totm nov 2023 SpaceX Discussion Thread

[magnemoe]

1 hour ago, sevenperforce said:

The black COPVs on the outside are cold-gas nitrogen to supply the current RCS thrusters. They do not press the tanks; tank pressurization is maintained by autogenous vapor tapoff from the Raptor(s). Word of Elon:

It's possible that they have regulators attached directly to the tapoff lines currently; that would be the simplest way of doing it while they still have the nitrogen COPVs for cold-gas RCS. But I would not be surprised if they replaced the nitrogen COPVs with GOX and GCH4 accumulators. 

Presumably they won't need this during the test flights, but yeah, once they are conducting operational missions they'll definitely need a way to replenish.

Let's say, for the sake of argument, that there are no accumulators: the tapoff lines vent directly into the tanks with pressure regulators, and the hot-gas thrusters are in turn fed directly from the tanks. If this was the case, then using the hot-gas thrusters on orbit or during re-entry would reduce pressure in the tanks, which means Raptor has to be able to accommodate a variable range of inlet pressures. During orbital maneuvers, repeated RCS use could drop the tank pressures so low that the RCS could no longer fire. Accordingly, Starship would need resistance heating vaporization manifolds (not a gas generator) and low-flow electric pumps. It would have to pump propellant out of the tanks, vaporize it via resistance heating, and then vent it back into the tanks. This would be further complicated by the need for ullage in order to reliably pump the propellants out.

It would be much simpler, I think, to just use large enough accumulators that they simply never have to worry about it. Then they'd only need the vaporizers on really, really long-duration missions, which won't be an issue for quite some time. Or they could add more accumulator tanks for specialized missions requiring greater persistence or longer RCS burns (e.g. the lunar Starship). Tank pressures would remain constant and the RCS could have a much higher-pressure feed. They could even use multiple accumulator tanks in series (rather than in parallel) to control boil-off.

Next step: thrust simulator, right?

Did not know they was for nitrogen. However I assume this will change down the line as you say.
First off 6 bar is a low pressure to run an engine on and you will get losses in the pretty thin pipes to the trusters. 
As I understand they plan to land the moonship with the gas-gas trusters and they are supposed to have 20 ton trust at sea level.
 
Now I expect them to reduce pressure in the main tanks during long zero g periods like flying to mars or using one an an temporary space station. Pressurizing them again is easy with an vaporizer. 
Now the only issue I see is the moonship if it using gas-gas engines for landing but you can add more COPVs or go fancy like the IC engine on the centaur replacement. This might also be nice if you do lots of orbital operations. 

1 hour ago, tater said:

I think it's already under there. Yeah, a pressure test, then lift and remove thrust simulator, then engines, then static fire?

Thought they had two stands now one for pressure tests and trust puck simulation and another for static fire. 

[sevenperforce]

1 hour ago, magnemoe said:

Did not know they was for nitrogen. However I assume this will change down the line as you say.
First off 6 bar is a low pressure to run an engine on and you will get losses in the pretty thin pipes to the trusters. 

Right, they have not yet switched away from nitrogen. They're borrowing the cold-gas thrusters used by Falcon 9, for now.

Because these are gas-fed thrusters rather than liquid, they won't have any problems with piping losses...as long as the flow rate is not a significant percentage of the speed of sound in the gas (which it definitely will not be), the entire feed line will be at full pressure the entire time.

6 bar is low, but the diagrams show 3 bar, which is obviously even lower. Of course, it's not unheard-of to have low-pressure pressure-fed engines; the Kestrel was only at 9 bar. But it really does seem like they would be better off if they were fed from accumulators. Accumulators also solve the problem of liquid propellant ingestion in the RCS thrusters at zero-gee.

1 hour ago, magnemoe said:

As I understand they plan to land the moonship with the gas-gas trusters and they are supposed to have 20 ton trust at sea level.
 
Now the only issue I see is the moonship if it using gas-gas engines for landing but you can add more COPVs or go fancy like the IC engine on the centaur replacement. This might also be nice if you do lots of orbital operations. 

