Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion  (Read 385010 times)

Online FutureSpaceTourist

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #600 on: 12/29/2017 01:24 PM »
Quote
A quick check of the coast reveals no #FalconHeavy on pad. Although up in the late night hours, it appears to possibly be back in the barn. Is it all good or adjustments needed? Nobody knows yet. @SpaceX

https://twitter.com/julia_bergeron/status/946737095565107204

So FH spent less than a day at the pad doing fit checks.

Is that what people expected? Good news, or not?! I dont know what the procedures would be for something like this. Assuming there were some snags to fix, would they try and do that with FH at the pad or would it go back to the HIF first?

Offline Ben the Space Brit

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #601 on: 12/29/2017 01:27 PM »
I imagine that there will be more appearances of the vehicle at the pad. After all, they have to complete the launch campaign for Zuma before SpaceX's East Range team doing any serious work with the FH demonstration flight. I imagine, for now, they're going through connection tests and taking the opportunity of having an FH assembled to make sure the umbilicals and command and control data lines all work properly for a three-core stack.
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Online dnavas

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #602 on: 12/29/2017 01:53 PM »
I think the static fire test has the potential to be interesting for exactly the same reasons as you list for launch - getting all 27 engines to fire up in a balanced manor without RUD... (e.g. torque stresses ripping the rocket apart, not to mention 3 times the potential failure points of a standard F9)

I think it also wise to remember that all companies have an operating philosophy, and that when operation falls outside of well-practiced norms, bad things can happen.  SpaceX is more of a design, test, and fix company than is standard in the industry (at least, from what I've seen), and that suits them because it allows them to try things other companies won't.  Other companies have designed rockets with higher "throw weight to orbit" [dodging 'payload'] where two human beings were going to be part of that "throw weight" on first launch -- that requires a different operating philosophy.  I don't want to be distracted by better or worse, it's just different.  The real problem for SpaceX is that there hasn't been a test of all 27 going off outside of sims, and sims don't tend to model random corrosion problems in nuts (for example).  What is it that they've missed?  Untested is always dangerous.

I'm short, and a little past middle-aged, but I'm not that short or that old (or that wise), and I don't run around forests fronting my direct objects, so I'll try not to act as if I am, but ...  But, if I had to lay down odds for full mission success, they would not be extraordinarily high.  Their first stage landings, which are amazing, were "hard fought".  And two of the first three Falcon 1 launches had problems with stage recontact.  The entire launch regime has "new" written all over it.  Because, hey, while we're at it, why not just go interplanetary....  I'm sure that SpaceX believes there is a reasonable chance of success here, but there's also a reason why they're not launching a "pay"load.

I really, really want to see a success here.  I'm going to be completely distracted from work until launch.  As an engineer, I'll worry about what's being forgotten or overlooked even if I will be concocting plans for building a moon colony and launching a Stanford Torus in my head.  I really hope a successful launch proves every fear I have wrong.  But it seems to me that an ounce of humility goes a long way until then.  The thing I know is, whether the first rocket fails or succeeds, there will be one that works.  Whatever bad thing happens, that thing will get fixed.  Because that's what SpaceX does.

["The cave.  Remember your failure at the cave!"  Urk .. Damn.]

Online Johnnyhinbos

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #603 on: 12/29/2017 02:06 PM »
Personally I give this mission high probably of success. This is not the SpaceX of Falcon 1, nor is it the SpaceX of the first landing attempts, or of the rammed 2nd stage, or of the LOX curfuffle last year.

This is the SpaceX of now - a SpaceX that has solved booster return, stage separation, densified props, fairing separation, TEL protection, precision RADAR distance measurement, engine relights, ... (I can go on, but you get the idea).

SpaceX has fought hard to learn hard lessons - and these lessons are directly applicable to the FH.

