totm nov 2023 SpaceX Discussion Thread

[kerbiloid]

Peaks + pulsation.

Also, it's 30 points of applied pressure, not uniformly distributed presure.

Sp, the local maximums may exceed the average tens times.

[mikegarrison]

On 5/8/2023 at 7:41 AM, sevenperforce said:

Raptor yeets 650 kg/s of exhaust out the back end at 3,210 m/s. Assuming all the exhaust plumes generally merge under the 10.3-meter base of Starship, that's a dynamic pressure of 3.71 megapascals. Really quite shockingly low if you think about it -- less than the water pressure in the output of your typical coin-operated car wash spray nozzle. The coolant loops in a pressurized water reactor run 4-5x higher.

I am pretty sure that you could point a car wash spray nozzle at that concrete pad all week long and not see it pulverized and spread all over South Padre Island.

I suspect there is some flaw with your analysis.

[Elthy]

Dont forget the temperature. A blowtorch can cut through steel even though its pressure is in the range of canned air. This will also complicate things with water-cooling, superheavy will literarely vaporize tons of water per second. All that steam will add to the dynamic pressures below the pad.

[tater]

 

[mikegarrison]

36 minutes ago, tater said:

 

 

[tater]

^^^ haven't seen it tried. That said, the static test facility at Stennis has a deluged system over a curved steel ramp.

Deluge from above, then below it seems like maybe holes in diverter:

https://www.nasa.gov/centers/stennis/news/releases/2022/Fire-in-the-Hole-NASAs-Stennis-Space-Center-Preparing-Stand-for-RS-25-Testing

Sounds like holes in the sloped steel for water?

Quote

To prolong the life of the test stand and reduce ongoing maintenance costs, crews are now in the process of performing critical modifications on the Fred Haise Test Stand flame deflector. A key part of the work is drilling a new, highly specialized hole pattern to improve water cooling and protect the infrastructure. The hole pattern will be uniquely tailored for the RS-25 testing program.

“An engine plume is essentially a supersonic blowtorch,” Stennis engineer Danny Allgood said. “There are extreme forces at play, such as high temperature and pressure, that are factored in to where we need to drill additional water-cooling holes. The objective is to ensure a layer of water constantly flows over the deflector during testing.”

 

[mikegarrison]

There are multiple things going on there in that video.

#1 is mass flow. To carry away a lot of heat, mass flow is your best friend.

#2 is transpiration cooling. It's related to #1. The way it works is that the heat gets into the metal, and from there it's hard to get it out. With transpiration cooling, you have forced convection in the passage through the metal from the metal to the fluid flowing in it, and then you can have conduction from the rest of the metal to the surface of the hole.

Anyway, in that video they are mostly relying on the water spray from those nozzles on the top to carry away the heat, but in order to keep the steel plates cooled they have some transpiration cooling happening also. You see it about 1 minute into the video.

[darthgently]

1 hour ago, tater said:

 

My understanding is that there will be a layer of water flowing on top of the plate also as the water flowing through it exits on top of the plate or thereabouts 

[sevenperforce]

10 hours ago, mikegarrison said:

On 5/8/2023 at 10:41 AM, sevenperforce said:

Raptor yeets 650 kg/s of exhaust out the back end at 3,210 m/s. Assuming all the exhaust plumes generally merge under the 10.3-meter base of Starship, that's a dynamic pressure of 3.71 megapascals. Really quite shockingly low if you think about it -- less than the water pressure in the output of your typical coin-operated car wash spray nozzle. The coolant loops in a pressurized water reactor run 4-5x higher.

I am pretty sure that you could point a car wash spray nozzle at that concrete pad all week long and not see it pulverized and spread all over South Padre Island.

I suspect there is some flaw with your analysis.

Water isn't coming out of a car wash spray nozzle at temperatures greater than the melting point of steel.

[tater]

 

[Codraroll]

3 hours ago, sevenperforce said:

Water isn't coming out of a car wash spray nozzle at temperatures greater than the melting point of steel.

Maybe not at your local car wash ...

