Atmosphere in Shuttle / Iss

[Brian Gaff]

OK, I've tried to understand exactly what the atmosphere in the Shuttle and
ISS is, but am presented with a bewildering set of figures....

I was wondering whether any of the assembled folk would care to explain the
pressure and make up and how much it differs from the Earth's and the
pressurisation in a typical high flying jet.

I was interested mainly because of the implications in a fire. I noted in
some reports from the Iss, for instance, that current spikes were seen from
a fan motor, which must mean, I'd say that its a brushed motor and that the
brushes/comutator are getting worn and probably sparking a lot!

Brian

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[jeff findley]

"Brian Gaff" > writes:
>
> OK, I've tried to understand exactly what the atmosphere in the Shuttle and
> ISS is, but am presented with a bewildering set of figures....

I thought it essentially an O2 and N2 mix at very nearly the mixture
and pressure found on Earth at sea level. Is this not the case?

Jeff
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[Greg D. Moore \(Strider\)]

"jeff findley" > wrote in message
...
> "Brian Gaff" > writes:
> >
> > OK, I've tried to understand exactly what the atmosphere in the Shuttle
and
> > ISS is, but am presented with a bewildering set of figures....
>
> I thought it essentially an O2 and N2 mix at very nearly the mixture
> and pressure found on Earth at sea level. Is this not the case?

It is. Especially on ISS they want to replicate it fairly close to
sea-level air-pressure. It makes experiments easier to control.

Also, you can rely on convection for cooling.

The shuttle will lower pressure to I think around 10psi before a spacewalk
to reduce pre-breath time for the astronauts performing the EVA.



>
> Jeff
> --
> Remove "no" and "spam" from email address to reply.
> If it says "This is not spam!", it's surely a lie.

[Herb Schaltegger]

In article >,
jeff findley > wrote:

> "Brian Gaff" > writes:
> >
> > OK, I've tried to understand exactly what the atmosphere in the Shuttle and
> > ISS is, but am presented with a bewildering set of figures....
>
> I thought it essentially an O2 and N2 mix at very nearly the mixture
> and pressure found on Earth at sea level. Is this not the case?
>
> Jeff

It is nominally (within a small range of variability) 20% O2, 80% N2 at
14.7 pisa. The next-highest levels of trace constituents are H20 vapor
and CO2, both of which are actively (and specifically) controlled. All
other trace gases (methane, some CO, ammonia, and more than a few
others) are actively reduced and controlled by the station ECLSS.

A standard commercial aircraft pressurization system will maintain the
aircraft at approximately 8,000 feet ASL-equivalent pressure.

--
Herb Schaltegger, Esq.
Chief Counsel, Human O-Ring Society
"I was promised flying cars! Where are the flying cars?!"
~ Avery Brooks

[HOST Comp JimS]

> [what is] the pressure and make up and how much it differs
>from the Earth's and the pressurisation in a typical high flying jet.


The air on the shuttle is kept close to sea level conditions on Earth,
with 14.7 pounds per square inch of pressure, and an oxygen/nitrogen
mixture that contains 21% oxygen.

I believe it's about the same on the ISS.

A high-flying commercial jet doesn't try to maintain sea-level pressure
(14.7 pounds) because the pressure differential would add strain to the
fuselage and would require a stronger, more expensive fuselage, so
they just pressurize it to what you'd find at an an altitude of 5,000 to
8,000 feet.


>I was interested mainly because of the implications in a fire.

Fire is indeed a major concern on spacecraft. The most famous and
tragic incident was the Apollo 1 fire that resulted in the death of 3
astronauts while on a training exercise on the pad. But in that
instance, the capsule was pressurized to a much higher oxygen
content than normal (90% pure oxygen at over 16 psi, I think), causing
the fire to burn much more intensely than it normally would.

Another major incident was a fire on board the Mir space station. Although
downplayed by officials at the time, it was actually a very serious incident
and the astronauts and cosmonauts initially thought that they'd probably
have to abandon ship. Their fire extinguishers had little effect and dense
smoke filled the station, but the fire eventually burned out on its own.

Jim

[Hallerb]

>Another major incident was a fire on board the Mir space station. Although
>downplayed by officials at the time, it was actually a very serious incident
>and the astronauts and cosmonauts initially thought that they'd probably
>have to abandon ship. Their fire extinguishers had little effect and dense
>smoke filled the station, but the fire eventually burned out on its own.
>
>Jim
>

The problem was the fire was between the astronauts and their soyuz escape
craft. It was a very bad problem nd they were very lucky.

