Jump to content

SpaceX Discussion Thread


Recommended Posts

Just now, JIMMY_the_DOG said:

Oh... now the blocks are snapping together....

didnt they turn down the thrust at t-1 sec for a high thrust? so they problably turned down the thrust and that's your consequence.

Keep in mind that this is a guess.

The initial abort was caused by an overly conservative high thrust limit. There wasn't anything wrong with the amount of thrust the engines were producing, the sensor was simply erroneously reporting a problem.

 

Link to post
Share on other sites

I guess that they have some severe issues with Raptors they are not willing to publish. Now engines had clearly different colored flames in ascent. I suspect it was not intentional or good sign (or could they make some strange tests, for example mixing ratios). They seem to do Raptor testing at the same time they test SNs. It is quite kerbal way to test rocket engines with flying prototypes. Fortunately radio controlled command pods was before full staged combustion in human's tech tree. Test piloting those ships would otherwise be a little bit too dangerous work.

Link to post
Share on other sites
1 minute ago, Hannu2 said:

They seem to do Raptor testing at the same time they test SNs.

Every Raptor is tested at their facility in McGregor, Texas before it is flown. They don't just build an engine and say 'yeah, seems good, send it'.

Link to post
Share on other sites
8 minutes ago, Hannu2 said:

They seem to do Raptor testing at the same time they test SNs. It is quite kerbal way to test rocket engines with flying prototypes.

Sounds like fun!

6 minutes ago, RealKerbal3x said:

Every Raptor is tested at their facility in McGregor, Texas before it is flown. They don't just build an engine and say 'yeah, seems good, send it'.

Still, there's some stuff that can be different when it's attached to the vehicle or in flight. I wouldn't be surprised if they are at least tweaking parameters to find the right balance for each Starship test.

Link to post
Share on other sites
7 minutes ago, Hannu2 said:

I guess that they have some severe issues with Raptors they are not willing to publish. Now engines had clearly different colored flames in ascent. I suspect it was not intentional or good sign (or could they make some strange tests, for example mixing ratios). They seem to do Raptor testing at the same time they test SNs.

All three raptors successfully relit for the flip, so I really don’t think they were having any serious problems. Differences in color on ascent were likely related to mixture ratios and deep throttling.

The only “testing” they are doing during flight is figuring out how Raptor performs with the force and pressure transients of actual flight. 

15 minutes ago, RealKerbal3x said:

The initial abort was caused by an overly conservative high thrust limit. There wasn't anything wrong with the amount of thrust the engines were producing, the sensor was simply erroneously reporting a problem.

I understood Elon’s tweet a little differently: there was something a little wrong with the amount of thrust being produced, but it wasn’t wrong enough to be a reason not to fly.

Link to post
Share on other sites
Just now, sevenperforce said:

I understood Elon’s tweet a little differently: there was something a little wrong with the amount of thrust being produced, but it wasn’t wrong enough to be a reason not to fly.

Hmm, this is the problem: Elon's tweets are always just ambiguous enough to cause confusion :sticktongue:

Link to post
Share on other sites
3 minutes ago, tater said:

 

That landing sequence is not quite what I would expect - there is a lot of lateral movement for something so heavy.  I would have expected every frame to be moved up one spot with the final frame before landing being directly above the landed photo. 

 

Also - am I wrong to assume SX can recycle all the steel recovered from the past SNs? 

Link to post
Share on other sites
9 minutes ago, RealKerbal3x said:

Every Raptor is tested at their facility in McGregor, Texas before it is flown. They don't just build an engine and say 'yeah, seems good, send it'.

Of course they are tested as well as they can. But it seem there have been problems with underperforming Raptors in SN9 and SN10. Something may be going on and they have to find a solution. I hope I am wrong and they had some sporadic problems easy to fix, of course.

That strange flight profile may also be engine testing. They ascent very slowly and burn engines several minutes. At apoapsis they almost hover a minute or two with very small velocity. If it was just aerodynamic test they could ascend probably in less than a minute. I do not see other reasons for such profile than get important test minutes for engines at (almost) realistic flight conditions.

Link to post
Share on other sites
Just now, Hannu2 said:

Of course they are tested as well as they can. But it seem there have been problems with underperforming Raptors in SN9 and SN10. Something may be going on and they have to find a solution. I hope I am wrong and they had some sporadic problems easy to fix, of course.

Raptor is a comparatively immature engine right now, and a complex one at that. It's a test program so it's a good thing that they're finding issues now and not when they're flying commercial payloads or, worse, crew.

2 minutes ago, Hannu2 said:

That strange flight profile may also be engine testing. They ascent very slowly and burn engines several minutes. At apoapsis they almost hover a minute or two with very small velocity. If it was just aerodynamic test they could ascend probably in less than a minute. I do not see other reasons for such profile than get important test minutes for engines at (almost) realistic flight conditions.

 That's probably a part of it, but it also looks like they don't want to break the sound barrier during ascent, or put too much stress on the airframe. 

Link to post
Share on other sites
2 minutes ago, JoeSchmuckatelli said:

That landing sequence is not quite what I would expect - there is a lot of lateral movement for something so heavy.  I would have expected every frame to be moved up one spot with the final frame before landing being directly above the landed photo. 

 

Also - am I wrong to assume SX can recycle all the steel recovered from the past SNs? 

