Spacesuit question

"John Doe" wrote in message
s.com...
Bill Porter wrote:

This is probably a stupid question, but why can't they just move the
Orlan
suits from the Pirs to the Quest Airlock instead of going out the Pirs
and
having to translate all that distance to the Destiny module?

Going from 14.7 PSI indoors to 0 PSI outdoors requires a slow
decompression.
Astronauts go from 14.7 to about 4 or 5 PSI (forget which is used on
Russian
suits) of pure oxygen.

The transition takes time. For one thing, the crew needs to follow special
precedures to avoid getting the "bends" (blood releasing disolved nitrogen
which then forms bubbles in your body which are a big problem - think of
what
happens when you open a soda bottle).

During that time, the crew has their suits "plugged" into the airlock
systems
for power and O2, thus preserving their limited reserves inside their
suits.

What you are suggesting would require that once the crew have completed
their
acclimatization to pure O2 at 5PSI, they would repressurize the airlock so
they could ingress the station, then go to Quest, close the door and
slowly
depressurize that airlock to finally go outside. This would end up taking
much
more time than just opening the door in Pirs once theu are at 0 PSI and
walking to the work site. While NASA brags about the station being huge,
in
human terms, it isn't THAT big and from Pirs, it isn't THAT far to Z1
where
the CMGs are located.

But this brings up a question:

What happens if a US or Russian EVA suit, ready to go outdoors with pure
O2
are ~5 PSI, moves back into 14.7 PSI environment ? Will the crewmember be
able
to remain at 5 PSI ? Will the suit be able to continue to maintain a lower
pressure inside the suit than outside environment ?

Actually what I meant was why couldn't they just carry the suits over to the
Quest and put them on there... but your answer did bring up an interesting
question.

"hop" wrote in message
om...

{Rest of answer and other reply snipped]

You should really watch one of these things on NASA TV or the web
stream sometime. What you describe would most likely only work if the
entire station were depressureized (which, BTW would most likely kill
some of the avionics and control systems). Both kinds of spacesuits
use sublimators for cooling, and these are only effective in vacuum.
When inside a closed airlock, they are attached to fluid umbilicals.
Two reasons orlans can't currently use quest, AFAIK, are the two suits
systems use different coolant mixes (orlan is water plus glycol, US is
just water ?) and there isn't an orlan compatable communication system
in quest. Comms while setting up the suits is very useful, to make
sure the crew has followed the checklist and watch suit telemetry.

Aside from the cooling issue, getting out the airlock isn't a matter
of stepping into your suit, pressing the button, and stepping outside.
It takes a significant time, with various steps of depressurization
and leak checks (both of airlock-station and the suits). The suits
themselves operate around 5 PSI w/pure oxygen, while the station runs
around 15 PSI and 20% oxygen. This requires pre-breath of pure oxygen
to avoid the bends. All of the above requires time, which gets us back
to the cooling issue.

That said, the moving from the RS to the US didn't seem to give them
any serious trouble. The Strela is designed to hoist space walkers
around, and looked like a helluva ride. Imagine being on the end of a
very springy 50ft long pole, hanging out out in space...

Thanks! I was just wondering why go through all that trouble instead of just
moving the suits and putting them on in the Quest.

I figured it was probably an incompatability issue.... which brings up the
question of why, when they were planning for station equipment and
construction, didn't they either build in an "adapter" in the respective
airlocks so you can use one suit in the other airlock or just work on
designing new suits (or refitting current Orlan and US suits) to use a
standard "ISS" system.

..

Bill Porter wrote:
I figured it was probably an incompatability issue.... which brings up the
question of why, when they were planning for station equipment and
construction, didn't they either build in an "adapter" in the respective
airlocks so you can use one suit in the other airlock or just work on
designing new suits (or refitting current Orlan and US suits) to use a
standard "ISS" system.


Quest is commonly called the "joint" airlock. Parts of Quest are actually
supplied by the russians (some of the high pressure pumps for instance). The
airlock was designed to be outfitted with both EMU and Orlan suit support
equipment. The intent was to launch Quest with only US suit support (since the
russian side already had Orlan support), and later launch the additional
equipment to support Orlans. Not sure exactly when this equipment was to have
been launched though (was it a Shuttle launch ? or to be launched by Russians ?)

Having Quest outfitted with Orlan support is a "nice to have". But at this
point in time, there are far more important priorities in the station outfitting.

"Jeff Findley" wrote in message . ..
wrote in message
...
Of course, the Quest Airlock was specifically designed to support both
EMUs and ORLANs.


This is true, but it currently lacks some necessary equipment needed to
support an EVA using Russian suits.

Anyone who's really interested in the details can look them up themselves.
Google is your friend (and does newsgroup as well as Internet searches).

Jeff

Apparently, Google Groups 2 isn't posting my replies under the correct
messages - or I'm doing something wrong.

My reply to a similar post is:

Like what? What equipment is missing in the Quest airlock to support
ORLAN use?

