Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion  (Read 389562 times)

Offline meekGee

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #720 on: 01/01/2018 12:56 AM »
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 :)

Usually the IIP is the thing to watch, but this assumes the rocket continues as an inert solid body - as if the engines are shut off and nothing else breaks.

In an early failure scenario, two things will likely happen - off-axis thrust will move the IIP very quickly in some random directions, and then FTS will make the whole thing "stop cold" and fall straight down, but influenced by wind.

At some altitude, the liquid fuel will have time to burn on the way down, or disperse enough that it doesn't pool on the ground, and that will already be a "safe" situation.
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Offline joek

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #721 on: 01/01/2018 02:44 AM »
Usually the IIP is the thing to watch, but this assumes the rocket continues as an inert solid body - as if the engines are shut off and nothing else breaks.

IIP is a point spread function based on numerous parameters.  You can only state "probability of IIP at point X,Y is Z based on parameters T, P, Q, R, ...".  Constrain the parameters sufficiently and you can assert that it "continues as an inert solid body".  However, most real-world models (probabilistic-time-based) do not apply such constraints or make such assumptions--unless the parameters are well bounded and understood  (e.g., close to lift off).  Which is why the models tend to vary their parameters over the flight path (in particular, probability vs. time, as spread-uncertainty tends to increase with time).

Offline meekGee

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #722 on: 01/01/2018 05:16 AM »
Usually the IIP is the thing to watch, but this assumes the rocket continues as an inert solid body - as if the engines are shut off and nothing else breaks.

IIP is a point spread function based on numerous parameters.  You can only state "probability of IIP at point X,Y is Z based on parameters T, P, Q, R, ...".  Constrain the parameters sufficiently and you can assert that it "continues as an inert solid body".  However, most real-world models (probabilistic-time-based) do not apply such constraints or make such assumptions--unless the parameters are well bounded and understood  (e.g., close to lift off).  Which is why the models tend to vary their parameters over the flight path (in particular, probability vs. time, as spread-uncertainty tends to increase with time).
I forget where I saw a realtime IIP displayed, but I got the impression it was simply ballistic.

You're correct that a true IIP estimate is a stochastic thing.
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Offline gadgetmind

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #723 on: 01/01/2018 09:47 AM »
I wonder how FH would handle an engine failure on a side booster? I guess it would need to throttle down the other side? Throw in scenarios of failures of two engines in various configurations and it could all get complicated.

Online SLC

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #724 on: 01/01/2018 01:57 PM »
I wonder how FH would handle an engine failure on a side booster? I guess it would need to throttle down the other side? Throw in scenarios of failures of two engines in various configurations and it could all get complicated.
Would it be too off-topic to give this link to the last time a rocket with this many engines made its (short) first flight -  the Soviet N1 moon rocket 49 years ago next month:

http://www.russianspaceweb.com/n1_3l.html

On that occasion the KORD control system did indeed diagnose an engine failure on one side, it did shut down the symmetrically opposite engine to compensate, and then it all got complicated ...

Online speedevil

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #725 on: 01/01/2018 02:11 PM »
I wonder how FH would handle an engine failure on a side booster? I guess it would need to throttle down the other side? Throw in scenarios of failures of two engines in various configurations and it could all get complicated.

Maybe.
From memory, it has been said that the first launch will be at 82% thrust.
This is considerably more than 9/8ths, so you can lose certain engines, and simply throttle up on others with no external changes in thrust vector.
For example, lose an inboard engine on a booster, and if you throttle the remaining outboard ones to 92%, the centre of thrust moves out from the core by perhaps half an engine diameter.

If you throttle the outer engine to nearly minimum, the ones next to the core to ~105%, then it may not move at all.

Only once you can no longer keep a booster or cores thrust vector within narrow limits would you need to make changes to the thrust profile of the stack as a whole.

Would it be too off-topic to give this link to the last time a rocket with this many engines made its (short) first flight -  the Soviet N1 moon rocket 49 years ago next month:
Yes.

More seriously, N1 failures are not comparable in so many ways, as overall QC and management was so terrible that it loses all meaning as a reasonable comparator.

« Last Edit: 01/01/2018 02:16 PM by speedevil »

Offline the_other_Doug

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #726 on: 01/01/2018 02:33 PM »
From memory, it has been said that the first launch will be at 82% thrust.

And from actuality (not your memory), it will fly at 92% thrust.  Not 82%.  And not just "has been said," but tweeted by Elon Musk.

It's refreshing to see other people have even worse memories than I do... :)
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Online speedevil

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #727 on: 01/01/2018 03:12 PM »
From memory, it has been said that the first launch will be at 82% thrust.

And from actuality (not your memory), it will fly at 92% thrust.  Not 82%.  And not just "has been said," but tweeted by Elon Musk.

It's refreshing to see other people have even worse memories than I do... :)

Thanks. This would put required thrust for other engines at ~103% on a core, and remove capability for playing with the thrust levels to bring the centre of thrust to the same place.
One engine out on any or even all cores is probably quite managable.
More than one a core especially early in flight might lead to problems.
 

