totm nov 2023 SpaceX Discussion Thread

[Cuky]

2 hours ago, Exoscientist said:

 I am dismayed by the level of unreliability of the Raptor. In this latest static fire test two of the Raptors had to be shut  down for only a 5 second test and 50% thrust level. But this is the same number that had to be shut down in the earlier static fire test prior to a test launch for only a 5 second test at 50% thrust level. Does anyone really believe the Raptor is more reliable than before? 

 At this point I don’t think anyone doubts that if there is another test launch in like two weeks there will be engine failures like before. The only question is how many. Will it this time be only four or six instead of eight? Or this time will it be 10 or 12 or more instead of eight? Nobody not even SpaceX knows the answer to that.

  Bob Clark

If Raptor was an engine that is being used in commercial applications then yes, those failures would be quite worrying. But Raptor is still very much a in development engine and new version is already in the pipeline.

 

As a comparison I would use the F1 engine from Saturn V... they were unable to go through any test without it going RUD, but by the time they got to operational status the bugs were ironed. out and they worked like a charm for the most part

[Kartoffelkuchen]

1 hour ago, Cuky said:

As a comparison I would use the F1 engine from Saturn V... they were unable to go through any test without it going RUD, but by the time they got to operational status the bugs were ironed. out and they worked like a charm for the most part

We've had this exact discussion  like two pages ago, what's the point about in discussing this again? 

We know the engine is not as reliable as one could hope for with another flight test coming up soon. Some like the approach, others don't. Apparently SpaceX has the money to give their vehicle a go anyway and see what happens.

Edited August 27, 2023 by Kartoffelkuchen

[.50calBMG]

How many RS-25s blew up during testing over how many years before becoming operational? IIRC only one RS-25 ever failed after that, and I have very few doubts that raptor will eventually get there as well. What you seem to be forgetting is that we are still very much in the testing phase of both starship and raptor, no one has ever stated that either was at an operational level of completion. Both are very high performance engines that push the envelope in their respective times, and both had to undergo a huge amount of testing. You seem to be the only one that fails to see this as a test campaign. If SpaceX claimed starship and raptor were operational, then I would have to agree, but they don't. How many "experimental landings" did falcon 9 make before they took out the "experimental" part? Most people already thought of the landings as routine by that point, and I'm sure that will be the case with starship to an even greater extent.

Like I said in the last post, people said every step of the falcon campaign would be impossible right up until SpaceX did it, then shifted the goalposts back a bit. I remember having a conversation with my father about them landing on a barge back in 2015, where he said it would never happen. Now, over multiple launches I've watched with him, he still giggles like a little kid when they do it. I've said it before and I'll say it again, SpaceX has gotten pretty good at doing impossible things.

Edited August 27, 2023 by .50calBMG

[CatastrophicFailure]

40 minutes ago, .50calBMG said:

SpaceX has gotten pretty good at doing impossible things.

ElonTime™: Making the Impossible Late® since 2002! 

[darthgently]

3 hours ago, tater said:

What we don't know regarding the engines is what if any problems are attributed by SpaceX to be GSE related (the outer engines are fed from the OLM for startup), what problems they think are cluster related (engine/engine interactions), and what issues are unknowns.

They test fire singleton engines a great deal at McGreggor, so I have to imagine it's more likely to be GSE/cluster related.

 

Yes, the outer engines get their spin prime from the OLM and there has been some speculation that there may be pressure issues when spinning up all at once and some are aborted because of low spin or related under full outer spin load.  But no one I'm aware of with any cred is thinking it is actual engine failures.  I'm dying to know what is really happening though

[RCgothic]

The midbay has been demolished. RIP midbay.

Demolition in progress:

[magnemoe]

15 hours ago, RCgothic said:

Flame trenches are primarily to direct the exhaust away from the vehicle and to prevent damage to the vehicle. 

Although there are examples of the refractory brick lining of flame trenches being damaged by rocket exhausts, that's an example of the sort of scouring effect SpaceX were expecting and prepared to put up with for one launch.

The Russians don't to my knowledge use deluge systems, even for the large rockets N1 and Energia. The pads at LC39 only had a minimal system for Saturn V, and it was upgraded for shuttle because of damage to the vehicle. The exhaust didn't seriously threaten the flame trench which was built for Nova, and the OLM at Boca Chica is taller than the flame trenches at LC-39 by a long way.

A large rocket had never before now cracked and excavated its own launch pad foundation through weight of thrust.

I guess the shuttle need more sound suppression because the fragile tiles was so close to the engines as in a meter I guess. 

