CDRA suffers another failure

NASA TV is currently showing 2 station crewmembers trying to fix the
CDRA (Carbon Dioxide Removal Assembly). Ground generated a plan to fix
it which will take about 6 hours of work.

The CDRA is much bigger than I had imagined it to be.

NASA TV commentator mentioned something about a heater controller, so I
assume this would have something to do with the "cleaning phase" to
outgas the accumulated CO2 to space.


What is the backup plan if it cannot be fixed ? Can they use EVA LiOH
filters into the station's ventilation system to clean the air ?

John Doe wrote:

NASA TV is currently showing 2 station crewmembers trying to fix the
CDRA (Carbon Dioxide Removal Assembly). Ground generated a plan to fix
it which will take about 6 hours of work.

The CDRA is much bigger than I had imagined it to be.

NASA TV commentator mentioned something about a heater controller, so
I assume this would have something to do with the "cleaning phase" to
outgas the accumulated CO2 to space.


What is the backup plan if it cannot be fixed ? Can they use EVA LiOH
filters into the station's ventilation system to clean the air ?

While the Shuttle was there it overheated and they were controlling it
from the ground, I guess they though a software patch could fix it.
Probably the backup plan is to use the Russian scrubber. I think they
said they have around a month of backup LiOH.

Can the Russian scrubber keep up?

OK, if I have this right the situation was that the heater main circuit
failed during the Shuttle docked period. Then the software refused to start
the bed up because of the heater problem, or so they thought. Saving time
they switched to the back up heater, and controlled it manually from the
ground. Remember this is only one of two alternating systems. One is gassing
while the other scrubs.

However, after some days, the thing gave indications of the controller
failing, which put that channel completely off line. Thinking logically, the
ground thought.. PSU has been damaged and it is why the heater and
controller are acting up. So the plan, as I gather it is to firstly check
for shorts or funny values of resistance in the system, then probably patch
in a spare supply. However, if the controller and heater are knackered, then
they would need to change the hardware in that channel out.

I've not heard the result of the resistance checks, but methinks that the
psu may well have totalled the heater and the controller in some way and
thus a new supply and assembly is going to be needed.

Does not sound awfully reliable to me, one would have thought psus and other
control equipment would be designed to fail safe.

Brian

--
Brian Gaff -
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"Craig" wrote in message
...
John Doe wrote:

NASA TV is currently showing 2 station crewmembers trying to fix the
CDRA (Carbon Dioxide Removal Assembly). Ground generated a plan to fix
it which will take about 6 hours of work.

The CDRA is much bigger than I had imagined it to be.

NASA TV commentator mentioned something about a heater controller, so
I assume this would have something to do with the "cleaning phase" to
outgas the accumulated CO2 to space.


What is the backup plan if it cannot be fixed ? Can they use EVA LiOH
filters into the station's ventilation system to clean the air ?

While the Shuttle was there it overheated and they were controlling it
from the ground, I guess they though a software patch could fix it.
Probably the backup plan is to use the Russian scrubber. I think they
said they have around a month of backup LiOH.

Can the Russian scrubber keep up?

As I have heard over the last day or so, the main channel a and b heater
pads, and there are several pads in each bed, are overlaid, one on top of
the other. The one which failed short, seems to have overheated in one spot,
damaging the back up heater pad, which has now failed open circuit. The
controller is suspect but the psu seems to have been ok. They were, when I
last heard, going to tell the system to pretend the heater pads in question
still worked in software, and clip the connections on the dodgy heaters, and
pull out some sensor connections that might otherwise trip the controller
due to uneven heating, and put the thing back together and run it. It would
be slightly less efficient on the bed with one heater down, but apparently
this failure has been tested for before.
The problem at the moment is, because of it being offline, and the russian
scrubber being near end of life, and therefor not working as efficiently as
it might, the Russians have added some of their liho into the mix to keep
things safe until the US device has proved to work reliably, then they will
replace their unit with a new one.

There is another co2 scrubber coming up for node 3 of course, and it could
be that they may fix any potential problems learned from the current one, on
that unit, then fly it and switch them over while they repair the current
one properly.

I gather the new unit being flown, is not due to go online until later
though.

I think this is the time to have all these failures, while in Earth orbit,
you would not want this to occur en route to mars, now would you?
Brian

--
Brian Gaff -
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!
"Brian Gaff" wrote in message
om...
OK, if I have this right the situation was that the heater main circuit
failed during the Shuttle docked period. Then the software refused to
start the bed up because of the heater problem, or so they thought.
Saving time they switched to the back up heater, and controlled it
manually from the ground. Remember this is only one of two alternating
systems. One is gassing while the other scrubs.

However, after some days, the thing gave indications of the controller
failing, which put that channel completely off line. Thinking logically,
the ground thought.. PSU has been damaged and it is why the heater and
controller are acting up. So the plan, as I gather it is to firstly check
for shorts or funny values of resistance in the system, then probably
patch in a spare supply. However, if the controller and heater are
knackered, then they would need to change the hardware in that channel
out.

I've not heard the result of the resistance checks, but methinks that the
psu may well have totalled the heater and the controller in some way and
thus a new supply and assembly is going to be needed.

Does not sound awfully reliable to me, one would have thought psus and
other control equipment would be designed to fail safe.

Brian

--
Brian Gaff -
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!
"Craig" wrote in message
...
John Doe wrote:

NASA TV is currently showing 2 station crewmembers trying to fix the
CDRA (Carbon Dioxide Removal Assembly). Ground generated a plan to fix
it which will take about 6 hours of work.

The CDRA is much bigger than I had imagined it to be.

NASA TV commentator mentioned something about a heater controller, so
I assume this would have something to do with the "cleaning phase" to
outgas the accumulated CO2 to space.


What is the backup plan if it cannot be fixed ? Can they use EVA LiOH
filters into the station's ventilation system to clean the air ?

While the Shuttle was there it overheated and they were controlling it
from the ground, I guess they though a software patch could fix it.
Probably the backup plan is to use the Russian scrubber. I think they
said they have around a month of backup LiOH.

Can the Russian scrubber keep up?

Brian Gaff wrote:
As I have heard over the last day or so, the main channel a and b heater
pads, and there are several pads in each bed, are overlaid, one on top of
the other.

What disapoints me is that they have had CDRA up for years now, and
reduced its use when it proved to be troublesome instead of increasing
its use to cause the flaws to appear and then fix them so that it would
have been reliable by the time the crew was increased to 6.