totm nov 2023 SpaceX Discussion Thread

[SOXBLOX]

4 hours ago, Silavite said:

it's record as the tallest structure in South Texas

Only if you gerrymander the definition of South Texas...

[RCgothic]

The idea of a stretched F9US is interesting! Likely an even better than its already incredible mass fraction. Even if it'll forever be on paper.

I had thought they were at structural limits for length.

 

[tater]

10 minutes ago, RCgothic said:

I had thought they were at structural limits for length.

They are already doing a stretch fairing for the USAF/USSF (whatever).

[SOXBLOX]

21 minutes ago, tater said:

the USAF/USSF (whatever).

As @kerbiloid said, the Airless Force.

[StrandedonEarth]

1 hour ago, RCgothic said:

I had thought they were at structural limits for length.

 

I thought they were close to the fineness limit. FH may have less issue with that due to reinforcing for Heavy mode. 

[Maria Sirona]

I just want you to appreciate the fact that soon the Saturn V will lose its status of the largest rocket ever built to SpaceX Starship.

Edited July 10, 2021 by Maria Sirona

[tater]

Cargo Dragon go for undocking in about an hour.

[RealKerbal3x]

RBoost #5 has arrived:

 

[SOXBLOX]

Why is Raptor's nozzle greenish? Is it the alloy, or is it discoloration from a test fire, or is it both?

[RCgothic]

I believe it's a sort of protective coating.

[zolotiyeruki]

I have to say that I'm extremely impressed with the packaging, i.e. how small they've been able to make the whole assembly.  I say this because at my last job I dealt with moving fluids through pipes, measuring flow, actuating vales, etc.  Valve actuators are big, and fast-acting actuators are really big.  Accurately measuring steady state fluid flow through a long, straight pipe is more difficult than you'd expect, and measuring rapidly-changing fluid flow through curved pipes in close proximity to pumps and turbines is simply an absurd problem.  And doing it in an extremely hot and violently vibrating tail end of a rocket?  Fuggetaboutit.

Seriously, my hat is off to those engine designers (and not just SpaceX's!)

[Rakaydos]

12 minutes ago, zolotiyeruki said:

I have to say that I'm extremely impressed with the packaging, i.e. how small they've been able to make the whole assembly.  I say this because at my last job I dealt with moving fluids through pipes, measuring flow, actuating vales, etc.  Valve actuators are big, and fast-acting actuators are really big.  Accurately measuring steady state fluid flow through a long, straight pipe is more difficult than you'd expect, and measuring rapidly-changing fluid flow through curved pipes in close proximity to pumps and turbines is simply an absurd problem.  And doing it in an extremely hot and violently vibrating tail end of a rocket?  Fuggetaboutit.

Seriously, my hat is off to those engine designers (and not just SpaceX's!)

You could call it a Pipe dream. :p

[sevenperforce]

Random question, but do turbopumps have transmissions? Obviously there is gearing between the turbine and the impeller but does anything in that ever need to “shift” in some way? I wouldn’t imagine so, but I am curious. 

[Elthy]

Are you even sure there is even gearing insinde the turbopump? I never hear of that and cant imagine it.

Edited July 8, 2021 by Elthy

[Rakaydos]

14 minutes ago, sevenperforce said:

Random question, but do turbopumps have transmissions? Obviously there is gearing between the turbine and the impeller but does anything in that ever need to “shift” in some way? I wouldn’t imagine so, but I am curious. 

I would imagine they do away with the gearing entirely, and use blade pitch on the impeller for any "gearing" that needs to be done.

[sevenperforce]

22 minutes ago, Elthy said:

Are you even sure there is even gearing insinde the turbopump? I never hear of that and cant imagine it.

I spoke too broadly; not all engines have gearing.

Raptor doesn't need gearing because it uses inline impellers on both its turbopump/preburner assemblies, and the both the Merlin 1D and the RD-180 use single-shaft dual-impeller turbopumps run by the turbine.

The RL-10 does need a gearbox, however, because it uses dual-shaft turbopumps operated by only one turbine. The hydrogen expansion through the single turbine drives the hydrogen turbopump, with its drive shaft geared to the separate drive shaft for the oxygen turbopump.

