Author Topic: SpaceX FH : Falcon Heavy Demo : Feb 6, 2018 : Discussion Thread 2  (Read 644898 times)

Offline CyndyC

And since this 3 stick launch had what appears to my eyes astoundingly underwhelming performance (the 3 stick launch of a ?1500kg? payload only accelerated the second stage to the same speed that some previous F9(s) have pushed very heavy payloads to) I'm lead to think that they were doing a lot of experimenting with what was going on behind that curtain of flame.

Agree!  Even given a bunch of experimenting, how did they manage to push so little so slowly?

Kind of the same way these people did


« Last Edit: 02/13/2018 06:05 am by CyndyC »
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Offline Steve D

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I submit for consideration an alternate theory on why they used more fluid than they needed.  Its based on Lou's theory but mine happens on the way up rather than the way down.  Perhaps on the way up rather than just throttling down the center core (which is visible) they also switched off a few engines and restarted them.

Nice theory.

During the reentry burn 3-engine portion, you can see an "Eye of Sauron" (got that from Lars Blackmore's talk) effect, in which the longer axis of the plume cross section is orthogonal to the line of the three lit engines.  Lars claims that SpaceX doesn't really know why that happens.  I didn't see any equivalent effect on the way up.  I wouldn't expect it near sea level with the exhaust overexpanded.  But once the plume bloomed out, I thought I'd see the effect again, and didn't.  Maybe that's because there was a different pressure pattern.

Quote
And since this 3 stick launch had what appears to my eyes astoundingly underwhelming performance (the 3 stick launch of a ?1500kg? payload only accelerated the second stage to the same speed that some previous F9(s) have pushed very heavy payloads to) I'm lead to think that they were doing a lot of experimenting with what was going on behind that curtain of flame.

Agree!  Even given a bunch of experimenting, how did they manage to push so little so slowly?

And why?  It would have been cooler to have enough battery lifetime and impulse to capture the view of doing a gravity assist off the moon.

At liftoff there is almost no difference in mass between no payload and full payload. You would not be able to just eyeball the difference.

Online LouScheffer

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And since this 3 stick launch had what appears to my eyes astoundingly underwhelming performance (the 3 stick launch of a ?1500kg? payload only accelerated the second stage to the same speed that some previous F9(s) have pushed very heavy payloads to) I'm lead to think that they were doing a lot of experimenting with what was going on behind that curtain of flame. 

There were at least 3 factors that contribute to the underwhelming performance:
 - A super conservative center thrust profile.  Not even full thrust at liftoff, leading to larger gravity losses.   Plus average 80% throttle over the first 2:30, leaving only 30 seconds left after the side cores separate.   A deeper throttle would save more fuel for after separation, where it would be more useful.
 - A fairly lengthy boostback burn for the core stage.  If they put the ASDS downrange, this could go towards more lift.
 - A lengthy coast, letting LOX evaporate.   Total second stage burn was about 25 seconds shorter than usual.

The NASA web site (which Elon said was for block 1) claims 4000 kg to Mars, re-usable.   For BulgariaSat, which was slightly less than 4000 kg single stick re-usable, the second stage spent 2800 m/s from parking orbit to GTO.  To get to Mars, you need about 800 m/s more from LEO.  Since the second stage is the same, and the payload the same, the second stage delta-V is the same, so the extra speed has to come from the first stage.  Since BulgariaSat had MECO at 2360 m/s, that implies the FH can stage at 3160 m/s and still recover, or about 520 m/s more than this flight demonstrated.    So this was indeed a super-conservative test flight.  Performance was not their goal.

Offline Kabloona

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On the other side, Buzz Aldrin went to the pad and watched the liftoff of Falcon Heavy.
Jeez... what a way to go!  RIP, Buzz...  :( :(
He had a hot time on the way out ;)  Seriously though, I'll bet he was either at the Saturn V Center viewing area, or on the roof of the VAB :)

I didn’t see him at the Saturn V center and didn’t hear talk of him being there

He said he was there at the Saturn V center (see photo caption).

https://twitter.com/TheRealBuzz/status/960972020166033408
« Last Edit: 02/13/2018 12:43 am by Kabloona »

Offline Nomadd

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 You kind of think that after losing a core because they didn't have enough hydraulic fluid, they wouldn't wouldn't cut it so close.
Those who danced were thought to be quite insane by those who couldn't hear the music.

Offline aleponcin

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Quote
A testament to the power of this first ever launch of the Falcon Heavy, Lt Col Stuker noted, “It was the first time we heard the rumble of the rocket over the sound of the rotor blades.”
  :)

http://www.afrc.af.mil/News/Article-Display/Article/1435111/reserve-citizen-airman-support-successful-spacex-falcon-heavy-milestone-launch/

Offline su27k

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https://twitter.com/elonmusk/status/963107229523038211
Quote from: Elon Musk
Elon Musk
‏Compte certifié @elonmusk
16 minil y a 16 minutes
En réponse ŕ @kerrbones @nextspaceflight

Not enough ignition fluid to light the outer two engines after several three engine relights. Fix is pretty obvious.

