SpaceX Tuesday...
Discussion
Timetable for manned Dragon flight testing has been revamped
http://spaceflightnow.com/2015/07/08/spacex-delays...
http://spaceflightnow.com/2015/07/08/spacex-delays...
Musk has released information on the suspected cause of the failure
http://www.i4u.com/2015/07/93422/elon-musk-says-fa...
http://www.i4u.com/2015/07/93422/elon-musk-says-fa...
Not sure that the reporter understands completely what he/she is trying to say.
He refers to the failure of a "strut holding down the helium tank". I'm not sure what he means by that.
Are they saying a strut is used to hold the tank within the rocket body structure and that this strut failed?
He refers to the failure of a "strut holding down the helium tank". I'm not sure what he means by that.
Are they saying a strut is used to hold the tank within the rocket body structure and that this strut failed?
Eric Mc said:
Are they saying a strut is used to hold the tank within the rocket body structure and that this strut failed?
yes. apparently failed at about 30% rated load. SpaceX have used hundreds of these, and have now tested thousands and a very small number have some kind of structural issue ( crystalline metal something) that means they fail.
The strut has been redesigned, will be manufactured differently, from a different supplier, in future.
Also they will test each strut rather than one of a batch.
Full text of e-mail issued:
CRS-7 Investigation Update
On June 28, 2015, following a nominal liftoff, Falcon 9 experienced an overpressure event in the upper stage liquid oxygen tank approximately 139 seconds into flight, resulting in loss of mission. This summary represents an initial assessment, but further investigation may reveal more over time.
Prior to the mishap, the first stage of the vehicle, including all nine Merlin 1D engines, operated nominally; the first stage actually continued to power through the overpressure event on the second stage for several seconds following the mishap. In addition, the Dragon spacecraft not only survived the second stage event, but also continued to communicate until the vehicle dropped below the horizon and out of range.
SpaceX has led the investigation efforts with oversight from the FAA and participation from NASA and the U.S. Air Force. Review of the flight data proved challenging both because of the volume of data —over 3,000 telemetry channels as well as video and physical debris—and because the key events happened very quickly.
From the first indication of an issue to loss of all telemetry was just 0.893 seconds. Over the last few weeks, engineering teams have spent thousands of hours going through the painstaking process of matching up data across rocket systems down to the millisecond to understand that final 0.893 seconds prior to loss of telemetry.
At this time, the investigation remains ongoing, as SpaceX and the investigation team continue analyzing significant amounts of data and conducting additional testing that must be completed in order to fully validate these conclusions. However, given the currently available data, we believe we have identified a potential cause.
Preliminary analysis suggests the overpressure event in the upper stage liquid oxygen tank was initiated by a flawed piece of support hardware (a “strut”) inside the second stage. Several hundred struts fly on every Falcon 9 vehicle, with a cumulative flight history of several thousand. The strut that we believe failed was designed and material certified to handle 10,000 lbs of force, but failed at 2,000 lbs, a five-fold difference. Detailed close-out photos of stage construction show no visible flaws or damage of any kind.
In the case of the CRS-7 mission, it appears that one of these supporting pieces inside the second stage failed approximately 138 seconds into flight. The pressurization system itself was performing nominally, but with the failure of this strut, the helium system integrity was breached. This caused a high pressure event inside the second stage within less than one second and the stage was no longer able to maintain its structural integrity.
Despite the fact that these struts have been used on all previous Falcon 9 flights and are certified to withstand well beyond the expected loads during flight, SpaceX will no longer use these particular struts for flight applications. In addition, SpaceX will implement additional hardware quality audits throughout the vehicle to further ensure all parts received perform as expected per their certification documentation.
As noted above, these conclusions are preliminary. Our investigation is ongoing until we exonerate all other aspects of the vehicle, but at this time, we expect to return to flight this fall and fly all the customers we intended to fly in 2015 by end of year.
While the CRS-7 loss is regrettable, this review process invariably will, in the end, yield a safer and more reliable launch vehicle for all of our customers, including NASA, the United States Air Force, and commercial purchasers of launch services. Critically, the vehicle will be even safer as we begin to carry U.S. astronauts to the International Space Station in 2017.
