Author Topic: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION  (Read 862084 times)

Offline FinalFrontier

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1560 on: 03/01/2016 05:24 PM »
Back on topic more, the stratified LOX issue, really bothers me.

I have been on the fence about using LOX cooled to the extent SpaceX is cooling it, its very tricky stuff and it requires really pushing the material design limits of some of the things in that rocket.

Particularly, although this was ruled out as the failure mode for CRS7 I still have my doubts as to how well the helium COPVS are handling these cold temperatures, I don't of course have access to SpaceX test data, but conventional wisdom still tells us composites do not like cryogenics.

Moreover and perhaps more concerning is the stratification and the helium bubble. Both of these can cause significant drops in performance, or if you had a large enough helium bubble at the wrong time in flight you could cause an engine stall.

SpaceX is taking alot of risks with this system. I think it will work, but its unnecessarily risky IMHO. I would not be surprised if SES9 failed in flight due to something related to the densified LOX, or a future flight for that matter.

However, provided it succeeds it will build data parameters for the next flight, and so forth, so each flight afterwards on the new system builds confidence and rationale.

Correct me if I am wrong but didn't OG2 use a FT Falcon 9? If so that provides a bit more confidence although I still think there are some substantial risks with this LV currently.
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Offline Confusador

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1561 on: 03/01/2016 05:46 PM »
....

SpaceX is taking alot of risks with this system. I think it will work, but its unnecessarily risky IMHO. I would not be surprised if SES9 failed in flight due to something related to the densified LOX, or a future flight for that matter.

However, provided it succeeds it will build data parameters for the next flight, and so forth, so each flight afterwards on the new system builds confidence and rationale.

Correct me if I am wrong but didn't OG2 use a FT Falcon 9? If so that provides a bit more confidence although I still think there are some substantial risks with this LV currently.

It's a risky business, and we all have different levels of tolerance.  Fortunately, the only opinions that matter about what level is 'unnecessary' are the customers, and they are responding accordingly (including negatively, see the recent ViaSat change).  On the whole, enough folks are satisfied that this level of risk seems justifiable.  And yes, Orbcomm-2 was FT.

Online wannamoonbase

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1562 on: 03/01/2016 05:52 PM »
Quote from: FinalFrontier link=topic=34 077.msg1498281#msg1498281 date=1456856652
Correct me if I am wrong but didn't OG2 use a FT Falcon 9? If so that provides a bit more confidence although I still think there are some substantial risks with this LV currently.

I don't think the risks are flight related.  The issue comes down to how many attempts to launch are they going to have to go through to get off the ground.

Like the Drake equation there is a long chain of variables that are multiplied together to produce the probability of getting a payload into the proper orbit.  SpaceX has now added 2 more variables, RP1 and LOx temp to that string (4 if you break it into first and second stage).

It's great they are trying and using this technology, perhaps they master it.  But their ability to respond to big launch windows appears limited for this vehicle configuration.
SpaceX, just a few things planned for 2018: FH, Starlink Prototypes, Block 5, Dragon 2, Increased launch rate.

Offline FinalFrontier

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1563 on: 03/01/2016 05:56 PM »
....

SpaceX is taking alot of risks with this system. I think it will work, but its unnecessarily risky IMHO. I would not be surprised if SES9 failed in flight due to something related to the densified LOX, or a future flight for that matter.

However, provided it succeeds it will build data parameters for the next flight, and so forth, so each flight afterwards on the new system builds confidence and rationale.

Correct me if I am wrong but didn't OG2 use a FT Falcon 9? If so that provides a bit more confidence although I still think there are some substantial risks with this LV currently.

It's a risky business, and we all have different levels of tolerance.  Fortunately, the only opinions that matter about what level is 'unnecessary' are the customers, and they are responding accordingly (including negatively, see the recent ViaSat change).  On the whole, enough folks are satisfied that this level of risk seems justifiable.  And yes, Orbcomm-2 was FT.
Okay then yes, that provides a bit more confidence. 

I will still feel alot better about this system after SES9 is orbited successfully. Helium bubbles and stratified LOX are not fun things.

Quote from: FinalFrontier link=topic=34 077.msg1498281#msg1498281 date=1456856652
Correct me if I am wrong but didn't OG2 use a FT Falcon 9? If so that provides a bit more confidence although I still think there are some substantial risks with this LV currently.

I don't think the risks are flight related.  The issue comes down to how many attempts to launch are they going to have to go through to get off the ground.

Like the Drake equation there is a long chain of variables that are multiplied together to produce the probability of getting a payload into the proper orbit.  SpaceX has now added 2 more variables, RP1 and LOx temp to that string (4 if you break it into first and second stage).

It's great they are trying and using this technology, perhaps they master it.  But their ability to respond to big launch windows appears limited for this vehicle configuration.

That is definitely an issue. But I expect the window issue will change after this flight, they have gained alot more experience with regard to tolerances as a result of all these aborts.
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Offline MarekCyzio

I checked this thread and it seems that one person mentioned this book:
http://tinyurl.com/h3gjerd

What surprises me is that I expected a very interesting discussion on cooling LOX with hellium bubbles and this discussion never happened. Apparently bubbling hellium through LOX can be a very effective way of cooling LOX down. Can anybody confirm that? Is this what SpaceX is doing to keep LOX cool in the rocket?
« Last Edit: 03/01/2016 06:19 PM by Chris Bergin »

Offline andrewsdanj

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1565 on: 03/01/2016 07:38 PM »
Both the technical and full webcasts were up and running and counting down towards 3:00:00. Then, just like that, they flipped to 'please stand by' and then 'This video has been removed'. Hope this isn't a bad omen...

