Shuttle Questions Q and A (2)

#480 by Jim on 02 Dec, 2006 19:38
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GLS - 2/12/2006 12:46 PM

Interesting question: At KSC there's the NTD (NASA Test Director). On the launches from VAFB, was it going to be a NTD or a "AFTD (Air Force Test Director)" or what???
NASA was going launch the shuttles with LSOC. The USAF would have manned some positions.

Whether it would have been a USAF launch director or what, the mix was still in discussion.

AFTD was an east coast call sign for the USAF payload test director
#481 by kneecaps on 07 Dec, 2006 23:59
Can I have a explanation of exactly what the 'SSME Delta' display on the Main Engine operators console is displaying? As seen in the booster console handbook, its rather unclear exactly what the deltas are being calculated from and how.

Also what is a 'tag' in the same context?
#482 by Jim on 08 Dec, 2006 02:14
TAG is Tested and Guaranteed.
#483 by kneecaps on 08 Dec, 2006 09:57
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Jim - 8/12/2006 2:57 AM

TAG is Tested and Guaranteed.

Thanks,
So the delta display provides information that is 'Tested and Guaranteed' ...I see. Does that mean values have been tested for reasonableness and are guaranteed by way of dual sensors/redundancy?
#484 by Jim on 08 Dec, 2006 10:53
I don't know how it relateds to the displays (don't have the book), but in launch vehicle vernacular, TAG values what an engine provides after testing. For example, engine serial number xyz has a TAG ISP of abc.

Edit:
Found the book and I was correct
"At approximately L-7 days, Marshall Space Flight Center (MSFC) (code
EE21-SSME Chief Engineers Office) supplies engine specific Tag data in what is commonly
called the MSFC Tag Letter (Fig. 1.4.2-I). The Tag data are the predicted values for the
operational parameters for each SSME at a mission elapsed time of 194 seconds (engine start +
200 seconds) and at an LO2 inlet pressure of 63 psia."

look at Figure 1.4.2-I SSME Tag letter example (Ref. 1).

After reading a bit, the delta display shows the differences between the tag and actual values. From the book

The Delta display, shown in Figure 3.1.2-VIII, shows the difference between the pre-flight
predicted (or in-flight replacement) and actual values of several parameters. Only the following
parameters are shown: HPOT DP, HPFT DP, HPOT TDT, HPFT TDT, OPOV, and FPOV. This
display can be configured to show either preflight tags or inflight tags by using the BOSS Menu
as explained above. Table 3.1.2-IV gives the MSID, nomenclature, units, and source for each
parameter displayed on the Delta display. The keymap for this table is shown in Figure 3.1.2-IX.
#485 by kneecaps on 08 Dec, 2006 14:17
Thanks very much Jim. That's really useful to me!

Heh, if I had scanned around the book some more I would have had the answers for myself.

That's the only problem I tend to have with these NASA books, some books ASSUME you know every term and concept discussed (or that you have the book to hand which explains), other books treat the reader as a novice and explain everything. Its difficult to know which kind one is currently reading.
#486 by Avron on 09 Dec, 2006 18:44
tried to ask this one on the launch thread - but its focused on press issues so here goes...

Could someone please confim, that if they do a hold a launch at T-5, drainback and APU start has not started, (Drainback start at T-4:55?) so if they do hold we are not loosing time , LOX or performance other than loss of window time?
#487 by mkirk on 09 Dec, 2006 19:10
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Avron - 9/12/2006 1:27 PM

tried to ask this one on the launch thread - but its focused on press issues so here goes...

Could someone please confim, that if they do a hold a launch at T-5, drainback and APU start has not started, (Drainback start at T-4:55?) so if they do hold we are not loosing time , LOX or performance other than loss of window time?

Yes that is correct. For International Space Station missions Hold capability at T-5 minutes is limited to the duration of the launch window. After T-5 the hold time is constrained by Drainback Hold Time which is a function of either "performance loss" or "start box" limit violations. Start Box (i.e. temperature limits for main engine start) has been discussed in earlier posts on the Shuttle Q&A thread.

Mark Kirkman
#488 by Avron on 09 Dec, 2006 19:33
Mark

your earlier post was awesome, got a lot out of it... now the next question that comes to mind if say you hold at T-5... there is no impact other than loss of window time, but at the same time you are "saving" LOX and thus performance, so if you release T-5 thus 5 mins before the end of the window, launch, would you not end up with some excess performace as you have not spend more than the five mins draining back, and would thus stay within the "start box" ( assume external conditions have impact here, i.e.. a warmer day would result in the 17in feed line having warmer LOX and thus could drain for more time before the cooler LOX take you out of the "start box" ). This extra "hold" (not lost in the hold) lox would be used to give you a slightly higher delta_v thus allow for a longer window?
#489 by LSainsbury on 09 Dec, 2006 19:46
Hello,

Just a very dumb question!

When a launch is scrubbed - what happens to all the fuel loaded into the ET? I assume it just gets pumped back out again?

