Starship / Superheavy autogenous pressurization questions

[livingjw]

- During main engine burns, they can tap off gases of different temperature and mix them to control temperature. They then use a pressure regulator to manage tank pressure.

- Max tank temperature will depend on tank material or possibly other items placed in the tanks. I would guess somewhere between 200 - 500 degrees F.

- After engine cut off in space, the tanks will be nearly empty and tank pressures will stabilize at some level which depends on heat loads, heat radiation, and insulation.

- An engine relight may need some re-pressurization before hand. If so, heating may be needed.

John

[josespeck]

- During main engine burns, they can tap off gases of different temperature and mix them to control temperature. They then use a pressure regulator to manage tank pressure.

- Max tank temperature will depend on tank material or possibly other items placed in the tanks. I would guess somewhere between 200 - 500 degrees F.

- After engine cut off in space, the tanks will be nearly empty and tank pressures will stabilize at some level which depends on heat loads, heat radiation, and insulation.

- An engine relight may need some re-pressurization before hand. If so, heating may be needed.

John

Is this what you want to say?

[envy887]

- During main engine burns, they can tap off gases of different temperature and mix them to control temperature. They then use a pressure regulator to manage tank pressure.

- Max tank temperature will depend on tank material or possibly other items placed in the tanks. I would guess somewhere between 200 - 500 degrees F.

- After engine cut off in space, the tanks will be nearly empty and tank pressures will stabilize at some level which depends on heat loads, heat radiation, and insulation.

- An engine relight may need some re-pressurization before hand. If so, heating may be needed.

John

Is this what you want to say?

No. The combustion chamber tap-off products are fuel-rich and you do not want to dump them in a LOX tank.

The "tap off" that John referred to is from earlier in the cycle. Since Raptor has hot fuel-rich gases coming out of the fuel preburner, and hot ox-rich gases coming out of the ox preburner, they could tap those separately and feed them to the fuel and LOX tanks.

[acsawdey]

- During main engine burns, they can tap off gases of different temperature and mix them to control temperature. They then use a pressure regulator to manage tank pressure.

- Max tank temperature will depend on tank material or possibly other items placed in the tanks. I would guess somewhere between 200 - 500 degrees F.

- After engine cut off in space, the tanks will be nearly empty and tank pressures will stabilize at some level which depends on heat loads, heat radiation, and insulation.

- An engine relight may need some re-pressurization before hand. If so, heating may be needed.

John

Is this what you want to say?

No. The combustion chamber tap-off products are fuel-rich and you do not want to dump them in a LOX tank.

The "tap off" that John referred to is from earlier in the cycle. Since Raptor has hot fuel-rich gases coming out of the fuel preburner, and hot ox-rich gases coming out of the ox preburner, they could tap those separately and feed them to the fuel and LOX tanks.

Questionable whether you'd want to do that as either of those will contain water as a combustion product which will freeze out in the fuel or oxidizer tanks. And the planetary geologists joke about how "ice is a mineral" at those temperatures, certainly not something you want clogging up fuel lines and injectors. Heat exchangers to boil a little methane or lox are simple by comparison.

[Jcc]

- During main engine burns, they can tap off gases of different temperature and mix them to control temperature. They then use a pressure regulator to manage tank pressure.

- Max tank temperature will depend on tank material or possibly other items placed in the tanks. I would guess somewhere between 200 - 500 degrees F.

- After engine cut off in space, the tanks will be nearly empty and tank pressures will stabilize at some level which depends on heat loads, heat radiation, and insulation.

- An engine relight may need some re-pressurization before hand. If so, heating may be needed.

John

Is this what you want to say?

No. The combustion chamber tap-off products are fuel-rich and you do not want to dump them in a LOX tank.

The "tap off" that John referred to is from earlier in the cycle. Since Raptor has hot fuel-rich gases coming out of the fuel preburner, and hot ox-rich gases coming out of the ox preburner, they could tap those separately and feed them to the fuel and LOX tanks.

Questionable whether you'd want to do that as either of those will contain water as a combustion product which will freeze out in the fuel or oxidizer tanks. And the planetary geologists joke about how "ice is a mineral" at those temperatures, certainly not something you want clogging up fuel lines and injectors. Heat exchangers to boil a little methane or lox are simple by comparison.