The centre core landing failure was caused by the fact that the need for ignition fluids (TEA/TEB) increases after several engine relights. They are adding more storage to fix the issue.
More critical about this.

One should always ask, if the fix was so simple, why wasn' t the issue determined before flight (i.e. simulation)?

People give SX too many "mulligans", too readily, at any time, and for any reason.

Yes it was good the demo launch succeeded.

Predicting an issue and fixing an issue are totally different things though, it's entirely possible for something to be hard to predict but easy to fix, i.e. it takes a supercomputer to predict when it will rain in the next few days, but the fix for getting wet is simply bringing an umbrella.

Offline Steven Pietrobon

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The performance numbers in this database are not accurate. In process of being fixed. Even if they were, a fully expendable Falcon Heavy, which far exceeds the performance of a Delta IV Heavy, is $150M, compared to over $400M for Delta IV Heavy.

https://twitter.com/elonmusk/status/963076231921938432

So we now have an actual price for an expendable Falcon Heavy.

So that is $90M for 8 t to GTO or $11,250/kg or $150M for 26.7 t to GTO or $5,618/kg. That means if you are sending large payloads to the Moon or Mars, its much cheaper to do it expendable!
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline GWH

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The performance numbers in this database are not accurate. In process of being fixed. Even if they were, a fully expendable Falcon Heavy, which far exceeds the performance of a Delta IV Heavy, is $150M, compared to over $400M for Delta IV Heavy.

https://twitter.com/elonmusk/status/963076231921938432

So we now have an actual price for an expendable Falcon Heavy.

So that is $90M for 8 t to GTO or $11,250/kg or $150M for 26.7 t to GTO or $5,618/kg. That means if you are sending large payloads to the Moon or Mars, its much cheaper to do it expendable!
Nope. Center core expendable and recovering boosters on ASDS only incurs 10% penalty as per a later tweet... for $95million
I speculate this is for reused boosters and is lower to suit the reused rocket prices that were just mentioned in an article on this site: https://www.nasaspaceflight.com/2018/02/falcon-heavy-success-paves-space-beyond-earth/
$62M for full 3 core reuse.
« Last Edit: 02/13/2018 05:12 am by GWH »

Offline Steven Pietrobon

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Nope. Center core expendable and recovering boosters on ASDS only incurs 10% penalty as per a later tweet... for $95million
I speculate this is for reused boosters and is lower to suit the reused rocket prices that were just mentioned in an article on this site: https://www.nasaspaceflight.com/2018/02/falcon-heavy-success-paves-space-beyond-earth/
$62M for full 3 core reuse.

That means a centre core costs only $5M to make. That would imply three expendable cores should only cost $15M, increasing the price to $110M, not $150 M. Anyway, $95M for 0.9*26.7 = 24.03 t is $3,953/kg, which is the cheapest option. If an expended core costs (150-90)/3 = $20M, that gives a price of $90+$20 = $110M for 24.03 t or $4,578/kg, which is still cheaper than fully expendable.
« Last Edit: 02/13/2018 05:23 am by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline GWH

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Nope. Center core expendable and recovering boosters on ASDS only incurs 10% penalty as per a later tweet... for $95million
I speculate this is for reused boosters and is lower to suit the reused rocket prices that were just mentioned in an article on this site: https://www.nasaspaceflight.com/2018/02/falcon-heavy-success-paves-space-beyond-earth/
$62M for full 3 core reuse.

That means a centre core costs only $5M to make. $95M for 0.9*26.7 = 24.03 t is $3,953/kg, which is the cheapest option.
It means the side cores are being reused a lot, so they only add about $5M to the price of an expendable F9.
https://twitter.com/elonmusk/status/963094533830426624

Also I suspect this is strategic pricing that doesn't reflect actual operational cost over expendable F9.

Offline TrueBlueWitt

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Nope. Center core expendable and recovering boosters on ASDS only incurs 10% penalty as per a later tweet... for $95million
I speculate this is for reused boosters and is lower to suit the reused rocket prices that were just mentioned in an article on this site: https://www.nasaspaceflight.com/2018/02/falcon-heavy-success-paves-space-beyond-earth/
$62M for full 3 core reuse.

That means a centre core costs only $5M to make. $95M for 0.9*26.7 = 24.03 t is $3,953/kg, which is the cheapest option.

No Legs, no Iconel Heat shield.. No Grid fins..
All of which would not only save cost but also reduce mass on core, which is much bigger benefit than on the boosters.  Also, what's the cost of deep ocean drone ship recovery for what would be a very very toasty core? You have to wonder how many times they figured they could re-use the core to start with.. if only a few times.. then maybe the new numbers make sense.

Offline darkenfast

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When thinking about the low cost difference between the a FH (center core expended) and a F9 (expended), remember that the actual cost of the FH operation at KSC is likely not a full three times as much as a single stick Falcon 9.  Some items have to be done three times (and completely separate), some only done once per campaign (Static Fire, for example), and some in-between (three times, but they can assemble the tool and workers once and do all three in a row, with some savings).  I doubt that we could even begin to guess how the hours break down, but if wages are the biggest cost at the launch site, it could be a big factor.

