totm nov 2023 SpaceX Discussion Thread

[CatastrophicFailure]

46 minutes ago, Nightside said:

Always interesting when the cars and concrete buildings are burned and the trees are still green.

We're going to need some major adjustments to how we build in the wildish west.

 

Someone mentioned that the trees are still full of sap and such, and really don’t like to burn (the underbrush is another matter). But cars and buildings are painted with flammium and conflagrium (and literally fueled with explodium) so...

Also...

At least they already have their costumes picked out. 

and they better be bringing candy...

[tater]

 

[tater]

 

[RealKerbal3x]

Highlight reel of Demo-2. What a flawless mission.

(oops, ninja'd by @tater)

Edited September 29, 2020 by RealKerbal3x

[tater]

 

[Scotius]

Tanker version of Cargo Dragon would be nice to have Only fuel, for all station keeping needs of ISS for a year or so. Then land it, pump more fuel in and send up again. I bet it would be more economical than Progress. Though it would probably require modifications to Zvezda module.

[cubinator]

21 minutes ago, Scotius said:

Tanker version of Cargo Dragon would be nice to have Only fuel, for all station keeping needs of ISS for a year or so. Then land it, pump more fuel in and send up again. I bet it would be more economical than Progress. Though it would probably require modifications to Zvezda module.

Eh, boosting has been done from forward and nadir positions before. Does this new cargo version use the IDA or the square hatch? Because certain large items don't fit through the round hatches...

[kerbiloid]

Can Cargo Dragon pump the fuel to the station?

It's Crew Dragon.

Spoiler

I can see IDSS rev C/E with no mechanical SCS strikers,
its SCS (soft capture system) - the inner ring with three petals,
its HCS (hard capture system) - the outer ring with twelve rectangular latches
two electromechanical connectors (large rectangles)
four nozzles.

But I can't see any pipes which should be around the HCS ring, nearly where the four nozzles are.

Cargo Dragon doesn't have even IDSS.

Spoiler

It's equipped with passive CBM.

Edited September 29, 2020 by kerbiloid

[RealKerbal3x]

49 minutes ago, Scotius said:

Tanker version of Cargo Dragon would be nice to have Only fuel, for all station keeping needs of ISS for a year or so. Then land it, pump more fuel in and send up again. I bet it would be more economical than Progress. Though it would probably require modifications to Zvezda module.

 

3 minutes ago, kerbiloid said:

Can Cargo Dragon pump the fuel to the station?

AFAIK the pressurised mating adapter doesn't have provisions for fuel pumping. So the docking port on Tanker Dragon would have to be redesigned to be compatible with the Russian segment's ports.

[kerbiloid]

Just now, RealKerbal3x said:

 

AFAIK the pressurised mating adapter doesn't have provisions for fuel pumping. So the docking port on Tanker Dragon would have to be redesigned to be compatible with the Russian segment's ports.

Afair, the current version of IDSS standard doesn't include pipes, just KOZ (keep-out zones) for them.

And CBM is just a ring with round hole, and four pairs of petals.

[sevenperforce]

On an unrelated note, thinking about Raptor and those fabled gas-gas RCS thrusters.

 

A couple of interesting observations which some of us have probably already made but bear repeating...

• Unlike a gas generator cycle, where the propellant goes from inlet to pump to chamber with part of the propellant going from the pump downstream to the preburner to exhaust, here there is no pumping directly into the chamber at all. The chamber is fed directly from preburner exhaust, and the turbine is driven by that exhaust pressure drop between the preburners and the chamber.
• The oxidizer flow is different from the fuel flow:
  • The LOX turbopump downstream feeds directly into the LOX preburner, with a small portion of the LOX being tapped off the LOX pump downstream to a heat exchanger for autogenous pressurization and a small portion being tapped off the LOX pump downstream to feed the CH4 preburner.
  • In contrast, the CH4 turbopump downstream doesn't feed into the CH4 preburner at all. Instead, it splits off a small portion to feed the LOX preburner and sends the rest through the chamber and nozzle regenerative cooling manifold; this then feeds back to the CH4 preburner with a small amount being tapped off for autogenous press.
• The CH4 is preheated before hitting its preburner but the LOX flows into its preburner cold.
• The LOX autogenous press line is vaporized via a turbopump heat exchanger, but the CH4 autogenous press line is vaporized via the engine/nozzle regen heat exchanger. It's not clear whether the CH4 feeds into the CH4 preburner in gas or liquid phase; if the latter, how is the CH4 autogenous press line actually vaporized?
• The highest pressures in the engine, by descending order, are:
  • CH4 turbopump downstream
  • LOX turbopump downstream
  • CH4 coolant cycle
  • LOX preburner
  • CH4 preburner
  • LOX preburner downstream
  • CH4 preburner downstream
  • Chamber

With all this being understood, I'm curious about these gas-gas thrusters for RCS. I'm guessing they'll use the same augmented spark igniters as the main chamber in the Raptor, though probably only a single one rather than multiple redundant ones. But that's beside the point.

