Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion  (Read 382873 times)

Offline TorenAltair

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #700 on: 12/31/2017 10:57 AM »
Not sure about the timing but I'll be holding my breath until it clears away from the pad. Would hate to damage/destroy all that. For me that's about 10/15 seconds and anything after that should be over the ocean.

...
My guess is it's around 30 seconds, give or take 10 seconds.  That's the moment on the mission clock that I'll be watching for ...

Sorry to be macabre.  It's what engineers do, anticipate everything that can go wrong, right?

And I thought I'm the only one who will hold my breath until 50-60 Seconds (and therefore H=10km) will have been passed.
Mission target 1 in my eyes: Don't destroy anything except the rocket.
Target 2: get to side-core-sep
Target 3: get rid of the central core
Then I would rate it as a 99% success. Landing (esp. 2 cores in parallel would be nice to watch of course) and stage 2 are just bonuses in my eyes.

Offline Oersted

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #701 on: 12/31/2017 02:44 PM »
If you look at this fabulous Falcon Heavy launch simulation vid by Zach and freeze it at the right time you should get an idea of when the stack wouldn't tumble back on the launch pad:



Looks like around 15 seconds elapsed mission time to me.

Online kevinof

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #702 on: 12/31/2017 03:58 PM »
If you look at this fabulous Falcon Heavy launch simulation vid by Zach and freeze it at the right time you should get an idea of when the stack wouldn't tumble back on the launch pad:



Looks like around 15 seconds elapsed mission time to me.
I saw that. At 15 secs it's 500m altitude but still right above the pad. Think I might stretch that 15 secs to 30.

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I think we can stop worrying when it clears land, not just the pad complex.
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Offline ChrisC

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #704 on: 12/31/2017 04:12 PM »
My guess is it's around 30 seconds, give or take 10 seconds.  That's the moment on the mission clock that I'll be watching for ...

If you look at this fabulous Falcon Heavy launch simulation vid by Zach and freeze it at the right time you should get an idea of when the stack wouldn't tumble back on the launch pad ... Looks like around 15 seconds elapsed mission time to me.

Thanks Oersted for the link to that GREAT simulation.

Zach (was that ZachS09?), could you run that with a view from the side, showing the IIP during the first 30 seconds?  (in other words, keep the ground in view, and we can use the stack height to estimate horizontal distance.

Per the simulation, the pitchover doesn't even start until +15 seconds, so +15 secs is definitely NOT long enough (it will fall straight back down, a la Antares as I mentioned).  By my guess, looking at downrange distance, altitude and apogee, it's not until about +25 seconds (+/- 5 secs) that the IIP would clear the LC-39A fenceline, 400 meters from the pad.  We are converging on a solution :)
« Last Edit: 12/31/2017 04:44 PM by ChrisC »
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Offline meekGee

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #705 on: 12/31/2017 04:30 PM »
My guess is it's around 30 seconds, give or take 10 seconds.  That's the moment on the mission clock that I'll be watching for ...

If you look at this fabulous Falcon Heavy launch simulation vid by Zach and freeze it at the right time you should get an idea of when the stack wouldn't tumble back on the launch pad ... Looks like around 15 seconds elapsed mission time to me.

Thanks Oersted for the link to that GREAT simulation.

Zach, could you run that with a view from the side, showing the IIP during the first 30 seconds?  (in other words, keep the ground in view, and we can use the stack height to estimate horizontal distance.

Per the simulation, the pitchover doesn't even start until +15 seconds, so +15 secs is definitely NOT long enough (it will fall straight back down, a la Antares as I mentioned).  By my guess, looking at downrange distance, altitude and apogee, it's not until about +25 seconds (+/- 5 secs) that the IIP would clear the LC-39A fenceline, 400 meters from the pad.  We are converging on a solution :)
Antares didn't activate the flight termination system, so it came down as two full tanks.

(I never saw an explanation why, btw)

Hopefully SpaceX will be faster on the trigger if it happens.

Propellant dispersal is really important in these situations.
« Last Edit: 12/31/2017 04:39 PM by meekGee »
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My guess is it's around 30 seconds, give or take 10 seconds.  That's the moment on the mission clock that I'll be watching for ...

If you look at this fabulous Falcon Heavy launch simulation vid by Zach and freeze it at the right time you should get an idea of when the stack wouldn't tumble back on the launch pad ... Looks like around 15 seconds elapsed mission time to me.

Thanks Oersted for the link to that GREAT simulation.

Zach, could you run that with a view from the side, showing the IIP during the first 30 seconds?  (in other words, keep the ground in view, and we can use the stack height to estimate horizontal distance.

Per the simulation, the pitchover doesn't even start until +15 seconds, so +15 secs is definitely NOT long enough (it will fall straight back down, a la Antares as I mentioned).  By my guess, looking at downrange distance, altitude and apogee, it's not until about +25 seconds (+/- 5 secs) that the IIP would clear the LC-39A fenceline, 400 meters from the pad.  We are converging on a solution :)
Antares didnt activate the flight termination system, so it came down as two full tanks.

Hopefully SpaceX will be faster on the trigger if it happens.

Propellant dispersal is really important in these situations.

Every gallon of propellant burned in the air is a gallon of propellant not burning the pad up.
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Offline nacnud

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #707 on: 12/31/2017 04:51 PM »
It's 975m from the pad due east to the ocean. Assuming that if the vehicle fails it travels ballistically from that point onwards the sim suggests that any time after 30 seconds the pad is safe. After 40 seconds or so the remains would land in the water and after a minute the vehicle is flying over the sea.

Sources: the above linked sim and the ruler buried in the left click menu of google maps.

