Author Topic: SpaceX Falcon 9 - Eutelsat 117W B & ABS 2A - SLC-40 - June - DISCUSSION  (Read 262200 times)

Offline the_other_Doug

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We never had any evidence that supports fuel depletion.

There's a definitive statement on L2 about what happened on SES-9, which I take at face value.

A more accurate statement on your part might be, "There's a post on L2 by someone who claims to know what happened on SES-9, but I don't believe him because he hasn't disclosed his source." Not quite the same thing as "no evidence."

https://forum.nasaspaceflight.com/index.php?topic=39345.msg1503255#msg1503255

I would not say there are statements by SpaceX insiders that I don't believe.  I would say we were told of a condition, by a reliable source, that could have more than one possible root cause, with no additional data on which root cause SpaceX thought was at fault.  I have then questioned the assumption of which possible root cause was, in fact, responsible for the condition.  That's all.

Ah, well... it's been sort of nice, while recovering, being able to sit and noodle on the forum whenever I felt like it.  But, seven weeks after being rolled into the ER for emergency surgery, today is the day when I actually start back working at my job (only half-time for the next couple of weeks).  Still on the happy pills, no way around that at this point, but capable of answering phones and explaining things to my customers.  So, I'll be back later... :)
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Offline Kabloona

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I would not say there are statements by SpaceX insiders that I don't believe.  I would say we were told of a condition, by a reliable source, that could have more than one possible root cause, with no additional data on which root cause SpaceX thought was at fault.  I have then questioned the assumption of which possible root cause was, in fact, responsible for the condition.  That's all.

Thanks for clarifying. Yes, there was more than one root cause suggested in that post and I understand your caution in assuming either one or the other was in fact the true cause.

It may be worth noting that the two suggested root causes may be synergetic, ie *both* conditions can interact and cause the phenomenon resulting in low thrust, so it may be impossible to say which condition was more at fault.

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But, seven weeks after being rolled into the ER for emergency surgery, today is the day when I actually start back working at my job (only half-time for the next couple of weeks).  Still on the happy pills, no way around that at this point, but capable of answering phones and explaining things to my customers.  So, I'll be back later...

Welcome back to life, and please share your happy pills if you have any extras.  ;)
« Last Edit: 06/16/2016 07:20 pm by Kabloona »

Offline ChrisC

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From the update thread:

USLaunchReport:  One of the three Merlin engines did not fire properly on Boost Back.

Thought there was no "Boost Back" burn on this mission, but only Re-entry Burn and Landing Burn.  Wasn't the problem with one of 3 engines on the Landing Burn?

I guess this means we should take USLR with a Wite-Out bottle full of salt.  I love and greatly appreciate their video reports, but this mis-quote (or whatever it is) tells me to not look beyond their raw footage.  At least not for now while they are still new at this.
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Offline starhawk92

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If the low-thrust condition is a random result of a low propellant level that allows occasional bubbles of helium into one of the turbopumps, the other engines can still run at full thrust until/unless another random bubble is ingested. So far it seems the low-thrust condition has affected only one engine (SES-9, and the most recent launch) during the landing burn. It may be that the propellant feed line geometry makes one engine more susceptible than the others to gas bubble ingestion.

There was a launch this year which was scrubbed because of a sputter in the engine, I'll have to check the scrubs thread.  But I think that occurrence rules out low-fuel/low-propellant being the only cause of reduced power on an engine startup.

Edit: 
The following is copied from the Scrubs Thread:


Falcon 9 Flight 22 - SES-9 (not verified)
payload mass: 5,271 kilograms, orbit: geosynchronous, delivered orbit: 334 x 40648 km x 27.96° [65], [69]
  F) 2016-02-22, Successful static fire [64]
  D) 2016-02-24, 24h delay to ensure liquid oxygen temperatures are as cold as possible in an effort to maximize performance of the vehicle (due to high winds) [66]
  C) 2016-02-25, Scrub at T-1:41, LOX loading issues [65]
  R) 2016-02-28, Delay, wayward boat got into range [65]
  C) 2016-02-28, Scrub at T-0, aborted on low thrust alarm. Rising oxygen temps due to hold for boat and helium bubble triggered alarm [65]
  D) 2016-03-01, Delay due to extreme high altitude wind shear [68]
  L) 2016-03-05, Successful launch (the one with the difficult landing attempt) [65]
  BL) 2016-03-05, Hard landing on the ASDS (3 engine landing burn, run out of propellant, no boostback burn) [65][74]