[Richard Cochran]

"Greg D. Moore \(Strider\)" > wrote in message >...
> "jeff findley" > wrote in message
> ...
> > "Brian Gaff" > writes:
> > >
> > > OK, I've tried to understand exactly what the atmosphere in the Shuttle
> and
> > > ISS is, but am presented with a bewildering set of figures....
> >
> > I thought it essentially an O2 and N2 mix at very nearly the mixture
> > and pressure found on Earth at sea level. Is this not the case?
>
> It is. Especially on ISS they want to replicate it fairly close to
> sea-level air-pressure. It makes experiments easier to control.
>
> Also, you can rely on convection for cooling.

Not in microgravity, you can't. Convection requires a gravity
field. Of course, you can still get cooling via conduction, and
fans can create airflow that makes it still more effective, but
strictly speaking, convection won't happen without gravity.

Jim Lovell talks about this in his "Lost Moon" book. When the
Apollo 13 astronauts were fighting cold, trying to sleep in the
CM, they could stay warmer by remaining as still as possible.
The air around them would be warmed by body heat, and with
no convection to carry it away, the warm layer would stay
right there. But any slight movement would disturb this
thin layer of warm air.

--Rich

[Bob Bernatchez]

On 18 Jul 2003 17:37:06 GMT, (HOST Comp
JimS) wrote:


>>I was interested mainly because of the implications in a fire.
>
>Fire is indeed a major concern on spacecraft. The most famous and
>tragic incident was the Apollo 1 fire that resulted in the death of 3
>astronauts while on a training exercise on the pad. But in that
>instance, the capsule was pressurized to a much higher oxygen
>content than normal (90% pure oxygen at over 16 psi, I think), causing
>the fire to burn much more intensely than it normally would.
>

>Jim
IIRC, the atmosphere on Apollo 1 was 100% oxygen at 5psi. This was
maintained throughout the program, although it was changed for ground
testing.

Regards,

Bob Bernatchez

[Greg D. Moore \(Strider\)]

"Richard Cochran" > wrote in message
om...

> Not in microgravity, you can't. Convection requires a gravity
> field. Of course, you can still get cooling via conduction, and
> fans can create airflow that makes it still more effective, but
> strictly speaking, convection won't happen without gravity.

Conduction is what I mean. :-)

[Brian Gaff]

"Bob Bernatchez" > wrote in message
...
| On 18 Jul 2003 17:37:06 GMT, (HOST Comp
| JimS) wrote:
|
|
| >>I was interested mainly because of the implications in a fire.
| >
| >Fire is indeed a major concern on spacecraft. The most famous and
| >tragic incident was the Apollo 1 fire that resulted in the death of 3
| >astronauts while on a training exercise on the pad. But in that
| >instance, the capsule was pressurised to a much higher oxygen
| >content than normal (90% pure oxygen at over 16 psi, I think), causing
| >the fire to burn much more intensely than it normally would.
| >
|
| >Jim
| IIRC, the atmosphere on Apollo 1 was 100% oxygen at 5psi. This was
| maintained throughout the program, although it was changed for ground
| testing.
|
| Regards,
|
| Bob Bernatchez
OK, so that would rule out the Apollo being used as a lifeboat on the Iss,
if that is so, and the Soyuz is used, does that imply that the Soyuz uses
the same pressurisation as the ISS? However, it cannot or the link up
between that Soyuz and Apollo who's anniversary we just went through, would
not have worked, would it?

Are you still with me?

Are we saying that the Soyuz can stand the pressure, but the Apollo could
not, or was the atmosphere just such a low pressure for weight reasons?

Brian

--
Brian Gaff....
graphics are great, but the blind can't hear them
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[Jorge R. Frank]

"Brian Gaff" > wrote in
:

> "Bob Bernatchez" > wrote in message
> ...
>| On 18 Jul 2003 17:37:06 GMT, (HOST Comp
>| JimS) wrote:
>|
>| >>I was interested mainly because of the implications in a fire.
>| >
>| >Fire is indeed a major concern on spacecraft. The most famous and
>| >tragic incident was the Apollo 1 fire that resulted in the death of
>| >3 astronauts while on a training exercise on the pad. But in that
>| >instance, the capsule was pressurised to a much higher oxygen
>| >content than normal (90% pure oxygen at over 16 psi, I think),
>| >causing the fire to burn much more intensely than it normally would.
>|
>| IIRC, the atmosphere on Apollo 1 was 100% oxygen at 5psi. This was
>| maintained throughout the program, although it was changed for ground
>| testing.
>
> OK, so that would rule out the Apollo being used as a lifeboat on the
> Iss,

Well, it would rule out a *stock* Apollo, sure. But the tooling to build a
stock Apollo doesn't exist any more, so you might as well re-engineer the
basic shape for 14.7 psia while you're at it.