The heat exchanger coils can use the tap off products as working fluid, then dump overboard.

[livingjw]

- During main engine burns, they can tap off gases of different temperature and mix them to control temperature. They then use a pressure regulator to manage tank pressure.

- Max tank temperature will depend on tank material or possibly other items placed in the tanks. I would guess somewhere between 200 - 500 degrees F.

- After engine cut off in space, the tanks will be nearly empty and tank pressures will stabilize at some level which depends on heat loads, heat radiation, and insulation.

- An engine relight may need some re-pressurization before hand. If so, heating may be needed.

John

Is this what you want to say?

No. The combustion chamber tap-off products are fuel-rich and you do not want to dump them in a LOX tank.

The "tap off" that John referred to is from earlier in the cycle. Since Raptor has hot fuel-rich gases coming out of the fuel preburner, and hot ox-rich gases coming out of the ox preburner, they could tap those separately and feed them to the fuel and LOX tanks.

Questionable whether you'd want to do that as either of those will contain water as a combustion product which will freeze out in the fuel or oxidizer tanks. And the planetary geologists joke about how "ice is a mineral" at those temperatures, certainly not something you want clogging up fuel lines and injectors. Heat exchangers to boil a little methane or lox are simple by comparison.

I meant tapping off pure methane gas and pure oxygen gas from downstream of the pumps. They may put a small heat exchanger in the lox pre-burner to heat up some Lox and gasify it. I believe the SSME used this approach. Methane could be tapped after exiting the coolant channels.

John

[Lar]

The heat exchanger coils can use the tap off products as working fluid, then dump overboard.

Dumping any tapoff has a negative effect on ISP I think.

[magnemoe]

The heat exchanger coils can use the tap off products as working fluid, then dump overboard.

Dumping any tapoff has a negative effect on ISP I think.

Yes but this is only used if pressure in tanks are to low for an secondary burn and you need to raise pressure.

Another benefit of the header tanks as its not much volume to pressurize so you might only use them for engine startup even if having fuel left in main tank.

[livingjw]

The heat exchanger coils can use the tap off products as working fluid, then dump overboard.

Dumping any tapoff has a negative effect on ISP I think.

Yes but this is only used if pressure in tanks are to low for an secondary burn and you need to raise pressure.

Another benefit of the header tanks as its not much volume to pressurize so you might only use them for engine startup even if having fuel left in main tank.

- There is no dumping of tapped methane or Lox during engine burn. Liquid propellants are tapped off as needed to keep the tank pressure at the desired pressure during the engine burn.

- After engine shut down, tank pressures will rise with temperature and may have to be vented to maintain desired pressure. This can be minimized by orienting the vehicle so that exposure to sunlight is minimized.

- After Mars transfer burn, the main tanks are empty and all remaining vapor vented to better insulate the header tanks for the long voyage. Tanks would have to be re-pressurized with vapor before Mars entry sufficient to maintain vehicle structural integrity.

John

[josespeck]

- During main engine burns, they can tap off gases of different temperature and mix them to control temperature. They then use a pressure regulator to manage tank pressure.

- Max tank temperature will depend on tank material or possibly other items placed in the tanks. I would guess somewhere between 200 - 500 degrees F.

- After engine cut off in space, the tanks will be nearly empty and tank pressures will stabilize at some level which depends on heat loads, heat radiation, and insulation.

- An engine relight may need some re-pressurization before hand. If so, heating may be needed.

John

Is this what you want to say?

No. The combustion chamber tap-off products are fuel-rich and you do not want to dump them in a LOX tank.

The "tap off" that John referred to is from earlier in the cycle. Since Raptor has hot fuel-rich gases coming out of the fuel preburner, and hot ox-rich gases coming out of the ox preburner, they could tap those separately and feed them to the fuel and LOX tanks.

