totm nov 2023 SpaceX Discussion Thread

[AtomicTech]

5 hours ago, obney kerman said:

Yeesh, that was a lot of issues for one flight. On the one hand, impressive how long the ship stayed in one piece with all that going on, on the other hand... there probably shouldn't have been so many things failing together. Fingers crossed this doesn't delay Artemis 3 by too much...

In the time it'll take them to launch Artemis 2, they'll probably have launched 10 Starships 

[obney kerman]

2 minutes ago, AtomicTech said:

In the time it'll take them to launch Artemis 2, they'll probably have launched 10 Starships 

And are they going to build 10 expendable launchpads for that?

[AtomicTech]

Just now, obney kerman said:

And are they going to build 10 expendable launchpads for that?

With ten more Starbases! 

[magnemoe]

2 minutes ago, obney kerman said:

And are they going to build 10 expendable launchpads for that?

Yes making stage 0 rapid reusable should be an priority. 
Its art 
http://freefall.purrsia.com/ff2000/fc01966.htm

Edited April 20, 2023 by magnemoe

[CastleKSide]

I hope we one day get an explanation of why the pad damage happened, what was overlooked in the calculations 

[Pthigrivi]

My guess is they thought, yeah, its gonna destroy the pad, but didn't really account for how much damage that much flying debris would cause and just accepted the risk. Installing a real deluge system and flame trench is a pretty hefty bit of engineering. Its definitely too bad because if they'd incorporated a proper deluge/flame trench system into stage zero from the beginning it might be ready by now, but if they're just getting started it might take 2 years to have that in place. 

Edited April 20, 2023 by Pthigrivi

[tater]

21 minutes ago, Pthigrivi said:

My guess is they thought, yeah, its gonna destroy the pad, but didn't really account for how much damage that much flying debris would cause and just accepted the risk. Installing a real deluge system and flame trench is a pretty hefty bit of engineering. Its definitely too bad because if they'd incorporated a proper deluge/flame trench system into stage zero from the beginning it might be ready by now, but if they're just getting started it might take 2 years to have that in place. 

They actually have a deluge system on site, it's just not installed yet.

[sevenperforce]

1 hour ago, Codraroll said:

It's not like they guessed 120 erosion units and got 125, but more like they guessed 80 and got 600.  What happened to that pad was so much worse than it was rated for, that I suppose we're looking at more than just a sloppy under-estimate of wear and tear. Because the engineers know the engine specs and they know the material properties. A thorough assessment would have been within the ballpark, especially with all the safety margins. Engineering calculations rarely miss by an order of magnitude.

I'm wondering if that happened because the rocket accelerated off the pad slower than expected, so the engines spent way more time torching the pad at close range instead of lifting off and getting away. The pad could have been rated for, say, three seconds of maximum exposure, and then got ten instead. After all, the rocket looked quite sluggish after the engines were ignited, as if it spent more time getting off the pad than it was supposed to.

It may have been that all of their estimates were slightly off, but they were all off in the wrong direction, and there were some exponential variables that all ended up combining to produce a Bad Day.

To take your "erosion unit" numbers, let's suppose that the equation for "erosion units" is (strength units)^{(time units)} x (plume interaction units) x (cascade variable)^{(time units)} x (sound pressure units)^{(plume interaction units)}. If combining all these units together gives you 80 erosion units, but it turns out that the actual numbers ended up being ~18% higher than expected on average, then it gives you 600 erosion units.

My best guess is that there was some sort of cascade effect. When the first engines started up, tank pressure dropped just slightly faster than expected, and so the staggered start took just slightly longer than planned, and the plume impingement was just slightly more damaging than anticipated, and plume interactions as the second set of engines started was just slightly more violent than expected, and so by the time the third bank started up the debris blowback was already greater than expected, and so on and so forth until the pad was getting absolutely rogered before the last bank of engines had even started up, and so engines were being fragged before it even lifted off. And so it lifted off slower, and then this extended proximity to a much more damaged pad fragged more engines, and so forth.

