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#1280
by
Yeknom-Ecaps
on 23 Jan, 2018 15:52
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Is there a set of actual dates WDRs for FH actually took place since it got back to the pad on Jan 9? Several comments on "maybe" or "could be" WDR occurring.
Thanks.
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#1281
by
Space Ghost 1962
on 23 Jan, 2018 16:37
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I'd say it's not surprising that FH is going through a fairly long series of WDR cycles, getting the GSE tuned up. The first Saturn V, AS-501, had a Wet CDDT (it's version of a WDR), scheduled to last four days, run out to 17 days. But all remaining Saturn V Wet CDDT's ran pretty well on schedule.
SpaceX is just coming to terms with Falcon Heavy, and just as it took a while for NASA to do so with the mighty Saturn, it will take as long as it takes to do so with FH.
How about comparing it to a more relevant vehicle like the Delta IV heavy. Saturn V does not compare at all.
Have been thinking a lot about what a relevant vehicle comparison might be. It's not so easy when you think about what each is like.
In many ways an Atlas V Heavy would have been a closer match, especially if it had taken the added step of sub-cooled props. (DIVH's LH brings that a bit closer.) But both DIV and Atlas are single engined boosters, and multiengined does make a significant difference.
And in considering how history might have been different if there were a Atlas V Heavy, FH as a provider business offering seems to bring that back too.
Less significant are the mods for landing boosters.
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#1282
by
foragefarmer
on 23 Jan, 2018 16:46
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Does someone have a comparison between Delta IV Heavy and FH first launch preparations? My search skills couldn'the locate anything yet.
Delta IV Heavy first went vertical Dec. 10th 2003 and launched Dec. 21st 2004. So Delta IV Heavy preparations took over a year. And the payload did not deploy to the correct orbit.
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#1283
by
Jim
on 23 Jan, 2018 16:57
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But both DIV and Atlas are single engined boosters, and multiengined does make a significant difference.
Not for the heavy, since it was proven on F9 single cores
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#1284
by
DaveS
on 23 Jan, 2018 17:24
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I'd say it's not surprising that FH is going through a fairly long series of WDR cycles, getting the GSE tuned up. The first Saturn V, AS-501, had a Wet CDDT (it's version of a WDR), scheduled to last four days, run out to 17 days. But all remaining Saturn V Wet CDDT's ran pretty well on schedule.
SpaceX is just coming to terms with Falcon Heavy, and just as it took a while for NASA to do so with the mighty Saturn, it will take as long as it takes to do so with FH.
How about comparing it to a more relevant vehicle like the Delta IV heavy. Saturn V does not compare at all.
Here's a write-up on some of the challenges that the Delta team faced when they were fielding their heavy:
https://spaceflightnow.com/news/n0410/31d4hchallenges/
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#1285
by
clongton
on 23 Jan, 2018 17:34
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But both DIV and Atlas are single engined boosters, and multiengined does make a significant difference.
Not for the heavy, since it was proven on F9 single cores
Not sure what you're driving at Jim. I don't think either Saturn or DIVH compare in any way. DIVH sequenced 3 engine starts for liftoff divided over 3 cores while FH will sequence 27 engines divided over 3 cores. Saturn sequences 5 engines in a single core. Ghost has a valid point that multi-engine sequencing on this scale is unprecedented. The last time this was tried was the Soviet N1 7L on Nov 23, 1972. But that, like the Saturn, was a single core. The FH is 3 multi-engined cores strapped together. I don't think there really is any other vehicle that it can be compared to. The only way DIVH compares at all is 2 strap-on boosters, but they were each single engine cores. FH is completely different from the Saturn and the DIVH and, as far as I know, anything else we have ever tried especially with the use of super-cooled propellants. There's some [L2] deformation that really comes into play here, which afaik didn't affect either of these 2. This is totally new.
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#1286
by
Jim
on 23 Jan, 2018 17:51
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But both DIV and Atlas are single engined boosters, and multiengined does make a significant difference.
