totm nov 2023 SpaceX Discussion Thread

[darthgently]

sometimes Thrust Vexing Chaos

[mikegarrison]

48 minutes ago, Minmus Taster said:

Hate to be that guy but what exactly is "TVC"?

It's some sort of cable TV home shopping channel, I think.

 

[RCgothic]

4 hours ago, Minmus Taster said:

Hate to be that guy but what exactly is "TVC"?

It's Thrust Vector Control as @SunlitZelkovasuggested.

[Exoscientist]

On 4/30/2023 at 12:28 AM, Brotoro said:

I think they need a thrust stand where they can do full-thrust, long-duration test firings of Super Heavy stages to properly learn how to startup all those engines and see that they'll work properly for extended periods. 

Well put.

  Bob Clark

[tater]

A 33 engine test stand is not a thing.

Static fires? Sure. Maybe working up to a nominal 2-4 second static fire? Absolutely. They can't do a stand for long duration 33 engine burns a number of reasons.

1. It would have to be at Boca Chica—because that's where the rockets are.

2. The risk is pretty much the same as launch risk, except no launch.

3. Such a stand is horizontal? if it's vertical it's a launchpad—except it has to be far tougher to sustain a 2.5-3 minute burn (vs 2-3 seconds).

4. The critters nearby have to sustain not the seconds of launch, but minutes?

5. Involves what is effectively a launch level closure for not a launch.

Just not gonna happen.

Edited May 2, 2023 by tater

[mikegarrison]

This is why engineers get paid the big bucks.

OK, the medium bucks. The dentists get paid the big bucks. But you get the point.

[Shpaget]

3 hours ago, mikegarrison said:

This is why engineers get paid the big bucks.

OK, the medium bucks. The dentists get paid the big bucks. But you get the point.

I thought it was the deer hunters.

[kerbiloid]

4 hours ago, tater said:

A 33 engine test stand is not a thing.

(c) S.P. Korolyov about the N-1 testing.

4 hours ago, tater said:

Static fires? Sure. Maybe working up to a nominal 2-4 second static fire?

Only first three failed in 2..4 seconds. Other three did it later.

4 hours ago, tater said:

The risk is pretty much the same as launch risk, except no launch.

On-ground tests don't blow a 1 000 t tank, they can be fed by pipe.

4 hours ago, tater said:

Such a stand is horizontal?

A 9 m wall isn't too high.

4 hours ago, tater said:

if it's vertical it's a launchpad

Or a torch blowing up.

***

Quote

How big is a circus tent?

 

 

Most common sizes range from an 80′ x 120′ up to a massive 154′ x 262′ and everything in between.

80' = 24 m, enough to hide the whole stand from rain.

[tater]

^^^^

If we see them building a giant test stand—pretty much right now—then I am wrong. Otherwise, they're not building a giant test stand. Feel free to watch one of the many 24/7 cameras and see what they are building, pretty sure it's pad repair, not a new test stand.

[kerbiloid]

4 minutes ago, tater said:

^^^^

If we see them building a giant test stand—pretty much right now—then I am wrong. Otherwise, they're not building a giant test stand. Feel free to watch one of the many 24/7 cameras and see what they are building, pretty sure it's pad repair, not a new test stand.

I'm sure they won't. Because of the N-1 way.

[tater]

 

[RCgothic]

Wow:

 

 

[Exoscientist]

Three quite alarming facts were revealed in Elon’s twitter Spaces discussion:

Elon Musk - Spaceship update after explosion - Spaces Twitter.
https://www.youtube.com/watch?v=pe4B2eIeXfs

First, the Raptors likely were not damaged by the concrete thrown up. If so, then 8 Raptors failed on their own during the flight. Second, thrust vector control, TVC, failed at some point during the flight. Third, the FTS took far too long to destroy the vehicle at 40 seconds.

These three facts together could have led to catastrophic results to the public. If that many Raptors had failed and without TVC closer to the ground, the FTS would not have been able to destroy it before it was over densely populated area if headed in that direction.

The multiple failures of Raptors during tests, and not just shutting down or being shut down, but actually leaking fuel and catching fire, led to my arguing SpaceX should be required by the FAA to construct a separate all-up test stand for full thrust, full flight duration testing. Had this been done then both the launch pad damage and the likely Raptor failures would have been picked up.

I also argued there should be an independent review aside from the FAA by space safety experts on the safety of the launch. If so, the inadequacy of the FTS likely also would have been picked up. I say it’s likely it would have been seen beforehand because assuming the FTS did activate there seems to be only one reason why it did not destroy the vehicle immediately: the strength of the explosives used were not sufficient to penetrate beyond the tank wall strength. This SHOULD have been seen beforehand. 

Tank wall thickness depends on the width of the tanks and the material used. Because of its size, the closest analog to the SuperHeavy stage was the Saturn V’s  S-1C first stage. It’s max wall thickness was in the range of ~6.5 mm while for the SuperHeavy it’s in the range of ~8mm, about 25% thicker. BUT it’s also important to remember the specialty high strength stainless steel used on the SuperHeavy is much stronger than the standard aerospace grade aluminum used on the S-1C. 