Edited April 21, 2023 by sevenperforce

[sevenperforce]

From the NSF forums:

Quote

 

I just had a conversation with one of the SpaceX engineers...

Key takeaways:

1.) No, the booster did not lose hydraulic power as far as he knew. Everything was fine except for the engine anomalies.

2...(This is wild)...The initial "loss of control / tumble" that we observed was not a loss of control...it was supposed to be the stage separation maneuver, but the stages did not separate properly. The separation failure lead to a true loss of control due to the inability of the vehicle to understand or respond to its condition. The person I spoke with clarified that the maneuver was to be much more dramatic than what people were generally anticipating; a very substantial change in attitude that would look really odd to us. The ship was then supposed to use TVC to straighten itself out and continue.

The person I spoke with is uncertain as to why the stage separation failure occurred.

3.) The person I spoke with was definitely pleased with the test and did not express any sort of disappointment or concern for the program.

 

Really fascinating. This is honestly what I initially thought, given that the flip started at the time planned for the separation, and I was sure I could see the engines gimbaling, but I doubted myself after seeing a lot of people arguing that the HPU had gotten fragged and all the Raptors immediately stopped gimbaling.

It makes sense, though. There was already a thrust imbalance from engine-outs. If all gimbal authority was instantly lost, it would have instantly spun out of control a la Challenger.

Additional commentary:

Quote

The engines were intended to remain lit the entire time. Nothing was wrong. It was supposed to flip sideways, then flip back the way it came (under full power + TVC) and throw the ship. MECO was intended to occur on the way back, but the maneuver never completed due to the failure of stage separation.

God, what an amazing, beautiful thing it will be when we see that.

[Ultimate Steve]

46 minutes ago, sevenperforce said:

From the NSF forums:

Really fascinating. This is honestly what I initially thought, given that the flip started at the time planned for the separation, and I was sure I could see the engines gimbaling, but I doubted myself after seeing a lot of people arguing that the HPU had gotten fragged and all the Raptors immediately stopped gimbaling.

It makes sense, though. There was already a thrust imbalance from engine-outs. If all gimbal authority was instantly lost, it would have instantly spun out of control a la Challenger.

Additional commentary:

God, what an amazing, beautiful thing it will be when we see that.

I have never heard this before and I am having a hard time seeing this being correct even though it might be coming from an insider. Even a few raptors, possibly just one, would be enough to keep starship pinned to super heavy given how light super heavy is by then, unless it was actually spinning at a ludicrous rate, at least is my assumption. I can do the math later on to verify.

Why would they not:

1. Hard gimbal

2. Engine cutoff

3. Starship gets yeeted in like 30 degrees instead of 270

4. Starship starts up at proper distance

5. Boostback starts with booster properly oriented?

Doing a full 360 under full engine power with the drops of fuel that matter the most can't possibly be better than that, unless it's an engine clearance issue. Like I understand why they don't want a proper separation mechanism, but surely it has got to be better than the 540 degree turn they are planning on?

 

Only reasons I can think of to do it this way are that the additional boostback TWR means it is better to waste the fuel flipping than to cut boostback TWR, or they *really* need more separation distance than they can get with a short yeet.

Granted, this would explain why they kept the engines on for so long afterwards.

 

Even though the more I think about it the more it makes sense, anything is greater than zero. If this actually happens it is going to be the most bat-excrement insane thing ever in the launch vehicle world and I will be surprised.

Most people on the discord servers I frequent thought that the 30 degree kick flip was too radical, and now apparently Starship is a beyblade.

 

[Ultimate Steve]

Well they've done it again. First with the whole mechazilla thing, now with the 540 flip. The more I think about it the more sense it makes, but that doesn't make it any less ludicrous.

Other discord sources are saying beco at 270 into the flip and restart at around 500. The starship would be yeeted and well clear and pointing in the right direction for second stage startup. I still think a beco somewhere is required to actually allow starship to break away, but who knows, I could be wrong about this too.

