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#120
by
Star One
on 02 Nov, 2017 10:56
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#121
by
mn
on 02 Nov, 2017 13:34
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Thanks Chris G for the excellent article. (as usual)
a: Where can I find more info on the issue of thrust torque, I don't remember seeing it and it doesn't come up in searches.
b: Can we assume the range is available any time in late December once FH is ready and SpaceX requests it? or are there also specific windows they need to squeeze into?
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#122
by
abaddon
on 02 Nov, 2017 13:53
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b: Can we assume the range is available any time in late December once FH is ready and SpaceX requests it? or are there also specific windows they need to squeeze into?
Don't know about holiday schedule for the range, but nobody else has any scheduled launches in December from Canaveral/Kennedy. So they should be relatively free to fit it in as they can.
The next scheduled flight from Florida for a non-SpaceX launcher is an Atlas V from SLC-41 in the middle of January.
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#123
by
wannamoonbase
on 02 Nov, 2017 14:29
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#124
by
intrepidpursuit
on 02 Nov, 2017 14:40
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Nice article.
The info about the staggered startup was interesting, but I would have liked to see some mention or discussion of any testing that SpaceX has done to support that kind of startup. Before AMOS-6, I could have imagined them trying it for the first time on 39A during the static test - it’s hard to believe that they’d try that now.
I'm sure they've tested it on the stand at McGregor. If I understand the plumbing on F9 it can currently only start the engines in two groups, 3 used for boost back and the remaining 6, so they wouldn't be able to do the staggered startup on a standard static fire. They are probably building the granularity into Block 5 for uniformity, but I'd guess this is one of the modifications they made in Hawthorne to the flight proven boosters.
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#125
by
cscott
on 02 Nov, 2017 15:15
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Intrepidpursuit: I think you're confusing *restart* with *start*. Only three of the F9's engines are equipped with on-board TEA/TEB reservoirs and plumbing necessary for in-flight restarts. The other engines get their TEA/TEB plumbed from ground supplies pre-liftoff.
The 1/3 engine restrictions in-flight probably have nothing to do with "staggered start", which happens on the ground.
That said, it's reasonable to assume that staggered start would require GSE changes or maybe even additional valves on-vehicle. I'm inclined to agree with you that staggered start (including GSE-side changes) would have been tested at McGregor when the FH cores went through there. But the necessary replumbing might not have been done on the LC39A TEL yet.
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#126
by
russianhalo117
on 02 Nov, 2017 15:49
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What does that mean? They start 9 at a time now right?
F9 can start all 9 at once but for FH to allow SLC-39A and SLC-4E to avoid a domino effect of pad damage they are to be started differently to preserve the pad's flame trench (the results of the acoustic, vibration, and thrust impingement damage estimate models and concluded reasoning were discussed in detail in multiple previous threads). It is also my understanding as I remember reading about in a thread ages ago that liftoff will be at slighlty reduced thrust until clear of the pad and FSS before switching to full thrust mode.
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#127
by
Star One
on 02 Nov, 2017 15:56
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Was reading in a current book how demanding each Saturn V launch was on the launch infrastructure. How likely is this launch to damage the infrastructure, I mean a launcher this powerful hasn’t been launched in sometime, beyond the DH, and it’s not possible to perfectly model an event like this beforehand?
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#128
by
wannamoonbase
on 02 Nov, 2017 16:01
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Nice article.
The info about the staggered startup was interesting, but I would have liked to see some mention or discussion of any testing that SpaceX has done to support that kind of startup. Before AMOS-6, I could have imagined them trying it for the first time on 39A during the static test - it’s hard to believe that they’d try that now.
I'm sure they've tested it on the stand at McGregor. If I understand the plumbing on F9 it can currently only start the engines in groups two groups, 3 used for boost back and the remaining 6, so they wouldn't be able to do the staggered startup on a standard static fire. They are probably building the granularity into Block 5 for uniformity, but I'd guess this is one of the modifications they made in Hawthorne to the flight proven boosters.
Machines work on a different time scale than humans. The start up maybe staggered but appear almost simultaneous to us humans.
The side booster staging event is going to be the money event of this launch. We haven't seen a staging event like that since shuttle.
Likely with this first flight they can have extra time (fractions of a second perhaps) to be safe and those times can be trimmed with experience in successive flights.
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#129
by
meberbs
on 02 Nov, 2017 16:04
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What does that mean? They start 9 at a time now right?
F9 can start all 9 at once but for FH to allow SLC-39A and SLC-4E to avoid a domino effect of pad damage they are to be started differently to preserve the pad's flame trench (the results of the acoustic, vibration, and thrust impingement damage estimate models and concluded reasoning were discussed in detail in multiple previous threads). It is also my understanding as I remember reading about in a thread ages ago that liftoff will be at slighlty reduced thrust until clear of the pad and FSS before switching to full thrust mode.
The article says that it is because of a thrust torque problem damaging the ocotwebs, not because of impingement damage to the flame trench. This makes sense due to the different load paths on the Falcon Heavy. There will always be a small difference in engine start time whether intentional or not. If one side booster started all engines slightly before the other one, this would create a massive torque. Starting 2 engines at a time with a pause in between reduces the maximum unbalanced torque.