Given the greater thickness and greater material strength, these two facts together give a tank wall tensile strength for the SuperHeavy about 3 times higher than that of the S-1C.The amount of explosives used should have been adjusted accordingly.

  Bob Clark

Edited May 3, 2023 by Exoscientist

[tater]

29 minutes ago, Exoscientist said:

The multiple failures of Raptors during tests, and not just shutting down or being shut down, but actually leaking fuel and catching fire, led to my arguing SpaceX should be required by the FAA to construct a separate all-up test stand for full thrust, full flight duration testing. Had this been done then both the launch pad damage and the likely Raptor failures would have been picked up.

That's not going to happen any more than SLS should have had a test stand for the entire SLS stack to fire (the heating from the SRBs does impact the RS-25s, after all). Nor should it happen.

 

29 minutes ago, Exoscientist said:

I also argued there should be an independent review aside from the FAA by space safety experts on the safety of the launch. If so, the inadequacy of the FTS likely also would have been picked up. I say it’s likely it would have been seen beforehand because assuming the FTS did activate there seems to be only one reason why it did not destroy the vehicle immediately: the strength of the explosives used were not sufficient to penetrate beyond the tank wall strength. This SHOULD have been seen beforehand. 

How about no? Independent review.

How about we just give up on doing anything interesting with spaceflight and use crappy existing rockets forever, instead? Maybe we can tack some existing stage onto some other existing stage and make a garbage rocket that can maybe get 2 humans someplace useless? Maybe our great, great grandchildren can do something fun in space long after we're all dead? Or we can slow down good rocket progress in the hopes of getting SSTOs, instead (or the heat death of the universe, which will likely come before useful SSTOs).

[mikegarrison]

There is a (possibly anecdotal) story about when the Tacoma Narrows Bridge failed only a few months after it opened, and supposedly some local politician promised they were going to rebuilt it just exactly as it had been.

I presume that SpaceX isn't going to rebuilt their pad exactly as it had been, but so far they haven't had a great track record of accurately assessing the durability of their pad structure. Guess we'll see if they finally get it right.

[tater]

 

[cubinator]

Very impressive to survive that unscathed. It's interesting to see the structure flexing during the variable loading.

[Nuke]

wonder if you could surf down from orbit darkstar style on one of those. 

6 hours ago, RCgothic said:

Wow:

 

 

this may be the libertarian in me talking, but this is what happens when you don't have to get approval from a dozen different government bureaucracies to get something done. though they probibly did have to apply for a building permit (otherwise they would have done this last week).

Edited May 3, 2023 by Nuke

[Meecrob]

Edit: made a bad joke...thought I could perceive as fast as I can read.

 

Edited May 3, 2023 by Meecrob

[kerbiloid]

Will they investigate, why the engine failure indicator failed?

Spoiler

 

Look, six engines are off (two wide gaps), but the indicator shows just 5?

[SunlitZelkova]

16 hours ago, kerbiloid said:

I'm sure they won't. Because of the N-1 way.

Starship also resembles N1 in how it started as a Mars rocket but has become a Moon rocket.

I have to wonder, will Mars Starship be delayed or put on hold by Starship HLS? It just seems totally unrealistic to think both could be developed at a reasonable pace at the same time. That's just not how it works.

8 hours ago, tater said:

How about no? Independent review.

How about we just give up on doing anything interesting with spaceflight and use crappy existing rockets forever, instead? Maybe we can tack some existing stage onto some other existing stage and make a garbage rocket that can maybe get 2 humans someplace useless? Maybe our great, great grandchildren can do something fun in space long after we're all dead? Or we can slow down good rocket progress in the hopes of getting SSTOs, instead (or the heat death of the universe, which will likely come before useful SSTOs).

Overreacting much? Independent review does not imply the end of innovative spaceflight.

Speed towards space should not be pursued at the expensive of transparency and oversight. Otherwise we are asking for another Challenger disaster.

[Piscator]

29 minutes ago, SunlitZelkova said:

I have to wonder, will Mars Starship be delayed or put on hold by Starship HLS? It just seems totally unrealistic to think both could be developed at a reasonable pace at the same time. That's just not how it works.

As far as I undestand it, there is considerable overlap between both systems. The booster and launch infrastructure is always the same and a dedicated tanker starship would be needed for both mission types as well. At the point when people land on the moon in starship you're three quarters done with the Mars variant of the system as well.

[CatastrophicFailure]

42 minutes ago, SunlitZelkova said:

Independent review does not imply the end of innovative spaceflight.

The FAA IS the independent reviewing authority. 
 

Once again, we don’t have all the data. They do. 

[tater]

45 minutes ago, SunlitZelkova said:

Overreacting much? Independent review does not imply the end of innovative spaceflight.

Speed towards space should not be pursued at the expensive of transparency and oversight. Otherwise we are asking for another Challenger disaster.

"Independent review" implies something other than the FAA—which is already tasked with exactly what is needed.

There are no people on this, there can be no "Challenger disaster."

 

NASA would do the review on HLS crew... who else would be the independent reviewer that would be better than NASA? Some random congressman? The VP? LOL.

[kerbiloid]

11 hours ago, RCgothic said:

Wow:

 

 

Just watched.

So, to stop the exhaust from digging a hole in the ground, let's reflect it back to the engines with concrete slab. Makes sense.