Could the multiple rings of engines make the ground pressure higher? hitting the ground the exhaust will move outward but the center engines exhaust was blocked by the outer engines so the force was directed downward. Falcon 9 has this issue but here its just one weaker engine, N1 would be an closer parallel. 
But you can use flame diverters to push the flames sideways. SpaceX don't want to use them as they restrict access to under the tower. 
I see one weakness, the center looks like it get less water but takes most beating. But even if this fails it will simply breach the top getting most water to flow there. 

[darthgently]

36 minutes ago, magnemoe said:

I see one weakness, the center looks like it get less water but takes most beating. But even if this fails it will simply breach the top getting most water to flow there. 

My understanding is that the center doesn't see that much heat as there is no center engine and that there is plenty of water wherever an engine points.  But I agree that it seems like the center could see a lot of pressure spikes if one imagines the engines as a phased array of pressure wave emitters.  The implied interference zone down the centerline almost certainly has to be interesting

Edited August 27, 2023 by darthgently

[magnemoe]

12 hours ago, darthgently said:

My understanding is that the center doesn't see that much heat as there is no center engine and that there is plenty of water wherever an engine points.  But I agree that it seems like the center could see a lot of pressure spikes if one imagines the engines as a phased array of pressure wave emitters.  The implied interference zone down the centerline almost certainly has to be interesting

They have no engine exactly in the center but they have 3 in center then two rings of engines around it, N1 is the closest but only one ring around the center 5 engines and not as packed.

Edited August 28, 2023 by magnemoe

[tater]

If they move in any new engines that would perhaps be diagnostic of if they perceive it as an engine vs non-engine issue. New engine(s) means an engine issue, no new engine means something else.

[magnemoe]

1 hour ago, tater said:

If they move in any new engines that would perhaps be diagnostic of if they perceive it as an engine vs non-engine issue. New engine(s) means an engine issue, no new engine means something else.

Agree, I think its either an spin up issue or methane or LOX pressure getting to low during startup. Then flight computer shuts down the engine. 

[sevenperforce]

On 8/26/2023 at 4:26 PM, Exoscientist said:

First, make a smaller rocket with, say, 9 Raptors... Test the heck out this vehicle at full up, full thrust, and full flight duration static tests. Just they like did and still do for the Falcon 9...

SpaceX does not conduct "full flight duration" static fire tests of any of its launch vehicles. When SpaceX announces that it has completed a "full duration" static fire, it means that the static fire went the full duration it was intended to go. This is rarely more than a few seconds; the longest Falcon Heavy static fire went for a dozen seconds. AFAIK, no launch vehicle in history has ever conducted a full thrust, full flight duration static fire test. The closest analogue is probably the Green Run testing campaign for SLS which sometimes goes full flight duration but of course is only operating at a little over 20% of full liftoff thrust.

On 8/26/2023 at 4:26 PM, Exoscientist said:

Only after multiple full static tests where all engines successfully pass...

...something that has never been done on any rocket, ever...

On 8/26/2023 at 4:26 PM, Exoscientist said:

...do they send this up for a test flight.

What, precisely, is the advantage of this imagined full-thrust full-flight-duration static fire over a test launch?

If your goal is to line the pockets of whatever company is supplying parts for ultra beefy hold-down clamps, I suppose this makes sense. No other reason though.

On 8/26/2023 at 4:26 PM, Exoscientist said:

Such a two-stage rocket could do 100 tons to LEO. That is sufficient to do single-launch lunar and Mars missions. Now, make money on that rocket made from the start to be reusable.

How do you figure?

A booster with a third of the liftoff thrust of Superheavy cannot possibly deliver 100 tonnes to LEO with full reusability when Superheavy+Starship can only do 120-150 tonnes to LEO with reusability.

If you mean flying smaller payloads with full reusability, then it becomes really questionable whether you're reaching any advantages over Falcon 9 and Falcon Heavy, since the reuse of your "mini-Starship" becomes challenging. How do you EDL the upper stage? You can't just scale down the current Starship design, because even the "skydiver" entry works the same way, your landing won't: Raptor Vacuum is vastly overpowered for a hoverslam landing. 

If you mean smaller payloads with only first-stage reuse, then you really have no advantage over the Falcon family.

On 8/26/2023 at 4:26 PM, Exoscientist said:

Fly that rocket very many times all the while making profit with it.

SpaceX already has the market cornered with Falcon 9 alone. Why do you think they aren't flying Falcon Heavy more often? The answer is simple: when Falcon 9 can deliver virtually every commercial payload with first stage reuse, there's really no need to add more cores.

On 8/26/2023 at 4:26 PM, Exoscientist said:

THEN after flying so many times...form your superheavy lift vehicle by using triple cores, like what happened with the Falcon Heavy.

