totm nov 2023 SpaceX Discussion Thread

[SOXBLOX]

I think the more engines they build, the better. Keep all six Raptors on LSS, and take advantage of economies of scale, I guess.

[wumpus]

9 hours ago, RCgothic said:

Yes, gimballing only works when the main engines are on. RCS is for control at speeds where aero surfaces are ineffective (e.g. slow on landing) or where there's no atmosphere at all. They're also used to "quench" the gyroscopes when they get close to their limits.

The X-15 had RCS, but I'm sure it used aero surfaces while in the atmosphere (it had enormous and draggy aero surfaces for stability).  I don't think it could  gimbal, I strongly suspect that aero surfaces worked  far better than gimbaling could.

[RealKerbal3x]

Heat shield around Booster 4 Raptors looks mostly complete:

 

[StrandedonEarth]

1 hour ago, SOXBLOX said:

I think the more engines they build, the better. Keep all six Raptors on LSS, and take advantage of economies of scale, I guess.

Pretty much. They may be able to replace the three SL engines with a single gimballed RVac, but they’d like to limit variants, especially complicated ones. But I think differential thrust should be enough control, except for roll. That could be achieved with steering vanes, I suppose; but again, that’s more complexity. 

[magnemoe]

2 hours ago, RealKerbal3x said:

There's definitely room for gimbal systems around the RVacs, but the problem is that the engine bells are tucked up right next to the skirt with no room to move. You could move the engines closer to the centre, but it sounds like a lot of work compared to just leaving the engine configuration as it is and benefiting from the extra thrust and control authority the sea-level engines provide.

One problem is that the bottom is the bottom dome of the tank  so moving the RVacs inward will also lower them so you need an longer skirt or shorter RVac with lower performance. As they are so long its also limited how much you could gimbal them. Better to just use trust control for orientation. Now if you loose one of the RVac you can use the high gimbal of the surface engines to compensate and make up for the missing engine. Yes this will reduce performance. But for Moonship I assume it would reach an low moon orbit even if one of the RVac failed on liftoff from the moon who is worst case scenario. 

[mikegarrison]

8 hours ago, SOXBLOX said:

I think the more engines they build, the better. Keep all six Raptors on LSS, and take advantage of economies of scale, I guess.

That's not really how economies of scale work. Yeah, mass-production is cheaper per unit than one-off, but not so much cheaper that it actually costs negative resources to produce things. (Usually, anyway.)

[tater]

I think Raptors are still decently expensive until they move to Raptor 2—they are building the facility to make those in TX right now.

[SOXBLOX]

1 hour ago, mikegarrison said:

That's not really how economies of scale work. Yeah, mass-production is cheaper per unit than one-off, but not so much cheaper that it actually costs negative resources to produce things. (Usually, anyway.)

I meant it would probably be better to not produce as many niche variants, and just stick to the three current types. I guess I botched my terminology.

[tater]

I think that is the plan with R2 as well.

SL R2 would be like current SL Raptor, but improved. Gimbal, etc.

Rvac is as now, with improvements.

Rboost are no gimbal, and no restart (unsure on throttle) like the current booster engines  that are in the outer ring (they will be started on the pad with GSE).

[Beccab]

59 minutes ago, tater said:

no restart

Are you sure about that? Never heard of that part before, and they need to fly the booster again obv

Another thing with Raptor 2 is that it's much more simple than Raptor 1, removing all that spaghetti cables mess. It's supposed to be cheaper and safer this way, which even if R1 have now become quite reliable (no aborts on the S20 static fire, nor for B3 I think) doesn't hurt

[tater]

23 minutes ago, Beccab said:

Are you sure about that? Never heard of that part before, and they need to fly the booster again obv

Another thing with Raptor 2 is that it's much more simple than Raptor 1, removing all that spaghetti cables mess. It's supposed to be cheaper and safer this way, which even if R1 have now become quite reliable (no aborts on the S20 static fire, nor for B3 I think) doesn't hurt

The GSE on the launch table seems to be rigged for starting the outer engines. That just the outside ring of fixed engines. Not never restarted, not restarted in flight. They don't gimbal, and once the booster hits MECO, the next time they are used is the next liftoff. The best part is no part, leave the igniters on stage 0.

