Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion Thread 1  (Read 534802 times)

Offline Lar

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #340 on: 12/17/2017 05:42 AM »
Have the strap-ons been mated to the core?
I think the preferred term is side booster? Strap-ons? Mating? Might be a different forum you're thinking of?

That said I think they have been but we haven't seen any public pics yet IIRC.

Even though I thought you were too critical of my wording, thanks for the answer! :D

I wasn't CRITICAL, I was having some fun with it. As often is my wont, because I love words and word play...

I'll elaborate a bit further, I now know for a fact the side boosters have been connected to the center core but that's all I can say. That really shouldn't be all that surprising given the calendar...
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline docmordrid

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #341 on: 12/17/2017 09:19 AM »
Have the strap-ons been mated to the core?
I think the preferred term is side booster? Strap-ons? Mating? Might be a different forum you're thinking of?

That said I think they have been but we haven't seen any public pics yet IIRC.

The term in longest use in the industry is strap-on boosters. I remember this term from back in the 60's and 70's. But there are many variations and almost any of them are readily identifiable for what they are.
At least they don't look like New Shepard.

My first thought on seeing NS was "Flesh Gordon!"

/sorry
/sort of

Offline shuttlefan

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #342 on: 12/17/2017 01:01 PM »
Have the strap-ons been mated to the core?
I think the preferred term is side booster? Strap-ons? Mating? Might be a different forum you're thinking of?

That said I think they have been but we haven't seen any public pics yet IIRC.

Even though I thought you were too critical of my wording, thanks for the answer! :D

I wasn't CRITICAL, I was having some fun with it. As often is my wont, because I love words and word play...

I'll elaborate a bit further, I now know for a fact the side boosters have been connected to the center core but that's all I can say. That really shouldn't be all that surprising given the calendar...

I apologize for taking you the wrong way, Lar. Thanks again for that information.

Offline Tea Party Space Czar

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #343 on: 12/18/2017 05:16 PM »
Just like Falcon pushed the ball forward - Falcon Heavy will open the gateway to the moon... and beyond.

Hang in there kids.

Respectfully,
Andrew Gasser

Offline JAFO

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #344 on: 12/18/2017 05:59 PM »
Have the strap-ons been mated to the core?
I think the preferred term is side booster? Strap-ons? Mating? Might be a different forum you're thinking of?

That said I think they have been but we haven't seen any public pics yet IIRC.

The term in longest use in the industry is strap-on boosters. I remember this term from back in the 60's and 70's. But there are many variations and almost any of them are readily identifiable for what they are.

It's been an AWFUL long time since some members of this forum have thought about anything except in terms of rockets, it appears.

C'mon, guys -- humans are animals too, y'know... :D


We know that rockets arenít Legos, but the way we talk about them, I believe a lot of us feel like rockets are human, or at least, sentinent.


(In before the trim, btw.)
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Online gongora

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #345 on: 12/18/2017 07:30 PM »
This thread is specifically for the demo mission.  Let's please get this back on topic.

Offline sevenperforce

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #346 on: 12/18/2017 07:38 PM »
In CRS-13, the camera angle made it look like the booster flipped horizontally (yaw-wise) rather than vertically (pitch-wise). This was not the case, but it got me thinking...if the side boosters for Heavy do a yaw-flip rather than a pitch-flip, then boostback would tend to push them further away from each other, providing additional clearance and reducing the chance of interactions.

I'd imagine they'd want the closest approach (after separation) to be the landing itself.

Offline ugordan

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #347 on: 12/18/2017 08:03 PM »
It does get me thinking, though. Ideally, they'd want as much separation between the two side boosters as possible, to prevent any possible interactions. Flipping horizontally and firing up the three boostback engines mid-flip would push the boosters as far away from each other as possible; then they'd be following a trajectory such that their closest approach would be the landing burn itself.