Cheers

Lee
#490 by mkirk on 09 Dec, 2006 19:47
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Avron - 9/12/2006 2:16 PM

Mark

your earlier post was awesome, got a lot out of it... now the next question that comes to mind if say you hold at T-5... there is no impact other than loss of window time, but at the same time you are "saving" LOX and thus performance, so if you release T-5 thus 5 mins before the end of the window, launch, would you not end up with some excess performace as you have not spend more than the five mins draining back, and would thus stay within the "start box" ( assume external conditions have impact here, i.e.. a warmer day would result in the 17in feed line having warmer LOX and thus could drain for more time before the cooler LOX take you out of the "start box" ). This extra "hold" (not lost in the hold) lox would be used to give you a slightly higher delta_v thus allow for a longer window?

No not exactly, it is an either or situation. You will either have enough performance in terms of LOX based on when in the window you launch or you will violate start box limits. Hold time AFTER T-5 will be based on which of the two events occurs first - you either eat up your performace margin (i.e. lox) or you will violate the start box limit at a set time after the start of drain back.

Mark Kirkman
#491 by Chris Bergin on 09 Dec, 2006 19:53
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LSainsbury - 9/12/2006 8:29 PM

Hello,

Just a very dumb question!

When a launch is scrubbed - what happens to all the fuel loaded into the ET? I assume it just gets pumped back out again?

Cheers

Lee

Yep, it gets pumped back out "Detanking" ready to be used on the next attempt.
#492 by LSainsbury on 09 Dec, 2006 19:58
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Chris Bergin - 8/12/2006 8:36 PM

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LSainsbury - 9/12/2006 8:29 PM

Hello,

Just a very dumb question!

When a launch is scrubbed - what happens to all the fuel loaded into the ET? I assume it just gets pumped back out again?

Cheers

Lee

Yep, it gets pumped back out "Detanking" ready to be used on the next attempt.

Thought so - thanks...

(Sorry for posting a new thread btw!)
#493 by psloss on 09 Dec, 2006 19:59
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mkirk - 9/12/2006 3:30 PM

No not exactly, it is an either or situation. You will either have enough performance in terms of LOX based on when in the window you launch or you will violate start box limits. Hold time AFTER T-5 will be based on which of the two events occurs first - you either eat up your performace margin (i.e. lox) or you will violate the start box limit at a set time after the start of drain back.
Sorry, this might essentially be the same question as Avron's, but...

For the first launch attempt, the LOX drainback hold time for the preferred T-0 was exactly five minutes; since that was exactly the amount of hold time left in the window at that point, I assumed that really meant they had less launch window than performance...is that right or were the two hold times the same?

Thanks, Mark.
#494 by mkirk on 09 Dec, 2006 20:30
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psloss - 9/12/2006 2:42 PM

Sorry, this might essentially be the same question as Avron's, but...

For the first launch attempt, the LOX drainback hold time for the preferred T-0 was exactly five minutes; since that was exactly the amount of hold time left in the window at that point, I assumed that really meant they had less launch window than performance...is that right or were the two hold times the same?

Thanks, Mark.

Actually by definition Drainback Hold Time is limited to a maximum of 5 minutes and is based on the time it takes for the LOX in the Downcomer (i.e. the LO2 feedline on the outside of the tank) to drain back. If start box temperature is not viloated befor that, then Performance becomes the constraint. During the T-20 minute Brief the NTD gave the hold time and the reason...performance in the case of the first attemt.

I know I am not explaining this well and in fact I am starting to trip myself up, but I will try and find the "Text Book" answer again when things calm down after launch if someone else does not come along and give a better answer.

Mark Kirkman

Mark Kirkman
#495 by psloss on 09 Dec, 2006 20:43
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mkirk - 9/12/2006 4:13 PM

I know I am not explaining this well and in fact I am starting to trip myself up, but I will try and find the "Text Book" answer again when things calm down after launch if someone else does not come along and give a better answer.
Every little bit helps (I think); I did hear NTD say that it was based on performance in the briefing at T-20 and I'm starting to remember you might have made this distinction between the timing of going in/out of start box and the downcomer somewhere. Need to throw some bookmarks on those...actually, "downcomer" probably makes for a distinctive search.

Thanks again.

Edit: hope this is OK, but for anyone else who is interested, here's Mark's original post (it might be a little slow to highlight that particular post tonight):
http://forum.nasaspaceflight.com/forums/thread-view.asp?tid=625&posts=588&mid=23596&highlight=down+comer&highlightmode=2&action=search#M23596
#496 by Jim on 09 Dec, 2006 21:02
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nathan.moeller - 9/12/2006 4:31 PM

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paulhbell07 - 9/12/2006 3:24 PM

I still admire what they do. Are they all volunteer's or are they just picked by USA.

Ice Team is volunteers. There's at least one astronaut on the close out crew so I don't know if they're paid or not. But let's keep this thread to live updates. Shuttle Q&A thread is good for this type of question.

Just their jobs, nothing special. They get paid just like everyone else. They are part of the "forward shop", which includes the SCO's, and their regular jobs deal with the forward part of the orbiter
#497 by paulhbell07 on 09 Dec, 2006 22:21
thanks nathan and jim for answering. thought it would be ok to ask in the other thread because it was happening at the time i wrote it. sorry if i asked in the wrong thread.
#498 by hornet on 09 Dec, 2006 23:08
why is the shuttle commander not refered to as captian?
#499 by Jim on 10 Dec, 2006 11:21
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hornet - 9/12/2006 6:51 PM

why is the shuttle commander not refered to as captian?

The shuttle is not a ship, same as previous manned spacecraft