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#320
by
Austin
on 05 Sep, 2006 23:49
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Svetoslav - 5/9/2006 3:45 PM
We know there's always a slight difference between the performance of the two SRBs. What will happen if a significant difference is noticed during launch?
If the thrust differential is minimal, it could throw off the shuttle's trajectory. If the deviation is significant and threatend populated areas as a result, RSO could be forced to make a difficult decision. Rather not go there, but I think you know what I mean.
Perhaps someone else could get into the specific structural changes/stress that a severe thrust differential would cause, but I would imagine that there would be a great deal of stress on the SRB attach points.
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#321
by
astrobrian
on 06 Sep, 2006 00:11
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not to mention all the control surfaces on the Orbiter itself trying to right its course.
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#322
by
MKremer
on 06 Sep, 2006 00:12
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You'd have to define "significant". About the only way there could be a major thrust differential is if one SRB had a major joint failure and leak. Otherwise the nature of the SRB propellant loading and casting design pretty much assures relatively balanced thrust once they're lit, and both the SRB and SSME TVC can compensate for any differences.
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#323
by
MKremer
on 06 Sep, 2006 00:17
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astrobrian - 5/9/2006 6:58 PM
not to mention all the control surfaces on the Orbiter itself trying to right its course.
The orbiter aero control surfaces are locked into a pre-programmed pattern after launch (way too much stress on the orbiter structure and ET attach points to do otherwise). The SRB and SSME TVC's are what's used to control the flight path.
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#324
by
astrobrian
on 06 Sep, 2006 00:18
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I guess significant could be any number of things. Challenger coped with its thrust issue just fine until the ET let go.
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#325
by
mkirk
on 06 Sep, 2006 00:46
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Svetoslav - 5/9/2006 5:45 PM
We know there's always a slight difference between the performance of the two SRBs. What will happen if a significant difference is noticed during launch?
A significant difference – and it is hard to quantify what significant would be - in SRB performance between the two SRMs would be bad!!!!
The flight control system can handle some of this, but it is the manufacturing/propellant loading process of the SRBs at the contractor plant that is designed to minimize these kinds of dispersions. Propellant in any given booster set comes from the same batch just for this reason.
Mark Kirkman
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#326
by
mkirk
on 06 Sep, 2006 00:59
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MKremer - 5/9/2006 7:04 PM
The orbiter aero control surfaces are locked into a pre-programmed pattern after launch (way too much stress on the orbiter structure and ET attach points to do otherwise).
Actually that is not a completely accurate statement.
The elevons (inboard and outboard) move to manage wing loading during load relief. Load Relief begins at about 25 seconds into the flight and works by allowing the guidance and control system to prioritize lateral accelerations over attitude control. In other words the vehicle is more responsive to errors in acceleration over errors in attitude.
While there is a preprogrammed schedule for the elevons they can & do react to sensed pressure differences at the actuators.
If you look closely at the profile shots of the launch that show a close-up view of the aft end you will see the elevons move (differentially) during ascent. Another good shot of this came from the forward SRB cameras from STS-121 – In those shots you see the elevons slowly move out of frame as first stage progresses.
Mark Kirkman
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#327
by
astrobrian
on 06 Sep, 2006 01:14
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I used the forward SRB footage in my last completed music video, sped it up a good deal and it shows the movement very clearly
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#328
by
MKremer
on 06 Sep, 2006 01:32
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mkirk - 5/9/2006 7:46 PM
MKremer - 5/9/2006 7:04 PM
The orbiter aero control surfaces are locked into a pre-programmed pattern after launch (way too much stress on the orbiter structure and ET attach points to do otherwise).
Actually that is not a completely accurate statement.
I know.
I should have just said the wing surfaces only move to reduce stress on the orbiter, but aren't actually used to help control the flight of the entire stack itself.
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#329
by
Avron
on 06 Sep, 2006 04:18
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MKremer - 5/9/2006 9:19 PM
mkirk - 5/9/2006 7:46 PM
MKremer - 5/9/2006 7:04 PM
The orbiter aero control surfaces are locked into a pre-programmed pattern after launch (way too much stress on the orbiter structure and ET attach points to do otherwise).
Actually that is not a completely accurate statement.
I know.
I should have just said the wing surfaces only move to reduce stress on the orbiter, but aren't actually used to help control the flight of the entire stack itself.
Challengers wing surfaces did some moving in the last few secs..
Ref: Rogers Commission report (1986)
T+62.484
Challenger's computers order the shuttle's right-hand "elevon," or wing flap, to move suddenly.
T+63.924
A pressure change is recorded in the right-hand outboard elevon, indicating movement.
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#330
by
Avron
on 06 Sep, 2006 04:20
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nacnud - 5/9/2006 7:16 PM
In a worst case senario where the right SRB lights and the other doesn't the stack would loop up and down into the VAB! Dunno about smaller variations.
I think the stack would just tear apart.. but lets not worry about this now..
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#331
by
astrobrian
on 06 Sep, 2006 04:27
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It wouldn't even make it back to the VAB. It probably wouldn't even get beyond the complex if off the pad before the SRB joints would fail. Just a hypothetical though Avron, no worries
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#332
by
ianeck
on 08 Sep, 2006 00:09
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Hi folks. This is just my second post on the forums (on any of the threads). I continue to be amazed by the complete wealth of information (both here and L2, which i just joined yesterday). As I said in my first post (on the sts-115 portion of the forums), I'm simply just a layman, average-joe fan of the shuttle program, and so I hope the question I have isn't too simplistic.