Going from Falcon 9 to Falcon Heavy was a nightmarish dev path. The Falcon Heavy core is a completely new rocket compared to the Falcon 9 booster. If you want a Raptor-based vehicle with more than 9 engines, it's a better plan to just go big from the start.

On 8/26/2023 at 4:26 PM, Exoscientist said:

you’ll be making money on the smaller version and be able even to make both single-launch Moon and Mars missions with it

A scaled-up Falcon 9 upper stage powered by a single Raptor Vacuum would suffer from high dry mass, making it much less useful for single-launch missions BLEO.

On 8/26/2023 at 5:58 PM, mikegarrison said:

On 8/26/2023 at 4:30 AM, RCgothic said:

The new foundation isn't going to fail again. It's over two meters thick reinforced concrete capped with steel and with many more support pilings than previously.

That's what they thought the first time....

Unless I misremember, SpaceX was very much anticipating that substantial pad damage would be a potential outcome. They thought there was a chance it might survive, but they knew there was a chance that it wouldn't, and figured that as long as they got good launch data, it would be worth it.

They didn't anticipate the degree of pad destruction, but clearly it wasn't catastrophic given that they have already gotten it functional again.

On 8/27/2023 at 10:24 AM, Exoscientist said:

I am dismayed by the level of unreliability of the Raptor.

Do you have any data to support your dismay?

On 8/27/2023 at 10:24 AM, Exoscientist said:

In this latest static fire test two of the Raptors had to be shut  down for only a 5 second test and 50% thrust level.

Do you have any data that suggest the early shutdowns were an engine reliability issue?

On 8/27/2023 at 10:24 AM, Exoscientist said:

I don’t think anyone doubts that if there is another test launch in like two weeks there will be engine failures like before.

I don't think anyone outside of SpaceX and perhaps certain people at the FAA know whether there were actually any engine failures in the first flight or not.

There were engine shutdowns, yes. There are no data that suggest one way or another whether these engine shutdowns were commanded.

22 hours ago, .50calBMG said:

How many RS-25s blew up during testing over how many years before becoming operational? IIRC only one RS-25 ever failed after that...

While I think we are generally in agreement, I will note that RS-25 failures have been responsible for a total of seven launch aborts: six with the Shuttle and one with SLS. In one case the RS-25 failure was seconds away from causing LOCV.

This just goes for the proposition that engine-out capability is generally a very good thing.

Edited August 28, 2023 by sevenperforce

[.50calBMG]

The one failure I was thinking of was STS-93, which I was referencing. Looking back through flight history, there was also STS-51f which had the abort to orbit, but that was a faulty sensor, so wasn't the engine's fault anyway.  If we start counting on pad aborts pre launch as actual failures, then every rocket in us history goes from at a minimum decently reliable to abysmal, especially Delta IV.

I'm only counting failures in this instance as either catastrophic engine failure resulting in at least loss of mission, if not vehicle. I don't really consider being careful about anomalous readings pre launch as failures, but that's just me

Edited August 28, 2023 by .50calBMG
Clarification

[tater]

22 minutes ago, sevenperforce said:

SpaceX does not conduct "full flight duration" static fire tests of any of its launch vehicles.

To be fair, they have done so with at least a few boosters at McGreggor. But building a stand that can deal with 9 Merlins and the associated RUD risk is far easier than the same kind of stand for SH. No such test ever on FH for this reason. Saturn V I think tested stage 1 for full duration, but that's still ~1/2 SH, right? But would even Stennis be able to handle a SH test run without running the same risk should it RUD?

Spoiler

 

 

22 minutes ago, sevenperforce said:

What, precisely, is the advantage of this imagined full-thrust full-flight-duration static fire over a test launch?

More importantly given his concern about explosion/deflagration risk, how would such a test be less risky than a launch?

https://nuclearsecrecy.com/nukemap/?&kt=13&lat=30.3657728&lng=-89.5798416&airburst=0&hob_ft=0&casualties=1&psi=20,5,1&zm=12.171597004786989

Looks pretty similar to the same, way over estimated map for Starbase—except that it's surrounded by forest which could then catch on fire, and it's very close to a highway.

Spoiler

 

 

Edited August 28, 2023 by tater

[Codraroll]

On 8/26/2023 at 7:08 AM, Exoscientist said:

 “Fool me once, shame on you. Full me twice, shame on me.”

    Bob Clark

Fool you into parroting bogus claims 10664 times, shame on whom?

My username is next to my post, it should be unneccessary to repeat it.

