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#120
by
Austin
on 14 Feb, 2007 04:31
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Did anyone notice that during the launch of sts 116, about 26 seconds into flight, the launch commentator reported Discovery's speed at 1000 mph? Obviously a mistake (closer to 400 mph at that point). The shuttle gets out in a hurry, but not that fast!
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#121
by
joema
on 14 Feb, 2007 11:19
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Austin - 13/2/2007 11:31 PM
Did anyone notice that during the launch of sts 116, about 26 seconds into flight, the launch commentator reported Discovery's speed at 1000 mph? Obviously a mistake (closer to 400 mph at that point). The shuttle gets out in a hurry, but not that fast!
Actually the number sounds about right. Vehicle liftoff mass is about 4.5 million lbs (2.041 million kg), total liftoff thrust is about 6.781 million lbf (3.076 million kgf), so liftoff thrust:weight ratio is about 1.5-to-1. Therefore liftoff and initial acceleration would be about 1.5 g. From v = a*t, this would give 32.2 ft/sec/sec * 1.5 * 26 = 1256 ft/sec (857 mph) @ T+26 sec.
SRB sea level thrust increases from about 2.8 million lbf/each at liftoff to about 3.0 million lbf/each at T+10 sec, then to about 3.1 million lbf/each at T+25 sec. Don't know exact combined SRB+SSME mass flow rate, but a rough estimate would be about 11,400 kg/sec for the SRBs and 1,400 kg/sec for the SSMEs, for a total of 12,800 kg/sec.
So at T+10 sec vehicle is about 128,000 kg (282,200 lbs) lighter, combined with increasing SRB thrust giving a thrust:weight ratio of 1.7. At T+26 sec it's about 332,800 kg (734,000 lbs) lighter, giving a thrust:weight ratio of 1.96.
Just crudely approximating by taking the thrust:weight ratio at T+10 sec gives 32.2 ft/sec/sec * 1.7 * 26 = 1423 ft/sec or 972 mph @ T+26 sec, very close to what the announcer said.
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#122
by
elmarko
on 14 Feb, 2007 13:28
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By the way, any comments on the wiki idea?
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#123
by
nathan.moeller
on 14 Feb, 2007 14:25
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Austin - 13/2/2007 11:31 PM
Did anyone notice that during the launch of sts 116, about 26 seconds into flight, the launch commentator reported Discovery's speed at 1000 mph? Obviously a mistake (closer to 400 mph at that point). The shuttle gets out in a hurry, but not that fast!
I noticed that too. He also said it was one mile high (correct) but four and a half miles downrange (wrong). I think he just got a little excited
Speed at T+26 seconds is in the neighborhood of 350-400 mph. The shuttle doesn't hit 1000 mph until after 1 minute into the flight. And downrange distance isn't greater than altitude until after they even out around 25 miles altitude/25 miles drd. But yeah...even the commentators make mistakes but oh well.
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#124
by
Austin
on 14 Feb, 2007 14:39
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joema - 14/2/2007 4:19 AM
Austin - 13/2/2007 11:31 PM
Did anyone notice that during the launch of sts 116, about 26 seconds into flight, the launch commentator reported Discovery's speed at 1000 mph? Obviously a mistake (closer to 400 mph at that point). The shuttle gets out in a hurry, but not that fast!
Actually the number sounds about right. Vehicle liftoff mass is about 4.5 million lbs (2.041 million kg), total liftoff thrust is about 6.781 million lbf (3.076 million kgf), so liftoff thrust:weight ratio is about 1.5-to-1. Therefore liftoff and initial acceleration would be about 1.5 g. From v = a*t, this would give 32.2 ft/sec/sec * 1.5 * 26 = 1256 ft/sec (857 mph) @ T+26 sec.
SRB sea level thrust increases from about 2.8 million lbf/each at liftoff to about 3.0 million lbf/each at T+10 sec, then to about 3.1 million lbf/each at T+25 sec. Don't know exact combined SRB+SSME mass flow rate, but a rough estimate would be about 11,400 kg/sec for the SRBs and 1,400 kg/sec for the SSMEs, for a total of 12,800 kg/sec.
So at T+10 sec vehicle is about 128,000 kg (282,200 lbs) lighter, combined with increasing SRB thrust giving a thrust:weight ratio of 1.7. At T+26 sec it's about 332,800 kg (734,000 lbs) lighter, giving a thrust:weight ratio of 1.96.
Just crudely approximating by taking the thrust:weight ratio at T+10 sec gives 32.2 ft/sec/sec * 1.7 * 26 = 1423 ft/sec or 972 mph @ T+26 sec, very close to what the announcer said.
Joe -- thanks for your response but that's not correct. Take a look/listen to the launch of sts 114, for example...
In this video of Discovery's Return to Flight mission, Discovery's speed at 26 seconds is 400 mph at an altitude of 12,000 feet. At the 60 second mark, the vehicle is travelling at 900 mph.