Edit of Edit:
If only I were as quick as Kabloona!!
« Last Edit: 06/16/2016 07:07 pm by starhawk92 »

Offline Kabloona

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If the low-thrust condition is a random result of a low propellant level that allows occasional bubbles of helium into one of the turbopumps, the other engines can still run at full thrust until/unless another random bubble is ingested. So far it seems the low-thrust condition has affected only one engine (SES-9, and the most recent launch) during the landing burn. It may be that the propellant feed line geometry makes one engine more susceptible than the others to gas bubble ingestion.

There was a launch this year which was scrubbed because of a sputter in the engine, I'll have to check the scrubs thread.  But I think that occurrence rules out low-fuel/low-propellant being the only cause of reduced power on an engine startup.

That was SES-9, too.

Offline rsdavis9

So maybe the fix is better insulation so the lox doesn't warm up.

Might be only insulation on the pipes.

I also like the geometry possibility for bubble rejection.

Don't they have separaters for bubbles. I have one on my forced hot water system. Not sure how it can reliably collect the bubbles. And it probably doesn't work at the velocity and volume that spacex does in their engines.
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Offline starhawk92

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That was SES-9, too.

Man, what a harsh corner for the engineering team -- the only time it happens the rocket explodes.  Maybe parts and pieces of 8 engines mixed up to look at for any help, otherwise what?

This seems to be one of those hurdles which makes rocket science as hard as Rocket Science!!

Offline tjchambers

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I will probably be blasted for lack of knowledge here, but I have a question.

Does the first stage rotate/spin in attempt to reduce the needed engine gimbal angles and more directly use the thrust to reduce speed during the "parabolic" arc it is making towards it's destination? By spin I don't mean continually, just using spinning as a mechanism to better utilize the thrust of the 3 engines which are in some orientation - vertical? horizontal? - relative to the arc.


Offline Kabloona

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Maybe parts and pieces of 8 engines mixed up to look at for any help, otherwise what?

Telemetry from the engines, LOX temp sensors, etc. I expect they have a pretty good idea what happened on the landing burn.
« Last Edit: 06/16/2016 07:24 pm by Kabloona »

Offline MattMason

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I will probably be blasted for lack of knowledge here, but I have a question.

Does the first stage rotate/spin in attempt to reduce the needed engine gimbal angles and more directly use the thrust to reduce speed during the "parabolic" arc it is making towards it's destination? By spin I don't mean continually, just using spinning as a mechanism to better utilize the thrust of the 3 engines which are in some orientation - vertical? horizontal? - relative to the arc.

Welcome!

Falcon 9 does not use spin stabilization in either launch or landing mode.
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Offline rsdavis9

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Maybe parts and pieces of 8 engines mixed up to look at for any help, otherwise what?

Telemetry from the engines, LOX temp sensors, etc. I expect they have a pretty good idea what happened on the landing burn.

Thats my guess. They know what the problem is. The fix they have in mind is going to take some changes in shapes of things. Therefore later this year when the fix can get thru the supply line.
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline Stan-1967

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So maybe the fix is better insulation so the lox doesn't warm up.

Might be only insulation on the pipes.

I also like the geometry possibility for bubble rejection.

Don't they have separaters for bubbles. I have one on my forced hot water system. Not sure how it can reliably collect the bubbles. And it probably doesn't work at the velocity and volume that spacex does in their engines.

I believe I recall the issue of helium bubbles on SES-9 was postulated to be due to the time the LOX propellant was at superchilled temperature.   The helium is soluble in the LOX, so the longer it sits on the pad with tanks pressurized, the more helium that dissolves into the LOX.   That launch had several "holds" due to a stray boat in the launch zone.   When the He saturated LOX goes through the pump, the helium can then bubble out of the LOX from cavitation effects.   

Where I am going with this is that the SES-9 thrust issues are probably separate from the fuel starvation issues with hoverslam landings.

Offline rsdavis9

Bubble separator in action.

