Starship / Superheavy autogenous pressurization questions

[envy887]

Can a single heat exchanger produce enough hot gaseous methane to 1. Pressurize the CH4 tank. 2. Produce bleed gas for the TPS. 3. Produce pressurized gas for the RCS cold gas system?

If it’s only on one engine you’ve got a critical SPoF. If it’s on multiple engines you’ll have tons of piping and complexity with when it’s used from one engine or another. I guess shuttle did it with 3 engines so it’s solvable.

They probably aren't going to use methane for the cold gas RCS. Flaring gaseous fuel near the vehicle is generally a bad idea in a highly oxygen rich atmosphere.

[livingjw]

Can a single heat exchanger produce enough hot gaseous methane to 1. Pressurize the CH4 tank. 2. Produce bleed gas for the TPS. 3. Produce pressurized gas for the RCS cold gas system?

If it’s only on one engine you’ve got a critical SPoF. If it’s on multiple engines you’ll have tons of piping and complexity with when it’s used from one engine or another. I guess shuttle did it with 3 engines so it’s solvable.

- 1) Very small flow rate is needed to pressurize the tanks. A small heat exchanger in the Lox pre-burner is all that is needed. As stated before, Methane can be tapped after it exits MCC regenerative cooling loop, so it probably does not need additional heating. The mass fraction needed to fill the tanks is the ratio of density of the vapor to the density of the liquid.

- 2) Engines are not on when reentry is taking place. Methane gas is coming from the full methane header tank which is probably pressurized to about 3 bar (45 psi). 

- 3) RCS cold gas system will probably be from separate higher pressure methane tanks and will already be in a warm gaseous state prior to launch and reentry. I would guess a minimum of 66 bar (1000 psi) and a temperature of around 350-400 C (662-752 F)

- During launch, the autogenous pressurization system only needs regulators and valves to work. It relies on the engines for pure gases at the right temperature and pressure. Reentry with 3 engines gives triple redundancy, which should be more than sufficient.

- During launch and reentry, cold gas RCS only requires regulators and valves to work. Warm high pressure gas is made available prior to launch or reentry.

John

[Restless]

This thread seems to assume that sub-cooling will be used for LOX and LNG for hopper and SS and the booster. F9 needed the sub-cooling to stretch fuel for fly back of the booster and extra heavy missions. Has Spacex indicated that sub-cooling will be used at Boca? It adds extra equipment and may not be necessary for the hopper and SS prototype.

[alienmike]

This thread seems to assume that sub-cooling will be used for LOX and LNG for hopper and SS and the booster. F9 needed the sub-cooling to stretch fuel for fly back of the booster and extra heavy missions. Has Spacex indicated that sub-cooling will be used at Boca? It adds extra equipment and may not be necessary for the hopper and SS prototype.

I think the assumption is that they will test like they fly. It helps retire a lot of risk.

[Lar]

This thread seems to assume that sub-cooling will be used for LOX and LNG for hopper and SS and the booster. F9 needed the sub-cooling to stretch fuel for fly back of the booster and extra heavy missions. Has Spacex indicated that sub-cooling will be used at Boca? It adds extra equipment and may not be necessary for the hopper and SS prototype.

I think the assumption is that they will test like they fly. It helps retire a lot of risk.

Agreed. Also, subcooling can be added on later, especially if provisions are made (any through berm piping, for example, is placed even if just stubbed out at both ends (and filled with nitrogen maybe?) after the first few hopper tests. But I think by the time the first prototype starship flies they will be doing propellants as close to final as they can even if they start out not doing so initially with hopper.

[livingjw]

This thread seems to assume that sub-cooling will be used for LOX and LNG for hopper and SS and the booster. F9 needed the sub-cooling to stretch fuel for fly back of the booster and extra heavy missions. Has Spacex indicated that sub-cooling will be used at Boca? It adds extra equipment and may not be necessary for the hopper and SS prototype.

Did I miss something. I haven't assumed sub-cooling in anything I have assumed. Doubtful that it is needed or desirable in this case. I think this post was inadvertently placed here.

John

[guckyfan]

Without looking it up, I am pretty sure Elon mentioned subcooled propellant in 2016. I recall a question, how they will have subcooled propellant for landing on Mars and Elon replied, initially just venting some propellant to vacuum, active coolers maybe later.

[Llian Rhydderch]

This is how the SSME does it, no combustion products going into tanks.  H2 doesn't need heating but methane might and so a heat exchanger like the LOX side could be employed.

That is an awesomely well-done image, Jim, of how another historical launch vehicle design has handled the provision of autogenous pressurization gases for propellant tanks.

Would anyone on this forum be willing to have a go at trying to schematicize a design in that fashion for what might work for Starship and/or Super Heavy?