Offline Semmel

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #728 on: 01/01/2018 04:32 PM »
If the engine failure at the side booster happens before the throttle back of the center core, the situation may become hairy as the thrust difference between center and side boosters might not work with the structure of the heavy assembly. Maybe the center would have to throttle back prematurely.
The thrust to weight at launch should be around 1.5. With 11% thrust missing it should still be launching without much problems.

Online AncientU

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #729 on: 01/01/2018 05:08 PM »
If the engine failure at the side booster happens before the throttle back of the center core, the situation may become hairy as the thrust difference between center and side boosters might not work with the structure of the heavy assembly. Maybe the center would have to throttle back prematurely.
The thrust to weight at launch should be around 1.5. With 11% thrust missing it should still be launching without much problems.

One engine is 3.7%
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Online Gotorah

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #730 on: 01/01/2018 05:30 PM »
This is not comparing Falcon Heavy 1 vs Falcon Heavy 2. It is comparing right side vs left side for balanced thrust. If one is lost on one side, those remaining on that side can be throttled up a few percent and if needed the ones on the opposite booster can be throttled down a few.  I bet a dollar to a doughnut that the SpaceX Flight Software engineers have it all programmed. All we have to do is watch in awe !

Offline Semmel

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #731 on: 01/01/2018 05:50 PM »
If the engine failure at the side booster happens before the throttle back of the center core, the situation may become hairy as the thrust difference between center and side boosters might not work with the structure of the heavy assembly. Maybe the center would have to throttle back prematurely.
The thrust to weight at launch should be around 1.5. With 11% thrust missing it should still be launching without much problems.

One engine is 3.7%

If center and opposite core need to match the loss of thrust, it's 11.

Online Lars-J

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #732 on: 01/01/2018 07:22 PM »
If the engine failure at the side booster happens before the throttle back of the center core, the situation may become hairy as the thrust difference between center and side boosters might not work with the structure of the heavy assembly. Maybe the center would have to throttle back prematurely.
The thrust to weight at launch should be around 1.5. With 11% thrust missing it should still be launching without much problems.

One engine is 3.7%

If center and opposite core need to match the loss of thrust, it's 11.

Since running at 92%, the remaining engines in a core can throttle up to compensate - at any point in the flight.

Offline Johnnyhinbos

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #733 on: 01/01/2018 08:34 PM »
I think this is an interesting conversation. However I believe it would be better suited to be on the general Falcon Heavy discussion thread rather than on this mission specific thread?
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Offline Nomadd

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #734 on: 01/01/2018 09:25 PM »
I think this is an interesting conversation. However I believe it would be better suited to be on the general Falcon Heavy discussion thread rather than on this mission specific thread?
The 92% thrust level might only be for this mission.

Online gongora

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #735 on: 01/01/2018 09:33 PM »
The 92% thrust level might only be for this mission.

I've wondered if the thrust "reduction" on this mission is just because he's giving thrust numbers for FH Block 5 and this vehicle is running at Block 3 levels.
« Last Edit: 01/01/2018 09:33 PM by gongora »

Offline ZachS09

The 92% thrust level might only be for this mission.

I've wondered if the thrust "reduction" on this mission is just because he's giving thrust numbers for FH Block 5 and this vehicle is running at Block 3 levels.

Maybe this Falcon Heavy is running at 92% of the Block 3 thrust level, which is about 4.14 million pounds as opposed to 4.5 million pounds.
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Offline CyndyC

The 92% thrust level might only be for this mission.

I've wondered if the thrust "reduction" on this mission is just because he's giving thrust numbers for FH Block 5 and this vehicle is running at Block 3 levels.

Here's the tweet that was threaded with the photos. Agree the older side cores wouldn't be capable of taking this flight to 100% of 5.1

https://twitter.com/elonmusk/status/943590152181448704
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Online butters

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #738 on: 01/02/2018 12:22 AM »
It's safe to say that this will be only Falcon Heavy ever to use pre-Block 5 cores. After re-scoping Falcon Heavy to chase F9 iterations to v1.1 and then to FT specifications, now there's Block 5 coming. SpaceX needed to make the decision whether to bring the FH demo vehicle up to Block 5 spec with bolted octowebs etc. and accept further delays to a program already repeatedly delayed by F9 iteration churn -- or to simply launch the damn thing already even though it will end up being a one-off. This will forever be the unique "albino" FH demo vehicle.

Offline jpo234

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #739 on: 01/02/2018 12:55 AM »
It's safe to say that this will be only Falcon Heavy ever to use pre-Block 5 cores. After re-scoping Falcon Heavy to chase F9 iterations to v1.1 and then to FT specifications, now there's Block 5 coming. SpaceX needed to make the decision whether to bring the FH demo vehicle up to Block 5 spec with bolted octowebs etc. and accept further delays to a program already repeatedly delayed by F9 iteration churn -- or to simply launch the damn thing already even though it will end up being a one-off. This will forever be the unique "albino" FH demo vehicle.
As mentioned in the STP - 2 thread, there might only be one other FH. Reason: B5 cores should have more flights in them than there are FH missions on the manifest.
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