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SpaceX Dragon to the ISS

Posted by: Lourens - Tue Apr 17, 2012 10:34 am
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SpaceX Dragon to the ISS 

How much of the upcoming SpaceX Dragon mission to the ISS will be successful?
Poll ended at Fri May 18, 2012 10:34 am
Launch failure, F9/Dragon never reaches orbit 0%  0%  [ 0 ]
Launch successful, some issue during checkout prevents Dragon from attempting to berth with ISS 0%  0%  [ 0 ]
Dragon attempts to berth with ISS but fails 6%  6%  [ 1 ]
Dragon successfully berths with ISS, but has to undock early due to some unforeseen problem 0%  0%  [ 0 ]
Dragon successfully completes ISS visit, but fails to return to Earth in one piece or is not recovered successfully 6%  6%  [ 1 ]
Mission is a complete success 56%  56%  [ 9 ]
After reaching orbit successfully, Dragon broadcasts the cryptic message "Screw you guys, I'm outta here" and autonomously fires its Draco thrusters to enter a Mars transfer orbit, never to be heard of again until humanity reaches Mars in person in 2042 31%  31%  [ 5 ]
Total votes : 16

SpaceX Dragon to the ISS 
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Post Re: SpaceX Dragon to the ISS   Posted on: Sat May 19, 2012 11:03 pm
Quote:
“Today’s launch was aborted when the flight computer detected slightly high pressure in the engine 5 combustion chamber. We have discovered root cause and repairs are underway.

“During rigorous inspections of the engine, SpaceX engineers discovered a faulty check valve on the Merlin engine. We are now in the process of replacing the failed valve. Those repairs should be complete tonight. We will continue to review data on Sunday. If things look good, we will be ready to attempt to launch on Tuesday, May 22nd at 3:44 AM Eastern.”

http://www.parabolicarc.com/2012/05/19/ ... n-tuesday/

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Post Re: SpaceX Dragon to the ISS   Posted on: Sat May 19, 2012 11:14 pm
That was quick! Swap out the part, and ready to fly again!

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Post Re: SpaceX Dragon to the ISS   Posted on: Sun May 20, 2012 7:37 am
Yeah. They've shown quick turnaround like this before, with the cracked nozzle. They found the crack, decided that the engine would work well enough with a couple of inches less nozzle, grabbed an angle grinder and cut off the cracked bit. And then successfully launched the rocket. No management meetings, lengthy discussions or piles of paperwork, but just a couple engineers who know their stuff figuring out the simplest solution and applying it. And the vehicle has enough margin that they can do these things too. So now they just swap the part, test that it works, and then launch. Kind of like what an aeroplane mechanic at an airline would do I imagine. Very promising.

Of course, to achieve reusability with quick turnaround they'll have to make it so that these things only happen very rarely, but then they've just started production. No doubt it will improve once the production line gets settled down and they've built a couple hundred Merlins.

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Post Re: SpaceX Dragon to the ISS   Posted on: Sun May 20, 2012 1:12 pm
If the Livestream picture at SpaceflightNow is for real, it looks like they haven't even rolled back to the hangar.

So, would they do another test firing in this situation, before the launch window? Is it surprising that the original test firing didn't discover this issue?

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Post Re: SpaceX Dragon to the ISS   Posted on: Mon May 21, 2012 9:13 am
I doubt they will do another test firing. I think the test firing at the cape is done to see if the complete, integrated vehicle works as intended, which has already been shown. If engine problems continue, than they can (and I say will) catch them during the next hold down before the launch.

Personally I don't find it surprising that this issue has not been discovered during the static test fire. I was wondering the same thing at first, but if you think about it, there is a reason why it is so hard to make rocket engines reusable. In my opinion, the valve simply failed after the static fire, possibly in the middle of the ignition process. Maybe it had been "weakened" in some way and could not handle another run, who knows.
In engineering there is this saying, that you do not learn anything from a successful test. You have to test something until it fails to learn how much it can handle.

Contrary to what some naysayers believe, this failure is not a reason to worry. The way SpaceX does operations allowed them to safely detect this problem. Now they can easily fix the problem (just swap the valve) and try again. In addition they can use the time until the next launch (the one after COTS2+) to figure out WHY the valve has failed and how to prevent this from happening again.

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Post Re: SpaceX Dragon to the ISS   Posted on: Mon May 21, 2012 1:48 pm
Exactly. And I read somewhere that their simulations indicated that the thing would have launched successfully even with the broken valve. That makes sense, since they do have an engine-out capability. But since they also have a hold-down, they didn't need to use it this time. It really does feel as if SpaceX are cheating somehow. Fast, cheap and good. That's not supposed to be possible in engineering :).

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Post Re: SpaceX Dragon to the ISS   Posted on: Mon May 21, 2012 7:03 pm
Thanks Marcus and Laurens, that was illuminating for me.

I don't think this abort should be a source of embarassment for SpaceX, but what about that early tweet by Elon Musk that they would simply increase the pressure limit and try again on Tuesday. Gwynne Shotwell dismissed it as being based on "early data", but it seems to me that he was suffering from what airline pilots call "get-there-itis". Has his personal credibility taken a dent, or am I being unfair?

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Post Re: SpaceX Dragon to the ISS   Posted on: Tue May 22, 2012 6:47 am
xiphius wrote:
Thanks Marcus and Laurens, that was illuminating for me.

I don't think this abort should be a source of embarassment for SpaceX, but what about that early tweet by Elon Musk that they would simply increase the pressure limit and try again on Tuesday. Gwynne Shotwell dismissed it as being based on "early data", but it seems to me that he was suffering from what airline pilots call "get-there-itis". Has his personal credibility taken a dent, or am I being unfair?


I think it's not the case here. SpaceX has previously had to abort launch due to very tight safety envelopes. If the pressure spike they observed was outside their limits, but well within construction limits of the engine, one of viable solutions would be expand safety limits. As more data came in, it became obivious that the spike was due to mechanical failure instead, and can not be resolved by software trocks.


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Post Re: SpaceX Dragon to the ISS   Posted on: Tue May 22, 2012 8:03 am
All looks good thus far! :) :)

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Post Re: SpaceX Dragon to the ISS   Posted on: Tue May 22, 2012 8:11 am
This was sooo exciting! I can't feel my thumbs any more :p
(hint: in German speaking countries we hold/press our thumbs to wish for luck instead of crossing fingers ;))

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Post Re: SpaceX Dragon to the ISS   Posted on: Tue May 22, 2012 8:22 am
Haha, do you push your thumb into your first finger? Or wrap your knuckles around them?

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Post Re: SpaceX Dragon to the ISS   Posted on: Tue May 22, 2012 8:32 am
we wrap the other four fingers around the thumb, so basically you make a fist with your thumb inside. Something you never, ever want to do in a fist fight, lol! :D

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Post Re: SpaceX Dragon to the ISS   Posted on: Tue May 22, 2012 10:56 am
here is a really good (technical) article on the pad abort on Saturday:
http://www.wired.com/autopia/2012/05/sp ... lve-abort/

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Post Re: SpaceX Dragon to the ISS   Posted on: Tue May 22, 2012 11:22 am
I wonder if we will be able to see it approach the station as the ISS crosses the night sky?

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Post Success!   Posted on: Tue May 22, 2012 2:14 pm
Just so everyone knows, Dragon made it successfully to orbit. More at the press conference, goto spacex.com

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