Edited August 28, 2023 by Codraroll

[tater]

 

[Exoscientist]

12 hours ago, sevenperforce said:

SpaceX does not conduct "full flight duration" static fire tests of any of its launch vehicles. When SpaceX announces that it has completed a "full duration" static fire, it means that the static fire went the full duration it was intended to go. This is rarely more than a few seconds; the longest Falcon Heavy static fire went for a dozen seconds. AFAIK, no launch vehicle in history has ever conducted a full thrust, full flight duration static fire test. The closest analogue is probably the Green Run testing campaign for SLS which sometimes goes full flight duration but of course is only operating at a little over 20% of full liftoff thrust.

...something that has never been done on any rocket, ever...

…..

 

 The Saturn V F-1 engines were tested all together multiple times at full thrust and full flight duration static tests:

 And SpaceX has tested the Falcon 9 for full thrust, full flight duration tests:

  As for the reason for doing a full 100% thrust static test firing, the test launch back in April showed testing at 50% was not sufficient to show the launch procedure was safe. 

 That’s just for the 5 second long tests SpaceX wants to do. I don’t think they fully fill up the vehicle with propellant during these short tests for safety’s sake.

 But as I mentioned I don’t agree these 5 second tests are adequate. They didn’t pick up how many engines would fail and even explode as happened in the April test launch. Again, instead of dismissing the lessons of Apollo, SpaceX should learn from them. Construct a separate test stand to do full up, full thrust, full flight duration tests like was done with the Saturn V first stage.

  Bob Clark

Edited August 29, 2023 by Exoscientist

[tater]

41 minutes ago, Exoscientist said:

 But as I mentioned I don’t agree these 5 second tests are adequate. They didn’t pick up how many engines would fail and even explode as happened in the April test launch. Again, instead of dismissing the lessons of Apollo, SpaceX should learn from them. Construct a separate test stand to do full up, full thrust, full flight duration tests like was done with the Saturn V first stage.

It's not "dismissing the lessons of Apollo."

Apollo was done the way it was done because they literally had no other option. There were not going to model a launch with slide rules and a PDP-8 at the fidelity required.

A full duration SH test requires a full SH. Such a test would operate the engines under an unrealistic flight regime (burning at sea level the full ~200+ seconds). Hold downs have to deal with exceptional forces (as the vehicle lightens). Such a test means the flame-diverter/deluge system needs to deal with ~200+ seconds, not a handful of seconds. Having done so, it still fails to test the vehicle in flight conditions. How does the propellant flow function under X gs? Who knows. How is heating at the appropriate expansions as alt increases? Who knows. Etc, ad nauseum.

Wanting a full flight duration static fire is asking for a metric for the sake of wanting a metric. The ideal static test is the one that provides the data required for an accurate model run. They run a simulation based on current data. Static fire, then compare how the real system functions WRT the model. Change the model to replicate the static fire more accurately, try again. Maybe their modeling people tell the testing peeople that they would ideally have X seconds of steady-state, so they need a 7.2 second static fire (or whatever).

Edited August 28, 2023 by tater

[tater]

 

[JoeSchmuckatelli]

8 minutes ago, tater said:

 

Wen Hop? 

Edited August 28, 2023 by JoeSchmuckatelli

[darthgently]

1 hour ago, Exoscientist said:

But as I mentioned I don’t agree these 5 second tests are adequate. They didn’t pick up how many engines would fail and even explode as happened in the April test launch. Again, instead of dismissing the lessons of Apollo, SpaceX should learn from them. Construct a separate test stand to do full up, full thrust, full flight duration tests like was done with the Saturn V first stage.

Why do all that when they have a deep bench of lined up test boosters from an on site assembly line?  As noted in tater's reply, the only way to test everything in realistic conditions is to just go for it (to paraphrase).   Why not just launch, learn, modify, repeat?  How deep was the hardware test bench for Saturn V?   What percentage of Saturn V was built on site from an assembly line? Exactly.  

[tater]

5 hours ago, darthgently said:

Why do all that when they have a deep bench of lined up test boosters from an on site assembly line?  As noted in tater's reply, the only way to test everything in realistic conditions is to just go for it (to paraphrase).   Why not just launch, learn, modify, repeat?  How deep was the hardware test bench for Saturn V?   What percentage of Saturn V was built on site from an assembly line? Exactly.  

It's not just "go for it," it's the question: What is required to learn what they need to learn to continue?

 

The pros of extended static firing of all engines are:

1. Characterizes long duration burns of 33 engines.

2. Assuming a new facility can do this for just the booster, the RUD risk at ground level only includes the booster.

3. ?