CRS-7 Investigation Update
On June 28, 2015, following a nominal liftoff, Falcon 9 experienced an overpressure event in the upper stage liquid oxygen tank approximately 139 seconds into flight, resulting in loss of mission. This summary represents an initial assessment, but further investigation may reveal more over time.
Prior to the mishap, the first stage of the vehicle, including all nine Merlin 1D engines, operated nominally; the first stage actually continued to power through the overpressure event on the second stage for several seconds following the mishap. In addition, the Dragon spacecraft not only survived the second stage event, but also continued to communicate until the vehicle dropped below the horizon and out of range.
SpaceX has led the investigation efforts with oversight from the FAA and participation from NASA and the U.S. Air Force. Review of the flight data proved challenging both because of the volume of data —over 3,000 telemetry channels as well as video and physical debris—and because the key events happened very quickly.
From the first indication of an issue to loss of all telemetry was just 0.893 seconds. Over the last few weeks, engineering teams have spent thousands of hours going through the painstaking process of matching up data across rocket systems down to the millisecond to understand that final 0.893 seconds prior to loss of telemetry.
At this time, the investigation remains ongoing, as SpaceX and the investigation team continue analyzing significant amounts of data and conducting additional testing that must be completed in order to fully validate these conclusions. However, given the currently available data, we believe we have identified a potential cause.
Preliminary analysis suggests the overpressure event in the upper stage liquid oxygen tank was initiated by a flawed piece of support hardware (a “strut”) inside the second stage. Several hundred struts fly on every Falcon 9 vehicle, with a cumulative flight history of several thousand. The strut that we believe failed was designed and material certified to handle 10,000 lbs of force, but failed at 2,000 lbs, a five-fold difference. Detailed close-out photos of stage construction show no visible flaws or damage of any kind.
In the case of the CRS-7 mission, it appears that one of these supporting pieces inside the second stage failed approximately 138 seconds into flight. The pressurization system itself was performing nominally, but with the failure of this strut, the helium system integrity was breached. This caused a high pressure event inside the second stage within less than one second and the stage was no longer able to maintain its structural integrity.
Despite the fact that these struts have been used on all previous Falcon 9 flights and are certified to withstand well beyond the expected loads during flight, SpaceX will no longer use these particular struts for flight applications. In addition, SpaceX will implement additional hardware quality audits throughout the vehicle to further ensure all parts received perform as expected per their certification documentation.
As noted above, these conclusions are preliminary. Our investigation is ongoing until we exonerate all other aspects of the vehicle, but at this time, we expect to return to flight this fall and fly all the customers we intended to fly in 2015 by end of year.
While the CRS-7 loss is regrettable, this review process invariably will, in the end, yield a safer and more reliable launch vehicle for all of our customers, including NASA, the United States Air Force, and commercial purchasers of launch services. Critically, the vehicle will be even safer as we begin to carry U.S. astronauts to the International Space Station in 2017.
ash73 said:
Kerbal is a space simulation game where you construct your own rockets. Early versions suffered from wobbly rockets, and the standard solution was always to add more struts. You should try it Eric, you would absolutely love it. It's great fun and you learn a lot about orbital mechanics.
First thing that sprang to mind. 
And yeah, it really is very good.Very good job this failed now rather than on a manned mission. A bit of a time bomb that, could have gone another 10 missions without anything happening, then boom.
I do know what Kerbal is - it was the struts I was interested in - which has been explained nicely.
I hadn't realised that a "belt and braces" approach was still applied to rockets stages. I thought that approach went out with the V2 (and maybe the Saturn V). I know the German technicians behind these early designs were rather conservative and tended to beef up the structures by adding a bit of triangulation here and there.
I had supposed that modern designs were cleverer with more strength built into the structure itself (the Colin Chapman philosophy).
If a strut failed, I presume it must have been the vibrations of the lift off that caused it to go.
I hadn't realised that a "belt and braces" approach was still applied to rockets stages. I thought that approach went out with the V2 (and maybe the Saturn V). I know the German technicians behind these early designs were rather conservative and tended to beef up the structures by adding a bit of triangulation here and there.
I had supposed that modern designs were cleverer with more strength built into the structure itself (the Colin Chapman philosophy).