And as a side note - its also the same reason I marvel when people place New Glenn in the mix as if its a done deal. BO has a huge and daunting task ahead of itself before the have a dependable orbital class launcher. Im sure theyll succeed, but SpaceX has already put many of these lessons behind them and will keep pushing forward while BO has still to learn those same lessons...
John Hanzl. Author, action / adventure www.johnhanzl.com

Offline wannamoonbase

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #604 on: 12/29/2017 02:09 PM »
I think the probability of success is pretty high, but not as high as a F9 of course.

SpaceX has experience, latest design and modeling technology.  Things can happen but I dont think there are many unknowns and that SpaceX will be conservative on this first one, as much as they can be anyway.   
Excited to be finally into the first Falcon Heavy flow, we are getting so close!

Offline mn

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #605 on: 12/29/2017 02:28 PM »
Quote
torque stresses

So I've seen this mentioned several times but I never saw an explanation.

Can someone please explain what this is about, and in particular why it would be more difficult on 3 cores vs 1 core.

(My simple mind would think that whatever stress is induced by the engines is local to the core, so you don't have 3 times the stress, you just have the same stress 3 times)

Online Johnnyhinbos

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #606 on: 12/29/2017 02:40 PM »
Quote
torque stresses

So I've seen this mentioned several times but I never saw an explanation.

Can someone please explain what this is about, and in particular why it would be more difficult on 3 cores vs 1 core.

(My simple mind would think that whatever stress is induced by the engines is local to the core, so you don't have 3 times the stress, you just have the same stress 3 times)
Generally speaking single propeller boats can only back down in one direction - this is because the propeller is rotating in one direction, thereby imparting a rotational torque on the boat (visualize a prop "walking" along the ground as it turns - that will show you the direction of the torque.) In forward this torque is offset by the prop wash hitting the rudder and the rudder counter acting this torque, but in reverse the wash runs in the opposite direction and therefore the rudder loses it's effectiveness.

Twin prop boats deal with this torque issue by spinning the props in opposite directions.

The FH is a 27 prop boat... with three groups of nine props, each group arranged in a circle, and the three groups of circles all in a line. That line will get torqued as the three circles want to rotate.

So what imparts the torque within each engine? I'll leave that for you to answer... :-)
« Last Edit: 12/29/2017 02:47 PM by Johnnyhinbos »
John Hanzl. Author, action / adventure www.johnhanzl.com

Offline mhenderson

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #607 on: 12/29/2017 02:46 PM »
What are the logistical factors involved in sourcing fuel, liquid oxygen, helium, and igniter hypergolics in the quantities required for a Falcon Heavy static fire test or launch? 

1) Many of these are no biggie to keep on hand.  I would expect RP1 fuel to be stable for storage, probably already on site for a static fire test. I would expect Helium to be stable, but prone to leakage losses.  Hypergolics are probably nasty to keep around (toxic and corrosive), but stable to store under the proper conditions.  Am I correct?  And do they fully tank all of these fluids during a static fire or do they "cheat" and just load a lesser amount sufficient for a brief firing? (I assume they top each of them off completely for a valid test run, but hey, you guys are the experts.)

2) My expectation is that LOX is both dangerous to handle and the most costly to store for any period of time. FH requires ~3X the amount of an F9 launch ... how far in advance of a static fire or launch does the supplier need to gear up production? Are those quantities substantial to a big liquid air supplier?  i.e. Is it even produced as a big special run or is it made in a more routine and steady fashion and stored? LOX has a boiling point of -297.3F  = -183C = 162R = 90K, but SpaceX uses it at a much colder temperature to get the benefit of packing more oxidizer into the tanks.  Is it stored in bulk at the subcooled temperature?  Or do they store it at a temperature close to the boiling point and 'finish' it during the transfer/loading process?  Here's a NASA doc on subcooling on the run:
 https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050203875.pdf
« Last Edit: 12/29/2017 02:53 PM by mhenderson »

Offline zhangmdev

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #608 on: 12/29/2017 03:10 PM »

First, can anyone tell if the TE is providing support to the top of the side boosters or are they only supported by the attachment to the center core?

