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#100 by rdale on 06 Sep, 2006 13:24
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NASA TV just updated their schedule to add this afternoon's briefing:
September 6, Wednesday
1 p.m. EDT - STS-115 Post Mission Management Team Briefing - HQ (All Channels) -
#101 by psloss on 06 Sep, 2006 13:26
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rdale - 6/9/2006 9:11 AM
That's NET, though.
NASA TV just updated their schedule to add this afternoon's briefing:
September 6, Wednesday
1 p.m. EDT - STS-115 Post Mission Management Team Briefing - HQ (All Channels)
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#102 by shuttlefan on 06 Sep, 2006 13:30
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Gerald Richling - 6/9/2006 6:53 AM
Hello! Murphy's Law is now strictly enforced! It is very likely that Atlantis will be rolled back to VAB, demated and swap out the fuel cell. If NASA keeps daylight only launch restriction in place, the launch of STS-115 will not occur until February 19, 2007 when next extended daylight launch opportunies opens up. If NASA relaxes this daylight restriction, permitting night launches, Lauch will likely occur perhaps in mid October, 2006. Frustrating, isn't it?
They DID replace a fuel cell on the pad before STS-69 I believe.
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#103 by Felix on 06 Sep, 2006 13:35
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Florida Today:
"The suspect fuel cell that prompted NASA to scrub today's Atlantis launch is not believed to have failed. NASA believes the problem lies with an associated freon coolant loop, which prevents the electricity-generating device from overheating."
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#104 by rdale on 06 Sep, 2006 13:40
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RE: Replacement on the pad -
At the 10:30am press conference on 8/31/95, Bob Sieck estimated the countdown would pick back up on Monday with a launch late in the week. The scrub was called due to a temperature spike in the Fuel Cell #2 exit temperature. The fuel cell is located in the right side of the payload bay. Fuel cell #2 had 1700 hours of operation and cells are typically kept in service until 2400 hours of operation. A similar fuel cell problem was previously detected on orbit during the Spacelab D-1 mission STS-61A and on the launch pad during STS-6. During STS-6, the fuel cell was replaced on the pad and similar procedures will be used for STS-69.
http://science.ksc.nasa.gov/shuttle/missions/sts-69/mission-sts-69.html
However notice that the launch was delayed a week. -
#105 by Chris Bergin on 06 Sep, 2006 13:42
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Meeting with the vendor has begun. We have people at that meeting....presentations and reports to follow
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#106 by Chris Bergin on 06 Sep, 2006 13:43
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L2: Wednesday, September 06, 2006 8:03 AM 11776 Fly As-Is (Consequences).ppt - pending. Fuel Cell Photo.doc - pending.
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#107 by DaveS on 06 Sep, 2006 13:44
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Chris Bergin - 6/9/2006 3:29 PM
Just for the record: The vendor is UTC Power and they have little write-up on the shuttle orbiter fuel cells here: http://www.utcpower.com/fs/com/bin/fs_com_Page/0,9235,03557,00.html
Meeting with the vendor has begun. We have people at that meeting....presentations and reports to follow -
#108 by triddirt on 06 Sep, 2006 13:45
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mkirk - 6/9/2006 8:07 AM
Quotegordo - 6/9/2006 6:45 AM
In Laymans terms; think of each fuel cell as 3 fuel cells in one. The problem here lies in 1/9th of the system, but certain equipment needs each of the 3 different phases to run correctly.
I think you are confusing substacks with 3 phase AC power.
Motorized devices on the orbiter such as pumps, fans, drive units for the vent doors, payload bay doors, ET doors etc...require multiphase operation from the AC busses. In some cases you can loose a single phase and still retain operation of the particular motor - this is certainly not ideal.
AC power comes from the inverters which take the DC power produced by the fuel cells and distributed through the Main Busses and coverts it to AC. Main Bus A powers AC1, Main B AC2, and Main C AC3. Each AC bus is powered by 3 inverters (i.e. 3 phases).
Mark Kirkman
Mark's answer was helpful but I was struggling a little still (Longing for a picture). Here was the text from the NASA page that closed the loop for me.