[Exoscientist]

Brain Teaser: Why does Falcon Heavy disprove the SpaceX justification for building the SuperHeavy/Starship?
MAJOR hint: Why did Arianespace want to move away from the Ariane 5 to the Ariane 6?

After writing that, it occurred to me there are two different answers to my riddle. Hint for 2nd answer: how many Merlin’s flew on actual operational missions on Falcon 9’s before the Falcon Heavy flew? How many times did the Raptor before the SuperHeavy/Starship?

  Bob Clark 

[tater]

Which is why all US rockets ever have only used the Rocketdyne A-7 engine. It was good enough for the first US orbital rocket, Juno I, so nothing else ever should have been developed. Novelty is bad. Tie a bunch of Junos together, then maybe buy a second stage from some other country that already exists and stick that on top.

Or not.

Edited May 11, 2023 by tater

[Spaceception]

13 hours ago, Exoscientist said:

Brain Teaser: Why does Falcon Heavy disprove the SpaceX justification for building the SuperHeavy/Starship?
MAJOR hint: Why did Arianespace want to move away from the Ariane 5 to the Ariane 6?

After writing that, it occurred to me there are two different answers to my riddle. Hint for 2nd answer: how many Merlin’s flew on actual operational missions on Falcon 9’s before the Falcon Heavy flew? How many times did the Raptor before the SuperHeavy/Starship?

  Bob Clark 

Their sole justification is to enable human missions to Mars. That's been their thing for the better part of a decade, and a rocket with a fraction of the payload capacity and volume wasn't going to cut it. Even if that never pans out, their other thing was to build a fully and rapidly reusable rocket that's a significant step up from anything we have, not merely an incremental improvement. And the more you scale it up, the less that payload reductions from reuse matter. Especially from recovering both stages, rather than just recovering the 1st stage. Falcon 9 takes a 30% reduction from bringing back the first stage alone after all.

Ariane 5 to 6 doesn't really relate to Starship in regards to why SpaceX is developing it, if I'm not misunderstanding. Ariane 6 was a response to Falcon 9, because it undercut their costs and threatened to take payloads they otherwise would've flown. Similar reason why ULA moved to Vulcan, though that was also driven by moving away from the RD-180. The CEO themselves refused to invest in reusability because having a rocket able to be used multiple times, for them, meant that their teams would be without work. https://arstechnica.com/science/2018/05/ariane-chief-seems-frustrated-with-spacex-for-driving-down-launch-costs/  

If anything, Falcon Heavy proves SpaceX's justification for Starship, at least, to the extent that building a larger vehicle should work better than strapping boosters to an existing, smaller one. 3 cores improves the potential payload by a factor of ~3, but the second stage still can't be easily reused, and the payload volume is still the same. A new ground up vehicle, designed for reusability, while improving on the Falcon 9/Heavy's limitations, has a massively increased payload, and the second stage can be reused, and the payload volume is increased as well. Giving you a new range of missions to perform. Heavy co-manifesting/rideshare, larger telescopes, larger station modules, and satellite constellation support.

It also doesn't particularly matter how many Raptors have flown. Traditionally, new engines for new rockets are tested on the stand/static fired on the booster before their first flights ever leave the ground. SpaceX just combined this with sub/fullscale flight tests in addition to this. But how many Merlin engines flew on operational Falcon 1 missions before the Falcon 9 flew? 2. What about the number of Rutherford engines that flew operational missions before they were placed on Electron? 0.  How many BE-4 engines will fly operational missions before the first flight of Vulcan? 0.

Edited May 12, 2023 by Spaceception
Minor spelling error

[tater]

4 minutes ago, Spaceception said:

A new ground up vehicle, designed for reusability, while improving on the Falcon 9/Heavy's limitations, has a massively increased payload, and the second stage can be reused, and the payload volume is increased as well. Giving you a new range of missions to perform. Heavy co-manifesting/rideshare, larger telescopes, larger station modules, and satellite constellation support.

Yeah, and look at the delays in getting SS to orbit—fast as it is as a project.  NG was announced in Sept 2016, and was planned to fly before the next decade (now the current decade). In addition to their martian goal, SpaceX needed a vehicle that could compete with NG under the assumption they wanted to fund their efforts with commercial/government launches. As a result, going all-in for a new vehicle made a lot of sense.