Not for the heavy, since it was proven on F9 single cores
Not sure what you're driving at Jim. I don't think either Saturn or DIVH compare in any way. DIVH sequenced 3 engine starts for liftoff divided over 3 cores while FH will sequence 27 engines divided over 3 cores. Saturn sequences 5 engines in a single core. Ghost has a valid point that multi-engine sequencing on this scale is unprecedented. The last time this was tried was the Soviet N1 7L on Nov 23, 1972. But that, like the Saturn, was a single core. The FH is 3 multi-engined cores strapped together. I don't think there really is any other vehicle that it can be compared to. The only way DIVH compares at all is 2 strap-on boosters, but they were each single engine cores. FH is completely different from the Saturn and the DIVH and, as far as I know, anything else we have ever tried especially with the use of super-cooled propellants. There's some [L2] deformation that really comes into play here, which afaik didn't affect either of these 2. This is totally new.
The interaction of the three cores greatly override any affects from having multiple engines.
The multiple engines just means a long start sequences.
It is still is just 9 engines per core and that is known. The engines on one core do not affect the other cores.
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#1287
by
the_other_Doug
on 23 Jan, 2018 18:11
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But both DIV and Atlas are single engined boosters, and multiengined does make a significant difference.
Not for the heavy, since it was proven on F9 single cores
Not sure what you're driving at Jim. I don't think either Saturn or DIVH compare in any way. DIVH sequenced 3 engine starts for liftoff divided over 3 cores while FH will sequence 27 engines divided over 3 cores. Saturn sequences 5 engines in a single core. Ghost has a valid point that multi-engine sequencing on this scale is unprecedented. The last time this was tried was the Soviet N1 7L on Nov 23, 1972. But that, like the Saturn, was a single core. The FH is 3 multi-engined cores strapped together. I don't think there really is any other vehicle that it can be compared to. The only way DIVH compares at all is 2 strap-on boosters, but they were each single engine cores. FH is completely different from the Saturn and the DIVH and, as far as I know, anything else we have ever tried especially with the use of super-cooled propellants. There's some [L2] deformation that really comes into play here, which afaik didn't affect either of these 2. This is totally new.
The interaction of the three cores greatly override any affects from having multiple engines.
The multiple engines just means a long start sequences.
It is still is just 9 engines per core and that is known. The engines on one core do not affect the other cores.
So, since the engines on one core don't affect the other cores, all the work on preventing the startups from applying torque to the stack, and thus affecting the other cores, is just a bunch of hooey?!
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#1288
by
gongora
on 23 Jan, 2018 18:18
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Does the number of engines have anything to do with the GSE issues they've been working through, or just the fact that it's three cores? I think that's where Jim may have a point. When we get to the static fire then a new set of issues can arise.
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#1289
by
Lars-J
on 23 Jan, 2018 18:28
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The interaction of the three cores greatly override any affects from having multiple engines.
The multiple engines just means a long start sequences.
It is still is just 9 engines per core and that is known. The engines on one core do not affect the other cores.
So, since the engines on one core don't affect the other cores, all the work on preventing the startups from applying torque to the stack, and thus affecting the other cores, is just a bunch of hooey?!
I think the point may be that the torque issue has been resolved on individual cores (see the last 45+ launches), and this will not be significant factor to worry about. If so, why should there be any torque to pass on to the neighbor core?
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#1290
by
the_other_Doug
on 23 Jan, 2018 18:28
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Does the number of engines have anything to do with the GSE issues they've been working through, or just the fact that it's three cores? I think that's where Jim may have a point. When we get to the static fire then a new set of issues can arise.
Very fair point.
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#1291
by
Jim
on 23 Jan, 2018 18:30
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So, since the engines on one core don't affect the other cores, all the work on preventing the startups from applying torque to the stack, and thus affecting the other cores, is just a bunch of hooey?!
What work? What torque?
Each core has independent hold downs.