From http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-eps.html
ELECTRICAL POWER SYSTEM
The EPS consists of three subsystems: power reactant storage and distribution, fuel cell power plants (electrical power generation) and electrical power distribution and control.
The PRSD subsystem stores the reactants (cryogenic hydrogen and oxygen) and supplies them to the three fuel cell power plants, which generate all the electrical power for the vehicle during all mission phases. In addition, cryogenic oxygen is supplied to the environmental control and life support system for crew cabin pressurization. The hydrogen and oxygen are stored in their respective storage tanks at cryogenic temperatures and supercritical pressures. The storage temperature of liquid oxygen is minus 285 F and minus 420 F for liquid hydrogen.
The three fuel cell power plants, through a chemical reaction, generate all of the 28-volt direct-current electrical power for the vehicle from launch through landing rollout. Before launch, electrical power is provided by ground power supplies and the onboard fuel cell power plants until T minus three minutes and 30 seconds. Each fuel cell power plant consists of a power section, where the chemical reaction occurs, and a compact accessory section attached to the power section, which controls and monitors the power section's performance. The three fuel cell power plants are individually coupled to the reactant (hydrogen and oxygen) distribution subsystem, the heat rejection subsystem, the potable water storage subsystem and the EPDC subsystem. The fuel cell power plants generate heat and water as by-products of electrical power generation. The excess heat is directed to fuel cell heat exchangers, where the excess heat is rejected to Freon coolant loops. The water is directed to the potable water storage subsystem.
The EPDC subsystem distributes the 28 volts dc generated by each of the three fuel cell power plants to a three-bus system that distributes dc power to the forward, mid-, and aft sections of the orbiter for equipment in those areas. The three main dc buses-MNA, MNB and MNC-are the prime sources of power for the vehicle's dc loads. Each of the three dc main buses supplies power to three solid-state (static), single-phase inverters, which constitute one three-phase alternating-current bus; thus, the nine inverters convert dc power to 115-volt, 400-hertz ac power for distribution to three ac buses-AC1, AC2 and AC3-for the vehicle's ac loads.
The EPDC subsystem controls and distributes electrical power (ac and dc) to the orbiter subsystems, the solid rocket boosters, the external tank and payloads. Power is controlled and distributed by assemblies. Each assembly is a housing for electrical components, such as remote switching devices, buses, resistors, diodes and fuses. Each assembly usually contains a power bus or buses and remote switching devices for distributing bus power to subsystems located in its area. -
#109 by psloss on 06 Sep, 2006 13:45
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joncz - 6/9/2006 8:16 AM
Good note about the STS-69 experience; however, that was back in the internal airlock days. On that flight, I don't think the Spartan was any farther forward than Bay 3. (Here's a picture of the OPF install.)
My post immediately before yours suggested the R&R can be and has been done at the pad (the trusses may have to be removed, however). And given the potential for a Sep 24th window with relaxed lighting requirements I would expect that, barring weather forcing a rollback, is what they would plan to do.
They probably don't have an issue with access to the fuel cell, but I think a question is whether they have room to move the current unit and its replacement with the external airlock in place.
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#110 by psloss on 06 Sep, 2006 14:02
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Chris Bergin - 6/9/2006 8:02 AM
Sigh. Hey Chris, why not just make a friggin' Schadenfreude forum for those posts?QuoteGerald Richling - 6/9/2006 12:53 PM
If NASA relaxes this daylight restriction, permitting night launches, Lauch will likely occur perhaps in mid October, 2006. Frustrating, isn't it?
If NASA relaxes that restriction, there's an opportunity on September 24 (start of window). We published the document on L2 and there's a specific slide published on here showing this.
Most of your post was inaccurate.
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#111 by Chris Bergin on 06 Sep, 2006 14:03
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Five PDFs uploaded to L2, as they are being currently presented and evaluated to NASA at the Vendor meeting. More will follow.
