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SpaceX Discussion Thread

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20 minutes ago, IncongruousGoat said:

Okay, I could have sworn that, around the time the initial SpaceX report came out, I heard that the strut that failed was rated for 5,000 lbf, and failed at 1,000 lbf, which is a 5:1 safety factor. Does anyone have any hard figures for the rated load and actual load for that strut?

The rated load drops if it is struck because of its low temperature tolerance.  E.g. you place it under a load, and then some strike the load damaging the surface, at the point it tolerance drops. So for instance at -100'C it can tolerate a load of X and being struck, at -200'C it can also tolerate a load of X, but if it dented in any critical load bearing surface, its critical tolerance drops, if struck hard enough it drops to zero, this is because the metal is inelastic at the temperature.

 

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1 hour ago, IncongruousGoat said:

Okay, I could have sworn that, around the time the initial SpaceX report came out, I heard that the strut that failed was rated for 5,000 lbf, and failed at 1,000 lbf, which is a 5:1 safety factor. Does anyone have any hard figures for the rated load and actual load for that strut?

Yes, as @PB666 pointed out, it was rated for a load under certain circumstances. But -180°C and vibrations under g loads exceeded these circumstances. For example, a steel has, depending on the alloy and conditions, certain ductile values. But at low temperatures the material gets brittle, so that a relatively weak blow or heavy vibes can cause cracks and weaken the material and when it is under stress it will give in earlier than the rating states.

What NASA criticised is that the material SpaceX used was not suitable for the conditions, which makes it a potential and probable failure cause. SpaceX should have tested it before using it and/or used the right stuff in the first place.

It is history now, on to new failures adventures :-)

Edited by Green Baron
under stress not understressed

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I should point out that while there is no telemetry data for the entire flight, there is telemetry data for 1:46 (106 sec) to 2:30 (150 sec) including the 2:19 (139 sec) in which the anomaly appeared.
I was able to deduce from that telemetry that in the three seconds prior to explosion the average g-loading was 30.25 a (3.086 g). There may have been a bump event with average g-loading around 29.5 in the 134 to 135 second time period. It lasted for about a half of a second with total loading around 38 a. 2 passes produced the same result but there is no reference to verify it (other than really lousy altimetry).

In this case the accelerations do not appear to be exceptional. There could be really sharp bumps up to 50 but highly unlikely because around this time point (toward the end of the 2:14 time stamp) the borders are not sharp on either side, but gradual. Just to note that there are all sorts of vibration periods in the data, bumps that last than a 20th of a second are virtually invisible, about a quarter of a second can be parse out with many passes of the video, so if there are bumps they are more easily detected if the periods are longer, on the graph above there are common periods in the 6 to 8 second range.

So in this case it either was a structural defect or damage as Musk contends or an intrinsic material failure. There is one other possibility, that the attachment point itself had a defect (protrubance) that increase the depth of damage to the loop, in which case it would be an secondary material failure coupled with high g-loading and a primary material defect. Since the attachment point was not identified as a cause then its probably better that the upgrade the strut.

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A pic of Dragon II crew recovery test.

KSC-20170607-PH_SPX01_0001

seems about right doesn't it? XD

 

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2 minutes ago, NSEP said:

A pic of Dragon II crew recovery test.

KSC-20170607-PH_SPX01_0001

seems about right doesn't it? XD

 

I wanna to be the guy at SpaceX who has the job of shrink wrapping things to drop in the ocean.

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And to think we almost got a capsule able to land on any sufficiently flat and reinforced surface... But nooooo... old farts at NASA chickened out - and back in the drink we go. Just like 50 years ago. Yay! Circular progress!

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9 minutes ago, Scotius said:

And to think we almost got a capsule able to land on any sufficiently flat and reinforced surface... But nooooo... old farts at NASA chickened out - and back in the drink we go. Just like 50 years ago. Yay! Circular progress!

Well, they can’t just let them go and upstage Orion... or Boeing, for that matter.... <_<

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3 hours ago, IncongruousGoat said:

Okay, I could have sworn that, around the time the initial SpaceX report came out, I heard that the strut that failed was rated for 5,000 lbf, and failed at 1,000 lbf, which is a 5:1 safety factor. Does anyone have any hard figures for the rated load and actual load for that strut?


That's not how safety factors work.  If you have a strut that will experience 1,250 lbf and you want a 4:1 safety factor you design it to take 5,000 lbf before failure.  If it fails at 1,000 lbf that doesn't mean you had a 5:1 safety factor - it means you have a faulty part or a flawed design (or in rare cases, both).

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17 minutes ago, Scotius said:

And to think we almost got a capsule able to land on any sufficiently flat and reinforced surface... But nooooo... old farts at NASA chickened out - and back in the drink we go. Just like 50 years ago. Yay! Circular progress!

To be fair, chutes are just way, way safer.

