### Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion  (Read 402092 times)

#### LouScheffer

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #360 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....

#### AncientU

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #361 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.
"If we shared everything [we are working on] people would think we are insane!"
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#### shuttlefan

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #362 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.

#### LouScheffer

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #363 on: 12/19/2017 05:22 PM »
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.

If they can vector the closest engine enough to point through the center of gravity, then they can push away from the core without imparting any rotation.  In combination with the gas jets at the top, this should allow pure translation away from the core, then use thrust vectoring to keep it away.

#### GWH

##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #364 on: 12/19/2017 05:43 PM »
Hey guys there is already a multi page thread discussing this issue: https://forum.nasaspaceflight.com/index.php?topic=43255.0

#### mdeep

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #365 on: 12/19/2017 07:00 PM »
I want to pull this in from the update thread:

FAA thinks launch is close:

Quote
Second day of the Next-Generation Suborbital Researchers Conference starts with keynotes by FAA’s George Nield and NASA’s Steve Jurczyk. #NSRC2017

Quote
Nield: 2017 has been pretty exciting for commercial spaceflight, but 2018 will be even more exciting, starting with Falcon Heavy first launch in the next month. #NSRC2017

FH before Zuma?
Mike

#### russianhalo117

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #366 on: 12/19/2017 07:16 PM »
I want to pull this in from the update thread:

FAA thinks launch is close:

Quote
Second day of the Next-Generation Suborbital Researchers Conference starts with keynotes by FAA’s George Nield and NASA’s Steve Jurczyk. #NSRC2017

Quote
Nield: 2017 has been pretty exciting for commercial spaceflight, but 2018 will be even more exciting, starting with Falcon Heavy first launch in the next month. #NSRC2017

FH before Zuma?
In the same month around the same time as Zuma is now on SLC-40, but FH launch date is dependent solely on FH pad testing and static fires before a date is set. It depends if FH has teething issues or not.

#### gongora

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #367 on: 12/19/2017 08:08 PM »
FH before Zuma?

Not a chance (unless Zuma gets another big delay).

#### deruch

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #368 on: 12/20/2017 12:10 AM »
Quote
Nield: 2017 has been pretty exciting for commercial spaceflight, but 2018 will be even more exciting, starting with Falcon Heavy first launch in the next month. #NSRC2017

FH before Zuma?

I think you're misreading the (somewhat ambiguous) tweet.  Nield was saying that the debut launch of the Falcon Heavy is currently planned to happen next month (January).  Not that the FH launch will be the first launch of that month. So, no.  Zuma will very likely be first.
« Last Edit: 12/20/2017 12:11 AM by deruch »

#### MATTBLAK

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #369 on: 12/20/2017 09:06 AM »
There's something in my eye...
"Those who can't, Blog".   'Space Cadets' of the World - Let us UNITE!! (crickets chirping)

#### 0x32

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #370 on: 12/20/2017 09:10 AM »
Well, there it is, in all its glory. From Elon's Twitter.
« Last Edit: 12/20/2017 09:10 AM by 0x32 »

#### jimbowman

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #371 on: 12/20/2017 09:10 AM »
What is the ice from inside the nozzles? Or is that just soot from when they tested the stages?
« Last Edit: 12/20/2017 09:12 AM by jimbowman »

#### ugordan

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #372 on: 12/20/2017 09:11 AM »
Larger versions

Note that the overhead view was photoshopped, a composite of at least two frames, possibly 3. The interstage is too short and it's missing the obvious stage separation pusher that's visible above the FH logo in the other shot.

I guess they couldn't capture the entire vehicle from overhead in a single frame without gross fisheye distortion so they had to mosaic separate frames with significantly different perspective.

Anyway, nice to finally see the mated hardware, the cores are actually a bit closer together than I imagined them to be due to the leg spacing, etc.
« Last Edit: 12/20/2017 09:13 AM by ugordan »

#### ugordan

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #373 on: 12/20/2017 09:12 AM »
What is the ice from inside the nozzles?

The consensus seems to be that it might be TEA/TEB residue from previous firings.

#### jimbowman

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #374 on: 12/20/2017 09:14 AM »

The consensus seems to be that it might be TEA/TEB residue from previous firings.

Gotcha. Looked like icicles as first before I opened the higher res pictures. They would have had the hanger A/C on pretty low for that. Haha.
« Last Edit: 12/20/2017 09:20 AM by jimbowman »

#### FutureSpaceTourist

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #375 on: 12/20/2017 09:17 AM »
Can I just say how beautiful FH is?

Looks like titanium grid fins on the side boosters but aluminium on the central core.

#### octavo

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #376 on: 12/20/2017 09:18 AM »
Can I just say how beautiful FH is?

Looks like titanium grid fins on the side boosters but aluminium on the central core.
Lol, ninja'd. Yes and lots of pusher hardware on display.

It seems odd to be using such old hardware on a maiden flight. It's so incongruous to how space flight normally works, that my mind struggles with it.
« Last Edit: 12/20/2017 09:22 AM by octavo »

#### nacnud

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #377 on: 12/20/2017 09:19 AM »
Interesting the side boosters have Ti grid fins while the centre core has Al fins. I would have assumed the other way round as the centre core has the hotter reentry.

#### jebbo

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #378 on: 12/20/2017 09:28 AM »
Interesting that the two side boosters seem to be different ways up ...

--- Tony

#### vanoord

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##### Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #379 on: 12/20/2017 09:37 AM »
Interesting that the two side boosters seem to be different ways up ...

--- Tony

The two side cores are identical, ie the attachment points are at the same point on the radius of the octaweb - hence when attached to the centre core, they will be "different ways up".

From a point of view of ease of manufacture they only need to build one type of side core and presumably the only difference is to upload software that tells the core whether it's port or starboard (which they'd have to do if they built different 'handed' cores anyway).

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