totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

12 hours ago, RCgothic said:

Previously, word of Elon was that they would do a dual-bell. However given the visible flow separation, it appears they didn't do a dual bell design at all (if they did, the flow separation would occur at the discontinuity) and instead they have simply truncated the bell just below the point of flow separation. Less efficient at sea level than the altitude-compensating nozzle of the RS-25, but more efficient in vacuum. 

[CatastrophicFailure]

1 hour ago, zolotiyeruki said:

Well, you could do the math.  Let's say you've got a 50cm vertical jump on earth (because that makes the math easy).  0.5 = 1/2*9.8*t^2, and your fall time is about 1/3 second, and your vertical speed is 1/3*9.8 ~= 3.3m/s.  On the moon, with roughly 1.6m/s^2 gravity, your fall time would be about 2 seconds, so you'd make it 1/2*1.6*2^2 ~= 3.2 m off the floor.

That's a standing jump, upwards.  If you launched at a 45 degree angle, your initial vertical velocity would be .707*3.3 = 2.3m/s, which works out to a fall time of about 1.5 seconds.  If we neglect air resistance, you'd fly 1.5s * 2 * 2.3 = 6.9 meters.  If you're a bit more athletic, or you get a running start, then yeah, crossing a 9m room in a single bound is within the realm of possibility.

The math is easy (for those so blessed ),  but what does the reality actually look like? It took Neil & Buzz a bit of experimenting to figure out the best way to move around on the surface, and that was with a space suit basically doubling their weight. How will people actually move about inside a room large enough to actually do so, while staying controlled? We never see this accurately portrayed in movies & such. Might get ugly if someone jumped too far and knocked the bowl of water over into the moon cat. 
 

Also, best view yet:

 

 

 

 

Edited September 25, 2020 by CatastrophicFailure
Oh fer the love of Kerm...

[Nothalogh]

3 hours ago, sevenperforce said:

a version of the RD-270 which would have run on PENTABORANE

I sure do love the idea of several hundred tons of THAT sitting on the pad...

 

At least the fireball will be a nice green.

[sevenperforce]

1 hour ago, tater said:

 

Spoiler

So they have a racetrack up the dorsal spine of SS. Presumably at some point covered (not for SN8, but for orbital versions).

Seeing it with the wings folded back like that is just pure beauty. This angle shows how the wings are blended into the rest of the body. There should be a very significant negative stagnation behind those chines which will tend to promote passive aerodynamic stability. 

1 hour ago, tater said:

Wonder if the vehicle could get asymmetric legs?

Legs tucked inside on the windward (ventral) side, under the TPS, and something more F9 like on the dorsal surface? Not F9 legs, but widespread, using as much vertical space as needed to fold.

Yeah, I've thought of this too -- the current fold-out design on the windward side, but F9-style or ITS-style on the lee side.

21 minutes ago, CatastrophicFailure said:

Also, best view yet:

Just as I suspected when I saw the original failure:

 

 

[sevenperforce]

I think Elon really missed an opportunity with the naming on the first stage.

He should have gone with "Starbooster".

[mikegarrison]

30 minutes ago, sevenperforce said:

Just as I suspected when I saw the original failure:

 

 

So, now that you have a better view, I'm going to assume that the people who were gushing about how great it was that it didn't fail at a weld can see that it pretty obviously failed along the welds....

Just that one panel tore through the middle. The rest of it all clearly separated at the welds.

Edited September 25, 2020 by mikegarrison

[sevenperforce]

4 minutes ago, mikegarrison said:

So, now that you have a better view, I'm going to assume that the people who were gushing about how great it was that it didn't fail at a weld can see that it pretty obviously failed along the welds....

Not really. There was no propagation along the weld, merely failure at the weld. Look how jagged the marks are around the circumferential failure. There's one place with a little fracture propagation -- the sawtooth -- but it is short and arrested by the weld itself. The rest of the failure surface is uneven, which is what you expect from a failure of the steel itself at a stress point.

[PakledHostage]

On another note, I just discovered that the Tesla Roadster with Starman is included in NASA's Eyes On The Solar System application. It currently shows as being about 70 million km from Earth and 11 million km from Mars.

[CatastrophicFailure]

On another note, this is interesting. Apparently SpaceX was willing to consider an expendable Starship for the Air Force. 
 