[Semmel]

I cant draw that nicely, so here is a written discription:

Methane:
Tank -> Pump -> Tap-Off -> Heat Exchanger with Combustion Chamber -> Tank

LoX:
Tank -> Pump -> Tap-Off -> Heat Exchanger with Combustion Chamber -> Tank

Both cycles have nothing to do with each other. Both cycles never touch the combustion products, just the heat generated by the combustion. The heat exchanger might as well be mounted on the pre-burners, I am not sure about that part.

[josespeck]

I cant draw that nicely, so here is a written discription:

Methane:
Tank -> Pump -> Tap-Off -> Heat Exchanger with Combustion Chamber -> Tank

LoX:
Tank -> Pump -> Tap-Off -> Heat Exchanger with Combustion Chamber -> Tank

Both cycles have nothing to do with each other. Both cycles never touch the combustion products, just the heat generated by the combustion. The heat exchanger might as well be mounted on the pre-burners, I am not sure about that part.

Ok. That's the typical Tap-Off cycle. And combustion products can get water, unwanted, into the tanks.

[livingjw]

I cant draw that nicely, so here is a written discription:

Methane:
Tank -> Pump -> Tap-Off -> Heat Exchanger with Combustion Chamber -> Tank

LoX:
Tank -> Pump -> Tap-Off -> Heat Exchanger with Combustion Chamber -> Tank

Both cycles have nothing to do with each other. Both cycles never touch the combustion products, just the heat generated by the combustion. The heat exchanger might as well be mounted on the pre-burners, I am not sure about that part.

Ok. That's the typical Tap-Off cycle. And combustion products can get water, unwanted, into the tanks.

or:

Methane:
Tank -> Pump -> MCC regen output -> Tap-Off -> Tank

Lox:
Tank -> Pump -> Tap-Off -> Heat Exchanger in Lox pre-burner exhaust -> Tank

John

[matthewkantar]

I cant draw that nicely, so here is a written discription:

Methane:
Tank -> Pump -> Tap-Off -> Heat Exchanger with Combustion Chamber -> Tank

LoX:
Tank -> Pump -> Tap-Off -> Heat Exchanger with Combustion Chamber -> Tank

Both cycles have nothing to do with each other. Both cycles never touch the combustion products, just the heat generated by the combustion. The heat exchanger might as well be mounted on the pre-burners, I am not sure about that part.

Ok. That's the typical Tap-Off cycle. And combustion products can get water, unwanted, into the tanks.

No, the plumbing for the loops never have water in them. The propellants for autogenous pressurization go through a heat exchanger, they don't get burnt or mixed, just heated.

[Semmel]

or:

Methane:
Tank -> Pump -> MCC regen output -> Tap-Off -> Tank

Lox:
Tank -> Pump -> Tap-Off -> Heat Exchanger in Lox pre-burner exhaust -> Tank

John

Certainly a good option for the methane.
But I don't know how hot the LOX preburner exhaust will be. Do we have any estimation? 

[livingjw]

or:

Methane:
Tank -> Pump -> MCC regen output -> Tap-Off -> Tank

Lox:
Tank -> Pump -> Tap-Off -> Heat Exchanger in Lox pre-burner exhaust -> Tank

John

Certainly a good option for the methane.
But I don't know how hot the LOX preburner exhaust will be. Do we have any estimation?

- Probably no higher than 1500 F.
- It is how the SSME autogenous tap is done.

John

[josespeck]

I cant draw that nicely, so here is a written discription:

Methane:
Tank -> Pump -> Tap-Off -> Heat Exchanger with Combustion Chamber -> Tank

LoX:
Tank -> Pump -> Tap-Off -> Heat Exchanger with Combustion Chamber -> Tank

Both cycles have nothing to do with each other. Both cycles never touch the combustion products, just the heat generated by the combustion. The heat exchanger might as well be mounted on the pre-burners, I am not sure about that part.

Ok. That's the typical Tap-Off cycle. And combustion products can get water, unwanted, into the tanks.

No, the plumbing for the loops never have water in them. The propellants for autogenous pressurization go through a heat exchanger, they don't get burnt or mixed, just heated.

I said it for this comment:

https://forum.nasaspaceflight.com/index.php?topic=47068.msg1906265#msg1906265

[Jim]

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.

[cuddihy]

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.

[envy887]

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.

The methane already has a nice heat exchanger in the regen cooling system.