totm nov 2023 SpaceX Discussion Thread

[wumpus]

3 hours ago, tater said:

tweet

Didn't Scott Manley point out that the big shiny thing couldn't be Starship?   https://www.youtube.com/watch?v=VoegqRJKGE8

[tater]

 

40 minutes ago, wumpus said:

Didn't Scott Manley point out that the big shiny thing couldn't be Starship?   https://www.youtube.com/watch?v=VoegqRJKGE8

I just skimmed that, where did he say that? It's certainly a test article. As for actual starship (orbital)... Dunno.

Edited December 28, 2018 by tater

[sevenperforce]

1 hour ago, DDE said:

 

RCS is not necessarily cryo. Both ULA’s IVF and the Buran testify to that.

If it’s what was meant, “hot gas” was a very odd way to describe it.

Yes, that is what I meant. SpaceShip will use 10-tonne-class hot-gas bipropellant rocket motors, pressure-fed from the header tanks and spark-ignited.

As opposed to cold gas, where the exhaust is simply gas under pressure.

1 hour ago, IncongruousGoat said:

At those small scales spark ignition works, so it's not too much more complicated than a hypergolic thruster.

Spark ignition works on larger scales, too. Like Raptor. And SSMEs.

[magnemoe]

23 minutes ago, sevenperforce said:

Yes, that is what I meant. SpaceShip will use 10-tonne-class hot-gas bipropellant rocket motors, pressure-fed from the header tanks and spark-ignited.

As opposed to cold gas, where the exhaust is simply gas under pressure.

Spark ignition works on larger scales, too. Like Raptor. And SSMEs.

Yes, looks like all moves to autogeneous pressurization at least for deep space and BFR is definite deep space.  
Think spark plugs is hard with kerosene, Saturn 5 3rd stage used it with hydrogen so its not new nor restricted to small engines. (OT / OT diesel engines don't use them and its pretty much kerosene and it had been used it it gave any benefit) 

[magnemoe]

1 hour ago, wumpus said:

Didn't Scott Manley point out that the big shiny thing couldn't be Starship?   https://www.youtube.com/watch?v=VoegqRJKGE8

Bottom did not look like it to him, now the top should have ports for RCS, also feed lines for this. still the bottom is the hard part you need the engine plate "hexaweb" (oxtaweb for falcon 9), the ability to quickly pull an engine and replace is important.
Separating engines if catastrophic fail like turbopump wanting to be an fragmentation grenade is critical. 
Plumbing is another issue fuel flow is idiotic high, think hydro plant not engine as in m^3/s. 

Kind of why I think the 31 engines upgradable to 42 is an joke, yes you could use smaller nozzles with an ISP penalty but shut them down who is nice if lifting tankers. 
However the plumbing will change a lot, its not something you can easy change. 

[Green Baron]

So SpaceX is really planning to build (part of) the hull of the Starship of steel ? Or is this just for the grashopper and further material decisions must yet be felled ?

I mean, high-alloy steels can have fantastic properties if treated correctly, they can be incredibly hard, or very temperature and pressure resistant (am thinking of cooling circuits in power plants, large turbine elements and rests), keeping their strength even at 500/600°C. But they are also very dense, which would cost a lot of payload capacity when used as main construction material for a rocket hull. Anyway, few materials can withstand reentry heat. I can imagine that boiling of fuel for "ablative" cooling (taking the heat away) is more inefficient than an ablative shell, which can be made lightweight.

One thing for sure, it does look nice ;-)

Edited December 28, 2018 by Green Baron

[IncongruousGoat]

57 minutes ago, sevenperforce said:

Spark ignition works on larger scales, too. Like Raptor. And SSMEs.

Well, yes, but you need to mess around with start chambers and pilot flames and so fort, which makes starting the engine take a little bit. For RCS, it should just be possible to set them off with a spark in the combustion chamber.

[tater]

9 minutes ago, Green Baron said:

So SpaceX is really planning to build (part of) the hull of the Starship of steel ? Or is this just for the grashopper and further material decisions must yet be felled ?

I mean, high-alloy steels can have fantastic properties if treated correctly, they can be incredibly hard, or very temperature and pressure resistant (am thinking of cooling circuits in power plants, large turbine elements and rests), keeping their strength even at 500/600°C. But they are also very dense, which would cost a lot of payload capacity when used as main construction material for a rocket hull. Anyway, few materials can withstand reentry heat. I can imagine that boiling of fuel for "ablative" cooling (taking the heat away) is more inefficient than an ablative shell, which can be made lightweight.

One thing for sure, it does look nice ;-)

Mass is not a simple trade-off. Meaning that metal seems like it should include a penalty vs CFC construction, but CFC will also require TPS on top, the mass might come out in the wash. There's also the cost of reuse. Propellants are cheap, so if you lose some payload mass fraction, it still might be far cheaper to make more flights than spend a great deal of effort refurbing a TPS system. We'll have to see.

As for the orbital vehicle vs this boilerplate, I assume that the orbital has also migrated to metal, though it will not be built in a field, lol.

[Green Baron]

5 minutes ago, tater said:

... though it will not be built in a field, lol.

Yeah, that would have reminded us too much of Zephram Cochraine (sorry for any misspelling), wouldn't it ?