The cons:

1. They have to build an entirely different test facility capable of surviving a far longer duration launch burn than would ever happen.

2. This facility would also have a deluge system with far longer duration (all water might need capture?).

3. All environmental impacts would need to be reevaluated as the impact of such a static fire includes all the risks of a launch, but ADDS the risks of far longer duration firing on wildlife, etc.

4. The risk of a RUD is a complex calculation for flight, but assuming even any duration of flight, the risk moves, and overpressure, etc, increases briefly, then decreases as the vehicle climbs—both because of separation from the risk areas on the ground, but also as propellants are depleted the vehicle becomes continuously less explosive (less chemical energy stored inside). For a static fire, the props deplete with duration, but the distance never does.

5. The data gained on groups of engines firing in #1 above is in a regime they will not actually operate in for very long.

6. They still do not gain data on flight regimes (under g-load).

 

#1 in the pros is certainly a large plus, but is is a greater plus than the cons are minuses?

 

The pro of a launch test is:

1. Fully tests vehicle in flight conditions.

2. Tests pad in launch conditions.

3. Any RUD away from the pad while on/near the proper flight path has less impact than a RUD on the pad (including an FTS unzip).

Cons:

1. RUD risk at pad identical to static, but RUD risk downrange includes flight path deviance and FTS failure. Note that this failure mode exists regardless of successful static fire, this is a con to any launch.

 

I might have missed some for either.

 

Edited August 29, 2023 by tater

[tater]

3 hours ago, Exoscientist said:

  As for the reason for doing a full 100% thrust static test firing, the test launch back in April showed testing at 50% was not sufficient to show the launch procedure was safe. 

Missed this. A 100% static fire for some short time interval (the duration of 100% thrust on the pad—it could even start at 100%, and ramp down to mimic liftoff, I suppose) would indeed test the pad, and would be a plus data wise...

But IFT-1 was done knowing that the pad needed a deluge system—the system was on the ground nearby, uninstalled. So the test launch had 2 possible outcomes:

1. Pad needs the deluge system.

2. Pad is actually fine as-is.

SpaceX clearly was already assuming 1 was correct (since they were planning on installing the deluge after the launch), but they also underestimated the damage.

A 100% static fire would have shown #1 what?

I have not watched it in a while, but how many seconds in did the pad fail? If the pad failed in under 5-6 seconds, then they would learn #1, and would have had less damage to repair—course they might then miss some other things that were shown to need beefing up, and those happen with the subsequent launch anyway. If the pad failed in >5-6 seconds, then the static test would have risked pad RUD for 0 knowledge gained—they think the pad is OK, launch anyway, same damage happens.

Given the fact that a 100% test requires not just a full stack, but a loaded full stack (at some level at least, certainly not an empty Starship), what is to be gained by risking pad RUD with no upside? If they were hardware-poor, then losing the vehicle AND pad would be bad, but they stand to sustain pad damage if it is not good enough for 100% if they do a static fire, OR if they launch.

That's the problem, they risk pad damage for a 100% static fire, and for a launch. The risk there is almost the same—and indeed if FOD is an issue, a static fire might be worse (schedule risk) as the vehicle could sustain mortal damage but not be moving away from the pad. They you get an even more damaged GSE.

Edited August 28, 2023 by tater

[magnemoe]

27 minutes ago, Exoscientist said:

 

 The Saturn V F-1 engines were tested all together multiple times at full thrust and full flight duration static tests:

 And SpaceX has tested the Falcon 9 for full thrust, full flight duration tests:

  As for the reason for doing a full 100% thrust static test firing, the test launch back in April showed testing at 50% was not sufficient to show the launch procedure was safe. 

 That’s just for the 5 second long tests SpaceX wants to do. I don’t think they fully fill up the vehicle with propellant during these short tests for safety’s safe. 

 But as I mentioned I don’t agree these 5 second tests are adequate. They didn’t pick up how many engines would fail and even explode as happened in the April test launch. Again, instead of dismissing the lessons of Apollo, SpaceX should learn from them. Construct a separate test stand to do full up, full thrust, full flight duration tests like was done with the Saturn V first stage.

  Bob Clark

Now I'm seriously impressed by the flame diverter for the Saturn 5 first stage test. How was that designed? 
Also how much did it cost? And how long to build it? 

For safety you only need an test long enough to clear the tower and get out over sea, at this time an launch is safer than an static fire assuming you are fully fueled as in full burn. 
I don't see an need to static test farther than engines are running stable. 
Yes SpaceX has don't full duration tests of first stages but falcon 9 is more manageable. 

[kspbutitscursed]

Soooo wen launch september 8th????

i think Septmber 15th