SpaceX News

[Skipjack]

What I found interesting was the dragon cargo vessel did not have self preservation built into the software model. I would have taken this for granted.

True, but then it is quite possible that they were simply pushing this off to Dragon v2, expecting it to be available sooner than it ended up being.

[paperburn1]

What I found interesting was the dragon cargo vessel did not have self preservation built into the software model. I would have taken this for granted.

True, but then it is quite possible that they were simply pushing this off to Dragon v2, expecting it to be available sooner than it ended up being.

Dragon v2 does have this feature already build in. (assuming v2 is crew module)

[ladajo]

I've run into inconel parts on spacecraft before. It can achieve 300 ksi 0.02% yield strength ... remarkable stuff. It also is ridiculously difficult to work with ... give this to a machinist, tell them how you want it machined, come back a few hours later and they'll chase you out of the shop with a large wrench. They hate it worse than they hate titanium.

Ceramic inserts are making life more easy in the last years. Still not something you want an inexperienced Machinist to handle, or he will burn through your monthly stock of costly tools in few hours....

I have worked with Iconel as well. It is soft, interesting choice. As I recall, low on hardness, high on strength. Very corrosion resistant and a really broad temp range as well.

[Tom Ligon]

Regarding the softness of inconel, cast inconel typically is super soft, but that's part of its sneaky side. When I worked at Artech Corp, we got in some pieces of cast inconel propeller to test. The shop guys had never worked with it, but whacked off a chunk and put it on the Rockwell hardness tester. The indenter buried itself deep in the sample, and they declared this a cinch to machine. Then they sawed out a piece to put on the lathe. The tool bit in, and the material promptly work hardened to some enormous value, and stopped the lathe cold. The chasing with the wrench scene soon followed.

Experience machining steel does not prepare you for it.

But as for why this particular SpaceX strut failed, this blurb answers my question:

"The strut was holding down a high-pressure helium bottle in the liquid oxygen tank. If the strut snapped as engineers believe, according to Musk, the bottle would have shot to the top of the tank at high speed, dooming the rocket and its Dragon supply ship for the International Space Station." http://www.inc.com/associated-press/spa ... apped.html

Ah, it was swimming in LOX! Among the other things I've tested is fracture toughness of steels at low temperatures. LOX is not as cold as LN2, but it is cold enough ... steels generally and some steel alloys particularly have a thickness-dependent ductile-to-brittle transition temperature. This is likely a thin part, so the transition is lower than it would be for thick parts, but LOX is not just cold, it is, obviously, a pretty potent oxidizing agent.

Inconel is usually chosen for high temperature applications and corrosion resistance, and looking at the properties of one particular version, it is not clear to me that it is appropriate for a LOX bath, but I'll trust that the matter will have the full attention of SpaceX. The link below shows that inconel can show a fairly high temperature ductile to brittle transition, although the softer heat treatments may avoid this.

http://www.specialmetals.com/documents/ ... 0MA956.pdf

[ladajo]

Inconel can be used readily at cryogenic temps. It is a very versatile metal.
We would put dings in it all the time dropping tools or bumping it with various dragging stuff around evolutions, but never worried about structural integrity. It is really strong.
Mostly used as piping in the plant, but also as some key structural components. Not cheap either.

[Maui]

Is it prohibitively difficult to design the stage so that any one strut is not a single-point failure? I'm surprised the design isn't such that the neighboring struts aren't able to compensate for the added load...

[kunkmiester]

Iconel I'd on the list of exotics. An experienced machinist would know to look up info on machining an exotic he hasn't worked with before. Work hardening isn't unheard of and anything with an odd name should ring bells.

I'm qualified for several jobs SpaceX has open but I'd have to get out of a commercial lease to move to Florida. Also not sure if they'd make a machinist on the floor work the crazy 80 hour weeks I've heard of.

[Tom Ligon]

Inconel can be used readily at cryogenic temps. It is a very versatile metal.
We would put dings in it all the time dropping tools or bumping it with various dragging stuff around evolutions, but never worried about structural integrity. It is really strong.
Mostly used as piping in the plant, but also as some key structural components. Not cheap either.

These large chunks of marine propeller were, of course, highly irregular shapes for machining. The shop cut them down on a poor little Do-All bandsaw that was not really up to the task, and the blade wandered about an inch. So the basic blocks needed to run thru a shaper before doing anything else. The result was piles and piles of inconel chips. We'd never saved chips before, but the shop guys knew this stuff was expensive, and so they meticulously swept them all up and saved them in a bin. They had plans for a beer bash funded by the chips.

Then the customer (whom Ladajo works for) found out they'd saved them, and asked for them back.

Yeah, when it is expensive enough to save the chips, its expensive.

As for looking up the properties and machining procedures, I suspect our shop guys did what most shops do: run into trouble on the first attempt and THEN look it up. The problem is not messing up the first try, it is estimating the job as if it was going to be A36 construction steel. My rule of thumb for titanium and inconel is that it costs about 3x as much to work it. In this case, after they nearly wore out the DoAll bandsaw with some poor schmoe leaning on the piece 8 hours a day for a week, they caved in and bought the Marvel bandsaw, with a power feed, that cut reliably to 0.020" tolerances at about 10x the speed of the DoAll. And if they'd done that up front, the labor savings, both on machinist time and reducing the amount of shaper work afterwards, would have paid for the saw.

In this particular case, SpaceX may replace $20 struts with $500 struts, but if done up front would have saved, um, the cost of the rocket, the payload, the good will of the customer, a hefty rise in insurance premiums, and maybe a year of investigation and fixing the problem. $100M is probably a gross underestimate.

[D Tibbets]

A site that shows some probable details of the mishap, including analysis...

http://gizmodo.com/the-spacex-launch-ex ... 1719410274

Also, if they are going to use iconel, they already have the printing technology for iconel rocket engines for Dragon 2.
That still leaves the connection, assembly issues...

Dan Tibbets

[krenshala]

A site that shows some probable details of the mishap, including analysis...

http://gizmodo.com/the-spacex-launch-ex ... 1719410274

I find it quite humorous how often Kerbal Space Program is coming up to demonstrate and/or explain spacecraft related things lately. It definitely makes it easier to show someone with reasonable accuracy how things behave (generally) in space, even if it isn't an n-body simulation.

[AcesHigh]

I already said that KSP is the biggest contribution to Space exploration that came out of Brazil and Mexico...

[ladajo]

As I was reviewing some SpaceX stuff, a horrible thought occurred to me; I am now beginning to wonder if the some of the stunning silence out of ELon Muck & Co. about the strut failure has to do with the consideration that they will need to build new boosters for the upcoming launch manifest events.
How can you test struts that are already installed in built boosters?
Talk about a major hit to the bottom line. Makes me think that they are thinking to go after the strut supplier to recover damages, and thus the crickets.

Space is hard.

[mvanwink5]

Unless they can determine which struts are which and which belong to a failed batch of struts. It is conceivable IF each part has a serial number.

A lot of IF though.

[paperburn1]

From my limited interpretation of the news , it sounds like it was not a bad batch problem but found randomly though the series. That does imply throw everything built out and start over. And that's got to hurt as they were just stepping into large scale manufacturing.

[mvanwink5]

That still does not rule out bad batches as SpaceX may not be the only one receiving this material. It might also have been a supplier order fill error, etc. Material is not made one strut at a time, just saying... and not trying to be argumentative.