You can get away with a single-shaft dual-impeller turbopump (Merlin 1D, RD-180) when the density of your fuel and oxidizer are close enough to each other to allow it, like with kerosene and LOX or with hypergolic propellants (when you're using a power cycle other than pressure-feeding). But with a hydrolox engine, the turbopump impellers need to spin at significantly different speeds to pump propellant most efficiently, so you're more likely to need gearing.

The RS-68 and YF-77 avoid gearing by using dual turbine-impeller assemblies, each fed from the same central gas generator. The RS-25 avoided gearing by having two separate fuel-rich preburners: one for the high-pressure fuel turbopump and one for the high-pressure oxygen turbopump. However, one could very easily imagine a different version of the RS-25, with just a single fuel-rich preburner geared to the two turbopumps. 

34 minutes ago, Rakaydos said:

I would imagine they do away with the gearing entirely, and use blade pitch on the impeller for any "gearing" that needs to be done.

Now that I think more about it, I don't believe they'd even have blade pitch. All modern turbopumps use centrifugal impellers so they shouldn't have variable pitch. They can just reduce turbine RPM if they need to downthrottle. 

[zolotiyeruki]

14 minutes ago, sevenperforce said:

Now that I think more about it, I don't believe they'd even have blade pitch. All modern turbopumps use centrifugal impellers so they shouldn't have variable pitch. They can just reduce turbine RPM if they need to downthrottle. 

I think the idea is that if you had a common shaft, you could accomplish different "gearing" by using one pitch for the fuel impeller and a different pitch for the oxidizer impeller

[MKI]

1 hour ago, zolotiyeruki said:

I think the idea is that if you had a common shaft, you could accomplish different "gearing" by using one pitch for the fuel impeller and a different pitch for the oxidizer impeller

Why does this sound like Honda VTEC in a rocket hahaha. 

 

 

Edited July 8, 2021 by MKI
removed ref to VTEC meme, cuse I guess there was a shooting related to the term. No need so removed

[magnemoe]

2 hours ago, zolotiyeruki said:

I think the idea is that if you had a common shaft, you could accomplish different "gearing" by using one pitch for the fuel impeller and a different pitch for the oxidizer impeller

Read it like this myself,  now its now pitch on an centrifugal pump who works totally different from en propeller style pump. Later is used for low pressure-max volume. 
It might be ways around the gear box but this might well be heavier and more complex. 

[sevenperforce]

2 hours ago, magnemoe said:

Read it like this myself,  now its now pitch on an centrifugal pump who works totally different from en propeller style pump. Later is used for low pressure-max volume. 
It might be ways around the gear box but this might well be heavier and more complex. 

**looks up, ten pages into a 1975 NASA treatise on ideal impeller speed and its relation to flow density**

Apparently the problem is most serious with liquid hydrogen. LOX and denser fuels can operate well at speeds as low as 3,500 rpm but hydrogen impellers work best at speeds as high as 40,000 rpm.

One of the early Titan II main engines used a single turbine with a central driveshaft that was geared independently to both the fuel impeller and the oxidizer impeller. That allowed them to spin the main turbine at whatever speed was ideal for the exhaust itself and then gear that in one direction for the fuel and in the other direction for the oxidizer. A later Titan II main engine used an inline fuel pump and a geared oxidizer pump. The F-1 engine used a common shaft. 

[JoeSchmuckatelli]

6 hours ago, sevenperforce said:

looks up, ten pages into a 1975 NASA treatise on ideal impeller speed and its relation to flow density

I like the cut of your Jib, sailor!

 

(Thanks for posting stuff like this)

[James Kerman]

17 hours ago, Maria Sirona said:

...soon the Saturn V will lose its status of the largest rocket ever built to SpaceX Starship.

Overlapping topics have been merged.

[RCgothic]

Booster 3 completed ambient proof last night:

 

 

[RealKerbal3x]

Curved tiles on the forward flap aerocovers!

[sevenperforce]

7 hours ago, RealKerbal3x said:

Curved tiles on the forward flap aerocovers!

So there are.

I suppose that settles that question.