I've watched the STS-114 mcc ascent team film clip several times, and there's always one portion of it which I've found curious. Shortly after SRB sep and the "103 converged" call, we hear a call which goes something like "flight...system progress two good engines..." to which LeRoy Cain simply replies "copy" as if this was an expected event. What is being referred to when (whomever it was) says "two good engines"? There wasn't an SSME lost during ascent on 114 that I can recall at any time. Is this a call which is traditionally heard during the ascent phase?
Thanks for any responses, and I apologize if this was addressed elsewhere.
-Ian.
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#333
by
mkirk
on 08 Sep, 2006 00:19
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ianeck - 7/9/2006 6:56 PM
Hi folks. This is just my second post on the forums (on any of the threads). I continue to be amazed by the complete wealth of information (both here and L2, which i just joined yesterday). As I said in my first post (on the sts-115 portion of the forums), I'm simply just a layman, average-joe fan of the shuttle program, and so I hope the question I have isn't too simplistic.
I've watched the STS-114 mcc ascent team film clip several times, and there's always one portion of it which I've found curious. Shortly after SRB sep and the "103 converged" call, we hear a call which goes something like "flight...system progress two good engines..." to which LeRoy Cain simply replies "copy" as if this was an expected event. What is being referred to when (whomever it was) says "two good engines"? There wasn't an SSME lost during ascent on 114 that I can recall at any time. Is this a call which is traditionally heard during the ascent phase?
Thanks for any responses, and I apologize if this was addressed elsewhere.
-Ian.
The call you are refering to occurs in the Mission Control Center on the Flight Director's Loop - this call is referencing the start of the OMS Assist Burn which starts 10 second after staging (defined as the software changing to major mode 103). The two good engines are the OMS engines.
I would have to listen to the tape for the actual words but the call should go like this; "Flight, Prop, OMS Assist in progress, two good engines."
Mark Kirkman
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#334
by
ianeck
on 08 Sep, 2006 01:58
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mkirk - 7/9/2006 6:06 PM
ianeck - 7/9/2006 6:56 PM
Hi folks. This is just my second post on the forums (on any of the threads). I continue to be amazed by the complete wealth of information (both here and L2, which i just joined yesterday). As I said in my first post (on the sts-115 portion of the forums), I'm simply just a layman, average-joe fan of the shuttle program, and so I hope the question I have isn't too simplistic.
I've watched the STS-114 mcc ascent team film clip several times, and there's always one portion of it which I've found curious. Shortly after SRB sep and the "103 converged" call, we hear a call which goes something like "flight...system progress two good engines..." to which LeRoy Cain simply replies "copy" as if this was an expected event. What is being referred to when (whomever it was) says "two good engines"? There wasn't an SSME lost during ascent on 114 that I can recall at any time. Is this a call which is traditionally heard during the ascent phase?
Thanks for any responses, and I apologize if this was addressed elsewhere.
-Ian.
The call you are refering to occurs in the Mission Control Center on the Flight Director's Loop - this call is referencing the start of the OMS Assist Burn which starts 10 second after staging (defined as the software changing to major mode 103). The two good engines are the OMS engines.
I would have to listen to the tape for the actual words but the call should go like this; "Flight, Prop, OMS Assist in progress, two good engines."
Mark Kirkman
Thanks sir :-). Just for reference I downloaded what is likely an edited version of the flight control video from spaceflightnow.com. I'm a member of the "plus" section.
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#335
by
oakjon
on 09 Sep, 2006 19:21
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Questions from a simple mind.
I watched today's Atlantis lift-off and had a few questions. When they give the amount of thrust produced by the unit, is that measured at a standard distance throughout the industry? (rocket,jet)
Discounting torching everything, is there much difference between thrust at say, 10' from nozzle and the bottom of flame trench? Don't know if I asked this right.
After lift off, and while climbing, toward the end of the burns it looked like the trail turned from greyish to white. Why is that. Or is it just me?
In some camera views it looked like "rings" in the SSME exhaust path. How come it looks like they "pulse"?
I too am "Joe-Blow" watcher and not an engineer, so I just thought I'd ask.
Jon
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#336
by
MKremer
on 09 Sep, 2006 22:53
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- thrust is usually measured in newtons (KN = kilonewtons, MN = meganewtons), and also sometimes in ft-lbs.
- if you mean exhaust gas velocity, yes, air resistance will slow the exhaust gas velocity the farther it travels from the engine bell
- the SRB exhaust is a light greyish tan color close up, but from a distance it looks much whiter
- sounds like you're referring to mach diamonds (
http://en.wikipedia.org/wiki/Shock_diamond )
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#337
by
MKremer
on 10 Sep, 2006 08:38
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Really interesting that the Real (Realmedia/RealPlayer) feed from NASA-TV is about 40 seconds ahead of the Windows Media feed.
(which also means if you want to monitor something as close to real-time as possible, choose the Real feed rather then the Win-Media feed)
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#338
by
dutch courage
on 10 Sep, 2006 09:54
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MKremer - 10/9/2006 10:25 AM
Really interesting that the Real (Realmedia/RealPlayer) feed from NASA-TV is about 40 seconds ahead of the Windows Media feed.
The difference between the countdown clock (shuttle page) and the Windows Media feed is even more pronounced: 45 seconds.
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#339
by
MKremer
on 10 Sep, 2006 11:28
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Yeah, the main difference is the video processing between the camera feeds and the internet video stream. The KSC video and countdown pages just sample camera input frames every 45 seconds or so, and that tends to be updated much quicker than having to convert every frame of the real-time camera signals into several internet broadcast formats.
