Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion Thread 1  (Read 586369 times)

Offline Tonioroffo

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #740 on: 01/02/2018 06:53 AM »
I see a lot did posts concerning "when can it explode to not damage towers/endanger infra" but what about the aftermath?  If we do get late New Year fireworks, are we automatically looking at (long) stand down for the entire F9 family?  I would think months of delays for Crew effort?  Or am I wrong?

Offline MattMason

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #741 on: 01/02/2018 07:18 AM »
I see a lot did posts concerning "when can it explode to not damage towers/endanger infra" but what about the aftermath?  If we do get late New Year fireworks, are we automatically looking at (long) stand down for the entire F9 family?  I would think months of delays for Crew effort?  Or am I wrong?

Even with my limited understanding of launch mechanics, I know that an FH failure won't sideline any F9 flights. The worst case (explosion on pad; <1% chance) means that Commercial Crew flights may be delayed since they must use LC39A. The F9 is its own tried and true vehicle. FH is a new vehicle--thus, the test flight to rack up flight data.
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Offline CJ

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #742 on: 01/02/2018 08:06 AM »
I see a lot did posts concerning "when can it explode to not damage towers/endanger infra" but what about the aftermath?  If we do get late New Year fireworks, are we automatically looking at (long) stand down for the entire F9 family?  I would think months of delays for Crew effort?  Or am I wrong?

Even with my limited understanding of launch mechanics, I know that an FH failure won't sideline any F9 flights. The worst case (explosion on pad; <1% chance) means that Commercial Crew flights may be delayed since they must use LC39A. The F9 is its own tried and true vehicle. FH is a new vehicle--thus, the test flight to rack up flight data.

That's not necessarily true. There's a lot of commonality between FH and F9, so depending on what the failure is, it might cause an F9 stand down, in the same way that the F9R destruct at McGreggor caused an F9 stand down until they were sure the cause wasn't something that would affect a flight F9. 

Offline gadgetmind

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #743 on: 01/02/2018 08:31 AM »
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 ...

Thanks for the link. Interesting that they kept changing the control system to *not* shut down engines willy nilly even when things went very bad as they didn't want to destroy the pad. OK, they still destroyed the pad, but it was a good plan despite this.

Online Ictogan

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #744 on: 01/02/2018 10:12 AM »
I see a lot did posts concerning "when can it explode to not damage towers/endanger infra" but what about the aftermath?  If we do get late New Year fireworks, are we automatically looking at (long) stand down for the entire F9 family?  I would think months of delays for Crew effort?  Or am I wrong?

Even with my limited understanding of launch mechanics, I know that an FH failure won't sideline any F9 flights. The worst case (explosion on pad; <1% chance) means that Commercial Crew flights may be delayed since they must use LC39A. The F9 is its own tried and true vehicle. FH is a new vehicle--thus, the test flight to rack up flight data.
And what makes you so certain there's <1% chance of an explosion on the pad? Would you have said the same about F9 prior to AMOS-6?

Offline sevenperforce

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #745 on: 01/02/2018 12:11 PM »
I see a lot did posts concerning "when can it explode to not damage towers/endanger infra" but what about the aftermath?  If we do get late New Year fireworks, are we automatically looking at (long) stand down for the entire F9 family?  I would think months of delays for Crew effort?  Or am I wrong?

Even with my limited understanding of launch mechanics, I know that an FH failure won't sideline any F9 flights. The worst case (explosion on pad; <1% chance) means that Commercial Crew flights may be delayed since they must use LC39A. The F9 is its own tried and true vehicle. FH is a new vehicle--thus, the test flight to rack up flight data.
And what makes you so certain there's <1% chance of an explosion on the pad? Would you have said the same about F9 prior to AMOS-6?
Falcon 9 has had 46 launch attempts, with at least one static fire per launch attempt, plus one additional post-recovery static fire for most of the 20 recovered boosters. So we have well over 100 launch and ignition sequences, which means a single explosion during prop loading (AMOS-6) is still statistically <1%.

Offline Robotbeat

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #746 on: 01/02/2018 12:42 PM »

Also understand that the existing F9 or FH PAF can only accomodate up to 24k lbs.  .
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Offline Kaputnik

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #747 on: 01/02/2018 12:51 PM »
First time poster.

Regarding the 92% thrust.

