Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion Thread 1  (Read 586804 times)

Offline Comga

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #680 on: 12/30/2017 09:26 PM »
I know I am not going to make any friends by saying this but it needs to be said.

I would majorly hate to be a member of the generation that just can't stand to wait until it [whatever "it" may be] actually happens. I get the impression that they would never be able to stand the wait time of several YEARS while a probe makes its way to Jupiter, Saturn, Uranus, Neptune, Pluto or the Ort cloud. Their heads would explode. Try launching a probe like that knowing that you yourself may very well not live long enough to see it arrive and that children who are in 4th grade at launch date would likely be the scientists that would monitor and record the arrival. Do you have the patience for that?

Jeepers people. The solar system isn't your back yard that can be crossed in a leap and a bound.
SpaceX will provide photographs when it wants to and not one second before - they don't owe any of us a thing.
Falcon Heavy will launch when it is ready. - Give it a rest and have a cup of tea or coffee or latte-mocha-chi-whatever.
Chill. It will happen when it happens.
THIS site will be the first to let you know it's happening so just stay tuned and quit complaining.

Bah!
I DID wait through the 9.5 year journey to Pluto (Having worked on the mission)
One of my personal efforts has been in the works for twenty years, and it can't really yet be said to be a going concern.
But I want MORE PROGRESS.
I still remember the rapid progress of the "Space Race".
FASTER!
Fly that Heavy, already!

There.  I said it.  Now back to waiting.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline cscott

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #681 on: 12/30/2017 10:07 PM »


Yeah, judging from some coincidentally accurate porkchop plots and a few articles, Roadster can certainly make it to a rather close encounter with Mars, it just might take anywhere from a 12-24 month coast period to get there.

What's with the asymptote in that porkchop plot?  It seems like the required dV around Jan 15 is actually extremely sensitive to the exact date selected.  Is that just an artifact of some other choice made in the plot, or is there an actual orbital mechanics reason why Jan 15 would be so much worse than Jan 1?
I found the answer to my own question:
http://hopsblog-hop.blogspot.com/2013/01/deboning-porkchop-plot.html

So we're rapidly approaching the time period where an expensive 180 degree phase change is necessary to intercept Mars.  Unless SpaceX is willing to wait until late February, they are going to have to do a mid-course burn to do the necessary inclination change to intercept Mars.

This might have been a factor in SpaceX's desire to get the first FH launch off in December. Given that they don't seem like they're going to wait 50 days to launch it --- does that imply that the S2 can do a second inclination-change burn after a hundred days of loiter?  Or is there some other clever way to intercept Mars (a transfer that doesn't take 180 degrees of anomaly, for instance)?

Offline mme

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #682 on: 12/30/2017 10:18 PM »


Yeah, judging from some coincidentally accurate porkchop plots and a few articles, Roadster can certainly make it to a rather close encounter with Mars, it just might take anywhere from a 12-24 month coast period to get there.

What's with the asymptote in that porkchop plot?  It seems like the required dV around Jan 15 is actually extremely sensitive to the exact date selected.  Is that just an artifact of some other choice made in the plot, or is there an actual orbital mechanics reason why Jan 15 would be so much worse than Jan 1?
I found the answer to my own question:
http://hopsblog-hop.blogspot.com/2013/01/deboning-porkchop-plot.html

So we're rapidly approaching the time period where an expensive 180 degree phase change is necessary to intercept Mars.  Unless SpaceX is willing to wait until late February, they are going to have to do a mid-course burn to do the necessary inclination change to intercept Mars.

This might have been a factor in SpaceX's desire to get the first FH launch off in December. Given that they don't seem like they're going to wait 50 days to launch it --- does that imply that the S2 can do a second inclination-change burn after a hundred days of loiter?  Or is there some other clever way to intercept Mars (a transfer that doesn't take 180 degrees of anomaly, for instance)?
The Roadster is not going to Mars.  Itís going to orbit around the sun with its aphelion being about the same as Marsí orbit.
Space is not Highlander.  There can, and will, be more than one.

Offline rpapo

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #683 on: 12/30/2017 10:26 PM »
So we're rapidly approaching the time period where an expensive 180 degree phase change is necessary to intercept Mars.
Weren't we told that this would be a launch to a Mars transfer orbit equivalent, not the real thing?  In such a case, all they are trying to do is launch to an orbit which will have as its apogee the orbit of Mars, and the perigee somewhere around the Earth.  In such a case, "porkchop" plots are meaningless.
An Apollo fanboy . . . fifty years ago.

Offline Herb Schaltegger


Bah!
I DID wait through the 9.5 year journey to Pluto (Having worked on the mission)
One of my personal efforts has been in the works for twenty years, and it can't really yet be said to be a going concern.
But I want MORE PROGRESS.
I still remember the rapid progress of the "Space Race".
FASTER!
Fly that Heavy, already!