If you're talking about Falcon Heavy, they way the 2 thruster pods are located with respect to the booster raceways makes me think they might actually employ a combination of Delta IV Heavy separation (sideways) and Titan IV SRM separation (one mostly goes "up", the other "down"). FH side boosters only have one useful cold gas thruster pointed toward the center core (and has the problem of pushing the engine section actually *toward* the center core since it's below booster center of gravity), but two useful ones pointed sideways ("up/down" in this view, one pod on either side of the core). All things being equal that means they could impart a greater angular acceleration vertically. Something kind of like this type of motion as sketched below, primarily motion of the *top* of the booster, the engine section is heavier and would see less movement. That's probably what Titan SRMs do as well, but it mostly looks like they peel off in an up/down fashion)

Offline shuttlefan

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #348 on: 12/19/2017 12:38 AM »
Any set date yet for rollout to Pad A for fit checks, static fire, etc.? ;)

Offline russianhalo117

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #349 on: 12/19/2017 12:49 AM »
Any set date yet for rollout to Pad A for fit checks, static fire, etc.? ;)
nothing at this time.

Offline deadman719

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #350 on: 12/19/2017 12:54 AM »
I'd explain more as how this would apply to this and other potential missions, but it's the wrong thread for that apparently.

Only for the Demo mission, not for FH specific items, or other missions.

But, you should closely watch for how "horizontal staging" works on this Demo mission. SX has had problems with staging on other inaugural flights of new vehicles, especially Falcon 1, where they had issues for consecutive missions with recontact.

Watch for booster engine cutoff, notice if the combined vehicle "twists" (there are multiple engines, they don't tail-off all the same) or "oscillates" - the boosters should be entirely passive before separation.

One means that has worked well for SX separation events has been spring separation - constant force through distance (F=kX) rather than thrusters (or other) means a predictable trajectory that avoids contact (thrusters have variable impulse requiring different amounts of time to get the same cumulative force).

Also, observe the roll of the core and stages, to see if residual torques from the spin-down of the turbopumps/gas generators.
Could the thrusters be used to null out any roll that is induced during the spin-down?

Offline Wolfram66

I'm kind of curious about why one pad it black and the other white. If the black paint is radar reflective to make landings more precise, did they find radar reflective white paint, or integrate equivalent or better reflectivity in the concrete?
Perhaps there's a difference in the radar reflectivity of the two pads to enable the individual boosters to distinguish between the two, thereby reducing the chances of one booster getting confused and both attempting to land at the same pad?
I'm pretty sure radar is just for the altimeter.

So true, Nomadd. Also each booster has the GPS coordinates preprogrammed into return flight paths. Same reason why S1ís donít try and land on GO twins instead of OCISLY

Offline fthomassy

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #352 on: 12/19/2017 10:36 AM »
... constant force through distance (F=kX) ...
Not constant force. Unless you claim SX uses non-linear springs.
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Offline Rocket Science

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #353 on: 12/19/2017 02:07 PM »
Strap-on boosters or rocket motors (for solids) is an accepted terminology... For Falcon Heavy it may make sense for terminology to use; Booster one flies back to LZ-1 and Booster two to LZ-2, Core to Drone Ship... IMHO
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Offline Comga

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #354 on: 12/19/2017 02:49 PM »
... constant force through distance (F=kX) ...
Not constant force. Unless you claim SX uses non-linear springs.
...or with negative Hookís constants.
In fact, the comment is backwards. Thrusters provide constant thrust. Springs are nonlinear.

Space Ghostís other comments are good:  They need stable systems to avoid unmodeled torques so the can get clean separation and prevent recontact.