Is this not simply because it's an LV capable of lifting 16000kg to MTO that is in fact only lifting off with a 1500kg payload. An LV that can hoist 60000kg off the pad only lifting 1500kg (or whatever the weight of the tesla + mounting is) would go into a massive over g situation within seconds lifting that light a load. As it is I would imagine the 92% will only be until it clears the pad, then a massive throttle down until well past max q and throttling down all the way up. A lot of rockets auto throttle to constant 5g acceleration for structural reasons IIRC. This baby in its maiden config will have plenty of horses to spare.

Or am I wrong on that?

Edit: Does anyone know if there is extra ballast in the payload to counteract this? Or what the actual final payload weight actually will be?

You need to consider payload as a portion of gross lift of mass. Expecting the early stages of flight to be noticeably different due to the small payload is akin to being able to spot a HGV accelerating more quickly just because the driver lost some weight.
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Offline Kaputnik

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #748 on: 01/02/2018 12:53 PM »
Apologies in case this has been done to death, but am I correct in thinking that the initial FH side boosters are b3 and the core is b4?
What are people's thoughts on the likelihood of each of these cores flying again?
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Online ZachS09

Apologies in case this has been done to death, but am I correct in thinking that the initial FH side boosters are b3 and the core is b4?
What are people's thoughts on the likelihood of each of these cores flying again?

It's possible that both side boosters will be retired after landing while the center core COULD be reused for one reflight before retirement.
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Online hopalong

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #750 on: 01/02/2018 01:07 PM »
Apologies in case this has been done to death, but am I correct in thinking that the initial FH side boosters are b3 and the core is b4?
What are people's thoughts on the likelihood of each of these cores flying again?

I suspect between unlikely and zero.
SpaceX will want to take them apart after recovery to look for any cracks and alike in the load bearing structure and it has already been stated that future Heavies will be block 5 based.   

edited for spelling
« Last Edit: 01/02/2018 01:10 PM by hopalong »

Online wannamoonbase

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #751 on: 01/02/2018 01:27 PM »
Apologies in case this has been done to death, but am I correct in thinking that the initial FH side boosters are b3 and the core is b4?
What are people's thoughts on the likelihood of each of these cores flying again?

I’ve been thinking about this for awhile and I think it’s possible this FH team of 3 cores gets another flight. 

The 2 Block 3 Cores have been significantly reworked since their first flight, maybe they’ve been reworked enough to be considered fresh.  The core certainly is.

SpaceX could offer a new or existing FH customer to jump the queue with a FH ride.  They have spent a huge amount of money on developing FH and building this specific article.  If they can generate more revenue from this vehicle I think they’ll book a flight, after the Dragon 2 demo and LC39A has an open window.
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Offline Oersted

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #752 on: 01/02/2018 01:59 PM »
Only with SpaceX do you get people speculating about further flights of a launch vehicle that is about to embark on a perilous first flight... Sign of confidence!

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #753 on: 01/02/2018 02:05 PM »
Only with SpaceX do you get people speculating about further flights of a launch vehicle that is about to embark on a perilous first flight... Sign of confidence!

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Offline sevenperforce

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #754 on: 01/02/2018 02:06 PM »
First time poster.

Regarding the 92% thrust.

Is this not simply because it's an LV capable of lifting 16000kg to MTO that is in fact only lifting off with a 1500kg payload. An LV that can hoist 60000kg off the pad only lifting 1500kg (or whatever the weight of the tesla + mounting is) would go into a massive over g situation within seconds lifting that light a load. As it is I would imagine the 92% will only be until it clears the pad, then a massive throttle down until well past max q and throttling down all the way up. A lot of rockets auto throttle to constant 5g acceleration for structural reasons IIRC. This baby in its maiden config will have plenty of horses to spare.

Or am I wrong on that?

Edit: Does anyone know if there is extra ballast in the payload to counteract this? Or what the actual final payload weight actually will be?

You need to consider payload as a portion of gross lift of mass. Expecting the early stages of flight to be noticeably different due to the small payload is akin to being able to spot a HGV accelerating more quickly just because the driver lost some weight.
Putting this to rest...

A Falcon 9 first stage masses roughly 22.2 tonnes dry plus 411 tonnes of propellant. A Falcon 9 upper stage masses roughly 4 tonnes with 107.5 tonnes of propellant.

FH's theoretical maximum payload to LEO is 63.8 tonnes.

Thus, a Falcon Heavy with the maximum payload would come in at 1,475 tonnes. A Falcon Heavy with no payload (just a bare upper stage) would come in at 1411 tonnes. Thus, the TWR difference between launching with the maximum expendable LEO payload and no payload at all is just 4.3%. Nothing you'd ever notice.