[tater]

1 hour ago, sevenperforce said:

God, what an amazing, beautiful thing it will be when we see that.

Next page on the NSF thread someone else with a SpaceX contact:

Quote

My contact says essentially the same. They were legitimately ecstatic over today's events.

 

[darthgently]

2 hours ago, Pthigrivi said:

My guess is they thought, yeah, its gonna destroy the pad, but didn't really account for how much damage that much flying debris would cause and just accepted the risk. Installing a real deluge system and flame trench is a pretty hefty bit of engineering. Its definitely too bad because if they'd incorporated a proper deluge/flame trench system into stage zero from the beginning it might be ready by now, but if they're just getting started it might take 2 years to have that in place. 

A flame trench at Boca Chica is problematic as the water table is just a few feet down.  The planned deluge system is more of an aerial water droplet/spray system was my impression so most of the cooling would be well above the ground (?). 

Not sure now, am doubting my understanding as I also remember some very large diameter plumbing fixtures laying in wait for installation.  So maybe a combination of massive aerial mist/droplet cooling combined with a flood of water across the pad to take the main brunt of it?

So it beat N1's flight time and elevation achieved.  Did it win on TWR or was it shorted by a few dead engines, lol

[tg626]

15 hours ago, darthgently said:

A flame trench at Boca Chica is problematic as the water table is just a few feet down.

The Everglades would like a word. (Rightly pointed out, not the Everglades. But low lying wetlands none the less.)

That's why 39 is up on man made mounds. I can't fathom how one could plan to build a booster "Bigger than the Saturn 5" and not take the systems built for it (including the revisions after the first launch) and incorporate similar systems.

Edited April 21, 2023 by tg626

[darthgently]

2 minutes ago, tg626 said:

The Everglades would like a word.

That's why 39 is up on man made mounds. I can't fathom how one could plan to build a booster "Bigger than the Saturn 5" and not take the systems built for it (including the revisions after the first launch) and incorporate similar systems.

Pretty sure Canaveral is a couple of hundred miles north of the everglades, but point taken, the water table is near the surface in that area also

[tater]

2 minutes ago, tg626 said:

The Everglades would like a word.

That's why 39 is up on man made mounds. I can't fathom how one could plan to build a booster "Bigger than the Saturn 5" and not take the systems built for it (including the revisions after the first launch) and incorporate similar systems.

Yeah, but they have a limited footprint near the beach, 20-40 acres. A large mound would then require adding grade to the entire beach road to transport the vehicle, which also might not be allowed (they don't own the road).

[Motokid600]

I think the OLM just needs to be larger. Cant build down just like at KSC so build up. The OLM's height might be fine, but it needs something built around it akin to LC39 with a flame diverter.

Edited April 21, 2023 by Motokid600

[JoeSchmuckatelli]

6 hours ago, Minmus Taster said:

 

Except for the fact that the Flight Report MUST OBSCURE the explosion for it to be KSP2 

5 hours ago, RCgothic said:

 

 

Some architects use things like tracks in the grass to know where to put walkways... That theory seems applicable here. 

[Little 908]

You know, I guess spaceX proves that the fastest way to learn and advance, is to fail. Really puts the “Failure is the key to success” in play. I mean NASA takes a long time between missions because they go more strategically, while spaceX isn’t afraid to fail and mess up.

 

10 hours ago, Minmus Taster said:

I have a sneaking suspicion hoppy is not surviving this

Wait that reminds me…

Did starship hit a birb?

Edited April 21, 2023 by Little 908

[CatastrophicFailure]

1 hour ago, tater said:

Next page on the NSF thread someone else with a SpaceX contact:

 

Confirmed: 

 

 

 

[Motokid600]

This concerns me.

@1:17:22 - It makes me wonder how the heck SpaceX plans to deal with this on Mars.