> if that is so, and the Soyuz is used, does that imply that the
> Soyuz uses the same pressurisation as the ISS?

Yes.

> However, it cannot or
> the link up between that Soyuz and Apollo who's anniversary we just
> went through, would not have worked, would it?

Apollo carried a Docking Module for docking with Soyuz. It wasn't just a
docking adapter; it acted as an airlock for pressure equalization between
the two vehicles. At no time during Apollo-Soyuz were *all* the hatches
between the Apollo and the Soyuz open.

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[Tim Kozusko]

Ian Stirling > wrote in message
...
> "Greg D. Moore \(Strider\)" > wrote:

> If you substitute He for N, then you can improve conduction a bit.
> There are side effects though.

lol! True.
Clever use of pitch-shifting software could make it bearable.

[Tim Kozusko]

Bob Bernatchez > wrote in message
...

> IIRC, the atmosphere on Apollo 1 was 100% oxygen at 5psi.

In space it was. On the ground the capsule would have collapsed - if the
hatch would even seal with the over-pressure the wrong way round. So they
pumped it up to just over one atmosphere. Jesus what were they thinking...

At sea level the partial pressure of oxygen is a little less than 5psi. Due
to the way gasses behave, you can be in an atmosphere of pure O2 at that
pressure and get just as much O2 in your blood as in regular air at sea
level.

[jeff findley]

Bob Bernatchez > writes:
> IIRC, the atmosphere on Apollo 1 was 100% oxygen at 5psi. This was
> maintained throughout the program, although it was changed for ground
> testing.

Apollo 1 was 5 psig, which put it at nearly 20 psia, right? This is
what caused the fire to be so terrible. In orbit, 5 psi (absolute
pressure and gauge pressure being equal in vacuum) of O2 wasn't such a
fire hazard.

Jeff
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[Greg D. Moore \(Strider\)]

"jeff findley" > wrote in message
...
> Bob Bernatchez > writes:
> > IIRC, the atmosphere on Apollo 1 was 100% oxygen at 5psi. This was
> > maintained throughout the program, although it was changed for ground
> > testing.
>
> Apollo 1 was 5 psig, which put it at nearly 20 psia, right? This is
> what caused the fire to be so terrible. In orbit, 5 psi (absolute
> pressure and gauge pressure being equal in vacuum) of O2 wasn't such a
> fire hazard.

I've heard varying numbers from 17 to 19 psia. So you're in the ballpark.
And yes, it wasn't the O2 per se, it was extreme amount of it at that
pressure.

>
> Jeff
> --
> Remove "no" and "spam" from email address to reply.
> If it says "This is not spam!", it's surely a lie.

[Doug...]

In article <0M5Ta.25190$zy.3406@fed1read06>,
says...
> "Greg D. Moore (Strider)" > wrote in message
> ...
> >
> > "jeff findley" > wrote in message
> > ...
> > > Bob Bernatchez > writes:
>
> > > > IIRC, the atmosphere on Apollo 1 was 100% oxygen at 5psi. This was
> > > > maintained throughout the program, although it was changed for ground
> > > > testing.
> > >
> > > Apollo 1 was 5 psig, which put it at nearly 20 psia, right? This is
> > > what caused the fire to be so terrible. In orbit, 5 psi (absolute
> > > pressure and gauge pressure being equal in vacuum) of O2 wasn't such a
> > > fire hazard.
> >
> > I've heard varying numbers from 17 to 19 psia. So you're in the ballpark.
> > And yes, it wasn't the O2 per se, it was extreme amount of it at that
> > pressure.
>
> IIRC, After Apollo 1 they used 60/40 O2/He at 14.7 psi at liftoff, during
> ascent this was purged and they then switched to 5 psi pure O2 which was
> determined to be safe with the removal of combustibles to the maximum extent
> possible. I think the Apollo 1 was around 98% O2 at 16.2 psi when the fire
> started. I am going through my collection of Apollo 1 documents and I'll
> post a correction if the numbers I have cited are incorrect. The rapid
> increase in pressure within the Apollo 1 command module rose to 29 psi or so
> prior to rupturing.

He? I always thought it was nitrogen.

Otherwise, yes -- the Apollo 1 was pressurized to a relative psi of about
3 above ambient sea level, and it was very close to pure oxygen.

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