Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion Thread 1  (Read 586004 times)

Offline Pete

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1040 on: 01/13/2018 03:50 PM »
Think of the tail service mast at base of the core.  It is on the opposite side of the TEL.  Now take another core and make it the left booster.  The attach points of the booster to the core are on the right side of the booster.   Now, duplicate the left booster and to attach it to the core, it has to rotated 180 degrees.  This now puts TSM on the TEL side of the vehicle.

Titan had right and left boosters.  Delta IV Heavy had three unique cores, that is why it was expensive
It's these sorts of quite subtle design points that make the whole "Let's make a big rocket by clustering a bunch of common stage together" idea quite a bit trickier IRL than it seems on paper.

In hindsight it's pretty impressive that SX have gotten away with only needing 2 separate designs and being able to reuse single stick F9 boosters as the boosters, rather than a whole new booster design.

Atlas V Heavy would have only required one design for all three boosters since all cores can handle solid boosters.

Things would have been much different if Altas V had won the lionís share and heavies of the EELV order.
Wouldn't the Altas V's asymmetric profile have made bolting 3 side-by-side more difficult?

Offline Jim

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1041 on: 01/13/2018 04:44 PM »
Think of the tail service mast at base of the core.  It is on the opposite side of the TEL.  Now take another core and make it the left booster.  The attach points of the booster to the core are on the right side of the booster.   Now, duplicate the left booster and to attach it to the core, it has to rotated 180 degrees.  This now puts TSM on the TEL side of the vehicle.

Titan had right and left boosters.  Delta IV Heavy had three unique cores, that is why it was expensive
It's these sorts of quite subtle design points that make the whole "Let's make a big rocket by clustering a bunch of common stage together" idea quite a bit trickier IRL than it seems on paper.

In hindsight it's pretty impressive that SX have gotten away with only needing 2 separate designs and being able to reuse single stick F9 boosters as the boosters, rather than a whole new booster design.

Atlas V Heavy would have only required one design for all three boosters since all cores can handle solid boosters.

Things would have been much different if Altas V had won the lionís share and heavies of the EELV order.
Wouldn't the Altas V's asymmetric profile have made bolting 3 side-by-side more difficult?

No, Atlas V was designed from the beginning to do the 3 core heavy.  They just never finished the foreward attachment points and the pad GSE.

The two strapons would occupy where the solids would go.
« Last Edit: 01/13/2018 04:45 PM by Jim »

Offline hoku

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1042 on: 01/13/2018 07:00 PM »
Look like titanium grid fins on the boosters, Al on the core.
Yes, larger titanium fins are required for increased control authority on the boosters during atmospheric descent. This is due to the more aerodynamic shape of the booster's top, which becomes the "tail" during descent.

Core keeps its blunt top, thus smaller Al fins suffice for controlling atmospheric descent.

Offline meekGee

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1043 on: 01/13/2018 07:46 PM »
Look like titanium grid fins on the boosters, Al on the core.
Yes, larger titanium fins are required for increased control authority on the boosters during atmospheric descent. This is due to the more aerodynamic shape of the booster's top, which becomes the "tail" during descent.

Core keeps its blunt top, thus smaller Al fins suffice for controlling atmospheric descent.
I know this is what they said, but it sounds so odd...  The other alternative would have been spoilers that are aerodynamic on the way up, but separate the flow when flying backwards...

Not that I don't like the Titanium fins...
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Offline Semmel

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1044 on: 01/13/2018 08:13 PM »
Look like titanium grid fins on the boosters, Al on the core.
Yes, larger titanium fins are required for increased control authority on the boosters during atmospheric descent. This is due to the more aerodynamic shape of the booster's top, which becomes the "tail" during descent.

Core keeps its blunt top, thus smaller Al fins suffice for controlling atmospheric descent.
I know this is what they said, but it sounds so odd...  The other alternative would have been spoilers that are aerodynamic on the way up, but separate the flow when flying backwards...

Not that I don't like the Titanium fins...

My take on it is:
Titanium fins are required for the side boosters to work. For the reentry heating, they would need the centre core to also have titanium grids for the high velocity. But I guess the rocket has enough spare performance to perform a breaking burn instead of a boostback to reduce velocity to normal reentry conditions. The alternative is, they accept the fact that the centre core gets cooked fins and they dont care because they dont plan to reuse this particular core anyway. So great if the reentry works, no big loss if it doesnt.

Offline nicp

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1045 on: 01/13/2018 08:13 PM »
Does it not also suggest the core wonít be really fast? Or high? OCISLY is out I think?
EDIT: By out I mean deployed, in use in some manner, out of port.
« Last Edit: 01/13/2018 08:17 PM by nicp »
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Offline meekGee

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1046 on: 01/13/2018 08:15 PM »
Look like titanium grid fins on the boosters, Al on the core.
Yes, larger titanium fins are required for increased control authority on the boosters during atmospheric descent. This is due to the more aerodynamic shape of the booster's top, which becomes the "tail" during descent.

