QuoteWe 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
We never had any evidence that supports fuel depletion.
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.
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...
Quote from: catdlr on 06/16/2016 05:53 pmUSLaunchReport: 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?
USLaunchReport: One of the three Merlin engines did not fire properly on Boost Back.
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.
Quote from: Kabloona on 06/16/2016 06:21 pmIf 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.
Maybe parts and pieces of 8 engines mixed up to look at for any help, otherwise what?
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.
QuoteMaybe 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.
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.
Quote from: tjchambers on 06/16/2016 07:22 pmI 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.
Quote from: Kabloona on 06/16/2016 06:24 pmQuoteWe 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#msg1503255I 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...
Where I am going with this is that the SES-9 thrust issues are probably separate from the fuel starvation issues with hoverslam landings.
QuoteWe 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 will probably be blasted for lack of knowledge here, but I have a question.