Edited April 21, 2023 by Motokid600

[AVaughan]

On 4/20/2023 at 1:29 PM, tater said:

Yeah, I was assuming that a LSS has no need for 3.6 or 4mm steel. At 3mm, the 6 ring longer hull is ~42t. It needs no SL engines, so either 3 or 6 Rvacs (4.5t – 9t). Add 15t for fitting out, and we have a vehicle that is 63t – 66t. The props of just the 6 rings are ~450 – 510t, but some crew area could be eaten into to get the total props to that 1710t if needed (I didn't estimate the domes well). The 66t version just closes.

Obviously cargo is not much of an option, but that's what a cargo vehicle could be for (and at the lower mass end, it closes with 3t cargo)

Are you sure that they can afford thinner steel?  Wouldn't the fuel tanks still be pressurised to the same pressure?  Wouldn't the aerodynamic loads on launch likely be similar?   (Admittedly aero loads might be lower with no flaps, but hoop stress for the tanks would be the same, if the internal pressure is the same). 

Don't you still need at least one centre SL engine with it's gimbal for control during burns if one of the 3 vacuum engines fails?  (With 6 vacuum engines, you could shutdown the opposite engine instead, but all the same I'm not sure SpaceX and NASA would choose to make design changes from a standard starship in a way that might reduce redundancy in the event of an engine failure on the Lunar lander).   

Do you really want to make the lunar lander taller?  Isn't the CoM already going to be uncomfortably high?  (Yes that can be managed, but why would they choose to make the lander even taller)?    

I haven't done the maths, but wouldn't refuelling the lander in Lunar orbit (at/near gateway), then letting the fuel tanker aerobrake into Earth orbit, (or more likely re-enter directly from the Moon) be more fuel efficient than using fuel for the lunar lander to capture to LEO, especially given that under your proposal you need to land that fuel on the Moon, then launch it back into Lunar orbit?   Can't one stretched tanker make an LEO to Lunar Gateway trip with enough fuel in lunar orbit to refuel the lunar orbiter, and still have enough fuel to return to earth.  Possibly even with enough margin for a small cargo hold and some supplies/cargo.  And doesn't refuelling at Gateway allow the option of significantly heavier payloads to the Lunar surface?

If you are going to do an in space cargo transfer or in space resupply/refurbishment, then I'm not sure that LEO is enough better than gateway to justify the disadvantages?  Other than shorter round trip comms for any remote controlled operations controlled from Earth, what advantages does it have?  Doesn't anything that needs to replaced still need to wait for a launch from Earth?    (Ok yes, sending something to lunar orbit needs more than just a launch from Earth, but if you are already supporting Lunar Gateway with regular supply runs via starship, isn't it just some extra cargo next launch to Gateway)?
 

26 minutes ago, Motokid600 said:

This concerns me.

@1:17:22 - It makes me wonder how the heck SpaceX plans to deal with this on Mars.

I'm sure SpaceX is aware.  (In fact today was a pretty good reminder).  Why do you think their Lunar lander proposal seems to have small landing engines mounted high up.  

Edited April 21, 2023 by AVaughan

[Motokid600]

12 minutes ago, AVaughan said:

Why do you think their Lunar lander proposal seems to have small landing engines mounted high up. 

Its Mars I'm worried about.

[tg626]

2 hours ago, tater said:

Yeah, but they have a limited footprint near the beach, 20-40 acres. A large mound would then require adding grade to the entire beach road to transport the vehicle, which also might not be allowed (they don't own the road).

Again, 39A/B - big ol ramp to get from grade to the pad, crawler has to jack one end of the pad to keep it all plumb and level as it climbs up.

Now I'm not familar with the geography at Boca but I bet those big brains could work it out.

Edited April 21, 2023 by tg626

[SunlitZelkova]

This launch was a salute to the N1. Next launch Starship avenges the N1 and finishes the job left undone (getting to orbit, then Moon and Mars)