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  STS-1: Flash seen before solid rocket ignition

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Author Topic:   STS-1: Flash seen before solid rocket ignition
DC10LuxuryLiner
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posted 08-31-2011 11:58 AM     Click Here to See the Profile for DC10LuxuryLiner   Click Here to Email DC10LuxuryLiner     Edit/Delete Message   Reply w/Quote
I noticed on a video I was viewing that at solid rocket booster ignition there seemed to be a bright flash under the mobile launch platform and then both solids fired and the stack lifted off. I've never seen this on any other launch.

Was there something different in the ignition sequence on STS-1? I know that the main engines (SSME's) fired a bit longer before the solids were lit, but I wouldn't think that would account for the flash I saw.

Byeman
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posted 08-31-2011 12:48 PM     Click Here to See the Profile for Byeman   Click Here to Email Byeman     Edit/Delete Message   Reply w/Quote
The SSME's fired at the same time as all the other missions. The flash isn't anything different, it is from the ignitor.

DC10LuxuryLiner
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posted 08-31-2011 01:21 PM     Click Here to See the Profile for DC10LuxuryLiner   Click Here to Email DC10LuxuryLiner     Edit/Delete Message   Reply w/Quote
I meant on STS-1 I'd read the SSME's fired for a few seconds longer before SRB igniton. The flash I'm talking about has to to with the SRBs not the SSME's which were already up and running.

Ben
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posted 08-31-2011 01:30 PM     Click Here to See the Profile for Ben   Click Here to Email Ben     Edit/Delete Message   Reply w/Quote
No they were not fired longer than any other mission. Can you be more specific about what video you are looking at? I don't see any flash before ignition in any video I've seen.

DC10LuxuryLiner
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posted 08-31-2011 01:46 PM     Click Here to See the Profile for DC10LuxuryLiner   Click Here to Email DC10LuxuryLiner     Edit/Delete Message   Reply w/Quote
The view is from behind the stack at about the 5:08 mark on the video. It's a bright flash a millisecond before we see the actual plumes from the SRB. I've never seen this on any other launch footage from the same perspective.

Ben
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posted 08-31-2011 02:02 PM     Click Here to See the Profile for Ben   Click Here to Email Ben     Edit/Delete Message   Reply w/Quote
That is, as indicated, simply the ignitor firing and the SRB igniting a millisecond or less apart. Perhaps you have not seen it on any other video because they never used that view again for a shuttle launch that I recall.

heng44
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posted 09-02-2011 01:40 PM     Click Here to See the Profile for heng44   Click Here to Email heng44     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by DC10LuxuryLiner:
I know that the main engines (SSME's) fired a bit longer before the solids were lit, but I wouldn't think that would account for the flash I saw.

You are probably referring to the fact that on STS-1 the main engines ignited at T-3.8 seconds. They built up to a thrust level of 90 percent in three seconds, at which time the SRB ignition sequence began. There was approximately 2.64 seconds between T-0 and SRB ignition to allow for the 'twang'. At T+3 seconds the SRBs were ignited and the holddown bolts were blown. At that time the Mission Elapsed Time was reset to zero and the Shuttle lifted off. Starting with STS-2 the SSME ignition sequence began at T-6.6 seconds, so that SRB ignition came at T-0.

James Brown
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posted 09-02-2011 02:06 PM     Click Here to See the Profile for James Brown   Click Here to Email James Brown     Edit/Delete Message   Reply w/Quote
Found this in the comments of the YouTube video:
The sound suppression system on this mission was much smaller, and as a result, a shockwave was generated, shattering, or damaging almost 80% of the carbon carbon heat shields used for re-entry heat protection. The astronauts said had they known it, they probably would´╗┐ have aborted using the abort hatch. So they put in a larger water pump to dump more water to suppress the sound of the solid rocket boosters igniting.

DC10LuxuryLiner
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posted 09-02-2011 03:11 PM     Click Here to See the Profile for DC10LuxuryLiner   Click Here to Email DC10LuxuryLiner     Edit/Delete Message   Reply w/Quote
So they put in a larger water pump to dump more water to suppress the sound of the solid rocket boosters igniting.
Thanks James, that makes sense now. Dumping a larger amount of water at a higher rate under the MLP might very well visually mask the flash. Thanks to all of you for the replies. I always learn so much on this board.

Jay Chladek
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posted 09-05-2011 03:18 PM     Click Here to See the Profile for Jay Chladek   Click Here to Email Jay Chladek     Edit/Delete Message   Reply w/Quote
Added water suppression was going to be my answer as well. The igniters used on SRBs are something of a two stage igniter where one generates a spark hot enough to light the second one, which in turn is hot enough to light the SRB fuel itself. The igniters are at the top of the SRBs though, not the bottom.

Skylon
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posted 09-05-2011 08:20 PM     Click Here to See the Profile for Skylon     Edit/Delete Message   Reply w/Quote
The sound suppression system on this mission was much smaller, and as a result, a shockwave was generated, shattering, or damaging almost 80% of the carbon carbon heat shields used for re-entry heat protection. The astronauts said had they known it, they probably would´╗┐ have aborted using the abort hatch. So they put in a larger water pump to dump more water to suppress the sound of the solid rocket boosters igniting.
Right idea, but absurdly exaggerated, and a little mixed up.

80% of the TPS? I thought the only tiles lost were on the OMS pods (the belly tiles and RCC made out okay). But yikes, 80%? Young, Crippen and Columbia wouldn't have had a chance.

The issue that the astronauts had said they'd have bailed out over, were they aware, was the SRB pressure wave pushed Columbia's control surfaces out of alignment to such an extent that if they'd had real-time data of the damage, they would have concluded Columbia could not have safely landed, and ejected. Of course Columbia landed safely, but this was a risk enough for the orbiter, but in addition it stood a chance of damaging payloads on future flights.

dabolton
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posted 09-06-2011 08:24 AM     Click Here to See the Profile for dabolton   Click Here to Email dabolton     Edit/Delete Message   Reply w/Quote
Did this SRB pressure wave issue continue throughout the program or did they make a change that resolved it?

Byeman
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posted 09-06-2011 08:33 AM     Click Here to See the Profile for Byeman   Click Here to Email Byeman     Edit/Delete Message   Reply w/Quote
The SRB pressure pulse was reduced by upgrades to the water sound suppression systems some of which were the water wienies.

Byeman
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posted 09-06-2011 11:42 AM     Click Here to See the Profile for Byeman   Click Here to Email Byeman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Jay Chladek:
Added water suppression was going to be my answer as well. The igniters used on SRBs are something of a two stage igniter where one generates a spark hot enough to light the second one, which in turn is hot enough to light the SRB fuel itself. The igniters are at the top of the SRBs though, not the bottom.

Actually the ordnance train is longer. The ignition command fires NSIs into a pyro booster charge. The booster charge sets off the propellant in the igniter initiator; which starts the solid rocket motor igniter, which fires down the length of the solid rocket motor igniting the solid rocket motor propellant.

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