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2 minutes ago, DerekL1963 said:


That's not how safety factors work.  If you have a strut that will experience 1,250 lbf and you want a 4:1 safety factor you design it to take 5,000 lbf before failure.  If it fails at 1,000 lbf that doesn't mean you had a 5:1 safety factor - it means you have a faulty part or a flawed design (or in rare cases, both).

Maybe I phrased my comment badly. What I mean is that SpaceX took a strut that was rated by its manufacturer for 5,000 lbf, and then subjected it to 1,000 lbf. It was at this load of 1,000 lbf that the strut broke during the launch of CRS-7.

Then again, the point is moot, since as several others have pointed out the situation is a lot more complicated when one takes the environment the strut was exposed to into account.

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Quote

SpaceX received a $290 million firm-fixed-price contract for three GPS 3 missions. ULA was awarded a $351 million firm-fixed-price deal for Air Force Space Command (AFSPC)-8 and AFSPC-12 satellites launches

Of course, old pals are getting the meatier cut. For less work. Who would've guessed?..

 

Also, yay, my first thousand rep! :D

Edited by sh1pman

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2 minutes ago, sh1pman said:

Of course, old pals are getting the meatier cut. For less work. Who would've guessed?..

 

To be fair to Air Force procurement, they're putting the less replaceable and likely more expensive payloads on the rocket with the better reliability record. There may also be other factors such as additional overhead dealing with military and probably-classified payloads, that would expand the cost of the SpaceX launches as well. Cost of the rocket isn't the only factor going into these decisions.

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2 hours ago, Scotius said:

And to think we almost got a capsule able to land on any sufficiently flat and reinforced surface... But nooooo... old farts at NASA chickened out - and back in the drink we go. Just like 50 years ago. Yay! Circular progress!

Dragon needs the ability for an emergency water landing in case of a launch abort. SpaceX wants to focus on flying the Dragon 2 before they want to focus on landing it propulsively- a reasonable decision given that will all of the other unknowns of building a spacecraft, there might not be anything to land if other things, (life support, heat shield) aren't worked out first. 

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2 hours ago, Scotius said:

And to think we almost got a capsule able to land on any sufficiently flat and reinforced surface... But nooooo... old farts at NASA chickened out - and back in the drink we go. Just like 50 years ago. Yay! Circular progress!

Well, they tried to retropropulsively land their booster over the sea before over a ship and finally over land.

Hopefully we'll see enough launch and enough trust to see it happens.

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2 hours ago, Confused Scientist said:

Dragon needs the ability for an emergency water landing in case of a launch abort. SpaceX wants to focus on flying the Dragon 2 before they want to focus on landing it propulsively- a reasonable decision given that will all of the other unknowns of building a spacecraft, there might not be anything to land if other things, (life support, heat shield) aren't worked out first. 

They're not doing propulsive landing on Dragon.

If they are gunning for 2019 for BFS grasshopper style testing, and possible orbital flights a year after that... no need for propulsive Dragon.

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4 hours ago, sh1pman said:

Of course, old pals are getting the meatier cut. For less work. Who would've guessed?..

 

Also, yay, my first thousand rep! :D

But SpaceX will make more profit.

These are just some of their contracts. Apparentlt they a committed to 100+ launches. http://www.spacex.com/missions

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19 hours ago, NSEP said:

A pic of Dragon II crew recovery test.

KSC-20170607-PH_SPX01_0001

seems about right doesn't it? XD

 

All I see is a Kerbal Pod... :wink:

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20 hours ago, NSEP said:

A pic of Dragon II crew recovery test.

KSC-20170607-PH_SPX01_0001

seems about right doesn't it? XD

 

why the opening above and below the hatch?
Yes this is an boilerplate who is just supposed to simulate an splashed down dragon 2 in the water, but again why the holes. 
 

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IS that where a cover blows off for chutes, and has an attachment point for a hoist?

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38 minutes ago, magnemoe said:

why the opening above and below the hatch?
Yes this is an boilerplate who is just supposed to simulate an splashed down dragon 2 in the water, but again why the holes. 
 

More than just boilerplate, if they went through the trouble of shrinkwrapping (waterproofing) it, I think. Possibly a future flight article. 

Yes, the upper hatch is chute storage, the lower one is where the RMS grapple fixture pops out on the old Dragon, not sure what it’ll do now. I’ve seen it modeled as an antenna bay, but likely not if they’re training to have a wet dude sitting in it. 

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2 hours ago, CatastrophicFailure said:

More than just boilerplate, if they went through the trouble of shrinkwrapping (waterproofing) it, I think. Possibly a future flight article. 

Yes, the upper hatch is chute storage, the lower one is where the RMS grapple fixture pops out on the old Dragon, not sure what it’ll do now. I’ve seen it modeled as an antenna bay, but likely not if they’re training to have a wet dude sitting in it. 

That's where Elon hides his secret stash of munchies.

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8 minutes ago, PB666 said:

That's where Elon hides his secret stash of munchies.

Mars bars or Snickers? :D

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