So unless Discovery had an added set of SRBs strapped to the ET on sts 116 that were not visible (after all, it was a night launch : ), the report from the commentator was incorrect. I've seen every shuttle launch (without exception) and I remember that this one struck me when I heard that report. Clearly a mistake.
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#125
by
Austin
on 14 Feb, 2007 14:44
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nathan.moeller - 14/2/2007 7:25 AM
Austin - 13/2/2007 11:31 PM
Did anyone notice that during the launch of sts 116, about 26 seconds into flight, the launch commentator reported Discovery's speed at 1000 mph? Obviously a mistake (closer to 400 mph at that point). The shuttle gets out in a hurry, but not that fast!
I noticed that too. He also said it was one mile high (correct) but four and a half miles downrange (wrong). I think he just got a little excited Speed at T+26 seconds is in the neighborhood of 350-400 mph. The shuttle doesn't hit 1000 mph until after 1 minute into the flight. And downrange distance isn't greater than altitude until after they even out around 25 miles altitude/25 miles drd. But yeah...even the commentators make mistakes but oh well.
Nathan -- yepper. If memory serves me correct, that was his first time as launch commentator, and I think you're right. I didn't mean to rag on the guy, it just caught my attention.
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#126
by
mkirk
on 14 Feb, 2007 15:01
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Austin - 13/2/2007 11:31 PM
Did anyone notice that during the launch of sts 116, about 26 seconds into flight, the launch commentator reported Discovery's speed at 1000 mph? Obviously a mistake (closer to 400 mph at that point). The shuttle gets out in a hurry, but not that fast!
Here is the link (that I posted on page 2 of this thread) to a breakdown of the Ascent Events that Bill Harwood posted from the Ascent Data Package for 121.
http://spaceflightnow.com/shuttle/sts121/fdf/121ascentdata.htmlIn defense of the commentator there are two velocities that are used by the shuttle, Relative and Inertial. These are the reference frames with Relative – in simple terms – being the velocity of the vehicle along the ground track from the pad. In other words this is the more intuitive velocity you are used to because it tells you how fast the vehicle is going compared to a stationary point on the ground.
The inertial reference frame takes into account that the earth is rotating and therefore when the shuttle is sitting on the Pad it is traveling at almost 1000 feet per second.
In the cockpit the velocity tapes display relative velocity until SRB SEP and then they transition to Inertial – this causes an almost instantaneous jump in velocity of about 1 MACH number or 1000 feet per second on the airspeed/velocity indicator.
So PAO may have read out the inertial velocity rather than the relative on his console display in the Mission Control Center.
Mark Kirkman
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#127
by
STS-500Cmdr
on 14 Feb, 2007 15:11
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Yeah i think Kelly Humphries-who was the commentator for the STS-116 launch/ascent-he was new to doing ascent commentary--yeah i noticed him calling 1000 mph and 4 1/2 miles downrange prematurely--i get the feeling hes reading a script and maybe jumping to that part of the script- -do the PAO's read a script of some sort?? I notice Humphries sounded alot like James Hartsfield--sounded like he was borrowing from him.
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#128
by
nathan.moeller
on 14 Feb, 2007 16:49
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STS-500Cmdr - 14/2/2007 10:11 AM
Yeah i think Kelly Humphries-who was the commentator for the STS-116 launch/ascent-he was new to doing ascent commentary--yeah i noticed him calling 1000 mph and 4 1/2 miles downrange prematurely--i get the feeling hes reading a script and maybe jumping to that part of the script- -do the PAO's read a script of some sort?? I notice Humphries sounded alot like James Hartsfield--sounded like he was borrowing from him.
Yeah I think he just got excited - it being his first launch commentary and all. Yeah I think they read from scripts and follow timelines during commentaries. If so, he probably just got ahead of himself. As for sounding like James Hartsfield, I know exactly what you mean. Listen to Hartsfield's STS-114 launch commentary then take a listen to Humphries' STS-116 commentary. A lot of similarities in the wording quickly become apparent.
Hartsfield at Roll Program: 'Houston now controlling. CDR Eileen Collins confirming Discovery's rolling on course for a rendezvous with the International Space Station.'
Humphries at Roll Program: 'Houston now controlling. CDR Mark Polansky confirming Discovery's rolling on course to the International Space Station.'
In my opinion, he did an excellent job. Just got ahead of himself that's all. He got back on track pretty quick. Trust me...public announcing/commenting is difficult. I had a hard time talking over the store intercom at Target the first time I made the closing announcements. But I nailed it anyway
It takes practice.
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#129
by
spaceshuttle
on 14 Feb, 2007 17:13
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nathan.moeller - 14/2/2007 11:49 AM
STS-500Cmdr - 14/2/2007 10:11 AM
Yeah i think Kelly Humphries-who was the commentator for the STS-116 launch/ascent-he was new to doing ascent commentary--yeah i noticed him calling 1000 mph and 4 1/2 miles downrange prematurely--i get the feeling hes reading a script and maybe jumping to that part of the script- -do the PAO's read a script of some sort?? I notice Humphries sounded alot like James Hartsfield--sounded like he was borrowing from him.