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#130
by
rpapo
on 02 Nov, 2017 16:06
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The side booster staging event is going to be the money event of this launch. We haven't seen a staging event like that since shuttle.
Just how different is it from what happens on Delta 4 Heavy launches?
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#131
by
ZachS09
on 02 Nov, 2017 16:11
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The side booster staging event is going to be the money event of this launch. We haven't seen a staging event like that since shuttle.
Just how different is it from what happens on Delta 4 Heavy launches?
It's different than the Space Shuttle and Delta IV Heavy because the Falcon Heavy side cores are NOT equipped with separation rockets, or in KSP terms "sepratrons."
Cold-gas thrusters are too weak to help with the separation process.
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#132
by
rpapo
on 02 Nov, 2017 16:17
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The side booster staging event is going to be the money event of this launch. We haven't seen a staging event like that since shuttle.
Just how different is it from what happens on Delta 4 Heavy launches?
It's different than the Space Shuttle and Delta IV Heavy because the Falcon Heavy side cores are NOT equipped with separation rockets, or in KSP terms "sepratrons."
Cold-gas thrusters are too weak to help with the separation process.
I was only wondering about the "since the shuttle" remark. Delta 4 Heavy has flown since then. I agree that this will be quite a challenge for what SpaceX prefers: mechanical separators.
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#133
by
ZachS09
on 02 Nov, 2017 16:52
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The only crucial events that SpaceX is worried about are the initial liftoff followed by tower clearance, Max-Q, and side core separation.
After that, it's treated like a normal Falcon 9 mission with the addition of two simultaneous landings of the side cores.
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#134
by
mme
on 02 Nov, 2017 16:57
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The only crucial events that SpaceX is worried about are the initial liftoff followed by tower clearance, Max-Q, and side core separation.
After that, it's treated like a normal Falcon 9 mission with the addition of two simultaneous landings of the side cores.
That's a fairly long list to say "only." It's basically "everything up to second stage separation."
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#135
by
envy887
on 02 Nov, 2017 16:58
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The only crucial events that SpaceX is worried about are the initial liftoff followed by tower clearance, Max-Q, and side core separation.
After that, it's treated like a normal Falcon 9 mission with the addition of two simultaneous landings of the side cores.
Sounded like control authority during booster return was also a question mark since the nose cone doesn't have a good flow separation point.
Do we know if all the Heavy boosters will have Ti grid fins?
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#136
by
ZachS09
on 02 Nov, 2017 17:00
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I remember Elon Musk saying that he's worried about a possible pad explosion, so if Falcon Heavy clears the tower, he's relieved for the time being because then the vehicle has to go through Max-Q, which could potentially rip everything apart if there's one or more defects.
And about the side core separation, well, there's no separation rockets, so we'll hope for the best.
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#137
by
old_sellsword
on 02 Nov, 2017 17:01
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The only crucial events that SpaceX is worried about are the initial liftoff followed by tower clearance, Max-Q, and side core separation.
After that, it's treated like a normal Falcon 9 mission with the addition of two simultaneous landings of the side cores.
Sounded like control authority during booster return was also a question mark since the nose cone doesn't have a good flow separation point.
Do we know if all the Heavy boosters will have Ti grid fins?
The side boosters must have them for the control authority problems you mentioned, and it seems likely that the center core will have them due to higher than usual reentry velocities.
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#138
by
ChrisGebhardt
on 02 Nov, 2017 17:22
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b: Can we assume the range is available any time in late December once FH is ready and SpaceX requests it? or are there also specific windows they need to squeeze into?
Don't know about holiday schedule for the range, but nobody else has any scheduled launches in December from Canaveral/Kennedy. So they should be relatively free to fit it in as they can.
The next scheduled flight from Florida for a non-SpaceX launcher is an Atlas V from SLC-41 in the middle of January.
The only U.S federal holiday in December is Christmas Day, and holidays are not "absolutely no work under any circumstance" days. Launches have and will occur on holidays.
As for other launches on the range, Hispasat is out there in late-December as well, though that one has no confirmed target date yet. Hispasat is expendable, so it doesn't need the ASDS. And since all the Falcon family rockets have AFTS and are both Falcons, we won't need range reconfigurations.
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#139
by
russianhalo117
on 02 Nov, 2017 18:38
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What does that mean? They start 9 at a time now right?
F9 can start all 9 at once but for FH to allow SLC-39A and SLC-4E to avoid a domino effect of pad damage they are to be started differently to preserve the pad's flame trench (the results of the acoustic, vibration, and thrust impingement damage estimate models and concluded reasoning were discussed in detail in multiple previous threads). It is also my understanding as I remember reading about in a thread ages ago that liftoff will be at slighlty reduced thrust until clear of the pad and FSS before switching to full thrust mode.
The article says that it is because of a thrust torque problem damaging the ocotwebs, not because of impingement damage to the flame trench. This makes sense due to the different load paths on the Falcon Heavy. There will always be a small difference in engine start time whether intentional or not. If one side booster started all engines slightly before the other one, this would create a massive torque. Starting 2 engines at a time with a pause in between reduces the maximum unbalanced torque.
I was actually talking about to separate topics and didn't make that clear enough it seems.
