Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion  (Read 386652 times)

Offline Oersted

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #640 on: 12/29/2017 09:41 PM »
Things can happen but I don’t think there are many unknowns and that SpaceX will be conservative on this first one, as much as they can be anyway.

SpaceX conservative?

Flying with just one side booster would be the conservative choice. Going all out with two side boosters? Now that's gutsy.







;-)

Offline Alpha Control

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #641 on: 12/29/2017 10:20 PM »
I have a question that I don't think I've seen addressed yet:  Has a 2nd Falcon Heavy core been produced at this point?  As we know the FH core is considerably different from the standard F9, and I'm assuming they take longer to build than a standard core.  I haven't seen a mention of the status of a second core at this point in time.
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Offline John Alan

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #642 on: 12/29/2017 10:41 PM »
I have a question that I don't think I've seen addressed yet:  Has a 2nd Falcon Heavy core been produced at this point?  As we know the FH core is considerably different from the standard F9, and I'm assuming they take longer to build than a standard core.  I haven't seen a mention of the status of a second core at this point in time.

It seems widely accepted here at NSF, that the next FH flight on the manifest (STP-2) mid year would be using all new build 'block 5' class hardware...
My opinion is to agree with that idea, as it's a demo for the US Air Force... with payloads provided by them...
So it's likely that these three boosters are soon to be started on the assy lines...
More likely after this first flight... and using the data and post flight inspections to guide any changes needed...
The other thought was after this flight mid year... SpaceX would reuse these three boosters for the next two FH launches (assuming no losses)...
That said... I have no linkage or proof to back up these statements...  ???
« Last Edit: 12/29/2017 10:45 PM by John Alan »

Offline FutureMartian97

Are they going to take the fairing off for the static fire? It seems like a waste for this flight if they do. I mean, the payload is already attached, and its not a $100 million satellite, and it would be good to get vibration data on the full completed vehicle.

Offline R.Simko

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #644 on: 12/30/2017 02:04 AM »
Perhaps it's time we had a poll.
Example:
1. Flight complete success, with all 3 first stages landing intact.
2. Makes it past first stage separation and lands at least 2 first stages.
3. Makes it past max Q.
4. Does not make max Q.

Online Lars-J

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #645 on: 12/30/2017 02:20 AM »
Perhaps it's time we had a poll.
Example:
1. Flight complete success, with all 3 first stages landing intact.
2. Makes it past first stage separation and lands at least 2 first stages.
3. Makes it past max Q.
4. Does not make max Q.

There is already a poll in the poll section of the forum.

Edit/Lar: Indeed:  http://forum.nasaspaceflight.com/index.php?topic=44559
« Last Edit: 12/30/2017 11:17 AM by Lar »

Offline CyndyC

There are certainly some untested aspects of this vehicle, especially..... pogo.....  History is a guide.

I don't think "torque", or force of rotation around an axis, is the right word or focus. Where is everyone seeing so many spinning parts that can go wrong?

From everything I've Googled today, pogo oscillations appear to be the real risk, up and down variations in thrust & LOX & fuel flow. They brought down the 4th & final 30-engine N-1 launch, and have a long history of plaguing US launches as well. They also have a long history of mitigation by various kinds of engineering, the latest written up by our own Philip Sloss just this month, a 3D-printed POGO Suppression Accumulator built by Aerojet Rocketdyne for NASA's Space Launch System R-25 engines. In the past NASA instituted a safety level of G forces to be tolerated by such oscillations, +/-0.25G.

Here's one description related to the 4th N-1 launch:

Quote
Pogo oscillation is exactly what it sounds like – a violent up-and-down motion that could make anybody sick, but makes rockets really really sick. It results from a variation in thrust from different engines, and with thirty unreliable ones, you can get a lot of variation. Once it starts, it's very hard to correct, as the variable acceleration leads to variable fuel pump pressures, which leads to more variables acceleration, and so on and so on until eventually you match the vehicle's resonance frequency and vibrate the whole thing to death.
https://jalopnik.com/this-insane-rocket-is-why-the-soviet-union-never-made-i-1448356326
« Last Edit: 12/30/2017 02:58 AM by CyndyC »
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Offline Grandpa to Two

There are certainly some untested aspects of this vehicle, especially..... pogo.....  History is a guide.

I don't think "torque", or force of rotation around an axis, is the right word or focus. Where is everyone seeing so many spinning parts that can go wrong?

From everything I've Googled today, pogo oscillations appear to be the real risk, up and down variations in thrust & LOX & fuel flow. They brought down the 4th & final 30-engine N-1 launch, and have a long history of plaguing US launches as well. They also have a long history of mitigation by various kinds of engineering, the latest written up by our own Philip Sloss just this month, a 3D-printed POGO Suppression Accumulator built by Aerojet Rocketdyne for NASA's Space Launch System R-25 engines. In the past NASA instituted a safety level of G forces to be tolerated by such oscillations, +/-0.25G.

Here's one description related to the 4th N-1 launch:

Quote
Pogo oscillation is exactly what it sounds like – a violent up-and-down motion that could make anybody sick, but makes rockets really really sick. It results from a variation in thrust from different engines, and with thirty unreliable ones, you can get a lot of variation. Once it starts, it's very hard to correct, as the variable acceleration leads to variable fuel pump pressures, which leads to more variables acceleration, and so on and so on until eventually you match the vehicle's resonance frequency and vibrate the whole thing to death.
https://jalopnik.com/this-insane-rocket-is-why-the-soviet-union-never-made-i-1448356326

I also was researching pogo and believe it could be the greatest risk to this first flight. It’s impossible to check until the Heavy is running. Maybe we’ll see a much longer static fire so they can get an idea of how the vibrations affect the rocket. Once airbourne will come the real test for pogo. I’m glad Elon is going to keep thrust down to 92% for this flight.
"All truths are easy to understand once they are discovered; the point is to discover them" Galileo Galilei

Offline georgegassaway

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #648 on: 12/30/2017 04:16 AM »
Hmm, the historic examples of Pogo were with non-throttled engines (AFAIK). Makes me wonder if the rate of throttle response might be fast enough to reduce some Pogo effect., if programmed to do so.  But I do not know anything about the throttle response rate. 

