totm nov 2023 SpaceX Discussion Thread

[darthgently]

15 hours ago, StrandedonEarth said:

Ok, now wait a sec. That's right, these engines gimbal. Quite a bit, IIRC. And the entire engine gimbals, not just the nozzle, so those pump shafts are already moving around. I start to get the feeling that pump shaft/rotor gyro effects may be a red herring.

One other factor is that when the pumps swallow bubbles they speed up quite a bit because dropped resistance in the fluid.  So in addition to the sudden changes in resistance from bubbles causing pump strain issues, the centrifugal forces are probably spiking as Mikki suggests when swallowing a stream of bubbles or getting no fluid at all.  In short, a lot of factors leading to catastrophe perhaps?

Also, to your point, I think the vid below is at normal speed.  Very quick gimbaling

 

Edited November 22, 2023 by darthgently

[tater]

 

[JoeSchmuckatelli]

Looking @tater's vid above

They got all but one of the inner ring relit immediately.  Visual confirms what they showed on the graphic (Booster graphic 3:19 in Manley's vid) 

So given that, we can likely have confidence in the rest of the graphic showing how the Raptors lit then failing collapses away from the unlit one. (@ 3:30 - :40)

I cannot begin to speculate about the significance - but I do think it noteworthy. 

 

Edited November 22, 2023 by JoeSchmuckatelli

[JoeSchmuckatelli]

On 11/18/2023 at 8:35 AM, JoeSchmuckatelli said:

@Gargamel  -- Thanks for getting me back on the forums in time for this!

 

 

This was the first time I noticed I could access S&SF via my regular account.  The Temp Alt worked for a few days before this.

Just offering this as a 'timestamp' in case it helps figuring out what worked before.

(For non-Gargamel readers... apologies for the non-sequitur post)

[Exoscientist]

 This observer gives the proportion of propellant remaining according to time from the graphic on the SpaceX launch page. From this you can estimate the propellant flow rate, the slope. If accurate it appears to indicate a lower burn rate than full throttle:

https://x.com/Space_Josiah/status/1726731762347503745/

  Robert Clark

 

Edited November 25, 2023 by Exoscientist

[tater]

 

[Mikki]

I guess if SpaceX is keeping the the SH engine assembly as it is they will focus on a much more refined timing of booster separation.

The might try to keep SH running by rotating it way, waaaay slower than before. The structural strain on three Raptor 2 engines running at full speed is aequivalent to the torque exerted by a cargo train weighing roughly 18`000 10`000 metric tons (!) accelerating 1 meter/second, only by gyroscopic forces carried by the 6 center rotor nose and side bearings.

If the propellants can keep up with cooling this hellscape they might get away with SH  "return to launch site" profile.

I have read meanwhile that the middle ring of thrusters is kept spinning and flushed with LOX while flipping to keep the temperature of the pumps ready for re-ignition, correct me if i am wrong about this...

Bubbles have killed the SH in one or the other way, which is sure by now.

I am most courious for the next launch and really hope SpaceX can surprise us...

 

Edited November 23, 2023 by Mikki
Train weight sorry, carried, spell, typos

[Mikki]

...a bit off-topic the recent events at SpaceX...

I would slap some wings to SH and weld a proper cone on top (Blast cone hehe) and land SH like a glider...

Hoverslam is nice and all, mechazilla is great but i think landing like a plane would be more logical.

Or is this tube too bottom heavy to glide at all? 

[Minmus Taster]

Just now, Mikki said:

...a bit off-topic the recent events at SpaceX...

I would slap some wings to SH and weld a proper cone on top (Blast cone hehe) and land SH like a glider...

Hoverslam is nice and all, mechazilla is great but i think landing like a plane would be more logical.

Or is this tube too bottom heavy to glide at all? 

It's just too clunky to make practical I think. It's been proposed many times and since the 60s for even the Saturn V. Just too heavy and too light lift even with wings.

[CBase]

55 minutes ago, Mikki said:

Or is this tube too bottom heavy to glide at all? 