Yeah I think he just got excited - it being his first launch commentary and all. Yeah I think they read from scripts and follow timelines during commentaries. If so, he probably just got ahead of himself. As for sounding like James Hartsfield, I know exactly what you mean. Listen to Hartsfield's STS-114 launch commentary then take a listen to Humphries' STS-116 commentary. A lot of similarities in the wording quickly become apparent.
Hartsfield at Roll Program: 'Houston now controlling. CDR Eileen Collins confirming Discovery's rolling on course for a rendezvous with the International Space Station.'
Humphries at Roll Program: 'Houston now controlling. CDR Mark Polansky confirming Discovery's rolling on course to the International Space Station.'
In my opinion, he did an excellent job. Just got ahead of himself that's all. He got back on track pretty quick. Trust me...public announcing/commenting is difficult. I had a hard time talking over the store intercom at Target the first time I made the closing announcements. But I nailed it anyway It takes practice.
LOL, I like the Target comment. I wonder if Rob Navias plans to do anymore launches?
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#130
by
nathan.moeller
on 14 Feb, 2007 19:10
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spaceshuttle - 14/2/2007 12:13 PM
LOL, I like the Target comment. I wonder if Rob Navias plans to do anymore launches?
I don't know. I bet he will. He did four in a row from 2002-2003 (STS 111-107). In my opinion, Navias is the best at covering launches and landings. He's very precise and detailed and gets you riled up about what's going on. Don't get me wrong, the others do great as well, but Navias is a personal favorite. Hopefully he'll be back before too long.
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#131
by
joema
on 14 Feb, 2007 21:48
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Austin - 14/2/2007 9:39 AM
Joe -- thanks for your response but that's not correct. Take a look/listen to the launch of sts 114, for example...
Take a look at the attached Mach profile as a function of time, taken from actual STS-107 flight data. It indicates at about T+30 sec, the vehicle is at about Mach 2. It seems to show the velocity at T+26 sec would be pretty fast, at least 1000 mph. I don't understand the discrepancy. Would appreciate any further comments from anybody on this.
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#132
by
Jim
on 14 Feb, 2007 21:56
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Let's stop the mind numbing PAO discussion
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#133
by
Austin
on 14 Feb, 2007 22:17
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mkirk - 14/2/2007 8:01 AM
Here is the link (that I posted on page 2 of this thread) to a breakdown of the Ascent Events that Bill Harwood posted from the Ascent Data Package for 121.
http://spaceflightnow.com/shuttle/sts121/fdf/121ascentdata.html
In defense of the commentator there are two velocities that are used by the shuttle, Relative and Inertial. These are the reference frames with Relative – in simple terms – being the velocity of the vehicle along the ground track from the pad. In other words this is the more intuitive velocity you are used to because it tells you how fast the vehicle is going compared to a stationary point on the ground.
The inertial reference frame takes into account that the earth is rotating and therefore when the shuttle is sitting on the Pad it is traveling at almost 1000 feet per second.
In the cockpit the velocity tapes display relative velocity until SRB SEP and then they transition to Inertial – this causes an almost instantaneous jump in velocity of about 1 MACH number or 1000 feet per second on the airspeed/velocity indicator.
So PAO may have read out the inertial velocity rather than the relative on his console display in the Mission Control Center.
Mark Kirkman
Thanks Mark for the info. I've always wondered to what extent NASA provided technical training to Public Affairs Officers. Although many have journalism degrees, they obviously must have thorough knowledge of the shuttle's systems in order to field reporters' questions in an informed and intelligent manner.
Joe -- not sure where you got the "mach profile," but I can assure you that the shuttle is not traveling at mach 2 thirty seconds into flight.
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#134
by
joema
on 15 Feb, 2007 01:36
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Antares - 14/2/2007 5:26 PM
...Joema, you read that graph backwards. STS is not supersonic until T+~45s, Mach 2 at T+~72s...
You're right, thanks for the correction. I mistakenly looked at the qbar line instead of the Mach line.
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#135
by
rolly
on 15 Feb, 2007 18:07
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At what altitude is sts-115 during reentry when the plasma is at its brightest, how bright would it look like in a bedroom if there was an arc lamp that bright
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#136
by
Jamie Young
on 15 Feb, 2007 18:14
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#137
by
Mark Dave
on 15 Feb, 2007 18:26
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I noticed now the crane is completely removed from the LC-39 FSS. Why was that?
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#138
by
Jim
on 15 Feb, 2007 18:29
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It was more cost effective to use a portable crane for the few uses than to maintain the FSS crane
move to shuttle Q&A
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#139
by
SCE2Aux
on 15 Feb, 2007 18:31
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I've noticed changes in the TPS on the wings of the orbiters. Could anyone tell me why it's different?
Speed at T+26 seconds is in the neighborhood of 350-400 mph. The shuttle doesn't hit 1000 mph until after 1 minute into the flight. And downrange distance isn't greater than altitude until after they even out around 25 miles altitude/25 miles drd. But yeah...even the commentators make mistakes but oh well.
It takes practice.