Ideally of course they want a design/physical fix for Pogo as the primary solution, regardless.
« Last Edit: 12/30/2017 04:16 AM by georgegassaway »

Online Lars-J

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #649 on: 12/30/2017 04:16 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. “Surely SpaceX has not thought of *this*?”
« Last Edit: 12/30/2017 04:20 AM by Lars-J »

Offline Surfdaddy

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #650 on: 12/30/2017 04:23 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. “Surely SpaceX has not thought of *this*?”

I'm no expert, but wouldn't the pogo risk be increased because of potential flexibilities in the triple stage cluster that could impart motions/resonances and vibrations and flexing that would NOT be the same as the relative simplicity of single boosters?

Put simply. I disagree with the assumption that "since we know the F9 works fine, clustering 3 together will work fine without those problems as well".

Online vaporcobra

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #651 on: 12/30/2017 04:52 AM »
If the question starts with "I'm no expert...," the answer is almost invariably, "Yes, dozens of highly skilled and experienced engineers considered it and implemented the best possible solution over the course of many iterations of analysis, modeling, and testing."
« Last Edit: 12/30/2017 04:53 AM by vaporcobra »
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Offline cscott

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #652 on: 12/30/2017 05:20 AM »
Emily Lakdawalla points out that the FH demo launch is too early for an optimal earth-mara trajectory:
https://twitter.com/elakdawalla/status/946941586373451776

Can someone with the technical chops compute if FH has to capability to put a roadster-sized payload arbitrarily close to Mars (ie, for purposes of computation, on a path impacting Mars) even if launched mid-January?

Online Lars-J

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #653 on: 12/30/2017 05:47 AM »
Emily Lakdawalla points out that the FH demo launch is too early for an optimal earth-mara trajectory:
https://twitter.com/elakdawalla/status/946941586373451776

Can someone with the technical chops compute if FH has to capability to put a roadster-sized payload arbitrarily close to Mars (ie, for purposes of computation, on a path impacting Mars) even if launched mid-January?

It’s not going to Mars. It’s going out to Mars orbit. It will get close to Mars *eventually*, but the launch window(s) are not as rare as she thinks.
« Last Edit: 12/30/2017 05:50 AM by Lars-J »

Offline pargoo

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #654 on: 12/30/2017 06:05 AM »
So...let me get this strait.  We have the most eagerly-awaited rocket roll-out in decades, and all we get are long-distance shots and no up-close hi-res's from SpaceX?

Online vaporcobra

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #655 on: 12/30/2017 06:05 AM »
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. Rather improbable that S2 can remain functional over that period without some intense modifications (and solar panels).

Edit: Found a very convenient table of trajectory calculations over the 2017-2018 period and they look quite promising. Jan 2018 is certainly less efficient than the May that Emily mentions, but it's a minor improvement compared to 2017 (500-900 days, 5000-8000 m/s dV). The random forum user's calculations show that a launch to TMI from LEO in Jan 2018 would have a coast period of ~260 days and a dV cost of ~4500 m/s.

InSight's May 2018 launch will have a coast of ~250 days with a dV cost of ~3550 m/s.

https://www.orbiter-forum.com/showthread.php?t=37063
« Last Edit: 12/30/2017 06:30 AM by vaporcobra »
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Online vaporcobra

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #656 on: 12/30/2017 06:06 AM »
So...let me get this strait.  We have the most eagerly-awaited rocket roll-out in decades, and all we get are long-distance shots and no up-close hi-res's from SpaceX?

Patience, young Padawan.
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Offline deruch

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #657 on: 12/30/2017 06:21 AM »
Emily Lakdawalla points out that the FH demo launch is too early for an optimal earth-mara trajectory:
https://twitter.com/elakdawalla/status/946941586373451776

Can someone with the technical chops compute if FH has to capability to put a roadster-sized payload arbitrarily close to Mars (ie, for purposes of computation, on a path impacting Mars) even if launched mid-January?

My search results: It could do a flyby of Mars (view the 1st one with a Jan departure date [C3=20.1]) with a launch opportunity on January 2nd.  So, I guess, given the actual, likely date being mid-month, it probably still could if the payload had the ability to do some course correction (which it doesn't).  LSP's elvperf calculator says that a Falcon Heavy (with recovery) can launch 2960kg to the C3 that trajectory would require.  The roadster had a curb weight of 1305kg (though this one may have been modified, either for Elon's driving pleasure or in the effort to turn it into a spacecraft).  So, that is well within the capability of FH even if you added some weight to enable trajectory maneuvers, etc.
« Last Edit: 12/30/2017 06:50 AM by deruch »
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Offline Ben the Space Brit

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #658 on: 12/30/2017 06:53 AM »
I don't think that there is any realistic prospect of SpaceX confirming actively that the roadster gets to its destination orbit. All they will be able to do is monitor the second stage for as long as possible to confirm its trajectory. All they'll ever be able to say is: "With a high degree of confidence..."
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Offline pargoo

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #659 on: 12/30/2017 10:32 AM »
OK, I guess it's coming up to the New Year, but still..

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