Offline Space Ghost 1962

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #708 on: 12/31/2017 04:57 PM »
If you look at this fabulous Falcon Heavy launch simulation vid by Zach and freeze it at the right time you should get an idea of when the stack wouldn't tumble back on the launch pad:



Looks like around 15 seconds elapsed mission time to me.
Watch the bouncing IIP as it suddenly has a horizontal component. I'd say a half minute.

(Zach's video does a fine job. If I were to add anything it would be corrected sways/bends in combined flight, then minor twists during booster sep. Great work!)

One might fire it up on actual FH launch in side by side - then you'll notice the little differences more easily in the actual.

Offline Greg Hullender

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #709 on: 12/31/2017 04:59 PM »
I thought the center core was only going to fire until shortly after liftoff and then reignite when the side boosters separated. Has that changed?

Offline jak Kennedy

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #710 on: 12/31/2017 05:05 PM »
I seem to recall some rockets start moving actively move away from directly above the pad as soon as they clear the tower. ie sliding in a horizontal direction for a few seconds so that any debris would clear the pad.

Offline mme

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #711 on: 12/31/2017 05:16 PM »
The center core will throttle downn but it will not shutdown its engines.
Space is not Highlander.  There can, and will, be more than one.

Offline ZachS09

My guess is it's around 30 seconds, give or take 10 seconds.  That's the moment on the mission clock that I'll be watching for ...

If you look at this fabulous Falcon Heavy launch simulation vid by Zach and freeze it at the right time you should get an idea of when the stack wouldn't tumble back on the launch pad ... Looks like around 15 seconds elapsed mission time to me.

Thanks Oersted for the link to that GREAT simulation.

Zach (was that ZachS09?), could you run that with a view from the side, showing the IIP during the first 30 seconds?  (in other words, keep the ground in view, and we can use the stack height to estimate horizontal distance.

Per the simulation, the pitchover doesn't even start until +15 seconds, so +15 secs is definitely NOT long enough (it will fall straight back down, a la Antares as I mentioned).  By my guess, looking at downrange distance, altitude and apogee, it's not until about +25 seconds (+/- 5 secs) that the IIP would clear the LC-39A fenceline, 400 meters from the pad.  We are converging on a solution :)

It was a different Zach that ran that simulation. I had nothing to do with it.
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Offline Oersted

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #713 on: 12/31/2017 05:59 PM »
Watch the bouncing IIP as it suddenly has a horizontal component. I'd say a half minute.

Yup, true, 15 seconds is a bit too early. At half a minute into the flight the projected path has moved quite a bit away from the launch complex, in my estimation. Still a bit too early for comfort, though!

Here is a screenie of the dots you need to keep an eye on...

(Please note that the lift-off is 20 seconds in from the beginning of the movie. This screenie is consequently 11 seconds into the flight, where - if the engines were to stop immediately - the rocket would just rise by a bit more than its own length before it would fall back down.)
« Last Edit: 12/31/2017 06:01 PM by Oersted »

Offline nacnud

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #714 on: 12/31/2017 06:07 PM »
It's easier just to keep a note of the downrange distance displayed in the top left of the sim.

Offline speedevil

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #715 on: 12/31/2017 07:01 PM »
It's easier just to keep a note of the downrange distance displayed in the top left of the sim.

(altitude/downrange) gives a rough estimate of the current launch angle from vertical.
perigee*2/(altitude/downrange) is a conservative estimate of how far it will travel horizontally.

At 100m altitude, it's gone 20m, apogee is 87m.

200 24 233 55
400 24 540 64
1000 36 1562 112
1500 54 2300 165
2500 124 4200 416
3500 200 6000 685
5000 350 8400 1176

So, ~5km, ~40s in means the IIP is likely to be on water.

But, I don't believe this at all for a few reasons. Unless the stage just stops thrusting, and falls intact, it's really, really not going to be ballistic.
Once apogee hits ~1km or so, 12s in, if the FTS triggers, you're getting shards, not any part of the rocket.
So, hold your breath, and when you let it out it's fine.
If it explodes, once you're over a few hundred meters, most of the cloud of debris is going to be shards of sooty fuel tank, with the COPVs and engines falling intact.
Very small tweaks to the trajectory that are essentially free variables and have no impact on launch performance can change the impact dramatically.

Still, a minute in is certainly pad safe,
« Last Edit: 12/31/2017 07:20 PM by speedevil »

Offline wannamoonbase

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #716 on: 12/31/2017 09:26 PM »
If it makes it past the first few seconds itís likely fine till staging. 

Then, hey, who knows, if it survives staging the side boosters I think it will be completely successful.
Excited to be finally into the first Falcon Heavy flow, we are getting so close!

Offline zlynn1990

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #717 on: 12/31/2017 10:29 PM »
Oersted I'm the Zach who made the sim :) Most of that trajectory was done by OneSpeed, and he has the gravity turn starting at 10 seconds. Take the entire thing was a large grain of salt because there are a lot of unknowns right now.

Offline Surfdaddy

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #718 on: 12/31/2017 11:11 PM »
If it makes it past the first few seconds itís likely fine till staging. 

Then, hey, who knows, if it survives staging the side boosters I think it will be completely successful.

I want to believe you, but I've seen a lot of launch videos where problems happen in your "safe" time period.

Offline Oersted

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #719 on: 12/31/2017 11:27 PM »
Oersted I'm the Zach who made the sim :) Most of that trajectory was done by OneSpeed, and he has the gravity turn starting at 10 seconds. Take the entire thing was a large grain of salt because there are a lot of unknowns right now.

Yes, I realise it is a good guess more than anything else. Nevertheless, splendid effort. Thanks so much for putting the vid together. It is clear that a lot of love went into it. Kudos and happy new year!

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