LIVE: ISS US spacewalk (EVA-18) - August 30, 2012

[psloss]

An old (apparently circa ISS-12A.1), but useful public EPS reference, probably been posted here many times:
http://www.boeing.com/defense-space/space/spacestation/systems/docs/ISS%20Electric%20Power%20System.pdf

Maybe it only helps me, but there's a high-level block diagram on page 4.  (Also shows where the DCSUs are, at least schematically, as one of them is an open issue now, too.)

[psloss]

Yes, DCSU 3A tripped off due to a real over voltage.

Coming back to this, sort of, it appears that the critical maintenance task list is now twelve versus the fourteen we heard about two years ago:
http://forum.nasaspaceflight.com/index.php?topic=16584.msg624830#msg624830

Which tasks are no longer a part of that list?

[Space Pete]

So, ISS still has 100% of its normal available daily energy, but only 3/4 of its available power, which is only reduced because the remaining channels either lack sufficient rating to provide maximum power, or they can't be connected to the loads in such a way as that power could be distributed?

Okay, firstly, I think I see what you were saying earlier about the batteries reaching fully charged level, leading to open circuit voltage on the solar arrays - remember that the batteries are slightly discharged during night passes, since during those times the batteries actually feed some power back to the solar arrays via the DCSU, in order to provide heating power to some hardware, and so the batteries will always need to be charged during a day pass.

Thus, the 1A and 1B are still generating power to charge their corresponding batteries (there are a set of bats for the 1A array and the 1B array), and so you are correct that ISS is still generating 100% of its normal energy, however 25% of that cannot be distributed to the rest of the station since MBSU-1 is uninstalled. There is no way to send the channel 1A and 1B voltage to another MBSU, since MBSUs can only have two, direct hard-wired inputs, which all remaining MBSUs already have via the 6 remaining channels.

[erioladastra]

Yes, DCSU 3A tripped off due to a real over voltage.

Coming back to this, sort of, it appears that the critical maintenance task list is now twelve versus the fourteen we heard about two years ago:
http://forum.nasaspaceflight.com/index.php?topic=16584.msg624830#msg624830

Which tasks are no longer a part of that list?

I don't recall the actual list right now but it is just like the Big Ten football conference - doesn't really reflect the actual number which is always changing.

[psloss]

Yes, DCSU 3A tripped off due to a real over voltage.

Coming back to this, sort of, it appears that the critical maintenance task list is now twelve versus the fourteen we heard about two years ago:
http://forum.nasaspaceflight.com/index.php?topic=16584.msg624830#msg624830

Which tasks are no longer a part of that list?

I don't recall the actual list right now but it is just like the Big Ten football conference - doesn't really reflect the actual number which is always changing.

After watching the Cowboys Classic (well, while it was competitive), I'm not sure I want to take this metaphor too far, but I think there's a few of us who are interested in the current members of the conference.

(It's not urgent; just wondering if anyone had it handy.)

[MP99]

So, ISS still has 100% of its normal available daily energy, but only 3/4 of its available power, which is only reduced because the remaining channels either lack sufficient rating to provide maximum power, or they can't be connected to the loads in such a way as that power could be distributed?

Okay, firstly, I think I see what you were saying earlier about the batteries reaching fully charged level, leading to open circuit voltage on the solar arrays - remember that the batteries are slightly discharged during night passes, since during those times the batteries actually feed some power back to the solar arrays via the DCSU, in order to provide heating power to some hardware, and so the batteries will always need to be charged during a day pass.

Thus, the 1A and 1B are still generating power to charge their corresponding batteries (there are a set of bats for the 1A array and the 1B array), and so you are correct that ISS is still generating 100% of its normal energy, however 25% of that cannot be distributed to the rest of the station since MBSU-1 is uninstalled. There is no way to send the channel 1A and 1B voltage to another MBSU, since MBSUs can only have two, direct hard-wired inputs, which all remaining MBSUs already have via the 6 remaining channels.

If the energy from 1A & 1B arrays can't be discharged (did I understand that right?), can they be feathered so they don't generate too much power?

cheers, Martin

[Space Pete]

If the energy from 1A & 1B arrays can't be discharged (did I understand that right?), can they be feathered so they don't generate too much power?

The energy from the 1A and 1B arrays (stored in their corresponding batteries) is slightly discharged during night passes, when the batteries feed some power back to the array electronics for heating, and so the batteries still need some slight recharging during day passes - but yes, the arrays could be feathered to reduce power generation, if need be.