There.  I said it.  Now back to waiting.

I can relate. Some of the hardware I spec'd and other stuff I actually designed as a baby engineer 27 years ago still gets mention in the L2 ISS Daily Status Reports thread every few weeks. Does my crusty old heart good, it does. Wish it'd all been replaced by a moonbase or mission to Mars by now but ...

Anyway, if this thing manages to launch next month without an Earth-shattering kaboom, I'll be that much closer to someone, ANYONE, sending people to Mars than I've ever personally been in my lifetime. :)
« Last Edit: 12/31/2017 01:21 AM by Herb Schaltegger »
Ad astra per aspirin ...

Offline Space Ghost 1962

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #685 on: 12/31/2017 12:18 AM »
So FH spent less than a day at the pad doing fit checks.
Fit checks are short. No obvious issue present. If they were to repeat the rollout, then there may have been an issue. Looks fine.

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.
Your usual measure of success as the qualifier of the "50=50"?

Quote
The first Delta 4 Heavy failed...
Successful launch. Mission failure due to under performance (booster, US couldn't make up within margins).

It made it to a lower orbit due to a performance shortfall (main engine early shutdown was triggered by an empty tank signal from the fuel sensor during the first stage due to cavitation around the propellant feed). Unforeseen issue.

...

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.



The issue they are worried about is during ignition, not during flight.

(and we've seen many launches since then, I don't think they have a problem here)
The issue is the vehicle ensemble, not ignition.

Static fire includes assessing vehicle performance briefly while still on the launch mount.  It won't be released if anomalous on launch.

The gimbal of the engines is fully capable of eliminating or inducing any roll wanted or unwanted.
For each core. The concern is the ensemble acting unpredictably.

After release, your concern is clearing the pad/TE/tower/facility. Sufficient performance and control.

I'm not concerned by any flight control guidance authority issues, just potential pneumatics and unlatch hangs at  booster sep...
That's late in flight. Before that you'll have structural issues to contend with, as well as guidance.

Vehicle stability pre/post sep is as important as sep event itself.

Due to thrust torque (a thrust-induced rotation)...

I believe the torque mentioned is around a horizontal axis. A single stick might use an asymmetric engine ignition sequence without overstressing its own octaweb. But placed side by side, the asymmetric startup thrusts could overstress one or both webs. Now think of that happening on both sides of the center booster web simultaneously... complex.

I thought the problem would actually be in any mismatch in the overall thrust startup of the two side boosters, which could result (say) in the links on one side of the center booster being lift-loaded before the other. Could cause a center tube or link failure, I would imagine. Fireball.
Three axial, elastic cylinders each with roll/pitch/yaw and coupling. Also TO which is unpredictable with resonance in the ensemble.

Much of this has been well simulated so unlikely a fireball. More likely is stability/performance issues where the vehicle does not perform adequately, possibly to the point of RSO/AFTS termination, if the GNC can't handle it.

add:
Almost forgot - DIVH first flew 12/21/2004, so also at the turn of the year 13 years ago.


« Last Edit: 12/31/2017 01:52 AM by Space Ghost 1962 »

Offline LouScheffer

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #686 on: 12/31/2017 12:58 AM »
If they truly think that FH only has a 50% chance of succeeding, they are not going to launch. Period. They are going to want to be a lot more confident than that.

I don't agree.  I'm not sure it's possible to get more than 50% confident.

Of course, SpaceX will have addressed 100% of the problems that they have thought of.   But so has every other rocket maker, and historically about 50% of the first try of a new rocket have failed (see Rocketlab for the most recent example...).

So Musk might well believe, that after addressing every problem they know about, there is still a 50% chance of failure.  And there is nothing they can do about this, since they have already addressed every problem they could imagine.   The only way to proceed is to launch and let nature have a go at seeing what SpaceX could not.

Offline meekGee

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #687 on: 12/31/2017 03:02 AM »
If they truly think that FH only has a 50% chance of succeeding, they are not going to launch. Period. They are going to want to be a lot more confident than that.

I don't agree.  I'm not sure it's possible to get more than 50% confident.

Of course, SpaceX will have addressed 100% of the problems that they have thought of.   But so has every other rocket maker, and historically about 50% of the first try of a new rocket have failed (see Rocketlab for the most recent example...).