With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline JamesH65

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I will probably be blasted for lack of knowledge here, but I have a question.

Does the first stage rotate/spin in attempt to reduce the needed engine gimbal angles and more directly use the thrust to reduce speed during the "parabolic" arc it is making towards it's destination? By spin I don't mean continually, just using spinning as a mechanism to better utilize the thrust of the 3 engines which are in some orientation - vertical? horizontal? - relative to the arc.

Welcome!

Falcon 9 does not use spin stabilization in either launch or landing mode.

Poster specifically said not for stabilisation, but, in my reading, was talking about spinning the stage to orient/align the 3 engines either horizontally or vertically relative to the barge.

Offline Kabloona

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I will probably be blasted for lack of knowledge here, but I have a question.

Does the first stage rotate/spin in attempt to reduce the needed engine gimbal angles and more directly use the thrust to reduce speed during the "parabolic" arc it is making towards it's destination? By spin I don't mean continually, just using spinning as a mechanism to better utilize the thrust of the 3 engines which are in some orientation - vertical? horizontal? - relative to the arc.

Good question. From a thrust perspective, the stage shouldn't really care which way the 3 engines are oriented during boostback/entry/landing. The delta V gained from any given burn is the same. What matters is the pitch/yaw orientation of the stage during a burn, and that attitude should be controllable by the 3 engines  via thrust vectoring in any rotational orientation (or by the center engine only during landing burn).

The rotational orientation is probably more a question of guidance convenience, ie orienting the stage in such a way that IMU or guidance software finds most convenient.
« Last Edit: 06/16/2016 07:56 pm by Kabloona »

Offline Rocket Science

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We never had any evidence that supports fuel depletion.

There's a definitive statement on L2 about what happened on SES-9, which I take at face value.

A more accurate statement on your part might be, "There's a post on L2 by someone who claims to know what happened on SES-9, but I don't believe him because he hasn't disclosed his source." Not quite the same thing as "no evidence."

https://forum.nasaspaceflight.com/index.php?topic=39345.msg1503255#msg1503255

I would not say there are statements by SpaceX insiders that I don't believe.  I would say we were told of a condition, by a reliable source, that could have more than one possible root cause, with no additional data on which root cause SpaceX thought was at fault.  I have then questioned the assumption of which possible root cause was, in fact, responsible for the condition.  That's all.

Ah, well... it's been sort of nice, while recovering, being able to sit and noodle on the forum whenever I felt like it.  But, seven weeks after being rolled into the ER for emergency surgery, today is the day when I actually start back working at my job (only half-time for the next couple of weeks).  Still on the happy pills, no way around that at this point, but capable of answering phones and explaining things to my customers.  So, I'll be back later... :)
See ya' soon Doug! :)
"The laws of physics are unforgiving"
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Offline cscott

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Where I am going with this is that the SES-9 thrust issues are probably separate from the fuel starvation issues with hoverslam landings.

Not necessarily: the LOX has had a couple more minutes to be exposed to high pressure helium before the landing burn.  Could well be a combination of factors (G profile during re-entry, helium saturation, warming tank temps, lower propellent levels, supersonic retropropulsion startup issues, etc) combine to trigger the thrust deficit.
« Last Edit: 06/16/2016 08:00 pm by cscott »

Offline Semmel

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We never had any evidence that supports fuel depletion.

There's a definitive statement on L2 about what happened on SES-9, which I take at face value given the poster's location and familiarity with F9 evidenced in his previous posts.

A more accurate statement on your part might be, "There's a post on L2 by someone who claims to know what happened on SES-9, but I don't believe him because he hasn't disclosed his source." Not quite the same thing as "no evidence."

https://forum.nasaspaceflight.com/index.php?topic=39345.msg1503255#msg1503255

I concur,  that was an oversight on my part. Maybe I should have given him more attention to remember him and judge his statement differently.

Offline jaufgang

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I will probably be blasted for lack of knowledge here, but I have a question.

Blasting lack of knowledge on this forum tends to be reserved for statements, not questions.

Offline spacenut

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Would parachutes or inflatable ballons (from excess helium if there is any), help with landings?  Especially the GTO or GSO ones.

Seems like developing the Raptor based metholox upper stage would allow for lower staging to give enough kerolox for controlled landings. 


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