As currently configured, the ORLAN can be hooked up to a Quest
umbilical and receive the appropriate O2 pressure, water and power.
In fact, you can right now have 1EMU and 1ORLAN connected.

Comms may be an issue...I'm not sure if Quest is configured for ORLAN
comms.

So, unless you're aware of specific equipment missing, I suggest there
is a different issue involved - perhaps procedural.

Cache!

(hop) wrote in message

You should really watch one of these things on NASA TV or the web
stream sometime. What you describe would most likely only work if the
entire station were depressureized (which, BTW would most likely kill
some of the avionics and control systems). Both kinds of spacesuits
use sublimators for cooling, and these are only effective in vacuum.
When inside a closed airlock, they are attached to fluid umbilicals.
Two reasons orlans can't currently use quest, AFAIK, are the two suits
systems use different coolant mixes (orlan is water plus glycol, US is
just water ?) and there isn't an orlan compatable communication system
in quest. Comms while setting up the suits is very useful, to make
sure the crew has followed the checklist and watch suit telemetry.


Well said. ORLAN, however uses water plus silver chloride. The EMU
uses iodated water. Mixing the two can potentially give you
silver-iodine salts which may precipitate out and result in scale on
piping...but not likely. The system can always be flushed.

Aside from the cooling issue, getting out the airlock isn't a matter
of stepping into your suit, pressing the button, and stepping outside.
It takes a significant time, with various steps of depressurization
and leak checks (both of airlock-station and the suits). The suits
themselves operate around 5 PSI w/pure oxygen, while the station runs
around 15 PSI and 20% oxygen. This requires pre-breath of pure oxygen
to avoid the bends. All of the above requires time, which gets us back
to the cooling issue.

I believe at ORLAN pressures of around 5.8 psid (vs. EMU 4.3 psid),
prebreathe time is 30 minutes. Interestingly, at EMU pressures,
prebreathe is 4 hours.

The depress time for the airlock is a scandalous 30+ minutes.


That said, the moving from the RS to the US didn't seem to give them
any serious trouble. The Strela is designed to hoist space walkers
around, and looked like a helluva ride. Imagine being on the end of a
very springy 50ft long pole, hanging out out in space...

John DOe wrote in message ws.com...
Bill Porter wrote:
I figured it was probably an incompatability issue.... which brings up the
question of why, when they were planning for station equipment and
construction, didn't they either build in an "adapter" in the respective
airlocks so you can use one suit in the other airlock or just work on
designing new suits (or refitting current Orlan and US suits) to use a
standard "ISS" system.


Quest is commonly called the "joint" airlock. Parts of Quest are actually
supplied by the russians (some of the high pressure pumps for instance). The
airlock was designed to be outfitted with both EMU and Orlan suit support
equipment. The intent was to launch Quest with only US suit support (since the
russian side already had Orlan support), and later launch the additional
equipment to support Orlans. Not sure exactly when this equipment was to have
been launched though (was it a Shuttle launch ? or to be launched by Russians ?)


I thought I might argue your point regarding the intent to launch with
only US suit support, but on reflection, I think you're correct. The
Quest was launched with the necessary equipment to hook an ORLAN up
and supply it with appropriate consummables. You can do that now.
But I don't think MOD came up with any procedures for doing this.
Also, there is an issue about comms, ORLAN prep equipment, water
compatibility...but mostly procedures.

In an emergency, I believe 2 ORLANs could exit QUEST. They may not be
able to talk to ground control until they're outside...or to each
other...but they could do it.

It's a bit of a shame because a lot of money and time went into
designing and building this support equipment...and it's not being
used for its intended purpose.



Having Quest outfitted with Orlan support is a "nice to have". But at this
point in time, there are far more important priorities in the station outfitting.

Too true.


Cache!

John Doe wrote in message ws.com...
Bill Porter wrote:

This is probably a stupid question, but why can't they just move the Orlan
suits from the Pirs to the Quest Airlock instead of going out the Pirs and
having to translate all that distance to the Destiny module?

Going from 14.7 PSI indoors to 0 PSI outdoors requires a slow decompression.
Astronauts go from 14.7 to about 4 or 5 PSI (forget which is used on Russian
suits) of pure oxygen.

The transition takes time. For one thing, the crew needs to follow special
precedures to avoid getting the "bends" (blood releasing disolved nitrogen
which then forms bubbles in your body which are a big problem - think of what
happens when you open a soda bottle).

During that time, the crew has their suits "plugged" into the airlock systems
for power and O2, thus preserving their limited reserves inside their suits.

What you are suggesting would require that once the crew have completed their
acclimatization to pure O2 at 5PSI, they would repressurize the airlock so
they could ingress the station, then go to Quest, close the door and slowly
depressurize that airlock to finally go outside. This would end up taking much
more time than just opening the door in Pirs once theu are at 0 PSI and
walking to the work site. While NASA brags about the station being huge, in
human terms, it isn't THAT big and from Pirs, it isn't THAT far to Z1 where
the CMGs are located.