Key point on the fly as is:
Consequence of next failure
• Given the short is inside the fuel cell ECM (Electronic Control Module)
• The possibility of phase A re-shorting exists
– Worst case short would result in loss of center SSME primary controller and right
SSME backup controller similar to STS-93 shorting event
• The possibility of shorting phase B or phase C exists given unknown cause
of phase A problem
– Worst case short would result in loss of center SSME primary controller and right
SSME backup controller
– Also loss of fuel cell coolant pump if the circuit breaker is tripped or wire burns
open
• Useful Life limited to nine minutes – fuel cell overheats and stack integrity is
compromised
– During the transient condition, various equipment i.e. pumps and fans
will momentarily spin down, but will recover
• Nuisance alarms -
#112 by mkirk on 06 Sep, 2006 14:05
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Sorry I accidentally posted this in the wrong thread:
I have heard "fly as is" discussed all morning, but given the nature of the actual failure signature I don't see that as a realistic option!!!!!!!!!!
Mark Kirkman
P.S.
As you can see from Chris' post the cosequences can be significant.
The questions are what caused the short? Can it happen again? Are you going to loose multiple busses and equipment? What systems are affected? If it is the coolant pump you have to get that fixed - they ware not going to fly and hope that it will work.
In Training the thing they focus on a lot is the potential loss of the fuel cell within 9 minutes if you loose cooling. The stacks can litterally degrade and come apart... -
#113 by Chris Bergin on 06 Sep, 2006 14:06
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mkirk - 6/9/2006 2:52 PM
Sorry I accidentally posted this in the wrong thread:
I have heard "fly as is" discussed all morning, but given the nature of the actual failure signature I don't see that as a realistic option!!!!!!!!!!
Mark Kirkman
Do you have a rough timeline for Fuel Cell R&R, Mark? -
#114 by joncz on 06 Sep, 2006 14:07
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They probably don't have an issue with access to the fuel cell, but I think a question is whether they have room to move the current unit and its replacement with the external airlock in place.
I see your point.
http://science.ksc.nasa.gov/gallery/photos/2004/medium/KSC-04PD-1136.jpg
http://science.ksc.nasa.gov/gallery/photos/2005/medium/KSC-05PD-1357.jpg
http://science.ksc.nasa.gov/gallery/photos/1997/medium/KSC-97PC-0764.jpg -
#115 by rdale on 06 Sep, 2006 14:07
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"I have heard "fly as is" discussed all morning"
It's been discussed by "people with real input" into the situtation, or just something the workers are saying? -
#116 by mkirk on 06 Sep, 2006 14:11
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Chris Bergin - 6/9/2006 8:53 AM
Quotemkirk - 6/9/2006 2:52 PM
Sorry I accidentally posted this in the wrong thread:
I have heard "fly as is" discussed all morning, but given the nature of the actual failure signature I don't see that as a realistic option!!!!!!!!!!
Mark Kirkman
Do you have a rough timeline for Fuel Cell R&R, Mark?
No because I am not sure how hard it is to work around the airlock/ODS!!
In a clean payload bay they could be able to fly within a week or slightly less.
Mark Kirkman -
#117 by c.steven on 06 Sep, 2006 14:14
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With the possibility that two fuel cell losses on ascent would lead to loss of vehicle, I'm not seeing a decision to launch with one suspect fuel cell. Unless they find a smoking gun very quickly to explain the signature from startup, and unless they can definitively fix it, I'm thinking a replacement fuel cell is a given. The only question is when and where to replace it. Won't opening up the floor of the bay present FOD and other hazards to P3/P4? I would think for accessibility they would at least have to pull the payload out of the bay and put it in the canister temporarily if they attempt something at the pad.
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#118 by Chris Bergin on 06 Sep, 2006 14:15
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Update:
OPO Telecon with vendors (mdwright)
- A spare pump or qual pump will be cut up to get a better understanding of the pump design. In particular, the interest is in whether or not the phase windings are isolated from one another.
- Several scenarios for a short
- Thermal equilibrium is reached in about 26-30 minutes - Worst case next failure could result in motor controller shutdown during ascent -
#119 by mkirk on 06 Sep, 2006 14:17
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Another point, nobody likes to fool with AC power during powered flight becuase the Main Engine Controllers are very sensitive to transients in AC power - i.e. STS-93 as the most noted example.
Therefore "Fly As Is" - Is not an option if I had a vote.
Mark Kirkman