My understand is there is no need for additional support. Like Delta 4 Heavy

http://www.spaceflightinsider.com/wp-content/uploads/2014/10/delta-iv-raise.jpg

Online nacnud

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #609 on: 12/29/2017 03:21 PM »
There are arms on the TEL at the right height to support the boosters, see the pic in the post below.

https://forum.nasaspaceflight.com/index.php?topic=44376.msg1762298#msg1762298

Online Paul_G

What are the logistical factors involved in sourcing fuel, liquid oxygen, helium, and igniter hypergolics in the quantities required for a Falcon Heavy static fire test or launch? 

1) Many of these are no biggie to keep on hand.  I would expect RP1 fuel to be stable for storage, probably already on site for a static fire test. I would expect Helium to be stable, but prone to leakage losses.  Hypergolics are probably nasty to keep around (toxic and corrosive), but stable to store under the proper conditions.  Am I correct?  And do they fully tank all of these fluids during a static fire or do they "cheat" and just load a lesser amount sufficient for a brief firing? (I assume they top each of them off completely for a valid test run, but hey, you guys are the experts.)

2) My expectation is that LOX is both dangerous to handle and the most costly to store for any period of time. FH requires ~3X the amount of an F9 launch ... how far in advance of a static fire or launch does the supplier need to gear up production? Are those quantities substantial to a big liquid air supplier?  i.e. Is it even produced as a big special run or is it made in a more routine and steady fashion and stored? LOX has a boiling point of -297.3F  = -183C = 162R = 90K, but SpaceX uses it at a much colder temperature to get the benefit of packing more oxidizer into the tanks.  Is it stored in bulk at the subcooled temperature?  Or do they store it at a temperature close to the boiling point and 'finish' it during the transfer/loading process?  Here's a NASA doc on subcooling on the run:
 https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050203875.pdf

1. I believe that tanks are fully loaded - essentially the hot fire is as if the rocket were launching, except they turn off the engines after x seconds, and don't release the hold downs. The hypergolic for engine startup come from the pad, not from tanks on the stage - the stage stored hypergolic are used for engine restarts after stage separation.

2. I read recently that the Lox is stored at regular lox temperatures, and chilled down as part of the loading process.

Rgds

Paul

Offline Rocket Science

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #611 on: 12/29/2017 03:41 PM »
Allow me to borrow some lines from the film Marooned:
-"Yes or no, will the bird fly?"
-"It'll fly..." ;)
« Last Edit: 12/29/2017 03:43 PM by Rocket Science »
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Offline mn

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #612 on: 12/29/2017 03:43 PM »
Quote
torque stresses

So I've seen this mentioned several times but I never saw an explanation.

Can someone please explain what this is about, and in particular why it would be more difficult on 3 cores vs 1 core.

(My simple mind would think that whatever stress is induced by the engines is local to the core, so you don't have 3 times the stress, you just have the same stress 3 times)
Generally speaking single propeller boats can only back down in one direction - this is because the propeller is rotating in one direction, thereby imparting a rotational torque on the boat (visualize a prop "walking" along the ground as it turns - that will show you the direction of the torque.) In forward this torque is offset by the prop wash hitting the rudder and the rudder counter acting this torque, but in reverse the wash runs in the opposite direction and therefore the rudder loses it's effectiveness.

Twin prop boats deal with this torque issue by spinning the props in opposite directions.

The FH is a 27 prop boat... with three groups of nine props, each group arranged in a circle, and the three groups of circles all in a line. That line will get torqued as the three circles want to rotate.

So what imparts the torque within each engine? I'll leave that for you to answer... :-)

Thanks for explanation, but I'm still stumped by the 1 vs 3 core?

Whatever torque issues are on one core they have obviously solved, so what happens when you have 3 cores side by side? as I said in my question: why is it a larger problem and not the same problem 3 times (with the same solution applied 3 times)?