But this brings up a question:

What happens if a US or Russian EVA suit, ready to go outdoors with pure O2
are ~5 PSI, moves back into 14.7 PSI environment ? Will the crewmember be able
to remain at 5 PSI ? Will the suit be able to continue to maintain a lower
pressure inside the suit than outside environment ?

The suits would have to be maintained about 5-6 psid above ambient.
Think about the prebreathe protocol. They don't float around in a
vacuum for half an hour. Once they get in their suits, they just
pressurize them with pure O2 until they're at ~5.5 psid (for ORLAN,
~4.3 psid for EMU). During this time, they do leak checks (isolate O2
to the umbilical, check suit pressure for awhile). Then the airlock
is depressurized to ~5 psi (which means the suits are now at ~10 psi),
more leak checks. Finally, the airlock is depressurized to vacuum.

All of this is from the Quest airlock perspective...PIRS procedures
may be somewhat different, but the concept is the same.

If they had to move back to a 14.7 psi environment, the suits are
repressurized with O2 to maintain their d/p above airlock pressure.
O2 is used so as not to destroy the prebreathe (i.e. to avoid
introducing N2 back into the bloodstream).

If the outside environment pressure gets above suit pressure, suit
relief valves open up to allow pressure in. Technically, these are
negative pressure relief valves. If it weren't for these, you run the
risk of crushing an astronaut/cosmonaut in his/her own suit.
Similarly, if suit d/p was too high above environment, positive
pressure relief valves open to prevent suit damage. In fact, this is
how the EMU is depressurized when the airlock is going to vacuum...by
relying on the positive pressure relief to let the O2 out!

It's feasible to leave off the umbilical and make your way to another
airlock, but the loss of cooling means you'll start to overheat after
about 5 minutes...especially with any kind of exertion. There are
ways to mitigate this, but they use up lots of oxygen.

-Cache!

cache wrote:
vacuum for half an hour. Once they get in their suits, they just
pressurize them with pure O2 until they're at ~5.5 psid (for ORLAN,
~4.3 psid for EMU). During this time, they do leak checks (isolate O2
to the umbilical, check suit pressure for awhile). Then the airlock
is depressurized to ~5 psi (which means the suits are now at ~10 psi),
more leak checks. Finally, the airlock is depressurized to vacuum.

Why would they pressurize suits from 14.7 to about 19psi before reducing
pressure back ?

Wouldn't it be safer (from bends perspective) and faster to just lower airlock
pressure and only lower suit pressure once differential has reached the suit's
design pressure difference (~5psi) ?

"John Doe" wrote in message
s.com...
cache wrote:
vacuum for half an hour. Once they get in their suits, they just
pressurize them with pure O2 until they're at ~5.5 psid (for ORLAN,
~4.3 psid for EMU). During this time, they do leak checks (isolate O2
to the umbilical, check suit pressure for awhile). Then the airlock
is depressurized to ~5 psi (which means the suits are now at ~10 psi),
more leak checks. Finally, the airlock is depressurized to vacuum.

Why would they pressurize suits from 14.7 to about 19psi before reducing
pressure back ?

Wouldn't it be safer (from bends perspective) and faster to just lower
airlock
pressure and only lower suit pressure once differential has reached the
suit's
design pressure difference (~5psi) ?

Because the suits are pressurized with pure O2, so this would have no effect
on the bends (which is caused by excess N2 in the body).

Jeff

John Doe wrote in message ws.com...
cache wrote:
vacuum for half an hour. Once they get in their suits, they just
pressurize them with pure O2 until they're at ~5.5 psid (for ORLAN,
~4.3 psid for EMU). During this time, they do leak checks (isolate O2
to the umbilical, check suit pressure for awhile). Then the airlock
is depressurized to ~5 psi (which means the suits are now at ~10 psi),
more leak checks. Finally, the airlock is depressurized to vacuum.

Why would they pressurize suits from 14.7 to about 19psi before reducing
pressure back ?

Wouldn't it be safer (from bends perspective) and faster to just lower airlock
pressure and only lower suit pressure once differential has reached the suit's
design pressure difference (~5psi) ?

In the past, at least with EMUs, there was a 4-hour prebreathe and a
3rd crewmember onboard. Once you're in the suit, with the airlock at
ambient pressure and the 3rd crewmember assisting, you perform a leak
check. A proper leak check requires the suit to be at the operating
d/p of 4.3 psid. Once the leak check is complete, the prebreathe
timer is started and you hang out for 4 hours before the airlock is
buttoned up.

You don't have to remain at 4.3 psid during the entire
prebreathe...you can reduce pressure by opening a purge valve to get
down to ~0.9 psid, which makes for a more comfortable prebreathe.

There really is no reason to depressurize the airlock prematurely.
From the suit perspective, the ambient pressure is not important.
Only the d/p matters. From the crew perspective, the EVA team remains
accessible to the rest of the station, until the last half-hour, when
they start the rest of the depress preps.

Cache!