Author Topic: Keeping tanks pressurized during flight  (Read 1695 times)

Offline Mbhoward

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Keeping tanks pressurized during flight
« on: 11/06/2016 10:31 PM »
In a recent article in the WSJ, it was reported SpaceX's use of Helium to maintain pressure during flight in a LOX tank was highly unusual. I understand why you need to maintain some pressure but it made me wonder how it is typically done. The article stated the Falcon 9 was the only rocket in decades that uses this technique. Just curious, thanks!

Offline Jim

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Re: Keeping tanks pressurized during flight
« Reply #1 on: 11/06/2016 10:40 PM »
In a recent article in the WSJ, it was reported SpaceX's use of Helium to maintain pressure during flight in a LOX tank was highly unusual. I understand why you need to maintain some pressure but it made me wonder how it is typically done. The article stated the Falcon 9 was the only rocket in decades that uses this technique. Just curious, thanks!

The article was wrong.  The technique that Spacex uses is submerged helium tanks, which hasn't been used for awhile.

Helium, nitrogen or even heated oxygen is used to maintain pressure in various vehicles.

Offline Mbhoward

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Re: Keeping tanks pressurized during flight
« Reply #2 on: 11/07/2016 12:05 AM »
Thanks, but I thought nitrogen and heated oxygen would condense inside a tank, and be become ineffective?

Offline Davidthefat

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Re: Keeping tanks pressurized during flight
« Reply #3 on: 11/07/2016 12:15 AM »
The helium is heated in a heat exchanger downstream the turbine of the turbopump in the Merlin engine using the gas generator exhaust gasses that have been expanded through the turbine nozzles. The F9 only uses heated helium for the tank pressurization.

Offline Proponent

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Re: Keeping tanks pressurized during flight
« Reply #4 on: 11/07/2016 01:06 AM »
Thanks, but I thought nitrogen and heated oxygen would condense inside a tank, and be become ineffective?

Nitrogen's BP is lower (77 K at 1 atmosphere) than oxygen's (90 K), so condensation isn't such an issue for pressurizing oxygen; I think what people worry about in that case is the fact that nitrogen dissolves in oxygen.  And, of course, condensation isn't an issue if you're using nitrogen to pressurize, e.g., RP-1, as the Saturn I's first stage did (But not the Saturn IB's first stage: that was done with helium).  Nitrogen does have the disadvantage of being heavy.

Self-pressurization (using propellant vapor to pressurize the liquid form of the same propellant) no doubt makes control of pressurization more difficult, but it can and has been done.  Again, the Saturn I's (and IB's) first stage is an example: lox was vaporized with a heat exchanger.  I'll bet that controlling pressurization of a self-pressurized propellant that is sub-cooled would be quite a bit trickier.

Robert Goddard's first rockets used oxygen vapor for pressurization.  An alcohol lamp under the lox tank provided the vapor.  Believe it or not, gox was used to pressurize both the lox tank and the fuel (gasoline) tank!  After a few explosions, Goddard stopped using that trick. 

Offline Mbhoward

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Re: Keeping tanks pressurized during flight
« Reply #5 on: 11/07/2016 01:12 AM »
Thank you all, I appreciate the responses.

Offline Rei

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Re: Keeping tanks pressurized during flight
« Reply #6 on: 11/13/2016 11:00 AM »
Thanks, but I thought nitrogen and heated oxygen would condense inside a tank, and be become ineffective?

Nitrogen's BP is lower (77 K at 1 atmosphere) than oxygen's (90 K), so condensation isn't such an issue for pressurizing oxygen

In most cases, yes, but not in sub-cooled LOX.

Tags: Helium SpaceX