Core keeps its blunt top, thus smaller Al fins suffice for controlling atmospheric descent.
I know this is what they said, but it sounds so odd...  The other alternative would have been spoilers that are aerodynamic on the way up, but separate the flow when flying backwards...

Not that I don't like the Titanium fins...

My take on it is:
Titanium fins are required for the side boosters to work. For the reentry heating, they would need the centre core to also have titanium grids for the high velocity. But I guess the rocket has enough spare performance to perform a breaking burn instead of a boostback to reduce velocity to normal reentry conditions. The alternative is, they accept the fact that the centre core gets cooked fins and they dont care because they dont plan to reuse this particular core anyway. So great if the reentry works, no big loss if it doesnt.
I'm figuring Titanium fins were first developed for fast reentries, but once developed, it became simpler to use them on the slow-moving central cores - since they already existed.
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Offline TaurusLittrow

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1047 on: 01/13/2018 08:24 PM »
Any information or informed speculation on the launch window (UTC) for Falcon Heavy?

Online Lars-J

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1048 on: 01/13/2018 08:32 PM »
Any information or informed speculation on the launch window (UTC) for Falcon Heavy?

I think someone else drew a chart for this earlier (forgot who), but basically - If the idea is to launch the roadster on a direct transfer orbit, then 6pm (local) is the optimal time. But they probably want to launch during daylight, so my bet would be mid-to-late afternoon. (Which would still work, since the upper stage could coast until TMI)

So 3-5pm local time would be my educated guess. (20:00-2300 UTC)
« Last Edit: 01/13/2018 08:32 PM by Lars-J »

Offline mme

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1049 on: 01/13/2018 08:43 PM »
Does it not also suggest the core wonít be really fast? Or high? OCISLY is out I think?
EDIT: By out I mean deployed, in use in some manner, out of port.
No.  It just suggests that they have have aluminum grid fins and they're good enough for the core for this one mission.  I can't find the reference now but my understanding is that this FH will only fly once.  Next FH will be all Block 5 cores and therefore all titanium fins.
Space is not Highlander.  There can, and will, be more than one.

Offline nicp

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1050 on: 01/13/2018 09:03 PM »
But then why do the boosters have titanium grid fins? I believe these are all 'old' designs.
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Online ziceva

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1051 on: 01/13/2018 09:07 PM »
But then why do the boosters have titanium grid fins? I believe these are all 'old' designs.

It has been discussed here multiple times ... they need the big titanium grid fins because the different aerodinamics of the booster cores with their streamlined nosecaps ... (the air "adheres" to these and it seems that this decreases the control authority of the grid fins)

Online KaiFarrimond

But then why do the boosters have titanium grid fins? I believe these are all 'old' designs.

The nosecones give the side booster odd aerodynamics, so the titanium gridfins give them the extra authority they need.
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Offline Cherokee43v6

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1053 on: 01/13/2018 11:25 PM »
Look like titanium grid fins on the boosters, Al on the core.
Yes, larger titanium fins are required for increased control authority on the boosters during atmospheric descent. This is due to the more aerodynamic shape of the booster's top, which becomes the "tail" during descent.

Core keeps its blunt top, thus smaller Al fins suffice for controlling atmospheric descent.
I know this is what they said, but it sounds so odd...  The other alternative would have been spoilers that are aerodynamic on the way up, but separate the flow when flying backwards...

Not that I don't like the Titanium fins...

Think of it like the airflow off the back of a Tractor-trailer truck on the highway.  When you pull in behind one your car buffets around a lot because of the airflow being sucked into the low-pressure area formed by the truck's passage.  On the other hand, if you pull in behind one that has a 'trailer-tail' (the deployable fins that open off the back doors), those break that recirculation and its accompanying drag, resulting in less buffeting.

So the side boosters, with the aerodynamic nose cones need the slightly larger fins to induce the appropriate level of drag on the stage.
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Offline meekGee

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1054 on: 01/13/2018 11:28 PM »
Look like titanium grid fins on the boosters, Al on the core.
Yes, larger titanium fins are required for increased control authority on the boosters during atmospheric descent. This is due to the more aerodynamic shape of the booster's top, which becomes the "tail" during descent.

Core keeps its blunt top, thus smaller Al fins suffice for controlling atmospheric descent.
I know this is what they said, but it sounds so odd...  The other alternative would have been spoilers that are aerodynamic on the way up, but separate the flow when flying backwards...

Not that I don't like the Titanium fins...

Think of it like the airflow off the back of a Tractor-trailer truck on the highway.  When you pull in behind one your car buffets around a lot because of the airflow being sucked into the low-pressure area formed by the truck's passage.  On the other hand, if you pull in behind one that has a 'trailer-tail' (the deployable fins that open off the back doors), those break that recirculation and its accompanying drag, resulting in less buffeting.