That would be an awesome way to debate the merits of various approaches, with reference to a particular draft version of a schematic, here in the forum.

[alienmike]

This thread seems to assume that sub-cooling will be used for LOX and LNG for hopper and SS and the booster. F9 needed the sub-cooling to stretch fuel for fly back of the booster and extra heavy missions. Has Spacex indicated that sub-cooling will be used at Boca? It adds extra equipment and may not be necessary for the hopper and SS prototype.

Did I miss something. I haven't assumed sub-cooling in anything I have assumed. Doubtful that it is needed or desirable in this case. I think this post was inadvertently placed here.

John

If the Raptor is designed to take in sub-cooled LOX and LNG, which is denser, then wouldn't it require a slightly different design for propellants that are not sub-cooled, or as dense? Maybe this was a false assumption on my part. My memory says that Merlin was modified slightly to take in sub-cooled propellants, but my memory could be wrong too.

[envy887]

This thread seems to assume that sub-cooling will be used for LOX and LNG for hopper and SS and the booster. F9 needed the sub-cooling to stretch fuel for fly back of the booster and extra heavy missions. Has Spacex indicated that sub-cooling will be used at Boca? It adds extra equipment and may not be necessary for the hopper and SS prototype.

Did I miss something. I haven't assumed sub-cooling in anything I have assumed. Doubtful that it is needed or desirable in this case. I think this post was inadvertently placed here.

John

If the Raptor is designed to take in sub-cooled LOX and LNG, which is denser, then wouldn't it require a slightly different design for propellants that are not sub-cooled, or as dense? Maybe this was a false assumption on my part. My memory says that Merlin was modified slightly to take in sub-cooled propellants, but my memory could be wrong too.

Merlins are reportedly tuned for subcooled props, but can almost certainly burn boiling propellants just fine without hardware changes. Likely with less thrust, but the only time that thrust is really important is on ascent when the props are always subcooled anyway. After coasting they are likely boiling, especially on the 8 hour coast to direct GEO insertion but probably after the booster's rather toasty entry also.

[alienmike]

If the Raptor is designed to take in sub-cooled LOX and LNG, which is denser, then wouldn't it require a slightly different design for propellants that are not sub-cooled, or as dense? Maybe this was a false assumption on my part. My memory says that Merlin was modified slightly to take in sub-cooled propellants, but my memory could be wrong too.

Merlins are reportedly tuned for subcooled props, but can almost certainly burn boiling propellants just fine without hardware changes. Likely with less thrust, but the only time that thrust is really important is on ascent when the props are always subcooled anyway. After coasting they are likely boiling, especially on the 8 hour coast to direct GEO insertion but probably after the booster's rather toasty entry also.

So testing like you fly does not mean that sub-cooled propellants will be used, at least not initially. Thank you for clarifying.

[Semmel]

This is how the SSME does it, no combustion products going into tanks.  H2 doesn't need heating but methane might and so a heat exchanger like the LOX side could be employed.

That is an awesomely well-done image, Jim, of how another historical launch vehicle design has handled the provision of autogenous pressurization gases for propellant tanks.

Would anyone on this forum be willing to have a go at trying to schematicize a design in that fashion for what might work for Starship and/or Super Heavy?

That would be an awesome way to debate the merits of various approaches, with reference to a particular draft version of a schematic, here in the forum.

I was standing in front of the SSME for about 2 hours, with that chart in hand. I couldnt figure out all of it. Granted, its hard if you cant see the colors in the diagram also on the pipes and there were a hell of a lot more pipes on the engine than in the diagram. Not sure you could derive such a diagram from the images of Raptor or even when you would stand in front of it. Maybe livingjw could do it, I cannot.

[livingjw]

Raptor schematic. Started with the SSME schematic and changed it to reflect Raptor as I currently understand it.
Modified to add a heat exchanger in the methane pre-burner turbine exit flow. After adiabatic expansion pressurant gas was still too cold.

Modified (4 Feb 2019) changed source of methane to pump outlet for higher pressure to Lox pre-burner. Probably could use either source, but pressure after cooling MCC is only 10 -15 bar higher than lox pump pressure and and I would like to have more like more like 30 ish.

John

[vaporcobra]

Without looking it up, I am pretty sure Elon mentioned subcooled propellant in 2016. I recall a question, how they will have subcooled propellant for landing on Mars and Elon replied, initially just venting some propellant to vacuum, active coolers maybe later.

Correct.

[livingjw]

There is one possible, but improbable, problem that can happen with sub-cooled propellants.

During NASP, slush hydrogen was tested in a flight weight tank which was to undergo vibration testing. When the tank was shaken, the sub-cooled fluid interacted with the vapor cooling it and causing the tank to partially collapse due to negative pressure.

Since, severe vibrations occur only when the engines are running, there would always be plenty of pressurant gas to counter this.