[Royalswissarmyknife]

Idea to satisfy SpaceX doubters:

We all stay in the stone age and never make anything new or...

[CastleKSide]

11 hours ago, sevenperforce said:

Water isn't coming out of a car wash spray nozzle at temperatures greater than the melting point of steel.

If it were, my car would be a very different kind of clean. Sounds fun to try tho, maybe pitch it to a youtuber.

[CatastrophicFailure]

33 minutes ago, CastleKSide said:

If it were, my car would be a very different kind of clean. Sounds fun to try tho, maybe pitch it to a youtuber.

Mythbusters already did it. 
 

…sort of… 

 

 

 

 

[RCgothic]

8 hours ago, Exoscientist said:

MAJOR hint: Why did Arianespace want to move away from the Ariane 5 to the Ariane 6?

Ariane 6 was defined at concept level in 2012 about a year before Falcon 9 v1.1 had its first flight, and they faffed about a bit before settling on its final layout in 2014 about a year after F9 v1.1.

Arianespace knew at the time they had to cut costs in half, and even so planned to launch two sats for every 1 on Falcon 9, and use their better 2nd stage for precise orbital insertions with engine relights.

Times have moved on. Falcon 9 now has more payload total than Ariane 6 even without counting Falcon Heavy. It is regularly reused, can fly for under $20m internal cost, has an accurate restartable 2nd stage, and holds the record for most payloads deployed at once.

And have Arianespace responded to that at all? No. Their Ariane 6 design hasn't moved with F9's developing capabilities and is now a full decade behind the times. The only thing worse for them than choosing this design would be sticking with Ariane 5.

[Meecrob]

14 hours ago, Exoscientist said:

Brain Teaser: Why does Falcon Heavy disprove the SpaceX justification for building the SuperHeavy/Starship?
MAJOR hint: Why did Arianespace want to move away from the Ariane 5 to the Ariane 6?

After writing that, it occurred to me there are two different answers to my riddle. Hint for 2nd answer: how many Merlin’s flew on actual operational missions on Falcon 9’s before the Falcon Heavy flew? How many times did the Raptor before the SuperHeavy/Starship?

  Bob Clark 

I give up, what is the answer...?

[Ultimate Steve]

Apparently the Falcon family just hit 200 consecutive successful missions!

On the reddit post, the haters immediately crawled out of the weeds and one commenter was like "But you didn't count landing failures! But you didn't count all those times Falcon 9 exploded! But you didn't count all those times Falcon 9 failed to deliver its payload! It's a travesty that we wasted 15 billion dollars of taxpayer funding on a mediocre unreliable rocket from a company that over promises and under delivers!"

I have no idea what kind of rock he was living under, but I decided to steel man the argument. It turns out even by this man's ridiculous criteria, Falcon 9 is still amazing.

 

Last time a Falcon exploded in air was the in flight abort test was 143 flights ago, and it was an intentional explosion. Last time before that was CRS-7, 203 missions ago, although the last ground explosion was 194 missions ago. Counting Falcon Heavy this is 200, this is what most people consider to be the last true Falcon failure.

Last Falcon 9 to not deliver its payload was possibly Zuma, 175 flights ago. The details are classified but it is known that the customer supplied their own payload adapter, and if there was a separation failure, SpaceX is not to blame. To get something more concrete that isn't one of the two obvious failures, 218 flights ago, all the way back on flight 4, SpaceX failed to deliver a secondary payload due to inadequate fuel margin.

If you want to be very liberal in your definition of failure to deliver payload, Starlink 4-7, 82 flights ago, could be counted as a solar storm shortly after launch caused the atmosphere to swell up, and most of the satellites decayed as a result, but I imagine that the vast majority of people wouldn't count this as the fault of the Falcon 9, as it successfully placed the satellites into the specified orbit.

Last Falcon 9 that crashed during an attempted landing was 114 missions ago on Starlink 19. I think even the haters can agree that a mission that doesn't attempt landing isn't a failure so I won't look that up.

