions or during docking maneuvers. As pressure might cause material fatigue it would be interesting to know what medical needs require - or what pressure the MIR had. E.g. on the ASTP mission 1975 there was a difference (Wikipedia):

As the atmosphere aboard the Apollo pure oxygen was used with a pressure of 34% of the Earth's atmosphere. On board the Soyuz, on the other hand, normal air (nitrogen-oxygen mixture) was breathed under normal pressure.

Found on some Wiki page:
"There in the space station, where people are staying, there is an atmosphere that is adapted in terms of pressure and composition of the Earth (21% oxygen and 78% nitrogen at 1014 hPa)."

I've looked at a 37Mb pdf from Nasa where they explain how alien gases are found, how the recycling system works, that the space suits have 100% oxygen and many, many facts, but nothing about the cabin air conditions.

 

[256bits]

https://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/eclss/cabinpress.html
Space shuttle,

The cabin is pressurized to 14.7 psia, plus or minus 0.2 psia, and maintained at an average 80-percent nitrogen and 20-percent oxygen mixture by the air revitalization system. Oxygen partial pressure is maintained between 2.95 and 3.45 psi, with sufficient nitrogen pressure of 11.5 psia added to achieve the cabin total pressure of 14.7 psia, plus or minus 0.2 psia.

Kind of makes sense, as instrumentation and materials could all be tested at ground level under atmospheric conditions, rather than having one more design criteria of functionality under oxygen rich and reduced pressure.

 

[Steelwolf]

The All Oxy Atmosphere, aside from EVA in suits, was discontinued after the Apollo 1 fire on the ground, with Chaffee, White and Grissom. Since then it has been mixed gas due to the extreme fire hazard of the electronics and avionics packages.

 

[Cutter Ketch]

The All Oxy Atmosphere, aside from EVA in suits, was discontinued after the Apollo 1 fire on the ground, with Chaffee, White and Grissom. Since then it has been mixed gas due to the extreme fire hazard of the electronics and avionics packages.

But not always 1 atm

 

[fresh_42]

The All Oxy Atmosphere, aside from EVA in suits, was discontinued after the Apollo 1 fire on the ground, with Chaffee, White and Grissom. Since then it has been mixed gas due to the extreme fire hazard of the electronics and avionics packages.

This doesn't quite match up with

"Stafford and Slayton meanwhile had entered the docking module and closed behind them the hatch (no. 2) leading to the CSM. They raised the pressure from 255 to 490 millimeters by adding nitrogen to the previously 78 percent oxygen atmosphere. In Soyuz, the crew had reduced the cabin pressure to 500 millimeters before the docking. The pressure in the tunnel between the docking module hatch (no. 3) and the Soyuz hatch (no. 4) had been raised from zero to equal that of the docking module. Leonov and Kubasov were the first to open the hatch leading to the international greeting. During the transfer that was to follow, the pressure in the DM and Soyuz would be the same - 510 millimeters."
https://www.hq.nasa.gov/office/pao/History/SP-4209/ch11-4.htm

 

[Nugatory]

A bit of a digression, but the Apollo 1 fire has already been mentioned, and it is relevant to the tradeoffs between pressure and composition of atmosphere...

Apollo 1 was designed to operate in space with about 5 psi internal pressure, about what you'd find at the top of the highest mountain peaks. This lowered the required structural strength and hence the weight of the spacecraft , but required an oxygen atmosphere just as mountaineers require oxygen at altitude. (The oxygen atmosphere also simplified preparations for space walks, as the space suits operated on pure oxygen).

However, on the ground the capsule is subject to 14.7 psi external air pressure and cannot be operated with negative internal pressure, so the Apollo 1 test was done at an internal pressure of a bit over 16 psi. 16 psi oxygen is an extraordinarily high fire risk - any random spark can turn anything that will oxidize in air when heated into pyrotechnics, and that's what happened to Apollo 1.

There were several other oxygen atmosphere accidents at about that time and together they led to a consensus that the engineering advantages of pure oxygen atmospheres justified the fire risk only when low pressure and weight was absolutely paramount. And even then much effort goes into eliminating flammable materials around oxygen under pressure.

 

[LURCH]

It is true that radiation from the solar wind would be harmful to life as we know it. But non-carbon based life forms have been discussed many times on past PF threads. Lacking details, its hard to say how sensitive they might be to radiation.

It is also true that we have life on Earth at the mid-ocean vents so deep in water as to be unaffected by radiation at the surface.

So it comes down to the perpetually elusive problem, Provide an all-inclusive definition of life.

A bit of a digression, but the Apollo 1 fire has already been mentioned, and it is relevant to the tradeoffs between pressure and composition of atmosphere...

Apollo 1 was designed to operate in space with about 5 psi internal pressure, about what you'd find at the top of the highest mountain peaks. This lowered the required structural strength and hence the weight of the spacecraft , but required an oxygen atmosphere just as mountaineers require oxygen at altitude. (The oxygen atmosphere also simplified preparations for space walks, as the space suits operated on pure oxygen).

However, on the ground the capsule is subject to 14.7 psi external air pressure and cannot be operated with negative internal pressure, so the Apollo 1 test was done at an internal pressure of a bit over 16 psi. 16 psi oxygen is an extraordinarily high fire risk - any random spark can turn anything that will oxidize in air when heated into pyrotechnics, and that's what happened to Apollo 1.

There were several other oxygen atmosphere accidents at about that time and together they led to a consensus that the engineering advantages of pure oxygen atmospheres justified the fire risk only when low pressure and weight was absolutely paramount. And even then much effort goes into eliminating flammable materials around oxygen under pressure.

Brngs up an obvious question; how did they regulate pressure during the launch? If the capsule had to be at 1 atmosphere on the launch pad, but needed to be 1/3 atmosphere by the time it got to orbit, it sounds as if they would have needed to leave open a vent until they reached a certain altitude, then close it.

For that matter, how was the leak in the OP dealt with?

 

[Tom.G]

For that matter, how was the leak in the OP dealt with?

• First someones thumb, Sorry, can't find the reference now.
• "thermoresistant tape" (https://phys.org/news/2018-08-space-station-leak-crew-danger.html)
• and/or "Epoxy" (https://www.space.com/41694-space-station-air-leak-fixed.html)
• and/or "a sealant" (https://phys.org/news/2018-08-russia-space-station-air-pressure.html)

 

[anorlunda]

I wonder. How significant the internal pressure could be to the ISS structural rigidity calculations?

 

[Nugatory]

More on the ISS leak:
https://www.theatlantic.com/science...tional-space-station-nasa-russia-leak/569692/

Atlantic Monthly is a well-regarded publication, but all early reporting on failures of complex engineered systems should be considered provisional - there's a reason why the investigations take a long time.

 

[bob012345]

I wonder. How significant the internal pressure could be to the ISS structural rigidity calculations?

Very likely not too much. However other structures such as the Bigelow inflatable space habitat structures, it's everything.

https://en.m.wikipedia.org/wiki/Bigelow_Aerospace