Author Topic: Inside the eight desperate weeks that saved SpaceX from ruin - Ars Technica  (Read 3386 times)

Online kevinof

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Offline IainMcClatchie

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Linked video is good, I hadn't seen the collision before.

For an article about "Inside the eight desperate weeks...", it sure doesn't say much about what happened during those 8 weeks.  What did they change?  What did they fix?  We are left to infer that they tweaked the shutdown timing vs the firing of the first and second stage separation.

Offline Star One

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I didnít know a lot of what was in that article as I didnít note Space X at the time.

Hereís a comment from Eric Berger under the article talking about BFR/BFS.

Quote
I believe that SpaceX has the resources and institutional knowledge to make the BFR booster. That seems like an issue of scale, and they already have the engine.

Where I have serious questions is in regard to the BFS second stage. This vehicle appears to be considerably more ambitious than even the space shuttle, which required an 11-year development effort by tens of thousands of people. Moreover, while SpaceX has some experience with the Dragon capsules, that is a relatively simple vehicle compared to the enormous BFS.

I certainly wish them well.

Offline nacnud

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Linked video is good, I hadn't seen the collision before.

For an article about "Inside the eight desperate weeks...", it sure doesn't say much about what happened during those 8 weeks.  What did they change?  What did they fix?  We are left to infer that they tweaked the shutdown timing vs the firing of the first and second stage separation.

IIRC they increased the dwell time between MECO and stage sep. Probably not much more than a single line of code. So just what you were thinking.

Online Kang54

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For more on this period, read Kimbal's blog, starting with his first visit to Kwaj. There's some awesome images, and lots of neat info.

Offline ChrisWilson68

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Hereís a comment from Eric Berger under the article talking about BFR/BFS.

Quote
I believe that SpaceX has the resources and institutional knowledge to make the BFR booster. That seems like an issue of scale, and they already have the engine.

Where I have serious questions is in regard to the BFS second stage. This vehicle appears to be considerably more ambitious than even the space shuttle, which required an 11-year development effort by tens of thousands of people. Moreover, while SpaceX has some experience with the Dragon capsules, that is a relatively simple vehicle compared to the enormous BFS.

I certainly wish them well.

I think Eric Berger is off-base here.  BFS is not more ambitious than the space shuttle.  It's a far simpler design than shuttle.  The basic architecture of being the second stage of a two-stage vehicle just gives it enormous advantages.  Shuttle was saddled with a poor architecture that meant it was pushing the edge of what was possible with little margin to spare.  BFS not only has an easier job to do than shuttle, it gets the advantage of forty years of technological improvement.


Offline Star One

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Hereís a comment from Eric Berger under the article talking about BFR/BFS.

Quote
I believe that SpaceX has the resources and institutional knowledge to make the BFR booster. That seems like an issue of scale, and they already have the engine.

Where I have serious questions is in regard to the BFS second stage. This vehicle appears to be considerably more ambitious than even the space shuttle, which required an 11-year development effort by tens of thousands of people. Moreover, while SpaceX has some experience with the Dragon capsules, that is a relatively simple vehicle compared to the enormous BFS.

I certainly wish them well.

I think Eric Berger is off-base here.  BFS is not more ambitious than the space shuttle.  It's a far simpler design than shuttle.  The basic architecture of being the second stage of a two-stage vehicle just gives it enormous advantages.  Shuttle was saddled with a poor architecture that meant it was pushing the edge of what was possible with little margin to spare.  BFS not only has an easier job to do than shuttle, it gets the advantage of forty years of technological improvement.

Isnít the quote that itís easier to do something the second time?

Online kevinof

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I think both are true. We know a lot more about what makes a good design  and re-usability, cost etc and we also have one company (person) deciding the design requirements with BFR. That makes it far easier to get something out the door that will meet the requirements originally intended.

Hereís a comment from Eric Berger under the article talking about BFR/BFS.

Quote
I believe that SpaceX has the resources and institutional knowledge to make the BFR booster. That seems like an issue of scale, and they already have the engine.

Where I have serious questions is in regard to the BFS second stage. This vehicle appears to be considerably more ambitious than even the space shuttle, which required an 11-year development effort by tens of thousands of people. Moreover, while SpaceX has some experience with the Dragon capsules, that is a relatively simple vehicle compared to the enormous BFS.

I certainly wish them well.

I think Eric Berger is off-base here.  BFS is not more ambitious than the space shuttle.  It's a far simpler design than shuttle.  The basic architecture of being the second stage of a two-stage vehicle just gives it enormous advantages.  Shuttle was saddled with a poor architecture that meant it was pushing the edge of what was possible with little margin to spare.  BFS not only has an easier job to do than shuttle, it gets the advantage of forty years of technological improvement.

Isnít the quote that itís easier to do something the second time?

Offline deruch

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Linked video is good, I hadn't seen the collision before.

For an article about "Inside the eight desperate weeks...", it sure doesn't say much about what happened during those 8 weeks.  What did they change?  What did they fix?  We are left to infer that they tweaked the shutdown timing vs the firing of the first and second stage separation.

Yes, that's exactly what they tweaked.  Elon and Gwynne have both said that all they had to do was add a few extra seconds of delay.  The third failure was the first flight with the new regeneratively cooled Merlin 1C engine instead of the ablatively cooled Merlin 1A.  This change resulted in a change in shutdown timing/behavior of the engines, as some small amount of the propellant remained flowing though the cooling channels and into the combustion chamber where it produced a longer tail-off in thrust.  While SpaceX certainly knew about this behavior from ground testing the engines, they either failed to properly account for this change in their flight software or, due to the flight operation taking place in the thinner atmosphere at altitude, the effect was even more pronounced than they had expected.  This meant that they hadn't allowed for a long enough pause between MECO and stage separation.  So when the stages separated, the M1C on the first stage was still producing a small amount of thrust.  As a result, the first stage caught up to and collided with the second stage before the Kestrel engine (pressure-fed vacuum) on the upper stage could light.  The only change needed to prevent this was that there should be a few more seconds of delay between MECO and stage sep.  Given the very short timing between the third launch and the fourth, there really wasn't much else they could have changed without adding more delay. 

SpaceX's second flight--also a failure--had already shown that they could get through upper stage ignition and fairing separation.  So, the only things left to demonstrate were the sustained control and trajectory maintenance of the upper stage all the way through the Kestrel's burn, the relight to achieve proper orbit shape, and payload separation.  All of which were accomplished on the 4th launch (success!).


Oh, Iain- I just realized that your comment was likely more a criticism of what's left out of the article, given its title, as opposed to asking for information/clarification.  Oh well, I could just delete the above, but I'll leave it in case anyone not familiar with the events reads the thread.
« Last Edit: 09/22/2018 09:58 AM by deruch »
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline Star One

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I assume the above is why all launchers of the type do MECO and then hold onto the first stage a little bit before separating it.

Has SpaceX ever released a proper video of Flight 1 failing? With their 10 year celebration of success, and their tendency to embrace their failures, you'd think if a video exists, they'd share it!

Online strax

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« Last Edit: Today at 06:43 AM by strax »

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