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#1292
by
ATPTourFan
on 23 Jan, 2018 18:34
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For the GSE issues, this is least bit surprising. They're working in brand new tail service masts and hold downs for not one, but two new cores (the side boosters, of course). It was tricky enough getting LC-39A to support single stick F9 that first time last year. Now they're setting up support for two new cores and managing new fluid delivery challenges and who knows what else.
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#1293
by
Nomadd
on 23 Jan, 2018 19:07
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So, since the engines on one core don't affect the other cores, all the work on preventing the startups from applying torque to the stack, and thus affecting the other cores, is just a bunch of hooey?!
What work? What torque?
Each core has independent hold downs.
There's a reason F9s have 4 hold downs instead of 2. Since the FH will have 3 on the boosters and 2 on the core, it's not unreasonable to assume some interaction before liftoff between elements.
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#1294
by
Space Ghost 1962
on 23 Jan, 2018 19:12
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So, since the engines on one core don't affect the other cores, all the work on preventing the startups from applying torque to the stack, and thus affecting the other cores, is just a bunch of hooey?!
What work? What torque?
Each core has independent hold downs.
So each core during hotfire is like a singular core. Just three close together.
The real "inter/intra" core behavior (plus GNC) occurs after release on launch. Sensible.
add:
So, since the engines on one core don't affect the other cores, all the work on preventing the startups from applying torque to the stack, and thus affecting the other cores, is just a bunch of hooey?!
What work? What torque?
Each core has independent hold downs.
There's a reason F9s have 4 hold downs instead of 2. Since the FH will have 3 on the boosters and 2 on the core, it's not unreasonable to assume some interaction before liftoff between elements.
Also sensible.
You could have mode coupling and buckling issues. Given that there are off axial thrusts on starting (why you'd want to start in two's per core to cancel).
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#1295
by
Jim
on 23 Jan, 2018 19:18
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There's a reason F9s have 4 hold downs instead of 2. Since the FH will have 3 on the boosters and 2 on the core, it's not unreasonable to assume some interaction before liftoff between elements.
Because F9s have 4, because two is unstable.
Also, the core is modified to be stronger and accept only two hold downs and the boosters
All three boosters are starting engines in parallel and there shouldn't be any real interaction.
The core and this reaction frame is not the same as a regular F9 vehicle and pad. Both are beefed up.
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#1296
by
mn
on 23 Jan, 2018 19:23
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There's a reason F9s have 4 hold downs instead of 2. Since the FH will have 3 on the boosters and 2 on the core, it's not unreasonable to assume some interaction before liftoff between elements.
Because F9s have 4, because two is unstable.
Also, the core is modified to be stronger and accept only two hold downs and the boosters
All three boosters are starting engines in parallel and there shouldn't be any real interaction.
The core and this reaction frame is not the same as a regular F9 vehicle and pad. Both are beefed up.
SpaceX decided to stagger the engine start on the FH, unlike the regular F9 where they just start all 9 simultaneously.
They must know something we don't.
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#1297
by
Jim
on 23 Jan, 2018 19:26
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SpaceX decided to stagger the engine start on the FH, unlike the regular F9 where they just start all 9 simultaneously.
They must know something we don't.
The stagger start still has engines starting on all three cores at the same time
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#1298
by
Jim
on 23 Jan, 2018 19:30
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Delta IV Heavy changed recently its start sequence to alleviate GH2 build up. Instead of all three booster starting up at once, they went to a port, center and then starboard start sequence. This shows that you can treat them as independent until release.
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#1299
by
mn
on 23 Jan, 2018 19:31
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SpaceX decided to stagger the engine start on the FH, unlike the regular F9 where they just start all 9 simultaneously.
They must know something we don't.
The stagger start still has engines starting on all three cores at the same time
a: But WHY the staggered start? if there is no interaction between the cores, then why is this start different than any other F9 start? (as has been discussed several times already, but I've yet to see an explanation that I understood)
b: The only reference to a start sequence I have seen is from Chris G and it says 2 engines at a time (and it was asked if that meant per core or overall and I have yet to see an answer). If you have better info on the planned start sequence please do share. TIA