Shuttle Questions Q and A (2)

#100 by GLS on 18 May, 2006 09:58
A couple of interesting questions....
When you have a SSME lockup (hydraulic or electrical) at, let's say 82% like STS-3 had, is MECO commanded at the same time for all engines, or you shutdown the locked up SSME just, just before the others, to account for it's higher throttle level??
Also, if the 3 engines locked up, would they still go uphill and exceed the 3Gs, or would they shutdown at 3Gs and go ECAL or TAL or whatever?
#101 by mkirk on 18 May, 2006 17:56
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GLS - 18/5/2006 4:45 AM

A couple of interesting questions....
When you have a SSME lockup (hydraulic or electrical) at, let's say 82% like STS-3 had, is MECO commanded at the same time for all engines, or you shutdown the locked up SSME just, just before the others, to account for it's higher throttle level??
Also, if the 3 engines locked up, would they still go uphill and exceed the 3Gs, or would they shutdown at 3Gs and go ECAL or TAL or whatever?

There are 2 kinds of “stuck throttles”, an engine can be stuck at full power (104.5% for nominal ascent) or they can be stuck at a lower setting (such as 67% during the throttle down for maximum dynamic pressure). Technically any engine with the throttle stuck below 104.5% is referred to as “stuck in the bucket”.

If you have one or more engines stuck in the bucket then you have a performance problem (i.e. your ability to go uphill is degraded). Depending on the number of engines and type of failure (“Hydraulic/Electrical Lock Up” or “Command Path”) you will likely be in an Abort scenario. Some “Command Path” failures can be fixed with a “restring” of the GPCs (in simple terms this means the General Purpose Computer responsible for the engine is changed).

If the engine(s) is stuck at a high power setting you do not have a performance problem, but a manual shutdown will be required prior to the actual MECO (main engine cutoff). This is more of a problem if two engines are stuck. The reason is the engines will not be able to throttle back during “3G Throttling” which begins about 1 minute prior to MECO. In order to prevent an “Over G” of the orbiter, one of the engines must be shutdown early. The time of the shutdown will be dependent on the type of failure that caused the stuck throttle…typically shutdown will be at MECO minus 2 minutes or at a orbiter velocity > 23,000 feet per second.

Stuck throttles at a lower power setting will increase the MECO time since the rate of propellant consumption has been reduced.

In the case of STS-3 that you mentioned; engine 3 was in a hydraulic lock up condition because of the problem with APU 3. Hydraulic lock means the valves which control power and mixture for an engine are stuck in there last commanded position. On STS-3 the lockup occurred so late in the ascent that it did not pose a significant performance problem.

This is just a basic rundown. There are many other scenarios that can complicate matters.

Mark Kirkman
#102 by Naraht on 18 May, 2006 18:00
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mkirk - 13/5/2006 6:33 PM
I finally downloaded and listened to the audio…I have never bothered to listen to it before. When I get I chance I will have to get a copy of the whole flight loop and booster loops.
As I said before in the relevant thread, I would really, really love to hear those if there's any chance of them being posted here.
#103 by zerm on 20 May, 2006 03:04
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mkirk - 13/5/2006 6:33 PM
I finally downloaded and listened to the audio…I have never bothered to listen to it before. When I get I chance I will have to get a copy of the whole flight loop and booster loops.
As I said before in the relevant thread, I would really, really love to hear those if there's any chance of them being posted here.[/QUOTE]

I'll second that.

And here's my dumb question- perhaps it's been asked and answered, but these Q&A threads are so long, it's hard to tell.

Q: Looking at the SRBs, I've noticed that one has a thick black band at the top, but the other does not. Why is this?...please educate me.
#104 by Jim on 20 May, 2006 14:25
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zerm - 19/5/2006 10:51 PM

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mkirk - 13/5/2006 6:33 PM
I finally downloaded and listened to the audio…I have never bothered to listen to it before. When I get I chance I will have to get a copy of the whole flight loop and booster loops.
As I said before in the relevant thread, I would really, really love to hear those if there's any chance of them being posted here.
I'll second that.

And here's my dumb question- perhaps it's been asked and answered, but these Q&A threads are so long, it's hard to tell.

Q: Looking at the SRBs, I've noticed that one has a thick black band at the top, but the other does not. Why is this?...please educate me.

To tell them apart
#105 by zerm on 20 May, 2006 16:27
Seriously, or are you just trying to out-smart ars me?

Is the marking for photo tracking?
#106 by abacus on 20 May, 2006 16:38
It is obvious which one is which when they are connected to the ET, but i assume it allows you to tell them apart after separation and during recovery
#107 by Jim on 20 May, 2006 18:05
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abacus - 20/5/2006 12:25 PM

It is obvious which one is which when they are connected to the ET, but i assume it allows you to tell them apart after separation and during recovery

That is correct
#108 by zerm on 20 May, 2006 18:23
Simple answer to a simple question...thanks folks! Just one of those "hummmm... I wonder?" types of deals. I guess McCall would have simply painted a big red "1" and "2" on them.
#109 by GLS on 21 May, 2006 22:19
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mkirk - 18/5/2006 6:43 PM
In order to prevent an “Over G” of the orbiter, one of the engines must be shutdown early. The time of the shutdown will be dependent on the type of failure that caused the stuck throttle…typically shutdown will be at MECO minus 2 minutes or at a orbiter velocity > 23,000 feet per second.