Propably wouldn't matter if you place CoL close enough to CoM. Wings could translate vertical speed to horizontal speed on return, whichs saves fuel for a boostback. But they add weight which costs fuel on ascend. My gut feeling is that mostly the TWR difference makes it way more expensive at launch.

[Nuke]

we have kind of been down this road with skylon. it can work but the payload delivery will be a lot less than starship's. think it would be better using the engine in a suborbital space plane, and releasing the payload outside of the atmosphere so you just need a vacuum rated kick motor to circularize. sort of like air launch but release takes place above the karman line. the same ship could have orbital capability for lighter payloads (like astronauts), and maybe on return from orbital missions you can retrieve your kick stages and other space junk. it still solves a lot of launch infrastructure problems that starship has, and the ability to launch from anywhere with a sufficiently large airport will make more optimal orbits possible. i really dont think they need to be in direct competition either, there is a place for both. its just an ssto spaceplane is a harder nut to crack and will be late to the party. 

[PakledHostage]

3 hours ago, Mikki said:

The might try to keep SH running by rotating it way, waaaay slower than before. The structural strain on three Raptor 2 engines running at full speed is aequivalent to the torque exerted by a cargo train weighing roughly 18`000 10`000 metric tons (!) accelerating 1 meter/second, only by gyroscopic forces carried by the 6 center rotor nose and side bearings.

How fast is this pump spinning? For comparison, the core compressor/turbine stage in a big turbofan like the CF6-80 spins at about 9600 rpm and that core is bigger than me (6'2" male) and made out of heavy alloys like inconel. To my knowledge, there aren't any limitations on maneuvering a 747 where "ripping the engine off the pylon due to gyroscopic forces" are the governing factor. Why are the gyroscopic forces so large for this pump?

Edited November 23, 2023 by PakledHostage

[Mikki]

6 hours ago, PakledHostage said:

How fast is this pump spinning? For comparison, the core compressor/turbine stage in a big turbofan like the CF6-80 spins at about 9600 rpm and that core is bigger than me (6'2" male) and made out of heavy alloys like inconel. To my knowledge, there aren't any limitations on maneuvering a 747 where "ripping the engine off the pylon due to gyroscopic forces" are the governing factor. Why are the gyroscopic forces so large for this pump?

There are gyro forces on any turbine for sure. Rpm on Turbopumps is in the range of 30`000 to 110`000 Rpm. Raptor 2 output is stated at 30 and 36 MWatts per rotor.  I have read somewhere raptor 2 spins at 90-100`000 Rpm at full speed.

[Spaceception]

Next version of Starship is coming up. I wonder if they'll be keeping the version scheme, or moving to blocks like Falcon 9 eventually did. Starship Full Thrust? They could be getting close to the maximum performance from Raptor at this point.

Either way, I think we're going to see some big changes. Starship will obviously be using Raptor 3, but we'll also probably see the ship stretch, 3 more RVacs, forward flap redesign, and maybe the stubbier nose. This will likely be the operational version of Starship, and might be used for Artemis.

[JoeSchmuckatelli]

1 hour ago, Spaceception said:

the stubbier nose

What does that get you?  (First I'm hearing about this)

[Kartoffelkuchen]

28 minutes ago, JoeSchmuckatelli said:

What does that get you?  (First I'm hearing about this)

Probably a greater internal volume to use, and perhaps lower reentry thermal loading in the forward section due to the stubbier shape?

[Meecrob]

11 hours ago, Mikki said:

There are gyro forces on any turbine for sure. Rpm on Turbopumps is in the range of 30`000 to 110`000 Rpm. Raptor 2 output is stated at 30 and 36 MWatts per rotor.  I have read somewhere raptor 2 spins at 90-100`000 Rpm at full speed.

Yes, but the question isn't "Can you design a Raptor to withstand these forces?" It is "What is the mass penalty?" Or if it was a different mode of failure, there are always ways to fix engineering issues. The question is "How much Mass can you give up, and how much Time and Money do you have to throw at it?

