Author Topic: Problems with APU 1 and 3?  (Read 6035 times)

Offline c.steven

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Problems with APU 1 and 3?
« on: 07/12/2006 10:41 pm »
Bill Harwood is reporting that there are issues being studied with APU 1 and APU 3, which are differernt for each unit. Anyone got anything more substantive? Apparently APU 1 is losing either fuel or pressurizing nitrogen, and APU 3 has an erractic heater. According to Bill's story, the crew was told both are currently go for use, but the MER and MMT are looking closely at them.

Just for the record, anyone know the breakdown of single APU dependent systems for these units? Aero surfaces can be operated from any one of the three, but if I remember right, some systems are single-unit driven and divided up between the three APUs, for instance, nosewheel steering, etc. It seems like APU 1 is the most suspect at this point to me, so what does the crew lose if it enters without APU 1?
C. Steven
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Offline psloss

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RE: Problems with APU 1 and 3?
« Reply #1 on: 07/12/2006 10:48 pm »
Quote
c.steven - 12/7/2006  6:28 PM

It seems like APU 1 is the most suspect at this point to me, so what does the crew lose if it enters without APU 1?
They've started APUs late in entry before, so I assume that's an option...you might want to keep an eye on tomorrow's execute package for any further details...


Offline c.steven

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RE: Problems with APU 1 and 3?
« Reply #2 on: 07/12/2006 11:11 pm »
Found part of the answer to my own question by flipping through my STS Media Reference. The following is taken directly from the document's Hydraulic System section under APUs.

Only hydraulic system 1 is used for the deployment of the nose and main landing gear and nose wheel steering. When the nose and main landing gear down command is initiated by the commander or pilot on panel F6 or F8, hydraulic system 1 pressure is directed to the nose and main landing gear uplock hook actuators and strut actuators (provided the LG hyd isol vlv 1 switch is in the open position) to actuate the mechanical uplock hook for each landing gear and allow the gear to be deployed and also provide hydraulic system 1 source pressure to the nose wheel steering actuator. The main landing gear brake control valves receive hydraulic system 1 source pressure when the LG hyd isol vlv 1 is positioned to open . If hydraulic system 1 source pressure is unavailable, a pyrotechnic initiator attached to the nose and main landing gear uplock actuator automatically, one second after the gear down command, deploys the landing gear, actuates the mechanical uplock hook for each landing gear and allows the gear to be deployed. Because of the unavailability of hydraulic system 1 source pressure, powered nose wheel steering would not be functional; however, directional control of the orbiter can be maintained by differential braking to caster the nose wheel for steering.

The main landing gear brakes utilize hydraulic systems 1 and 2 as the primary source of hydraulic power and system 3 as a standby source of hydraulic power. Each of the four main landing gear wheel brake assemblies receives pressure from two different hydraulic systems in two separate brake chambers. One chamber receives hydraulic source pressure from hydraulic system 1 and the other chamber from hydraulic system 2. In the event of the loss of system 1 or 2 source pressure, switching valves provide automatic switching to the standby hydraulic system 3 when the active hydraulic system source pressure drops below approximately 1,000 psi. If hydraulic system 1 is unavailable, there is no effect to the braking system because standby system 3 would be automatically switched to replace system 1. Loss of hydraulic system 1 or 2 or both would also have no effect on the braking system because standby system 3 would automatically be switched to replace system 1 or 2 or both. Loss of hydraulic system 1 and 3 would cause the loss of half the braking power on each wheel and would require additional braking distance. Loss of hydraulic systems 2 and 3 would also cause the loss of half the braking power on each wheel, requiring additional braking distance.
C. Steven
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Offline mkirk

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RE: Problems with APU 1 and 3?
« Reply #3 on: 07/12/2006 11:40 pm »
I have not seen what Harwood wrote but I can confirm there are two APU issues.  APU 1 has a Fuel Tank Pressure that is bleeding down for unexplained reasons.  The pressure should have remained more or less constant since being shut down post MECO, but apparently it has dropped about 25psi.  APU 2 has a problem with the Primary Thermostat for the Gas Generator Fuel PUMP Temperature.

So far both APUs are considered functional!!!!