Offline topo334

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1566 on: 03/01/2016 07:48 PM »
Checked livestream.com for the launch and the countdown clock was showing 2:57:00 and counting at12:46 pm pacific.

Offline jimbowman

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1567 on: 03/01/2016 07:48 PM »
Moved to Friday per Musk on Twitter due to high upper level winds.
« Last Edit: 03/01/2016 07:49 PM by jimbowman »

Offline notsorandom

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1568 on: 03/01/2016 08:02 PM »
Winds peaking at 70 m/s (157mph) at 10km (32,000 ft). Those speeds are seen in category 4 hurricanes on the surface but are more common higher up.

Offline Bubbinski

Why Friday? Is the wind shear forecast not to improve till then, or do the teams need more time to rest and chill down the fuel, etc.?
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Offline ugordan

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1570 on: 03/01/2016 08:11 PM »
Winds peaking at 70 m/s (157mph) at 10km (32,000 ft). Those speeds are seen in category 4 hurricanes on the surface but are more common higher up.

It's not the speed itself that's the problem, it's the rapid variation in speed vs. altitude. Uniform speed all around would just make the rocket drift a bit, which the guidance can compensate for. On the other hand, shear like this can cause a sudden torque on the vehicle. At high Q which is around those altitudes, that's a bad thing.

Offline kenban

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1571 on: 03/01/2016 08:28 PM »
Why Friday? Is the wind shear forecast not to improve till then, or do the teams need more time to rest and chill down the fuel, etc.?

Simply due to the long range forecast.  Winds are likely to be too strong through Thursday.

Offline docmordrid

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1572 on: 03/01/2016 08:36 PM »
Animated forecasts through Sunday. Saturday actually looks better than Friday.

http://squall.sfsu.edu/scripts/namjetstream_model_fcst.html
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Offline BruceM

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1573 on: 03/01/2016 08:36 PM »
Did not want to post to the update page directly (so someone repost there if OK) but this from the SpaceX web site:

Quote
SpaceX  SpaceX
8 minutes ago
 
Launch update

Unfortunately upper-level winds continue to exceed acceptable limits and are expected to get worse as we approach tonight’s launch window, so we are forgoing today’s launch attempt. Winds are forecast to exceed acceptable limits through Thursday. Our team will continue working with the Air Force’s Launch Weather Officer to evaluate the best available opportunity for flight in the coming days.

Offline sdsds

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1574 on: 03/01/2016 09:18 PM »
Could someone address succinctly the issue of why (modern) guidance algorithms can't handle wind shear?

It can't really be a structural issue, can it? Just keep the pointy end into the (local relative) wind!?
« Last Edit: 03/01/2016 09:20 PM by sdsds »
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Offline Lar

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1575 on: 03/01/2016 09:20 PM »
Good question sdsds, I'm interested too but I suspect that it's the buffeting loads and in general quick changes in force.

On another topic maybe they'll use the time to run another static fire, with perhaps a simulated hold in the middle to see if they've got the issues they were facing under control, or at least gather some data...
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Offline leetdan

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1576 on: 03/01/2016 09:21 PM »
Could someone address succinctly the issue of why (modern) guidance algorithms can't handle wind shear?

It can't really be a structural issue, can it? Just keep the pointy end into the (local relative) wind!?

It's not the speed itself that's the problem, it's the rapid variation in speed vs. altitude. Uniform speed all around would just make the rocket drift a bit, which the guidance can compensate for. On the other hand, shear like this can cause a sudden torque on the vehicle. At high Q which is around those altitudes, that's a bad thing.

Offline mfck

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1577 on: 03/01/2016 09:23 PM »
Could someone address succinctly the issue of why (modern) guidance algorithms can't handle wind shear?

It can't really be a structural issue, can it? Just keep the pointy end into the (local relative) wind!?
Well, to quote Elon, it hits "like a sledgehammer", which sounds pretty structural to me

Offline Kabloona

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1578 on: 03/01/2016 09:26 PM »
It can't really be a structural issue, can it? Just keep the pointy end into the (local relative) wind!?

Doesn't work like that. There has to be a non-zero angle of attack during pitchover, and wind direction/speed during ascent is variable. Google "Q-alpha aerodynamics" for more detail. Q-alpha is basically the bending moment induced by dynamic pressure and angle of attack.

Or check out the "Analyses" section of this following paper for Monte Carlo simulations of Max Q-alpha for Ares, and the associated Q-alpha plot, and the subsection "Launch Probability due to Winds Aloft."

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090001903.pdf
« Last Edit: 03/02/2016 12:21 AM by Kabloona »

Offline Rocket Science

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #1579 on: 03/01/2016 09:31 PM »
Wind shear at Max Q could mean a bad day...
« Last Edit: 03/01/2016 09:33 PM by Rocket Science »
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