# Tag Info

25

At a pressure of 1 bar, the temperature of liquid boiling oxygen stabilizes at 90 K. For sub-cooling of LOX, the temperature should be lower. It is possible to cool LOX by forced evaporation by a pressure lower than 1 bar. But the LOX tank in a rocket should be as light as possible. If the pressure inside the tank is substantially lower than outside, extra ...

18

RP-1 isn't cryogenic actually. The subcooling for RP-1 is only to cool it to slightly below the freezing point of water, 20 F. At that temperature, no extreme cooling is required. The temperature difference is quite small compared to the larger LOX temperature difference, and the fuel is only there for 35 minutes. There likely isn't a need to cool the RP-1 ...

16

Confusion abounds. Spaceflight 101 has this to say about the NK-33: The NK-33 requires sub-cooled Oxygen with a temperature below its boiling point of -183 degrees Celsius to cool the turbopump bearings that would otherwise fail. Also, sub-cooled LOX has a higher density, close to that of Kerosene, reducing required tank volume and overall launch vehicle ...

15

In websites it is written a lot for the SpaceX and Falcon 9 FT space rocket because this rocket uses the liquid oxygen at -340 Fahrenheit (°F) or 66 Kelvin (K) which is far below compared to other operational rockets used in our days. SpaceX decided to operate different in colder temperatures because it was needed an extra performance for Falcon 9, to have ...

10

Cavitation is boiling, in this case it is caused by reduced pressure in the wake of blades. A boiling point is a combination of 2 factors; heat and pressure. If you can't do anything about the reduced pressure you can manipulate the other factor, which is the temperature. A liquid can stay in it's liquid state at a lower pressure if it is colder. I think the ...

8

The shuttle external tanks used liquid level sensors. You can see them on the left side of each tank in this schematic. Source: Page 95 of the old Press Manual Related sensors gained notoriety late in the program when the liquid hydrogen low level sensors, which were used as a safety system to cut off the main engines at fuel depletion, started indicating &...

8

The Soviet N1 rocket used subcooled liquid oxygen. The driving force behind this was to use a common shaft on the turbopump for the fuel and the oxidiser. By subcooling the liquid oxygen such that it's density was equal to the RP1 fuel they were able to simplify the rocket engine design and reduce weight. It's one of the reasons behind the very high thrust ...

7

There is no problem running Kerosene and Oxygen on the same turbopump shaft, at any temperature. provided both are liquid, the density variations are not sufficient to make any practical difference to the feasibility of a turbopump. From the OP, the densities of Oxygen and Kerosene are 1.18 and 0.8 g/cm3 , a ratio of 1.475. The pressure produced by a single ...

6

According to Sutton's Rocket Propulsion Elements: If the two propellants have similar densities (say within 40%) such as NTO & UDMH or LOX and kerosene, and the volume flow of oxidizer and fuel are similar, then the same type of impeller (running at the same speed) can be used on both of them on a single shaft. It goes on to say that with hydrogen/...

5

Since "I'd be happy with any an answer, not necessarily specifically related to this launch." here are some shuttle numbers. Once the External Tank (ET) was filled with LO2, it went into replenish mode in which the system replaced boiled off propellant. These charts show that the nominal replenish time was about 4 hours (including a built-in one hour hold) ...

5

We don't need to look into the phase diagram here, because it doesn't matter on which path we reach a certain end point. We can safely assume that we heat up the helium at constant pressure and then shrink its volume again. Density of liquid helium boiling at 1 atm pressure is 0.125 $\rm g/cm^3$. Density of gaseous helium at 273 K is 0.18 $\rm mg/cm^3$. ...

5

This answer is based mostly on the NPSH link Organic Marble shared (http://www.pumpschool.com/applications/NPSH.pdf) and the various properties you can infer about subcooled LOX. Subcooling lowers vapor pressure, which helps prevent bubble formation. Subcooling densifies the propellant, which allows lower fluid velocities at the same mass-flow rates, which ...

5

First, the only place I have been able to find the equal density claim is in the NK-33 Wikipedia article. (In fact it originates from the first version). There have never been provided any source for it. On the other hand, this paper seems to suggest that that is indeed the cases, although indirectly. Polymerization does not necessarily have to be a problem,...

5

I have not been able to find a reliable source for this, but according to this forum post, the Atlas ICBM used lox at 78 K in the first part of the launch, referred to as "supercooled". For comparison, the shuttle used lox at 90 K.

5

Once the tanks are no longer full, there's no point in keeping the propellants subcooled. When you start the engines, you just have to control the rate at which the tank and propellant warm up, to keep the pressure below its limit. The warm gas you inject into the headspace to pressurize the tank will start warming up the surface of the liquid. You'll ...

4

There is nothing wrong with a substance existing in both a liquid form and a gas form at the same time, like in this case. In fact, that is where the equilibrium is! Firstly, there is not really such a thing as a liquid in a vacuum, it will always attempt to fill it*, as the boiling point gets lower with the decreased pressure. Le Chatelier's principle is ...

4

For the Space Shuttle, liquid oxygen was used at boiling temperature (95 K). Rocketdyne did some successful tests with LOX subcooled to 88.9 K. In a quick search I've found no indications this was used operationally in the Shuttle, or will be used for the SLS.

3

Short answer: No, lots of them don't use oxygen at any temperature or density Long answer: Less no. If you take an engine that uses liquid oxygen and put subcooled liquid oxygen into it, it will be subject to additional thermal stresses and the turbopumps involved will be pumping a liquid denser than they were designed for. If neither of those problems ...

2

Hydrogen is liquid below 21.15 K and goes solid at 14.01 K. Helium is liquid below 4.15 K and goes solid at 0.95 K under huge pressure of 2.5 MPa. So it should be possible to use gaseous helium to sub cool liquid hydrogen. It is gaseous even below the temperature of solid Hydrogen. Methane boils at 111.65 K and solidifies at 90.7 K. Sub cooling it with ...

2

It's much easier to cool the He by placing the tank inside the LOX tank. If you had a He tank outside, you'd have to insulate it, and provide active cooling. Both add weight and complexity. Propellant tanks can be pressurized at the last moment: you fill them at atmospheric pressure and vent the boiloff (if any). For boiling-point LOX: when the tank is ...

1

The quote: "We sub-cool the oxygen and methane to densify it, so compared to... propellants normally used close to their boiling point in most rockets, in our case we actually load the propellants close to their freezing point, and that can result in a density improvement of up to around 10 to 12 percent, which makes an enormous difference in the ...

1

In fact, the system of sib-cooled (chilled) cryogenic liquid and its vapour (gas) is more stable than the same liquid near the boiling point. Condensation on the free surface of the liquid propellant is driven mainly by diffusion which is a slow process. From the other side, a sudden splash may increase the free surface a hundred times because of droplets ...

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