How To Prevent Raptors From Destroying Superheavy Pt.2
How To Prevent Raptors From Destroying Superheavy Pt.2
New CSI Starbase episode just dropped.
Edit: Additional background info from Zack: https://x.com/CSI_Starbase/status/1830325913776726136
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TL;DW:
Zack draws an allegory of a parasitic relationship between the Superheavy booster (host) and the Raptor 2 engines (parasite dependent on the host, but inflicting detrimental effects).
Overview of what is known of the current autogenous pressurization system:
- Raptor 2 uses methane in its regenerative cooling system, which provides a clean source of gaseous methane which is used to pressurize the methane tank.
- There is no equivalent clean source of gaseous oxygen on Raptor 2, so the easiest option is use dirty "oxygen rich" exhaust from the preburner. This exhaust is mostly oxygen, but contaminated with water and carbon dioxide.
Water ice floats on liquid oxygen, but CO2 ice sinks in liquid oxygen, settling on the bottom of the LOX tank and clogging the engine inlets.
Proposed failure mode of IFT-2: Roll and flip maveuvers caused the CO2 "snow" to collect on one side of the bottom of the LOX tank and overload the filters on that side.
Upgrades to B10 LOX filteration system prior to IFT-3: Two filters (likely mesh) each stretching across the entire cross-section of the LOX tank.
Proposed failure modes for IFT-3:
- The roll and flip maneuvers allowed ice to make it past the filters via gaps between the stringers at the edge of the tank.
- The roll and flip maneuvers caused shift in ice distribution on the filter which lead to a structural failure of the filter itself.
Upgrades prior to IFT-4: Optimized staging and boostback trajectory to minimize unnecessary roll maneuvers. Result: First successful splashdown of Superheavy.
Other notes:
- Even if the design of the filters has been perfected, the presence of ice likely precludes rapid reusabilty. While the CO2 ice would sublimate and could be vented, the water would need to be drained/pumped out between flights.
- All of these issues would be addressed if Raptor 3 includes an oxygen heat exchanger, which could provide a clean source of gaseous oxygen to pressurise the tank.
The full video has way more details than I could summarize here; definitely worth a watch!
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Excellent video & analysis, as always.
I was highly irritated by the erroneous claim that things would settle to the earth-facing side of the tank though. The damn thing's in free-fall, the direction of the gravity vector is entirely irrelevant! The conclusions mostly still work, but it has more to do with jostling and slosh causing the snow to move, not gravity
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The damn thing’s in free-fall, the direction of the gravity vector is entirely irrelevant!
Ooh, good point. I missed that. I suppose the gravity vector could play a role on reentry, depending on the angle of attack, but you're right, it's probably irrelevant at MECO.
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There was a lot to digest, so I might be wrong, but I was under the impression that he was referring to the boost back phase, so not in free fall. I’m not smart enough to figure out if the gravity vector plays any significant role compared to the one from the engines in that situation :) Neither during the landing burn. There is a huge amount of deceleration which would be a vector straight through the booster? There is a slight tilt to the booster most of the way down, but I don’t know if that could make the debris settle unevenly.
In between those burns nothing can settle as you say. If Zac was referring to that phase than that was indeed an oversight.
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No, even when the engines are firing it's in free-fall. The only forces on the booster or fuel (aside from internal ones like gyroscopic or centrifugal dynamics) are thrust, control thrusters, and depending on the phase of flight drag & aerodynamic control.
Thrust always points roughly along the length of the booster, and drag always acts against the direction of travel, so the external forces acting on the fuel are almost 100% up or down during all phases of flight. The only exceptions are manoeuvres when the attitude control systems is rotating the vehicle, either by grid-fin or thrusters, so any redistribution of the fuel or snow will be entirely driven by those movements, and their own inertia
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Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
Fewer Letters More Letters LOX Liquid Oxygen MECO Main Engine Cut-Off ~ MainEngineCutOff podcast Jargon Definition Raptor Methane-fueled rocket engine under development by SpaceX autogenous (Of a propellant tank) Pressurising the tank using boil-off of the contents, instead of a separate gas like helium cryogenic Very low temperature fluid; materials that would be gaseous at room temperature/pressure ~ (In re: rocket fuel) Often synonymous with hydrolox hydrolox Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer iron waffle Compact "waffle-iron" aerodynamic control surface, acts as a wing without needing to be as large; also, "grid fin" regenerative A method for cooling a rocket engine, by passing the cryogenic fuel through channels in the bell or chamber wall [Thread #54 for this sub, first seen 2nd Sep 2024, 07:50] [FAQ] [Full list] [Contact] [Source code]
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