Landing with one APU is doable but certainly not desired.  Landing with only APU 2 running would mean you have half of the normal braking.  Drive rates for the flight control system would be reduced (i.e. the orbiter will feel sluggish to the Commander/Pilot).  APU 1 is primary for nose wheel steering but system 2 can be used for that, and yes the loss of system 1 would mean Pyro Deploy would be required to release the uplocks.

Single APU landing procedures are well understood and trained for.  Since the highest hydraulic system demand occurs around preflare, final flare, touchdown, and derotation.  If the crew really had to land with a single APU they would set the speed brake manually at 3000 feet and leave it there, the would avoid making pitch and roll inputs at the same time (i.e. cross coupling), they would accept small misalignments and they would use the beep trim to derotate the nose after touchdown (which is the normal procedure for derotate anyway).

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Offline mkirk

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RE: Problems with APU 1 and 3?
« Reply #4 on: 07/13/2006 12:09 am »
Part of the game plan now is to try and understand what is going on with both systems.  Secondly a plan for the FCS (flight control system) check out needs to be formulated, this procedure is done the day before landing.  Also a decision will be made as to which APU will be started first on landing day (at least one APU is started prior to the Deorbit Burn.

However, I say again all APUs are currently go for landing.

Mark Kirkman
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Online Chris Bergin

RE: Problems with APU 1 and 3?
« Reply #5 on: 07/13/2006 02:30 am »
Here: http://www.cbsnews.com/network/news/space/current.html

I've heard, and been told, nothing.

Offline Mark Dave

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Re: Problems with APU 1 and 3?
« Reply #6 on: 07/15/2006 12:05 am »
The MMT also says that too, it looks fine, but still observing it. They aren't sure if this is GN2 leaking or hydrazine.

Offline Avron

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Re: Problems with APU 1 and 3?
« Reply #7 on: 07/15/2006 01:13 am »
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MarkD - 14/7/2006  7:52 PM

The MMT also says that too, it looks fine, but still observing it. They aren't sure if this is GN2 leaking or hydrazine.


but little temp changes on heaters that maybe caused by hydrazine...

Offline shuttlefan

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Re: Problems with APU 1 and 3?
« Reply #8 on: 07/15/2006 01:26 am »
Could any of these problems be similar to the APU problems at the end of STS-9?

Offline psloss

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Re: Problems with APU 1 and 3?
« Reply #9 on: 07/15/2006 01:44 am »
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shuttlefan - 14/7/2006  9:13 PM

Could any of these problems be similar to the APU problems at the end of STS-9?
As described in the post MMT briefing, no.


Online jacqmans

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RE: Problems with APU 1 and 3?
« Reply #10 on: 07/15/2006 08:06 am »

Offline rdale

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Re: Problems with APU 1 and 3?
« Reply #11 on: 07/15/2006 12:53 pm »
What flight accidentally fired the landing gear pyro's after landing?

Offline Jim

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Re: Problems with APU 1 and 3?
« Reply #12 on: 07/15/2006 03:09 pm »
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rdale - 15/7/2006  8:40 AM

What flight accidentally fired the landing gear pyro's after landing?

Do you mean where the brakes locked and  the tires blew?

Offline Avron

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Re: Problems with APU 1 and 3?
« Reply #13 on: 07/15/2006 03:20 pm »
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Jim - 15/7/2006  10:56 AM

Quote
rdale - 15/7/2006  8:40 AM

What flight accidentally fired the landing gear pyro's after landing?

Do you mean where the brakes locked and  the tires blew?

He just said that the pyro's had been used, but after the vehicle was on the ground..


Offline psloss

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Re: Problems with APU 1 and 3?
« Reply #14 on: 07/15/2006 03:29 pm »
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Avron - 15/7/2006  11:07 AM

He just said that the pyro's had been used, but after the vehicle was on the ground..

In the post MMT briefing yesterday, John Shannon mentioned in passing that on one mission the pyros for releasing the landing gear uplocks had been accidentally fired after landing.  (Whereas normally they are released by hydraulics.)


Online Chris Bergin

Re: Problems with APU 1 and 3?
« Reply #15 on: 07/15/2006 03:54 pm »
This story is "owned" (as we say in the media) by Bill Harwood, so I'm not going to copy unless I get anything new on this.

I do have a question that's suffering from all the orbiter techs I know being off work today: Does this affect processing for STS-116 in any way?

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