So the side boosters, with the aerodynamic nose cones need the slightly larger fins to induce the appropriate level of drag on the stage.
Exactly...  So to make a streamlined booster behave like the good old truncated blunt-tail ones, all you'd need is a spoiler.

(Spoilers cause the slipstream to detach)
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Offline ValmirGP

Look like titanium grid fins on the boosters, Al on the core.
Yes, larger titanium fins are required for increased control authority on the boosters during atmospheric descent. This is due to the more aerodynamic shape of the booster's top, which becomes the "tail" during descent.

Core keeps its blunt top, thus smaller Al fins suffice for controlling atmospheric descent.
I know this is what they said, but it sounds so odd...  The other alternative would have been spoilers that are aerodynamic on the way up, but separate the flow when flying backwards...

Not that I don't like the Titanium fins...

Think of it like the airflow off the back of a Tractor-trailer truck on the highway.  When you pull in behind one your car buffets around a lot because of the airflow being sucked into the low-pressure area formed by the truck's passage.  On the other hand, if you pull in behind one that has a 'trailer-tail' (the deployable fins that open off the back doors), those break that recirculation and its accompanying drag, resulting in less buffeting.

So the side boosters, with the aerodynamic nose cones need the slightly larger fins to induce the appropriate level of drag on the stage.
Exactly...  So to make a streamlined booster behave like the good old truncated blunt-tail ones, all you'd need is a spoiler.

(Spoilers cause the slipstream to detach)
If that is so and it causes so much pain to the control of the descending booster, wouldn't it be easier to just put the cone on top of a regular (or a shortened one) inter-stage? I know it would be a little heavier, but being on the boosters, I believe it would not translate in a huge loss to de capability of rocket.

Offline Kenp51d

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1056 on: 01/14/2018 12:29 AM »
But then why do the boosters have titanium grid fins? I believe these are all 'old' designs.
If I understand your question correctly, the aluminum grid fins are the older design. Titanium fins are the newest.
Hope that helps.

Ken

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Offline deruch

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1057 on: 01/14/2018 12:37 AM »
Exactly...  So to make a streamlined booster behave like the good old truncated blunt-tail ones, all you'd need is a spoiler.

(Spoilers cause the slipstream to detach)

Sure, they might have been able to go that route in designing the end cones.  But the point is that regardless of whether they had a spoiler system, they would still need the grid fins for control.  So, instead of adding a new system that could potentially cause additional problems on ascent and for which they don't yet have any operational experience, they decided to significantly increase the authority of the grid fins and solve the problem that way.  Brute force solution.
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Offline the_other_Doug

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1058 on: 01/14/2018 12:41 AM »
Look like titanium grid fins on the boosters, Al on the core.
Yes, larger titanium fins are required for increased control authority on the boosters during atmospheric descent. This is due to the more aerodynamic shape of the booster's top, which becomes the "tail" during descent.

Core keeps its blunt top, thus smaller Al fins suffice for controlling atmospheric descent.
I know this is what they said, but it sounds so odd...  The other alternative would have been spoilers that are aerodynamic on the way up, but separate the flow when flying backwards...

Not that I don't like the Titanium fins...

Think of it like the airflow off the back of a Tractor-trailer truck on the highway.  When you pull in behind one your car buffets around a lot because of the airflow being sucked into the low-pressure area formed by the truck's passage.  On the other hand, if you pull in behind one that has a 'trailer-tail' (the deployable fins that open off the back doors), those break that recirculation and its accompanying drag, resulting in less buffeting.

So the side boosters, with the aerodynamic nose cones need the slightly larger fins to induce the appropriate level of drag on the stage.
Exactly...  So to make a streamlined booster behave like the good old truncated blunt-tail ones, all you'd need is a spoiler.

(Spoilers cause the slipstream to detach)
If that is so and it causes so much pain to the control of the descending booster, wouldn't it be easier to just put the cone on top of a regular (or a shortened one) inter-stage? I know it would be a little heavier, but being on the boosters, I believe it would not translate in a huge loss to de capability of rocket.

SpaceX has a lot of really smart engineers.  Anything that seems obvious to you and I they decide not to do, I figure they have really good reasons for...
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Online Eer

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #1059 on: 01/14/2018 12:42 AM »
Exactly...  So to make a streamlined booster behave like the good old truncated blunt-tail ones, all you'd need is a spoiler.

(Spoilers cause the slipstream to detach)

Sure, they might have been able to go that route in designing the end cones.  But the point is that regardless of whether they had a spoiler system, they would still need the grid fins for control.  So, instead of adding a new system that could potentially cause additional problems on ascent and for which they don't yet have any operational experience, they decided to significantly increase the authority of the grid fins and solve the problem that way.  Brute force solution.

I recall, too, that the Titanium fins have a higher melting point, and so are robust for more reuses.  As they move towards Block 5, they want touch-free reuse, as near as they can get it, and titanium grids will better give them that.  So, they move the ball forward towards greater reuse and shorter turnaround, which is the ultimate goal for the boosters.

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