Offline rsdavis9

First time poster.

Regarding the 92% thrust.

Is this not simply because it's an LV capable of lifting 16000kg to MTO that is in fact only lifting off with a 1500kg payload. An LV that can hoist 60000kg off the pad only lifting 1500kg (or whatever the weight of the tesla + mounting is) would go into a massive over g situation within seconds lifting that light a load. As it is I would imagine the 92% will only be until it clears the pad, then a massive throttle down until well past max q and throttling down all the way up. A lot of rockets auto throttle to constant 5g acceleration for structural reasons IIRC. This baby in its maiden config will have plenty of horses to spare.

Or am I wrong on that?

Edit: Does anyone know if there is extra ballast in the payload to counteract this? Or what the actual final payload weight actually will be?

You need to consider payload as a portion of gross lift of mass. Expecting the early stages of flight to be noticeably different due to the small payload is akin to being able to spot a HGV accelerating more quickly just because the driver lost some weight.
Putting this to rest...

A Falcon 9 first stage masses roughly 22.2 tonnes dry plus 411 tonnes of propellant. A Falcon 9 upper stage masses roughly 4 tonnes with 107.5 tonnes of propellant.

FH's theoretical maximum payload to LEO is 63.8 tonnes.

Thus, a Falcon Heavy with the maximum payload would come in at 1,475 tonnes. A Falcon Heavy with no payload (just a bare upper stage) would come in at 1411 tonnes. Thus, the TWR difference between launching with the maximum expendable LEO payload and no payload at all is just 4.3%. Nothing you'd ever notice.

and for the second stage the payload fraction at stage 2 ignition is 63.8/(107.4+4)=.57 so much more significant here.
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Offline CyndyC

cyndy- That tweet references how the rocket thrust profile will work in general, not how the individual mission thrust profile will be deployed.

The thrust profile tweet was part of the thread announcing the maiden launch when it was planned for November, easily seen in its entirety by clicking on the link I included.

That profile obviously adds up to less than 100%, just as the maiden launch has been confirmed will. Although there is one customer payload currently on the manifest and I don't know what the thrust requirements will be for that one, I doubt they can plan on less than 100% for all time without knowing what their other future payloads will be.

There are at least 2 of us here who think the most logical reason for the lower center thrust is to match or coordinate with a lower maximum thrust on the much older side cores, and it appears the idea of a need to accommodate an underweight payload has been put to rest.

However, an interesting side note is that the Shuttle boosters were routinely responsible for 83% of the full assembly's thrust, if WikiP is to be believed. Whether or not the FH attachment points could or will withstand more discrepancy after the maiden launch has yet to be known.

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Online gongora

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #757 on: 01/02/2018 04:19 PM »
That profile obviously adds up to less than 100%, just as the maiden launch has been confirmed will.

Throttling down the center core early in flight will happen on every FH launch, that is what the vehicle is designed to do.  That part has nothing to do with the max thrust of the vehicle on any particular flight.

Offline CyndyC

That profile obviously adds up to less than 100%, just as the maiden launch has been confirmed will.

Throttling down the center core early in flight will happen on every FH launch, that is what the vehicle is designed to do.  That part has nothing to do with the max thrust of the vehicle on any particular flight.

ok
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Offline UKobserver

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #759 on: 01/02/2018 04:47 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.

There was some discussion about this in the Merlin 1D update thread a few days ago;

https://forum.nasaspaceflight.com/index.php?topic=41014.200

It was prompted by the following Instagram post from a SpaceX employee, showing off a new Block 5 booster engine, which he claimed was rated at 205,000lbf.

https://www.instagram.com/p/Bc8pqAng9rH/

While there have been suggestions that these new engines may have actually been tested on the stand at thrust levels as high as 245,000lbf, presumably to establish safety margins, it looks like they will be introducing a new flight rating of 205,000lbf when these engines debut on the new block 5 booster.

This first FH is a composite of B3 side boosters and a B4 core, whose Merlin 1Ds I believe run at 190,000lbf thrust. AncientU pointed out that 27 x 190,000lbf is 5.1Mlbf, which matches the thrust that Elon said FH would have at liftfoff.

190,000 is 92% of 205,000, so those facts combined would suggest that this first test will run at what are normal thrust levels for each of the respective cores (albeit that the centre core will throttle down after lift-off), but that the total thrust available on this flight is only 92% of what a full-up Block 5 Falcon Heavy will be capable of.
« Last Edit: 01/02/2018 04:49 PM by UKobserver »

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