 

[kerbiloid]

A reusable ICBM gets real?

[sh1pman]

2 hours ago, sevenperforce said:

Seeing it with the wings folded back like that is just pure beauty.

Starting to look like a proper Mars rocket instead of a grain silo, isn’t it?

[tater]

 

[sh1pman]

@tater High Stellarch of the Nose Cone Empire with his retinue

 

[magnemoe]

5 hours ago, sevenperforce said:

Previously, word of Elon was that they would do a dual-bell. However given the visible flow separation, it appears they didn't do a dual bell design at all (if they did, the flow separation would occur at the discontinuity) and instead they have simply truncated the bell just below the point of flow separation. Less efficient at sea level than the altitude-compensating nozzle of the RS-25, but more efficient in vacuum. 

Who makes sense as the vacuum engine will just be used at ground in an emergency or for test firings. 

[sh1pman]

Is it inefficient to run vacuum-optimized engine at sea level, or the only problem is risk of damaging the engine due to flow separation? 

[kerbiloid]

Don't they test them installed at sea level?

[sevenperforce]

2 hours ago, sh1pman said:

Is it inefficient to run vacuum-optimized engine at sea level, or the only problem is risk of damaging the engine due to flow separation? 

It is inefficient. See the Mach diamond? The entire space around that Mach diamond is where the atmosphere is producing parasitic pressure drag on the nozzle. Over expansion results in lower total thrust for a given propellant flow rate and correspondingly lower efficiency. 

When fired at sea level, the smaller Raptor has a higher specific impulse then the vacuum Raptor. The same thing was true with the space shuttle main engine. An RS-25 has a vastly more efficient turbopump cycle than the RS-68, and yet the RS-25 has only slightly better sea level specific impulse because of the parasitic overexpansion that reduces net thrust. 

13 hours ago, magnemoe said:

Who makes sense as the vacuum engine will just be used at ground in an emergency or for test firings.

Exactly. The only time the Raptor would be used operationally at sea level would be in an abort, when efficiency matters not at all. In contrast the RS-25 was designed to be fired from ground to orbit in every mission.

[magnemoe]

20 minutes ago, kerbiloid said:

Don't they test them installed at sea level?

Most like the Merlin vacuum engine is tested without the vacuum nozzle, you are testing the turbo pump and cooling after all. 

Now its an tricks putting the engine inside an larger tube and somehow have it create its own low pressure environment, assume the rocket flame pulls air out of the tube lowering the pressure but this is rare, guess only used to develop engines. 

[RealKerbal3x]

SN8 is on the move!

Edit: So pretty!

Edited September 26, 2020 by RealKerbal3x

[sevenperforce]

48 minutes ago, RealKerbal3x said:

SN8 is on the move!

 

Interesting that they fold the fins back like that for transportation. I don’t think they did that with Mk1. I suppose it makes sense, though. They want it to have a lower wind cross-section.

I anticipate that they will do a thrust puck test with the simulator first, before stacking the nosecone. It remains to be seen whether they will stack at the launch site or bring it back.

[RealKerbal3x]

4 minutes ago, sevenperforce said:

I anticipate that they will do a thrust puck test with the simulator first, before stacking the nosecone. It remains to be seen whether they will stack at the launch site or bring it back.

I think it makes more sense for them to simply roll the nosecone out to the pad. Otherwise they'd have to roll SN8 back and forth again.

Also, NASASpaceflight is live!

 

Edited September 26, 2020 by RealKerbal3x

[RCgothic]

28 minutes ago, sevenperforce said:

Interesting that they fold the fins back like that for transportation. I don’t think they did that with Mk1. I suppose it makes sense, though. They want it to have a lower wind cross-section.

I anticipate that they will do a thrust puck test with the simulator first, before stacking the nosecone. It remains to be seen whether they will stack at the launch site or bring it back.

Were mk1's fins actually driven at all? I don't remember any test flexing.

[RealKerbal3x]

11 minutes ago, RCgothic said:

Were mk1's fins actually driven at all? I don't remember any test flexing.

I wouldn't be surprised if they weren't, Mk1 was little more than a fancy backdrop for Elon's presentation.

[tater]

 

[RealKerbal3x]