So Musk might well believe, that after addressing every problem they know about, there is still a 50% chance of failure.  And there is nothing they can do about this, since they have already addressed every problem they could imagine.   The only way to proceed is to launch and let nature have a go at seeing what SpaceX could not.
Yup. Musk hasn't forgotten F1, or the two F9 failures.  I don't know how he got through 18 launches this year w/o a heart attack.
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Offline dorkmo

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #688 on: 12/31/2017 04:39 AM »
Larger versions
In the post (on the update thread) I'm referencing, the posted image of the 27-Merlin business end (FH-mated3.jpg) has four curious objects, a pair between each side booster and the main.  A colleague on another forum speculated that they might be damping devices, and I speculate they might be actuators in the separation system.  I've cropped a closeup from the cited photo and am attaching it as FH_Whazzat_0.jpg. 

Does anyone know what they are, or care to guess?

id guess the left side is the release mechanism. The right cylinder might be a dampener.

interesting white dots. Might be used to record video of dampener movement?

Offline wannamoonbase

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #689 on: 12/31/2017 04:42 AM »
I see very little (if any) risk for POGO for FH, since they are flying the same stages as F9. Same engines, same tank lengths. POGO - if present - will show up in early launches.

All this talk of possible failure points - one more dramatic than the next - starts to border on concern trolling, IMO. ďSurely SpaceX has not thought of *this*?Ē

Agreed, lots of smart people, with hands on experience doing very hard things have done tons of work on this.

I think it will work fine, but if something gets it, itís not likely something like structural analysis not being thorough enough.
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Offline ChrisC

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #690 on: 12/31/2017 04:51 AM »
I love Elon's remark (about a year ago) that if Falcon Heavy just lifts off and clears the LC-39A launchpad, he'll consider the test a success.  Certainly it would be a Bad Day for all involved to lose LC-39A.

Has anyone done the math for at what point during flight, if the whole stack breaks up, will the ballistics carry the debris back down to earth CLEAR of the launch complex?  (i.e. NOT do what Antares did to Wallops Pad 0 in Oct 2014)  Obviously this moment would be after the pitchover starts.

The simplest calc would be to just treat the whole stack as a point mass and then run that back down to ground -- i.e. just watch the instantaneous impact point (IIP) and wait for it to clear the fenceline, plus whatever distance is appropriate for the impact fireball.  The harder calc would be assuming that the stack detonates, and now you've got a debris cloud that's raining down, including some that was propelled BACK to the west.  So how much further would it need to be out for the propelled debris to also clear?

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?
« Last Edit: 12/31/2017 04:54 AM by ChrisC »
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Offline meekGee

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #691 on: 12/31/2017 05:53 AM »
I love Elon's remark (about a year ago) that if Falcon Heavy just lifts off and clears the LC-39A launchpad, he'll consider the test a success.  Certainly it would be a Bad Day for all involved to lose LC-39A.

Has anyone done the math for at what point during flight, if the whole stack breaks up, will the ballistics carry the debris back down to earth CLEAR of the launch complex?  (i.e. NOT do what Antares did to Wallops Pad 0 in Oct 2014)  Obviously this moment would be after the pitchover starts.

The simplest calc would be to just treat the whole stack as a point mass and then run that back down to ground -- i.e. just watch the instantaneous impact point (IIP) and wait for it to clear the fenceline, plus whatever distance is appropriate for the impact fireball.  The harder calc would be assuming that the stack detonates, and now you've got a debris cloud that's raining down, including some that was propelled BACK to the west.  So how much further would it need to be out for the propelled debris to also clear?

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?
I think the main damage is the unburned fuel.

The kinetics of the rocket structure coming back down can't be that destructive.

Going back to that Delta II, the pieces of the solids were I think mostly acting as incindiaries.

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Offline kevinof

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #692 on: 12/31/2017 07:31 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?

Offline john smith 19

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #693 on: 12/31/2017 07:34 AM »

I don't agree.  I'm not sure it's possible to get more than 50% confident.

Of course, SpaceX will have addressed 100% of the problems that they have thought of.   But so has every other rocket maker, and historically about 50% of the first try of a new rocket have failed (see Rocketlab for the most recent example...).

So Musk might well believe, that after addressing every problem they know about, there is still a 50% chance of failure.  And there is nothing they can do about this, since they have already addressed every problem they could imagine.   The only way to proceed is to launch and let nature have a go at seeing what SpaceX could not.
Bayesian statistics also look at the history of successful (or unsuccessful) "trials."

Obviously FH <> F9 but the question is how much different is it? The F9 has had a pretty successful year and the launch crew has had plenty of practice. The boosters are flight proven so the big unknowns are the core and the interactions between the cores and the whole assembly with the launch pad during launch.

I'd suggest that puts confidence > 50%. How  much above 50% is of course debatable.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline TorenAltair

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #694 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 #695 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.

Offline kevinof

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #696 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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Offline IanThePineapple

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

Offline ChrisC

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #698 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 #699 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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