Edited November 14, 2021 by tater

[tater]

 

free registration for livestream

Given the group he is addressing, I would assume it's partially about Starlink impact mitigation, and perhaps Starship launched space telescopes.

[tater]

 

[tater]

 

 

[RCgothic]

Woohoo! January Launch? Fingers crossed!

 

Also this is just twisting the knife, lol.

Edited November 15, 2021 by RCgothic

[tater]

 

 

[Beccab]

 

[Shpaget]

Regarding the envronmental impact study, what are the most troublesome aspects? While the fuel for SS is not the same as for F9, is it really that much of a difference? Both are relatively clean burning hydrocarbons.

Is it noise? Aren't the F9 and FH in the same, insanely loud, ballpark as SS?

Is it the size of the thing? Landing?

[Beccab]

4 minutes ago, Shpaget said:

Regarding the envronmental impact study, what are the most troublesome aspects? While the fuel for SS is not the same as for F9, is it really that much of a difference? Both are relatively clean burning hydrocarbons.

Is it noise? Aren't the F9 and FH in the same, insanely loud, ballpark as SS?

Is it the size of the thing? Landing?

Landing is definitely a concern, especially because of the sonic booms it causes not too far from the ground

Were the F9/H launches from Boca authorized to do RTLS?

Edited November 16, 2021 by Beccab

[tater]

 

 

 

 

 

 

 

[Brotoro]

Me like.

[tater]

Quote

Raptor 2 has significant improvements in every way, but a complete design overhaul is necessary for the engine that can actually make life multiplanetary. It won’t be called Raptor.

That's a pretty profound redesign then. That puts the 1000 Starships per synod in an odd place unless he means an even better engine that still works within the SS/SH system, since that is the supposed point of SS.

What overhaul would be needed, assuming it is still a methalox system? Raptor 2 has to be fairly optimum, what's the max I_sp for CH4? Rvac has to be pretty close I would think. So why redesign? Simplicity to reduce cost?

Edited November 17, 2021 by tater

[mikegarrison]

On 11/13/2021 at 10:22 PM, tater said:

The GSE on the launch table seems to be rigged for starting the outer engines. That just the outside ring of fixed engines. Not never restarted, not restarted in flight. They don't gimbal, and once the booster hits MECO, the next time they are used is the next liftoff. The best part is no part, leave the igniters on stage 0.

I have no idea whether this applies to a Raptor engine, but I will mention that sometimes airplane engines operate close enough to the flameout margin that they turn the ignitors on in flight. It's much easier to restart a flame that partially goes out than to restart an engine after the flame is completely out.

[JoeSchmuckatelli]

2 minutes ago, tater said:

That's a pretty profound redesign then. That puts the 1000 Starships per synod in an odd place unless he means an even better engine that still works within the SS/SH system, since that is the supposed point of SS.

What verhaul would be needed, assuming it is still a methalox system? Raptor 2 has to be fairly optimum, what's the max I_sp for CH4? Rvac has to be pretty close I would think. So why redesign? Simplicity to reduce cost?

Yeah - that caught my attention, too.  What do you want to bet they're already half-way to figuring that out?

[tater]

7 minutes ago, mikegarrison said:

I have no idea whether this applies to a Raptor engine, but I will mention that sometimes airplane engines operate close enough to the flameout margin that they turn the ignitors on in flight. It's much easier to restart a flame that partially goes out than to restart an engine after the flame is completely out.

True. I suppose the question is if they think the extra complexity—just for those outer engines—is worth it. If an engine had a flameout (is that likely in a rocket engine vs a jet engine?), would they simply burn longer withthe remaining engines, and maybe use some gimbaling?

5 minutes ago, JoeSchmuckatelli said:

Yeah - that caught my attention, too.  What do you want to bet they're already half-way to figuring that out?

Not called Raptor could just be Musk being odd about names (it's not like SpaceX is terribly consistent with version numbers, lol), but it sort of implies something profoundly different in a way that a cost optimized Raptor would not be.

Nukes?

(Shotwell's husband is a nuc e I think)

Edited November 17, 2021 by tater