Edited December 28, 2018 by Green Baron

[Scotius]

One can always use good old barn

[sh1pman]

2 hours ago, tater said:

 

I just skimmed that, where did he say that? It's certainly a test article. As for actual starship (orbital)... Dunno.

[sevenperforce]

If Elon's past boasts are any indication, the current starship being assembled in Boca has orbital capacity but will not be used as such.

2 hours ago, tater said:

Mass is not a simple trade-off. Meaning that metal seems like it should include a penalty vs CFC construction, but CFC will also require TPS on top, the mass might come out in the wash. There's also the cost of reuse. Propellants are cheap, so if you lose some payload mass fraction, it still might be far cheaper to make more flights than spend a great deal of effort refurbing a TPS system. We'll have to see.

Word.

2 hours ago, IncongruousGoat said:

Well, yes, but you need to mess around with start chambers and pilot flames and so fort, which makes starting the engine take a little bit.

Still better than dealing with TEA-TEB.

And pilot flames are a non-issue. The SSME is/was a FRSC (fuel-rich staged combustion) engine which used an augmented-spark igniter. If you have an augmentation igniter, you can ignite any time you want. If you are igniting via dual preburners in the main combustion chamber, that's a touch more challenging...but it is the sort of thing that can be readily tested.

3 hours ago, magnemoe said:

Think spark plugs is hard with kerosene, Saturn 5 3rd stage used it with hydrogen so its not new nor restricted to small engines. (OT / OT diesel engines don't use them and its pretty much kerosene and it had been used it it gave any benefit) 

The J-2 used an augmented spark igniter.

Quote

For RCS, it should just be possible to set them off with a spark in the combustion chamber.

Very easily. Hot-gas meth-oxy thrusters are hella easy to ignite. Case in point: your gas stove at home.

---------------------

For the record...

Yes, spark ignition of kerolox is a non-starter.

No one is suggesting spark ignition of kerolox.

Next topic.

Edited December 28, 2018 by sevenperforce

[Scotius]

8 minutes ago, sevenperforce said:

If Elon's past boasts are any indication, the current starship being assembled in Boca has orbital capacity but will not be used as such.

No way. It's too small and crude looking. If it isn't a stationary mock-up, at best it's a Grasshopper 2.0. for low altitude test hops. To me, it looks capable only of brute force testing of engines and landing legs, before real test article capable of suborbital hops will be rolled out. And i bet it' won't be hammered together in the open field.

[sh1pman]

This is how Jeb’s Junkyard and Used Rocket Parts manufacturing process looks like

[ThatGuyWithALongUsername]

1 hour ago, sh1pman said:

This is how Jeb’s Junkyard and Used Rocket Parts manufacturing process looks like

It looks more like the old Rockomax parts to me. 

[Xd the great]

2 hours ago, Scotius said:

No way. It's too small and crude looking. If it isn't a stationary mock-up, at best it's a Grasshopper 2.0. for low altitude test hops. To me, it looks capable only of brute force testing of engines and landing legs, before real test article capable of suborbital hops will be rolled out. And i bet it' won't be hammered together in the open field.

I bet it will, because cost savings.

[RedKraken]

Reading the active cooling re-entry (energy budget) threads on reddit and nsf.

Lots of assumptions flying around. Plenty of uncertainty. 

Some folks think film cooling is a must. Other folks want to add convective cooling beforehand.

Will be interested in seeing these ideas tighten up as the subject matter experts get involved.

I wonder if a re-entry test unit could be back on the cards.. not the hopper...something orbital.

 

Like the BFSmini but cheap and nasty.

F9 upper stage, clad with stainless, cooling channels and vents, drag fins, stainless cap as fairing, methane thermos and pumps as payload, instrumented up.

Push it out toward ~GTO for a high speed re-entry..

It doesn't have to survive, only the telemetry matters.

A ~3.66m, 20t vehicle is not a 9m, 100t vehicle, but it might be a cheap way to get data before the first starship is built..

The mass budget could be something like 10t including a few tonnes of methane coolant.

5mm SS armour for S2 is about 6t (12m x 4m diameter).

Edited December 29, 2018 by RedKraken

[Xd the great]

Is this what the metal bfs is for? Supersonic retropropulsion and the orbital tests?

[tater]

1 hour ago, Xd the great said:

Is this what the metal bfs is for? Supersonic retropropulsion and the orbital tests?

No, I'd expect terminal descent testing (hover, landing, etc). A lot of the issues will be software, I'd expect.

[DDE]

8 hours ago, sevenperforce said:

Yes, spark ignition of kerolox is a non-starter.

No one is suggesting spark ignition of kerolox.

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.

Edited December 29, 2018 by DDE

[tater]

 

[Green Baron]

Just wait, in a few days Elon twitters "Rocket ? Who thought we'd build a rocket from stainless steel ? We'll sell things there. Moichandising ! Come, i'll show you. SpaceX the towel, SpaceX the plushy, SpaceX the flamethrower, SpaceX the (flying) brick ...."

:-)

Edited December 29, 2018 by Green Baron

[tater]

 

[magnemoe]

19 hours ago, tater 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. 

If they needed more strength they would add that directly to the hull. 

 

[tater]

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