So, even with these ridiculous criteria, Falcon 9 has a 114 launch success streak, or 82 if you want to be edgy. 114 is still incredibly impressive and 82 is still very respectable. If anyone wants to disparage the Falcon 9 in this day and age, even if you stretch the facts as far as they will go, it isn't enough any more.

Soon I expect people to seriously suggest that Falcon 9 is an unreliable piece of junk because of failed fairing recoveries. Unless another Falcon blows up soon, that's about the last leg they can stand on, and it is mighty wobbly.

 

[Cuky]

47 minutes ago, Ultimate Steve said:

Soon I expect people to seriously suggest that Falcon 9 is an unreliable piece of junk because of failed fairing recoveries. Unless another Falcon blows up soon, that's about the last leg they can stand on, and it is mighty wobbly.

IMHO that just shows how far Spacex has came. From "they are crazy for talking about landing and reusing boosters, it can't be done" to "landing failures are super rare, but should be counted as launch failures"

[sevenperforce]

2 hours ago, Ultimate Steve said:

Last time a Falcon exploded in air was the in flight abort test was 143 flights ago, and it was an intentional explosion.

Did it reach orbit? No? Therefore, failure. An explosion is an explosion.

2 hours ago, Ultimate Steve said:

Last time before that was CRS-7, 203 missions ago, although the last ground explosion was 194 missions ago. Counting Falcon Heavy this is 200, this is what most people consider to be the last true Falcon failure.

SpaceX has never actually launched Falcon Heavy and successfully recovered all of the boosters from a single Falcon Heavy launch. Therefore all Falcon Heavy launches are failures. 

2 hours ago, Ultimate Steve said:

Last Falcon 9 to not deliver its payload was possibly Zuma, 175 flights ago. The details are classified but it is known that the customer supplied their own payload adapter, and if there was a separation failure, SpaceX is not to blame.

But if it wasn't for Zuma remaining attached to the upper stage, Zuma could have stayed in space maybe, and so it's the fault of the upper stage that dragged Zuma back down into the atmosphere. Failure.

2 hours ago, Ultimate Steve said:

To get something more concrete that isn't one of the two obvious failures, 218 flights ago, all the way back on flight 4, SpaceX failed to deliver a secondary payload due to inadequate fuel margin.

Proving Merlin engines are unreliable.

2 hours ago, Ultimate Steve said:

If you want to be very liberal in your definition of failure to deliver payload, Starlink 4-7, 82 flights ago, could be counted as a solar storm shortly after launch caused the atmosphere to swell up, and most of the satellites decayed as a result, but I imagine that the vast majority of people wouldn't count this as the fault of the Falcon 9, as it successfully placed the satellites into the specified orbit.

If Falcon 9 was more powerful and more reliable then it could have put them in an orbit where this wouldn't happen. Failure.

2 hours ago, Ultimate Steve said:

Last Falcon 9 that crashed during an attempted landing was 114 missions ago on Starlink 19. I think even the haters can agree that a mission that doesn't attempt landing isn't a failure so I won't look that up.

If it's supposed to be reusable then why don't all boosters get reused? Make it make sense.

[Ultimate Steve]

Now I'm going to have fun trying to symmetrically apply those standards!

1 minute ago, sevenperforce said:

Did it reach orbit? No? Therefore, failure. An explosion is an explosion.

I agree. It's insane that they actually flew people on Saturn IB considering Saturn I's abysmal safety record from those times they filled the upper stage tanks with water and blew them up in space.

6 minutes ago, sevenperforce said:

SpaceX has never actually launched Falcon Heavy and successfully recovered all of the boosters from a single Falcon Heavy launch. Therefore all Falcon Heavy launches are failures. 

Yeah, and nobody ever talks about the third space shuttle failure, STS-4. Dumb booster parachutes didn't work.

10 minutes ago, sevenperforce said:

If it's supposed to be reusable then why don't all boosters get reused? Make it make sense.

SLS is by definition the most unreliable rocket ever. By design it can't even succeed once as it is throwing away the reusable boosters and engines for every single launch!

[tater]

tomorrow night: