totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

On 12/29/2018 at 2:58 AM, DDE said:

Eeexcuse me.

Buran’s Unified Propulsion System (ODU) used Syntin+oxygen (in-flight) or gasoline+oxygen (ground testing) for all of the main (17D12; 90 kN, 362 sec), RCS (17D15; 4 kN, 275 sec, 295 sec for prograde thrusters with extended nozzles) and vernier (17D16; 200 N, 265 sec) thrusters; it drew from the same ultrachilled lOx tank as the hydrolox fuel cells, although for RCS and verniers the oxygen was purposefully evaporated in an oxygen-rich gas warm gas generator to pressurize the feed lines to above 2.5 MPa, for 5 MPa nominal (lOx tank pressurization was via helium; main engines used staged combustion). Mixture ratio was something like 4 to avert any soot. It used spark ignition in the two smaller engine types, obviously (specified for pulses of as less as 0.06 sec), while the mains used... something pyrophoric, good for 18 firings.

And it’s slated to be partially brought back as the new RCS on a future Block D upgrade.

...I’ll get off my high horse now.

All good info.

Syntin is similar to RP-1 but has higher density and lower viscosity, both of which make it easier to ignite via spark ignition. Moreover (as I understand it), the pyro-ignited mains used syntin+LOX while the spark-ignited verniers used syntin+GOX with a preheater (as you note above) which also aids in spark ignition. Running on GOX for the mains is not really feasible because of flow issues; you can't get very good thrust.

Spoiler

Note: one should differentiate between an engine that uses pressure-fed gas and an engine that uses pumped staged combustion (not even FFSC; can be FRSC or ORSC). With a pressure-fed gas, it gets difficult to push enough propellant through the feed lines to get a good TWR, so it's not suitable for main engines. The difference with staged combustion is that you pump liquid into the preburner and then the preburner exhausts into the combustion chamber, so you have no fuel flow issues.

To spark-ignite actual kerolox in a large main engine, you pretty much have to use a staged igniter a la SSME and you have to figure out a way to vaporize the kerosene, which is not easy. Gasoline (petrol) is much easier to vaporize than kerosene...one reason kerosene is much safer. You can't do FRSC with a kerosene-similar fuel because of coking.

27 minutes ago, magnemoe said:

Don't look like an rocket for me with that internal structure. I assume they will use an common bulkhead with an fat tube for LOX down to the engines. 
You also need an return tube for pressurization and overflow, this has to get all the way to the top for RCS for the BFS. 

Internal load-bearing structure doesn't preclude a monocoque tank; there's no reason they can't fill it straight up.

This is a flight article; it needs a load-bearing member for landing. At landing, the lower portion of the tank (and the engine thrust structure) is all effectively suspended from the top of the legs.

I anticipate internal trusses mating the thrust structure to the lower leg braces as well, so that the overall body has both compressive and tensile load-bearing capacity.

This may be one of the reasons they decided to make the switch back from composites to steel. Composites have better pressure-bearing capacity in terms of mass budget, but since the StarShip is not pressure-fed, it makes more sense to prioritize dynamic load-bearing, where steel blows composites away.

27 minutes ago, tater said:

It's an airframe, not a tank. Props will be internal tanks, it only needs to hop, after all.

Sure, that's possible. Not necessary, though. They seem to be spending quite a bit of time welding and polishing the outside if it's not going to be pressurized.

[tater]

21 minutes ago, sevenperforce said:

Sure, that's possible. Not necessary, though. They seem to be spending quite a bit of time welding and polishing the outside if it's not going to be pressurized.

You really think they'll put props in there? I suppose they make propane tanks all the time (I have one in my yard, lol)... dunno about lox tank manufacture.

[sevenperforce]

52 minutes ago, tater said:

You really think they'll put props in there? I suppose they make propane tanks all the time (I have one in my yard, lol)... dunno about lox tank manufacture.

If they can get unlined COPV to work for LOX, I imagine stainless will be no problem.

[tater]

3 minutes ago, sevenperforce said:

If they can get unlined COPV to work for LOX, I imagine stainless will be no problem.

True. I suppose I am needlessly conflating the real spacecraft with this hopper. For this purpose, it need not be constructed to aerospace standards.

[DDE]

49 minutes ago, tater said:

You really think they'll put props in there? I suppose they make propane tanks all the time (I have one in my yard, lol)... dunno about lox tank manufacture.

Try acid tank manufacture. IRFNA lasts for decades in stainless steel, but AFAIK the “inhibitor” (0.5% of hydrofluoric acid) accelerates corrosion of aluminium by a factor of 2000 and titanium by a factor of 5000. In the latter case the corroded material is spontaneously explosive, as learnt by the messy demise of a poor sod handling a few test sample strips at Edwards AFB. Thus military missileers have built load-bearing oxidizer tanks for missiles for decades; cryogens wouldn’t be a big leap.