Online nacnud

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #613 on: 12/29/2017 03:50 PM »
Because of the longer momentum arm the torque is applied on?

Online AncientU

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #614 on: 12/29/2017 03:57 PM »
Fast.  Barn to vertical.

And back to barn... one work day for fit-up*!

* assuming there isn't a second day planned in the future before roll-put for static fire.

Falcon Heavy on its way back to the HIF:



source
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Offline edkyle99

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #615 on: 12/29/2017 04:05 PM »
I think the probability of success is pretty high, but not as high as a F9 of course.
I think 50-50 is about right.  That's what Elon suggested, if I recall correctly. 

There are certainly some untested aspects of this vehicle, especially base heating, max-q transonic aerodynamic stresses, pogo, etc.  History is a guide.  The first Delta 4 Heavy failed, as did three of the first six Titan IIIC missions and one of the first two Saturn 5 launches, though only one of those five combined failures was an outright Fail to Orbit.

As Elon said, we'll all be happy if this thing gets off the pad and over the Atlantic without mishap.  I believe that the odds of at least that happening are pretty good.

 - Ed Kyle

Online abaddon

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #616 on: 12/29/2017 04:08 PM »
The Falcon 9 single stick clearly doesnt have any net torque when its flying (the very first Falcon 9 did have some unplanned roll immediately after liftoff).  I would assume the three boosters will be the same once flying.  However there might be torque in the startup sequence before the hold-down clamps are released.  Id imagine any torque concerns are in this part of the timeline, not in flight.

Offline cscott

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #617 on: 12/29/2017 04:12 PM »
Thrust asymmetries during startup cause torques.  With 27 engines, more of the engines are further from the centerline, and so the worst-case torques are higher.  With FH there's the additional problem of torques applied across the long moment arm of the booster, causing the nose of the booster to move in relation to the core.

Since SpaceX is doing a staggered start, we know that there is some combination of startup transients that would "break things".  The staggered start is intended to ensure that the worst-possible worst-case transients can't add together in the bad way.  But of course the staggered start of all 27 engines hasn't been tested yet.  There are some unknown unknowns there that could cause the "break things" result.

And with respect to the "are the tanks full" question: the weight of the propellants in the tanks is part of what keeps the rocket on the ground during the static fire.  If you were to fire with lower fuel quantities, you'd either have to beef up the hold down to handle the greater thrust loads or (as they do in McGregor) fit a weighted "beanie cap" on top of the rocket to apply an equivalent gravity load.

Offline yokem55

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #618 on: 12/29/2017 04:13 PM »


I think the probability of success is pretty high, but not as high as a F9 of course.
I think 50-50 is about right.  That's what Elon suggested, if I recall correctly. 

There are certainly some untested aspects of this vehicle, especially base heating, max-q transonic aerodynamic stresses, pogo, etc.  History is a guide.  The first Delta 4 Heavy failed, as did three of the first six Titan IIIC missions and one of the first two Saturn 5 launches, though only one of those five combined failures was an outright Fail to Orbit.

As Elon said, we'll all be happy if this thing gets off the pad and over the Atlantic without mishap.  I believe that the odds of at least that happening are pretty good.

 - Ed Kyle

You might be able to add the first shuttle flight to that list.

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #619 on: 12/29/2017 04:15 PM »
...

Thanks for explanation, but I'm still stumped by the 1 vs 3 core?

Whatever torque issues are on one core they have obviously solved, so what happens when you have 3 cores side by side? as I said in my question: why is it a larger problem and not the same problem 3 times (with the same solution applied 3 times)?
If you watch the the liftoff of the first Falcon 9, it clearly rotates.  For a single stick, that's not really a big deal.  But now bolt three of them together and rather than rotate freely in space they will be torquing the connections.


Space is not Highlander.  There can, and will, be more than one.

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