Does anyone have insight into how Delta IV Heavy launch site costs break down when compared to a bare (no solids) Delta IV? 
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Offline macpacheco

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In some ways, from an engineering perspective, this FH launch was a failure: so many things that could have gone wrong, didn't - and it would certainly be a shame if the only "lesson learned" was that they miscalculated the amount of starter fluid needed.  Is the rocket over-engineered?
 

Yes, it's a shame so many things worked properly that the engineers won't know what to fix.  ???

But judging from Elon's comment that FH was much harder than they expected, I'd guess they learned quite a lot in the design process about coupled loads, booster separation dynamics, modal analysis, etc, etc. And apparently they learned most, or all, of those lessons well.

I'd guess that there's still plenty to fix; just nothing so broken that it resulted in a loss of mission. More fine tuning; less coarse.
Are you perhaps mixing up fixing versus improving ?

Its impressive that SpaceX managed to get every first of F9 and FH right the first time.
F9 v1.0
F9 v1.1 Block I
F9 v1.1 Block II
F9 v1.1 Block III
F9 v1.1 Block IV
FH Block III/IV
No kabooms with each launch. Perfect payload delivery.
Two losses of payloads, but not on the inaugural launch.
Given how many substantial performance improvements and major redesigns for stages, tanks, helium storage, engine uprates, ...
It is A M A Z I N G the resulting stats.
Hopefully Block V F9 and FH will maintain the pattern.
« Last Edit: 02/13/2018 07:21 am by macpacheco »
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Offline macpacheco

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Nope. Center core expendable and recovering boosters on ASDS only incurs 10% penalty as per a later tweet... for $95million
I speculate this is for reused boosters and is lower to suit the reused rocket prices that were just mentioned in an article on this site: https://www.nasaspaceflight.com/2018/02/falcon-heavy-success-paves-space-beyond-earth/
$62M for full 3 core reuse.

That means a centre core costs only $5M to make. That would imply three expendable cores should only cost $15M, increasing the price to $110M, not $150 M. Anyway, $95M for 0.9*26.7 = 24.03 t is $3,953/kg, which is the cheapest option. If an expended core costs (150-90)/3 = $20M, that gives a price of $90+$20 = $110M for 24.03 t or $4,578/kg, which is still cheaper than fully expendable.

That price could be for a center core that already flew N times. For instance if SpaceX requires those launches only use the 9th or 10th flight of the center core...
As long as its a launch contract that gives SpaceX full flexibility on reuse, its unwise to assume the cores will be thrown away at their first launch.

I further submit that those prices are not even calculated like that for those cases. SpaceX wants a certain savings over the competition and they are willing to give away some profits to handle anything D4H can do for, say, 30 or 40% the price. Plus those prices can change... Introductory pricing. If lots of customers ask for launches that throw away cores, then prices rise cause they won't be able to get on average enough flights out of those cores to make $$$ sense.
« Last Edit: 02/13/2018 07:39 am by macpacheco »
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Offline Nomadd

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Its impressive that SpaceX managed to get every first of F9 and FH right the first time.
F9 v1.0
F9 v1.1 Block I
F9 v1.1 Block II
F9 v1.1 Block III
F9 v1.1 Block IV
FH Block III/IV
No kabooms with each launch. Perfect payload delivery.
Two losses of payloads, but not on the inaugural launch.
Given how many substantial performance improvements and major redesigns for stages, tanks, helium storage, engine uprates, ...
It is A M A Z I N G the resulting stats.
Hopefully Block V F9 and FH will maintain the pattern.

And 468 M1D flights without an failure. (Although, CRS-7 Vacuum never had a chance to fail)
« Last Edit: 02/13/2018 07:40 am by Nomadd »
Those who danced were thought to be quite insane by those who couldn't hear the music.

Offline marsbase

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I understand that the center core did not have the titanium grid fins.  Why is that?  Did Musk not expect the center core to make it back?  Since the center core experienced higher re-entry velocities,  you would think it would have the titanium GF as a high priority.

Online ugordan

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I understand that the center core did not have the titanium grid fins.  Why is that?

That has been addressed several times already. It did not need it, one of the reasons why titanium fins were needed for side boosters is for control authority as they have rounded nosecones instead of a cylinder which affects flow separation and thus controllability. The titanium fins are larger than the old aluminum fins so they provide more authority.

The center core on this flight apparently flew a conservative reentry profile, early MECO, long boostback burn. Very likely lower heating than a single stick GTO recovery.
« Last Edit: 02/13/2018 10:25 am by ugordan »

Offline marsbase

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I understand that the center core did not have the titanium grid fins.  Why is that?
one of the reasons why titanium fins were needed for side boosters is for control authority as they have rounded nosecones instead of a cylinder which affects flow separation and thus controllability. The titanium fins are larger than the old aluminum fins so they provide more authority.

Thanks ugordon.  I've also wondered why the side booster nose cones are not jettisoned like the fairing if that would add control.

Online ugordan

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I've also wondered why the side booster nose cones are not jettisoned like the fairing if that would add control.

Their goal is to recover as much of the hardware back as possible, like their fairing recovery experiments. Why would they discard the nosecones if they don't have to? They aren't exactly free, either.

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