We also know Elon absolutely loves the whole "no part is the best part" mantra. Sometimes, he is proven wrong. However,  time and time again, there has been a part on the drawing board seemingly inhumanely soon after there is a failure. For example. the Water Deluge plates seem to have been almost fully designed at time of IFT-1. It seems they took the data from the flight test, validated their models/made some tweaks, and sent their order to the fabrication shop very shortly after the test completed.

Having said that, my disclaimer is that I am going on logic. If anyone has actual data and not inferences, I'm all ears.

[Minmus Taster]

2 hours ago, Kartoffelkuchen said:

Probably a greater internal volume to use, and perhaps lower reentry thermal loading in the forward section due to the stubbier shape?

I believe elon has said that a flater nose is actually better for reentry but wanted to make it pointy. Classic Elon 

[tater]

 

14 minutes ago, Minmus Taster said:

I believe elon has said that a flater nose is actually better for reentry but wanted to make it pointy. Classic Elon 

Yeah, he said he thought it was funny after seeing The Dictator (Sasha Baron Cohen).

He added that a more blunt nose would actually be better.

[Mikki]

2 hours ago, Meecrob said:

Yes, but the question isn't "Can you design a Raptor to withstand these forces?" It is "What is the mass penalty?" Or if it was a different mode of failure, there are always ways to fix engineering issues. The question is "How much Mass can you give up, and how much Time and Money do you have to throw at it?

We also know Elon absolutely loves the whole "no part is the best part" mantra. Sometimes, he is proven wrong. However,  time and time again, there has been a part on the drawing board seemingly inhumanely soon after there is a failure. For example. the Water Deluge plates seem to have been almost fully designed at time of IFT-1. It seems they took the data from the flight test, validated their models/made some tweaks, and sent their order to the fabrication shop very shortly after the test completed.

Having said that, my disclaimer is that I am going on logic. If anyone has actual data and not inferences, I'm all ears.

SpaceX is obviously a private company with very flat operating hirarchy, they decide and construct their ideas "on the fly", with how it seems very capable and motivated staff and other small private contractors...

Instead of paying lots of "unproductive and questionable desktop" wages they actually get things off the ground, a classic enterpreneurs success story... I quite like it. SpaceX will definetly change human history or has allready.

 

[Deddly]

2 hours ago, Minmus Taster said:

I believe elon has said that a flater nose is actually better for reentry but wanted to make it pointy. Classic Elon 

I believe this is a case where his own rule No. 1 should be applied: 

Make your requirements less dumb

[tater]

 

[mikegarrison]

4 hours ago, Meecrob said:

time and time again, there has been a part on the drawing board seemingly inhumanely soon after there is a failure. For example. the Water Deluge plates seem to have been almost fully designed at time of IFT-1. It seems they took the data from the flight test, validated their models/made some tweaks, and sent their order to the fabrication shop very shortly after the test completed.

Water deluge has been used for 50 years, at least. The question is not "how did SpaceX design a water deluge system so quickly?", but rather "why did they think they didn't need one before?"

[tater]

20 minutes ago, mikegarrison said:

Water deluge has been used for 50 years, at least. The question is not "how did SpaceX design a water deluge system so quickly?", but rather "why did they think they didn't need one before?"

yeah, odd it was not done from the start—though they decided they needed it long before IFT-1, as they had built the hardware now in Boca Chica for 39A originally.

[Terwin]

39 minutes ago, mikegarrison said:

Water deluge has been used for 50 years, at least. The question is not "how did SpaceX design a water deluge system so quickly?", but rather "why did they think they didn't need one before?"

As best as I understand it, it looked like the high-temp high-strength concrete should be strong enough for them to do a test flight before the water deluge system was ready to install.  

I would guess that it was not as strong as they thought, but considering that S0 was not damaged enough to delay the next launch, and they got useful data from the first launch, I suspect they are reasonably happy with the results of taking that risk.

TLDR: Another example of 'move fast and break stuff'