I'm more interested in whether these RCS thrusters will be fed by an accumulator or directly off of tank pressure. There is a LOT of room between the 633-581 bar coming off the two press lines and the 3 bar tank pressures. Obviously, PV = nRT is going to have a little say in that particular exchange, but even so, I think it would make sense to run those feed lines into accumulators at some intermediate pressure. The accumulators would vent to the tanks but would also feed the gas-gas thrusters directly so that they would have remarkably high chamber pressures and thus be more efficient.

If this was the case, then you'd eventually want a resistance heating manifold and low-flow electric turbopump to replenish the accumulators from the tanks if they became depleted. 

[cubinator]

Crew-1's Dragon will be called 'Resilience'.

Also, the Americans will vote from space.

Edited September 29, 2020 by cubinator

[tater]

[magnemoe]

14 hours ago, sevenperforce said:

snip

With all this being understood, I'm curious about these gas-gas thrusters for RCS. I'm guessing they'll use the same augmented spark igniters as the main chamber in the Raptor, though probably only a single one rather than multiple redundant ones. But that's beside the point.

I'm more interested in whether these RCS thrusters will be fed by an accumulator or directly off of tank pressure. There is a LOT of room between the 633-581 bar coming off the two press lines and the 3 bar tank pressures. Obviously, PV = nRT is going to have a little say in that particular exchange, but even so, I think it would make sense to run those feed lines into accumulators at some intermediate pressure. The accumulators would vent to the tanks but would also feed the gas-gas thrusters directly so that they would have remarkably high chamber pressures and thus be more efficient.

If this was the case, then you'd eventually want a resistance heating manifold and low-flow electric turbopump to replenish the accumulators from the tanks if they became depleted. 

The black tanks on the outside. think they are 80 bar but might be higher. That is the pressurization system who currently keeps tanks at 6 bar and feed the cold gas trusters and will feed the gas-gas engines.
The gas-gas engines will be a bit like the raptors starters who also is gas-gas. Probably use multiple spark plugs to ensure smooth starts.
Guess they use an gas generator and perhaps electrical pumps to create pressurized gas in case they run low on it say during docking and then they need to pressurize the large tanks, that one however don't need high pressure. 
 

[tater]

 

[sevenperforce]

5 hours ago, magnemoe said:

The black tanks on the outside. think they are 80 bar but might be higher. That is the pressurization system who currently keeps tanks at 6 bar and feed the cold gas trusters and will feed the gas-gas engines.
The gas-gas engines will be a bit like the raptors starters who also is gas-gas. Probably use multiple spark plugs to ensure smooth starts.

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. 

5 hours ago, magnemoe said:

Guess they use an gas generator and perhaps electrical pumps to create pressurized gas in case they run low on it say during docking and then they need to pressurize the large tanks, that one however don't need high pressure. 

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.

35 minutes ago, tater said:

 

Next step: thrust simulator, right?

[tater]

8 minutes ago, sevenperforce said:

Next step: thrust simulator, right?

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

[sevenperforce]

27 minutes 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?

Ah, yep -- I see it now. I had to view the large size image.

This will be the first time we see a three-engine static fire!

[tater]

2 minutes ago, sevenperforce said:

This will be the first time we see a three-engine static fire!

Yeah, hopefully the GSE can take the pounding, their sound suppression system seems... rudimentary.

[Guest]

Is there even a sound suppression system?

[sevenperforce]

Just now, The Doodling Astronaut said:

Is there even a sound suppression system?

There's no deluge system, that's for sure.

I guess the Raptors need to be able to take a pounding themselves, since there's no deluge at the landing pad, but still.

[tater]

They have that remote control fire hose that moves around. You can see it start just before they do a fire.

[sevenperforce]

2 minutes ago, tater said:

They have that remote control fire hose that moves around. You can see it start just before they do a fire.

Oh, gotcha.

Dunno if it's enough for actual sound suppression or if it's just prophylactic fire suppression.

[tater]

8 minutes ago, sevenperforce said:

Oh, gotcha.

Dunno if it's enough for actual sound suppression or if it's just prophylactic fire suppression.

Yeah, like I said, rudimentary at best. They might have a sprayer, too, it's hard to tell given unofficial coverage.

It sprays right under the launch stand, and starts before launch. You can see it in the official video of SN5 right at the start. How much suppression is accomplishes? LOL.

With 3 Raptors.... ____ is gonna get real.

[sevenperforce]

2 minutes ago, tater said:

Yeah, like I said, rudimentary at best. They might have a sprayer, too, it's hard to tell given unofficial coverage.

None of the posted videos definitively show a spray system or other deluge. The particulate cloud kicked up at launch doesn't look a...erhm...steamy? as is typical of a water deluge.