If a strut failed, I presume it must have been the vibrations of the lift off that caused it to go.
The expected knock-on effect on Falcon 9 Heavy development has been confirmed. First flight delayed until next spring
http://spaceflightnow.com/2015/07/21/first-flight-...
http://spaceflightnow.com/2015/07/21/first-flight-...
The culprit
These are the struts believed to have failed. They actually hold the helium tanks down against their buoyancy when immersed in liquid oxygen - the failure of one would allow the He tank to float up inside the tank.
In layman's terms, one of these struts failed, allowing the He bottle to bob up in the tank under the force of its buoyancy in the LOX (over three times normal buoyancy because buoyancy per given volume increases in direct proportion to the acceleration force, in this case over three Gs). The He2 pressure went down as the bottle went upward, wrecking the plumbing, but Musk speculates that the manifold kinked as the bottle went up, just like kinking a garden hose, which is the most likely explanation for why the He pressure returned to normal.
The S2 MVAC engine had just started chilling, so the LOX tank was full. The rapidly expanding He2 had no space to expand into, so the pressure rose very rapidly, plus there is a possibility that the He2 bottle caromed off the insides of the tank, damaging it. High pressure LOX vented into the trunk as the tank failed, pressurizing the trunk and popping the Dragon off like a cork from a champagne bottle.
These are the struts believed to have failed. They actually hold the helium tanks down against their buoyancy when immersed in liquid oxygen - the failure of one would allow the He tank to float up inside the tank.
In layman's terms, one of these struts failed, allowing the He bottle to bob up in the tank under the force of its buoyancy in the LOX (over three times normal buoyancy because buoyancy per given volume increases in direct proportion to the acceleration force, in this case over three Gs). The He2 pressure went down as the bottle went upward, wrecking the plumbing, but Musk speculates that the manifold kinked as the bottle went up, just like kinking a garden hose, which is the most likely explanation for why the He pressure returned to normal.
The S2 MVAC engine had just started chilling, so the LOX tank was full. The rapidly expanding He2 had no space to expand into, so the pressure rose very rapidly, plus there is a possibility that the He2 bottle caromed off the insides of the tank, damaging it. High pressure LOX vented into the trunk as the tank failed, pressurizing the trunk and popping the Dragon off like a cork from a champagne bottle.
Edited by MartG on Tuesday 21st July 12:14
The He tank is believed to have ruptured when it broke free, and as it is at a considerably higher pressure than is normal for the Lox tank, this would have created the 'overpressure event' which destroyed the stage as with the Lox tank full there was no space for the escaped He to expand into.
A bit more detail here -
http://spaceflightnow.com/2015/07/20/support-strut...
This rocket science stuff has lots of factors to consider, doesn't it.
http://spaceflightnow.com/2015/07/20/support-strut...
This rocket science stuff has lots of factors to consider, doesn't it.
MartG said:
The culprit
These are the struts believed to have failed. They actually hold the helium tanks down against their buoyancy when immersed in liquid oxygen - the failure of one would allow the He tank to float up inside the tank.
Shows how much of a loser I am I thought that was a picture of that movie Stargate These are the struts believed to have failed. They actually hold the helium tanks down against their buoyancy when immersed in liquid oxygen - the failure of one would allow the He tank to float up inside the tank.
Edited by MartG on Tuesday 21st July 12:14
p1stonhead said:
MartG said:
The culprit
These are the struts believed to have failed. They actually hold the helium tanks down against their buoyancy when immersed in liquid oxygen - the failure of one would allow the He tank to float up inside the tank.
Shows how much of a loser I am I thought that was a picture of that movie Stargate These are the struts believed to have failed. They actually hold the helium tanks down against their buoyancy when immersed in liquid oxygen - the failure of one would allow the He tank to float up inside the tank.
Edited by MartG on Tuesday 21st July 12:14
Scott Manley (of KSP videos) has done a very good idiots guide to what they think went wrong;
https://www.youtube.com/watch?v=1i8hfpLNAIo
https://www.youtube.com/watch?v=1i8hfpLNAIo
a setback, nothing more, and an opportunity to further improve their vehicles and engineering mindsets...Gassing Station | Science! | Top of Page | What's New | My Stuff