Just a funny story.

John

[thxbmp3]

This is how the SSME does it, no combustion products going into tanks.  H2 doesn't need heating but methane might and so a heat exchanger like the LOX side could be employed.

That is an awesomely well-done image, Jim, of how another historical launch vehicle design has handled the provision of autogenous pressurization gases for propellant tanks.

Would anyone on this forum be willing to have a go at trying to schematicize a design in that fashion for what might work for Starship and/or Super Heavy?

That would be an awesome way to debate the merits of various approaches, with reference to a particular draft version of a schematic, here in the forum.

Sorry to stray a bit OT, but I had some questions re: the beautiful schematic Jim posted. Isn't SSME an FRSC engine? Why do each of the turbopumps have their own preburners?

Also, do the green areas represent anything (e.g. physically isolated volumes/chambers) or are they just there to highlight the locations of the turbines and pumps?

[meekGee]

This is how the SSME does it, no combustion products going into tanks.  H2 doesn't need heating but methane might and so a heat exchanger like the LOX side could be employed.

That is an awesomely well-done image, Jim, of how another historical launch vehicle design has handled the provision of autogenous pressurization gases for propellant tanks.

Would anyone on this forum be willing to have a go at trying to schematicize a design in that fashion for what might work for Starship and/or Super Heavy?

That would be an awesome way to debate the merits of various approaches, with reference to a particular draft version of a schematic, here in the forum.

Sorry to stray a bit OT, but I had some questions re: the beautiful schematic Jim posted. Isn't SSME an FRSC engine? Why do each of the turbopumps have their own preburners?

Also, do the green areas represent anything (e.g. physically isolated volumes/chambers) or are they just there to highlight the locations of the turbines and pumps?

Wikipedia (where that image is also posted) says Full Flow.

https://en.m.wikipedia.org/wiki/Space_Shuttle_main_engine

[rsdavis9]

This is how the SSME does it, no combustion products going into tanks.  H2 doesn't need heating but methane might and so a heat exchanger like the LOX side could be employed.

That is an awesomely well-done image, Jim, of how another historical launch vehicle design has handled the provision of autogenous pressurization gases for propellant tanks.

Would anyone on this forum be willing to have a go at trying to schematicize a design in that fashion for what might work for Starship and/or Super Heavy?

That would be an awesome way to debate the merits of various approaches, with reference to a particular draft version of a schematic, here in the forum.

Sorry to stray a bit OT, but I had some questions re: the beautiful schematic Jim posted. Isn't SSME an FRSC engine? Why do each of the turbopumps have their own preburners?

Also, do the green areas represent anything (e.g. physically isolated volumes/chambers) or are they just there to highlight the locations of the turbines and pumps?

Wikipedia (where that image is also posted) says Full Flow.

https://en.m.wikipedia.org/wiki/Space_Shuttle_main_engine

It uses 2 preburners but both are fuel rich.
For a FFSC you need one fuel rich and the other oxygen rich.

[Tuna-Fish]

Wikipedia (where that image is also posted) says Full Flow.

https://en.m.wikipedia.org/wiki/Space_Shuttle_main_engine

Don't get your information from wikipedia.

SSME is FRSC, with separate preburners and turbopumps for the oxidizer and fuel sides, but both of those are ran fuel-rich. In total, 76% of the fuel and 11% of the oxidizer go through the preburners, to be united with the rest of the propellants once they get injected into the chamber.

Source: Rocketdyne's presentation on SSME (pdf), see page 18.

[Llian Rhydderch]

This is how the SSME does it, no combustion products going into tanks.  H2 doesn't need heating but methane might and so a heat exchanger like the LOX side could be employed.

That is an awesomely well-done image, Jim, of how another historical launch vehicle design has handled the provision of autogenous pressurization gases for propellant tanks.

Would anyone on this forum be willing to have a go at trying to schematicize a design in that fashion for what might work for Starship and/or Super Heavy?

That would be an awesome way to debate the merits of various approaches, with reference to a particular draft version of a schematic, here in the forum.

Sorry to stray a bit OT, but I had some questions re: the beautiful schematic Jim posted. Isn't SSME an FRSC engine? Why do each of the turbopumps have their own preburners?

Also, do the green areas represent anything (e.g. physically isolated volumes/chambers) or are they just there to highlight the locations of the turbines and pumps?

Wikipedia (where that image is also posted) says Full Flow.

https://en.m.wikipedia.org/wiki/Space_Shuttle_main_engine

I looked at that Wikipedia article meekGee, and am not finding the "Full Flow" claim.  Searching for "full" or "flow" or "staged" don't seem to find any instance of even a statement to that effect, let alone a sourced statement to support the statement. 

Were you possibly looking at some other article than Space_Shuttle_main_engine?