Author Topic: Inside the eight desperate weeks that saved SpaceX from ruin - Ars Technica  (Read 8174 times)

Offline 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 didn’t know a lot of what was in that article as I didn’t note Space X at the time.

Here’s 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.

Offline 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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Here’s 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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Here’s 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.

Isn’t the quote that it’s easier to do something the second time?

Offline 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.

Here’s 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.

Isn’t the quote that it’s 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!

Offline strax

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« Last Edit: 10/20/2018 06:43 am by strax »

Offline CameronD

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Wow!  It's not until you look back at footage like this that you realise inflight video really has come a long way in a few short years.  :o
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline john smith 19

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I think Eric Berger is off-base here.  BFS is not more ambitious than the space shuttle. 
What an interesting definition of "easier" you use.  :(

A few things BFS is designed to do that Shuttle wasn't would include.

Spend 180+ days (both ways) in deep space (Shuttle managed 14 in LEO)

Lifting entry to Mars.

Provide life support for up to 100 people for a minimum of 32 months (26 on Mars, 3+ either way). Shuttle did 7 for 14 days inside Earths Magnetosphere.

Vertical landing on a patch of (hopefully) bare rock.

Precision landing to a target with no ground based navigation aids (on Mars).

Takeoff from a patch of bare rock

RE-entry into earths atmosphere after 180+ days of exposure to deep space and 26 Months of Mars surface conditions.

Quote from: ChrisWilson68
It's a far simpler design than shuttle. 
When you actually start thinking about what it has to do you realize it needs basically the same systems as Shuttle, but for
a) A lot longer
and
b) For a lot more people.
Quote from: ChrisWilson68
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.
Note that was driven by the budget. From the book "The Shuttle Decision" this started with the NASA HSF people saying "We can only spend $1Bn/year, and we can't role over any unspent money this year for big ticket items next year" IOW 1 full stage and 1 new engine design only. AFAIK only the Orbiter + RATO packs + Drop tank architecture (with a possible shot at a pure Bi- or Tri-amese) could do it for the money.

And ORFFSC is not a simpler cycle than fuel rich SC. Not using LH2 might ease the problem but a tank head start is tricky (more so in free fall). Then there's how they do O2 resistance. Good blade alloy or barrier coating?
IIRC the Russians used a blade coating, but that's not an issue with expendable engines.
Not such a good idea with reusable engines. NASA did the same with a Gold coating when they discovered their chosen alloy didn't handle the combination of hot GH2 mixed with superheated steam very well. I expect SX will do better if they can.

In terms of systems AFAIK the only area BFS is simpler is using PV arrays rather than fuel cells. Not surprising given Musks aversion to them. In principle simpler, but it depends on the deployment and stowing mechanism.

OTOH if you're talking about structure you'd be on safer ground.
I estimate Shuttle had 62 tanks, all with sensors, actuators and most with heaters. Eliminating hypergols and fuel cells and using common tanks radically lowers the tank count, while AFAIK the structure will not be vented, so that's another 18 holes, and their associated motors it won't need. Since what is not installed does not have to be serviced, inspected or maintained that all helps a bit. But you're still going to need an RCS for 3 axis, 6DOF translation and rotation and an OMS for orbital injection (unless you can run Raptor at very low thrust levels).

Quote from: ChrisWilson68
BFS not only has an easier job to do than shuttle, it gets the advantage of forty years of technological improvement.
Since it's more like 50 than 40 years less than 1/2 of that statement is accurate.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline eeergo


Try this:


Also (check out frames at 1:17-1:20):
-DaviD-

Offline envy887

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Quote from: ChrisWilson68
It's a far simpler design than shuttle. 
When you actually start thinking about what it has to do you realize it needs basically the same systems as Shuttle, but for
a) A lot longer
and
b) For a lot more people.

Same systems requirements does not mean it can't be simpler. Just as one example, solar+batteries is far simpler than fuel cells with cryo storage + hydrazine APUs.

As for "more ambitious", yes, the overall goal for BFR is more ambitious. Interplanetary spaceflight is always going to be more ambitious than LEO and back. But SpaceX has a much better plan for actually getting there: start with a FAR less ambitious goal, show progress, then iterate. Atmospheric hops > Suborbital hops > uncrewed orbital flight to LEO > Uncrewed BLEO > Crewed LEO > Crewed BLEO. The Shuttle program never lit the candle until they had crew on top and were committed to going to orbit.

Offline hkultala

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BFS not only has an easier job to do than shuttle, it gets the advantage of forty years of technological improvement.

Easier job?

BFS will be able to do EVERYTHING shuttle ever did, but also:

1) It's going to be able land on unprepared surface
2) It's capable of reaching much higher orbits than shuttle
3) It's capable of lifting much higher payload than shuttle
4) It's capable of travelling in outer space to different planets
5) It has many times longer mission endurance
6) It's capable of being refueled in space
7) It will need to be able to be reused with minimal maintainance between the flights.
8) It will be able to be FULLY reused, not just partially

Online meekGee

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BFS is definitely unprecedented in its mission complexity, but the comparisons to Shuttle are misdirected.  SpaceX is in a much better place to undertake BFS, exactly because it is such a smaller organization than the one that undertook Shuttle.

SpaceX has already achieved unprecedented development with a small fraction of the manpower required to develop comparable, but expendable, rocket systems.

I easily predict SpaceX will get BFS done faster, for less, and using less people than it took to get STS done.
ABCD - Always Be Counting Down

Offline su27k

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I think Eric Berger is off-base here.  BFS is not more ambitious than the space shuttle. 
What an interesting definition of "easier" you use.  :(

A few things BFS is designed to do that Shuttle wasn't would include.

BFR has several versions, ChrisWilson68's comment is correct if you limit the discussion to the initial BFS, i.e. the satellite launcher/tanker. All your concerns regarding longer/more people goes away if we are talking about the satellite launcher/tanker version, and it is indeed less ambitious than the space shuttle since: a. it doesn't carry people; b. it is not trying to be an airplane/glider with significant crossrange.

Offline Chris Bergin

Take your BFR comments to a BFR thread please.
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