[tater]

They tested moving it with the crane, apparently:

 

[Xd the great]

8 hours ago, tater said:

They tested moving it with the crane, apparently:

for dropping on kerbals.

[sevenperforce]

12 hours ago, tater said:

They tested moving it with the crane, apparently:

 

If it can't manage a load under suspension, that would be bad.

[cubinator]

2 minutes ago, sevenperforce said:

If it can't manage a load under suspension, that would be bad.

It's a key part of the mission architecture, with the streamlined swappability of the tanker ships. I trust they've designed that ship to take the forces with ease.

[tater]

They need to be able to stack it, then presumably move it someplace to fly it as well.

Also:

 

Apparently already another 2 rings on top of the image I just posted.

 

Edited December 31, 2018 by tater

[tater]

So far this makes the thing something like 46m high, assuming they add no more sections. The current final design is more like 55m.

[cubinator]

3 minutes ago, tater said:

So far this makes the thing something like 46m high, assuming they add no more sections. The current final design is more like 55m.

Would be very interesting to jump right over it on Phobos.

[tater]

 

[tater]

 

[CatastrophicFailure]

Just now, tater said:

 

Wait, what? 

Are those Merlins? They can’t have that many field-ready Raptors already... can they?

Dang, this is serious!

[Ultimate Steve]

Found on NSF:

 

[Spaceception]

Where's that Elon tweetstorm when you need it.

Edited December 31, 2018 by Spaceception

[NSEP]

20 minutes ago, tater said:

 

Why do they need three taps on the bottom for the water tank? Why do they have to bell shaped?

[magnemoe]

27 minutes ago, CatastrophicFailure said:

Wait, what? 

Are those Merlins? They can’t have that many field-ready Raptors already... can they?

Dang, this is serious!

Its three, main issue now is that i don't see any way to flex the landing legs and the design don't looks like two tanks with the structure including RCS for it. 
And no suspension for the legs, granted it could be in the pad itself 
On the other hand why make an boilerplate for the grasshopper? 
Yes it makes perfect sense for the BFS itself to have an boilerplate for training ground handling but you would including stuff like engine swapping and maintenance of RCS I think. Yes you could use test article engines or mock-ups but you would want something pretty realistic. 

[tater]

The bottom of the fins has a hole normal to the fin plane. I’ll expect some sort of shock absorber added.

[Ultimate Steve]

Maybe if the BFH isn't blown up during testing they will make it into a water tower afterwards...

[NSEP]

5 minutes ago, Ultimate Steve said:

Maybe if the BFH isn't blown up during testing they will make it into a water tower afterwards...

Speaking of explosions, im really looking forward to when this thing explodes. Because well, its gonna, it must happend sometime, right?

No explosion no lesson.

[Mad Rocket Scientist]

1 hour ago, CatastrophicFailure said:

Wait, what? 

Are those Merlins? They can’t have that many field-ready Raptors already... can they?

Dang, this is serious!

The size of them looks like raptors to me. They might be mockups for test fitting though. 

[Mad Rocket Scientist]

Actually, taking a closer look at the image it looks like there are small details on the powerhead area of the engine that makes me think that this is a real engine, and the slight misalignment of the middle engine is from the gimbal not being hooked up yet.

However, there's another weird thing, it looks like the curve of the bell is not continuous the entire way to the top. I saw some speculation that that was a dual bell nozzle for better efficiency in both SL and Vac environments, but I think that it is just shielding, since it does not appear to contract to a small enough throat at the top.

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=47022.0;attach=1536232;image

[Ultimate Steve]

1 minute ago, Mad Rocket Scientist said:

Actually, taking a closer look at the image it looks like there are small details on the powerhead area of the engine that makes me think that this is a real engine, and the slight misalignment of the middle engine is from the gimbal not being hooked up yet.

However, there's another weird thing, it looks like the curve of the bell is not continuous the entire way to the top. I saw some speculation that that was a dual bell nozzle for better efficiency in both SL and Vac environments, but I think that it is just shielding, since it does not appear to contract to a small enough throat at the top.

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=47022.0;attach=1536232;image

Hmm... Interesting theory on the gimbal. I'm still leaning towards mockups, as Elon tweeted that the redesigned raptor would not fire until January. It seems a bit early to see the New Raptors, unless they are sticking the old design on just to say they can fly, or as a test, which doesn't make much sense. Although they still could be real, for all we know... A few weeks ago we all thought this thing was a water tower.

As far as the dual bells, maybe the engine goes farther upwards and there is a hollow space. Although it could be structure. But then that raises the question of why the hopper would need vacuum Raptors... But, yeah, I'm leaning towards shielding as the bell diameter appears to be 1.3-1.4m, which is the old statistic for the SL Raptor.