sevenperforce

Another absolutely gorgeous render from Neopork: The one area where this remains tricky is human spaceflight. People won't just randomly begin flying without an launch abort system, no matter how reliable Starship seems to be. Beautiful.

Not to nitpick but there really is no significant amount of unburned propellant which burns outside the combustion chamber.

No. For a constant amount of reaction mass, adding more energy DOES add more thrust. How about a trimodal nuclear-thermal LOX-afterburning rocket engine? Or it could be a situation like running the SSMEs at 104%. Your generator provides enough power to run both the engines at full thrust as well as the shields at full power, so that you can make maneuvers while shielded, but if you cut power to the shields you can run the engines at 110% or 120% or some other number for a short period before they overheat.

I'm in somewhat of a better position to judge the maths and I concur with @Dragon01 on this.

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Scott Manley pointed out on Twitter that SpaceX consistently has more problems with new boosters than flight-proven boosters.

Yeah I’m lost too

Are these new legs? Or the same design? Also I really, really love this image of Starship SN8:

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.

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

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.

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

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.

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!

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?

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.

There’s a continuum to be sure. Hard science fiction (The Martian) Soft science fiction (Dune, Interstellar) Space opera (Star Trek) Science fantasy (Star Wars) Planetary romance (Dr. Who, The Space Trilogy) Epic fantasy (LOTR) Urban fantasy (Harry Potter) The questions you’re asking, Space, are mostly along the lines of what you’d be asking for hard sci-fi. But it seems like your setting is somewhere between soft sci-fi and space opera. Hence the incongruity. Try to focus less on getting the specific scientific details right and focus more on making your narrative and the rules of your fictional universe internally consistent.

That is not how antimatter works.

Scrub, weather violation.

I feel like that is a good idea, but what we should REALLY do is give Starship gluon-plasma-triggered pusher-plate nano-Orion ullage thrusters to save RCS propellant. Yep, this. Pusher plate designs were proposed ONLY because of technological limitations on the containment of thermonuclear weapons. They are extraordinarily inefficient. A pusher-plate spaceship is like running a train by having Superman sit in the engine and use his heat vision to boil water to make steam. It’s technically more efficient than running a steam engine on coal, but that’s about it.

Just a little something to keep in mind… The chamber pressure of the Kestrel engine on the Falcon 1 second stage was just 9.3 bar. In theory, then, the ullage pressure of Starship’s tanks is enough to pressure-feed a Kestrel.

Interesting that they fold the fins back like that for transportation. I don’t think they did that with Mk1. I suppose it makes sense, though. They want it to have a lower wind cross-section. I anticipate that they will do a thrust puck test with the simulator first, before stacking the nosecone. It remains to be seen whether they will stack at the launch site or bring it back.

It is inefficient. See the Mach diamond? The entire space around that Mach diamond is where the atmosphere is producing parasitic pressure drag on the nozzle. Over expansion results in lower total thrust for a given propellant flow rate and correspondingly lower efficiency. When fired at sea level, the smaller Raptor has a higher specific impulse then the vacuum Raptor. The same thing was true with the space shuttle main engine. An RS-25 has a vastly more efficient turbopump cycle than the RS-68, and yet the RS-25 has only slightly better sea level specific impulse because of the parasitic overexpansion that reduces net thrust. Exactly. The only time the Raptor would be used operationally at sea level would be in an abort, when efficiency matters not at all. In contrast the RS-25 was designed to be fired from ground to orbit in every mission.

Not really. There was no propagation along the weld, merely failure at the weld. Look how jagged the marks are around the circumferential failure. There's one place with a little fracture propagation -- the sawtooth -- but it is short and arrested by the weld itself. The rest of the failure surface is uneven, which is what you expect from a failure of the steel itself at a stress point.

I think Elon really missed an opportunity with the naming on the first stage. He should have gone with "Starbooster".