Scrap steel is not suitable for building of high strength structures anymore, but it is very pure stainless steel (compared to many other scrapped machines which have significant part of mass from other materials) and very effectively recycled to new steel in steel factory.

Link to post
Share on other sites

What are we thinking in terms of actual mechanism?

My best guess is that when the legs failed to lock out properly, it came down hard on the engine bells and damaged the thrust puck. The impact probably ruptured the methane downcomer, allowing the remaining liquid methane from the methane header tank to mix with residuals in the main oxygen tank. The oxygen tank was basically a fuel-air bomb. Of course, no big deal...until the fire outside the skirt made its way underneath and up to the thrust puck. And then, kablooey.

Link to post
Share on other sites
Just now, SOXBLOX said:

Wait, so, it landed? And then exploded? I just got here...

Yeah, an engine underperformed, so it landed in one piece, albeit hard. It seemed like the damage caused the propellants to ignite about 8 minutes later and boom.

Link to post
Share on other sites
10 minutes ago, JoeSchmuckatelli said:

What was crazy about the explosion was that it lifted itself a full body length (or more) into the air. 

Well it basically was another rocket engine. The ruptured thrust puck probably acted like a nozzle throat.

4 minutes ago, RealKerbal3x said:

Yeah, an engine underperformed, so it landed in one piece, albeit hard. It seemed like the damage caused the propellants to ignite about 8 minutes later and boom.

Do we have word of Elon that there was landing engine underperformance? It looked like a landing leg issue to me. 

Link to post
Share on other sites
Just now, sevenperforce said:

Do we have word of Elon that there was landing engine underperformance? It looked like a landing leg issue to me. 

I don't think there was any official confirmation that the engine underperformed but it sure looked like it. The landing legs failed to deploy properly but that doesn't account for how fast the touchdown looked.

Link to post
Share on other sites
17 minutes ago, sevenperforce said:

What are we thinking in terms of actual mechanism?

My best guess is that when the legs failed to lock out properly, it came down hard on the engine bells and damaged the thrust puck. The impact probably ruptured the methane downcomer, allowing the remaining liquid methane from the methane header tank to mix with residuals in the main oxygen tank. The oxygen tank was basically a fuel-air bomb. Of course, no big deal...until the fire outside the skirt made its way underneath and up to the thrust puck. And then, kablooey.

Yeah, and possibly more complex than that. Landing on the lend nominally engages the crush cores as needed, and some asymmetry in landing is likely designed in, they might have even simulated some legs undeployed. The dangling legs, however were not just undeployed, but possibly hanging down lower at the moment of impact, which could result in tearing the skirt, or even breaking them and throwing them up into the engines.

The bells are pretty close to the skirt edge, though (height off the ground distance), right?

Link to post
Share on other sites
34 minutes ago, RealKerbal3x said:

I don't think there was any official confirmation that the engine underperformed but it sure looked like it. The landing legs failed to deploy properly but that doesn't account for how fast the touchdown looked.

I guess we could compare the descent rate between SN10 and SN5/6 to get a feel for it. 

I don't think they have any "change your thrust rate by X if the landing legs don't fully deploy" programming. So if it shut down the engine as if the landing legs had deployed, that alone would have dropped it a meter or so (however long the legs are).

36 minutes ago, tater said:

Yeah, and possibly more complex than that. Landing on the lend nominally engages the crush cores as needed, and some asymmetry in landing is likely designed in, they might have even simulated some legs undeployed. The dangling legs, however were not just undeployed, but possibly hanging down lower at the moment of impact, which could result in tearing the skirt, or even breaking them and throwing them up into the engines.

The bells are pretty close to the skirt edge, though (height off the ground distance), right?

Yes, I believe they are very close -- probably only 20 cm or so. 

I remember looking at the closeup on the SpaceX feed and thinking it was odd how close the flaperons seemed to the ground:

2016074.jpg

For any fans of Doctor Who we have this lovely comment by John Insprucker:

GERONIMO!

We need better legs, now. But it does look like better legs may be in the works. From the DearMoon update:

Definitely a different design than before. How large are these exactly? It looks like they have reduced to just four legs, mounted externally. But they are REALLY wide now.

 

1 hour ago, tater said:

The bells are pretty close to the skirt edge, though (height off the ground distance), right?

Wreckage photos show that the Raptors are at least not completely crumpled.

Spoiler

index.php?action=dlattach;topic=53212.0;

 

Link to post
Share on other sites
15 minutes ago, StrandedonEarth said:

 

That wins Post of the Day! 

1 hour ago, sevenperforce said:

Well it basically was another rocket engine. The ruptured thrust puck probably acted like a nozzle throat

Or like the recoil on a cannon.  

 

I find the skirt acting like an impromptu rocket bell somewhat likely, but don't know enough about whether the thrust puck could have done it.  You are thinking that combustion happened higher in the stack?  

Link to post
Share on other sites
5 minutes ago, JoeSchmuckatelli said:

Or like the recoil on a cannon.  

I find the skirt acting like an impromptu rocket bell somewhat likely, but don't know enough about whether the thrust puck could have done it.  You are thinking that combustion happened higher in the stack?  

I'm not saying it was properly choked or anything. But yes, if you look at slow-motion captures it definitely appears the bulk of the explosion happened in the LOX tank.

 

Link to post
Share on other sites

Maybe those are large flaps that fold outwards (hinge on the skirt). Those large, flat areas should be easier to shield from reentry than more prominent/protruding thinner legs like on the old renders.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...