Personally I would think they would leave the center engines running to fly the boosters away from the core, but we will see their choices soon enough.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline john smith 19

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #355 on: 12/19/2017 03:14 PM »

If you looked at the inaugural launches for many vehicles, they had a slight roll rate (Falcon 1, 9, and most recently Electron) - that is because the estimated control to counteract the vehicle's movement (roll) wasn't sufficient.
Most notoriously on one of the Ariane 5 upgrades when the cooling channel in the nozzle was spiral and apparently got the flow spinning. Not easy to start, but not easy to stop either. :(
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Offline Rocket Science

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #356 on: 12/19/2017 03:46 PM »
The booster "cradle separation" method used on JAXA's HII is also interesting...
http://global.jaxa.jp/projects/rockets/h2a/f8/pdf/h-2af8.pdf
« Last Edit: 12/19/2017 03:49 PM by Rocket Science »
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Online LouScheffer

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #357 on: 12/19/2017 03:52 PM »
Personally I would think they would leave the center engines running to fly the boosters away from the core, but we will see their choices soon enough.
Keeping one engine burning seems reasonable.  They can throttle one down to about 300 kN.  The side booster masses at least 40,000 kg at that point (something like 27,000 at landing, plus boostback and re-entry burn fuel).  So at most 7.5 m/s^2 acceleration for the side booster.  Meanwhile the core has 9 engines x 845 kN = 7.6 MN.  Mass is at most 600,000 kg (that would be a full center booster (450,000 kg) plus a massive second stage + payload (this was at 125.000 kg for Falcon 9)).  So acceleration is at least 12.6 m/s and probably much more.  So the center core is definitely pulling away from the side cores, even though they still have an engine running.

However, if I had to pick an engine to keep running, I'd pick the one closest to the center core. This would add torque to point the side booster away from the core.  From previous estimates, we can guess the moment of inertia of the core about the engines to be about 15,000,000 kg/m^2.   300,000 N applied 1.66 m from the center line is about 500,000 N-m of torque.  This gives an angular acceleration of about 1/3 radian/s^2, or about 20 degrees in a second.  At this point the engine is pushing the booster away from the core at a substantial fraction of a G, and under very positive control.  The cold gas thrusters can help too.

Using the center engine is also possible, but the separation would be slower.  But maybe it's enough, and the center engine is already plumbed to run by itself.  Only SpaceX knows for sure....

Online AncientU

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #358 on: 12/19/2017 04:05 PM »
Personally I would think they would leave the center engines running to fly the boosters away from the core, but we will see their choices soon enough.
Keeping one engine burning seems reasonable.  They can throttle one down to about 300 kN.  The side booster masses at least 40,000 kg at that point (something like 27,000 at landing, plus boostback and re-entry burn fuel).  So at most 7.5 m/s^2 acceleration for the side booster.  Meanwhile the core has 9 engines x 845 kN = 7.6 MN.  Mass is at most 600,000 kg (that would be a full center booster (450,000 kg) plus a massive second stage + payload (this was at 125.000 kg for Falcon 9)).  So acceleration is at least 12.6 m/s and probably much more.  So the center core is definitely pulling away from the side cores, even though they still have an engine running.

However, if I had to pick an engine to keep running, I'd pick the one closest to the center core. This would add torque to point the side booster away from the core.  From previous estimates, we can guess the moment of inertia of the core about the engines to be about 15,000,000 kg/m^2.   300,000 N applied 1.66 m from the center line is about 500,000 N-m of torque.  This gives an angular acceleration of about 1/3 radian/s^2, or about 20 degrees in a second.  At this point the engine is pushing the booster away from the core at a substantial fraction of a G, and under very positive control.  The cold gas thrusters can help too.

Using the center engine is also possible, but the separation would be slower.  But maybe it's enough, and the center engine is already plumbed to run by itself.  Only SpaceX knows for sure....

Using the closest engine to core would tend to push tail into core engines... want the opposite effect.  Use the center engine and when the nose is rotating away from center core at good rate, use TVC to kick tail away from center core.  You'd be neutralizing some of the rotation, but physically pushing the tail away from contact.
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Offline shuttlefan

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #359 on: 12/19/2017 05:15 PM »
I would think with the static fire at the end of the month they would roll it out to the pad any day now for fit checks, etc.

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