So on an "Over G" case you shutdown 1 engine early... I thought you would kill the 3 engines (stupid thing to do)! Thanks alot!!!
#110 by wbmiller3 on 24 May, 2006 02:02
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PlanetStorm - 5/5/2006 3:37 PM

Not possible to redirect ISS power to the orbiter?

Actually this is in work. The SSPTS (Space Station Power Transfer System) will be added to the orbiters Real Soon Now allowing them to draw power from the ISS while docked. This will allow longer docked time.

Unfortunately, there are a lot of other reasons why the orbiter wouldn't make a good lifeboat.
#111 by wbmiller3 on 24 May, 2006 02:08
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mkirk - 12/5/2006 6:38 PM

For 51-F when the first engine exceeded it’s redline parameter and based on the limit switch being in Auto (always in Auto at launch), the engine controller shut the engine down and the orbiter’s general purpose computers automatically inhibited the limit software for the remaining to engines. Once an engine fails the crew is trained to expect to re-enable the limit software as soon as possible (i.e. abort capability). This is usually called up to the crew by mission control. Since the first engine failure was actually do to a sensor problem and not a real engine problem, and since the other engines were also in danger of being erroneously shutdown by faulty sensors, and since the shuttle was at an appropriate abort boundary; mission control called up to the crew “Main Engine Limits Inhibit”. This was done to prevent any additional engine shutdowns for bad sensors...if MCC or the crew had noticed a real problem with the engine a manual shutdown still could have been performed.

One of the great unsung heroes of the shuttle program, Jenny Howard, was the Booster that day. She realized from the signature on the first engine failure that the turbine discharge temperature ducers were flaking out, and made the call to inhibit limits. The ducers went sour on a second engine after that - this call prevented an unnecessary shutdown and subsequent abort.

Added - I see Mr. Kirkman already answered this, but I left it here as a salute to Ms. Howard.
#112 by psloss on 24 May, 2006 11:42
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wbmiller3 - 23/5/2006 9:55 PM

One of the great unsung heroes of the shuttle program, Jenny Howard, was the Booster that day. She realized from the signature on the first engine failure that the turbine discharge temperature ducers were flaking out, and made the call to inhibit limits. The ducers went sour on a second engine after that - this call prevented an unnecessary shutdown and subsequent abort.

Added - I see Mr. Kirkman already answered this, but I left it here as a salute to Ms. Howard.
Roy Bridges said as much back in the 1987 documentary, too. This actually reminds me of another question about what was going on in the MCC during that ascent: did the second fuel turbine temp transducer on the right engine go over the limit prior to MECO?

Just wondering,

Philip Sloss
#113 by nacnud on 24 May, 2006 15:26
I can't find if this has been asked yet but how do the components of the STS interact on launch? Do the SRBs efectively lift the ET and the Orbiter lifts itself, there by minimizing the forces between the Orbiter and the ET?

IE what are the forces between the ET, SRBs and the Orbiter?
#114 by astrobrian on 24 May, 2006 20:40
The Orbiter could lift itself, but needs tons of fuel to do it, hence the ET, that makes the wieght too heavy for the orbiter to life. So the boosters take up for that through the heavier air, by that point thrust to wieght is in the orbiters favor and the SRBs are jettisoned
#115 by Jim on 24 May, 2006 21:06
At liftoff (klb) Weight thrust
OV 260 1182
ET 1,658 0
SRB 2x 1,300 2x 3,300

The weights and thrust constantly and therefore the loads

At launch the SRB's help lift and accelerate the ET But the OV is always putting in a load of the SSME thrust minus the OV weight into the ET.
#116 by nacnud on 24 May, 2006 21:28
Thanks
#117 by shuttle_buff on 01 Jun, 2006 19:28
Question about space suits worn by the crew.

After the first 4 shuttle flights (STS-1 thru STS-4), all space suits were eliminated and a casual "jumpsuit" was worn? No helmet, gloves, pressurization or anything. Correct?

After Challenger, the pressurized space suits returned and have been used ever since.

I ask this because I look at old crew photographs after STS-4 and the crew is wearing jumpsuits not space suits.

I know the space suits are removed in orbit but was wondering about STS-5 to STS-twenty something.

Thanks,

shuttle_buff
#118 by Rocket Guy on 01 Jun, 2006 19:32
They did wear a helmet with their jump suits from 5-51L.
#119 by Jim on 01 Jun, 2006 19:36
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Ben - 1/6/2006 3:19 PM

They did wear a helmet with their jump suits from 5-51L.

LEH's (launch and entry helmets) and the crew wore standard flight suits with US military type flight boots/