The IC engine wouldn't help them here but adding more accumulators would definitely work.

1 hour ago, magnemoe said:

Thought they had two stands now one for pressure tests and trust puck simulation and another for static fire. 

They have one stand for pressure tests only -- that's the one they used to blow up SN7 -- but the other stand does the thrust sim as well as the static fire and launches. They need pad hold-down clamps for the thrust sim and static fire, but they don't need it for the pressure tests.

[tater]

Here's a view where you can see the thrust simulator:

 

[Flying dutchman]

3 hours ago, tater said:

Here's a view where you can see the thrust simulator:

 

It looks so clean compared tot MK1!

[sh1pman]

4 hours ago, sevenperforce said:

Right, they have not yet switched away from nitrogen.

What's the eventual plan for Starship RCS? Biprop hot gas thrusters, do I remember correctly? 

[sevenperforce]

4 minutes ago, sh1pman said:

What's the eventual plan for Starship RCS? Biprop hot gas thrusters, do I remember correctly? 

Pressure fed gas-gas methane-oxygen thrusters. They will feed pressurized GOX and pressurized methane gas to the chambers, which will combust at a slightly lower pressure, fed from the same autogenous pressurization system that the tanks use.

I'm wondering above whether these thrusters will be fed direct from the tanks at relatively low pressure or from separate pressurized-gas accumulator tanks. If the latter, then the autogenous press lines from Raptor can feed those accumulator tanks directly and then also supply tank pressures via regulator.

[sh1pman]

15 minutes ago, sevenperforce said:

I'm wondering above whether these thrusters will be fed direct from the tanks at relatively low pressure or from separate pressurized-gas accumulator tanks. If the latter, then the autogenous press lines from Raptor can feed those accumulator tanks directly and then also supply tank pressures via regulator.

Accumulator tanks make sense. Though I’m not sure how they’re going to generate more high pressure gases when the accumulators run out without using the Raptors.
 

Maybe they’ll use some kind of (electric?) boilers separate from the main autogenous pressurisation system.

Edited October 1, 2020 by sh1pman

[kerbiloid]

Buran RCS used kerolox from a gasifier device fed from main tanks.

[Guest]

Both methane and LOX will boil off on their own, so assuming the tanks aren't heavily insulated, a pair of pumps is all they'd need. 

[tater]

30 minutes

 

[Scotius]

Stream starts. Music is on.

[Ultimate Steve]

Apparently this is the third flight of one of the fairing halves!

Abort at T-18.

[cubinator]

T-18 abort.......due to a ground sensor reading

 

[Scotius]

Just now, cubinator said:

T-18 abort.......due to a ground sensor reading

 

Oh come on! Those dastardly moles!

[tater]

That's a scrub, they can't recycle it was an instantaneous window I think.

[RealKerbal3x]

[tater]

Doubleheader tomorrow.

[kerbiloid]

11 minutes ago, Scotius said:

Oh come on! Those dastardly moles!

 

11 minutes ago, tater said:

That's a scrub, they can't recycle it was an instantaneous window I think.

No... That's not a scrub...

Spoiler

That's a graboid.

It hates water towers.

***

(Yes, it's Nevada. But now in Texas, too.)

Spoiler

Dwarves woke up the balrog, Boring company disturbed the graboids.

 

Edited October 1, 2020 by kerbiloid

[tater]

Don't get 3 rockets in 1 pic often.

[RealKerbal3x]

Here it comes!

 

[StrandedonEarth]

3 hours ago, tater said:

Don't get 3 rockets in 1 pic often.

Nope. But it's something that will hopefully become more common, and should have been common (years? decades?) ago.

4 hours ago, cubinator said:

T-18 abort.......due to a ground sensor reading

 

Methinks the Space Coast has been invaded by these guys...

Spoiler

 

[sevenperforce]

Are these new legs? Or the same design?

Also I really, really love this image of Starship SN8:

 

[cubinator]

17 minutes ago, sevenperforce said:

Are these new legs? Or the same design?

I think those are still the short stubby legs. 

[tater]

 

[tater]