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One of the changes made to the Falcon 9 v1.1 Full Thrust was using supercooled liquid oxygen at 66 K (-340 F) as well as chilled RP-1.

I've seen various claims that this is a first in the industry. Clearly liquid oxygen has been chilled this low in a lab before, but is using this level of supercooled LOX a first for a real launch carrying a payload?

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    $\begingroup$ This seems to be a misuse of the term super-cooled, which refers to a liquid that is chilled below its freezing point without crystallizing (-380F?). Seems to be subcooled (temperature lower than saturation but higher than freezing) instead. $\endgroup$
    – user13737
    Commented Mar 11, 2016 at 19:52
  • $\begingroup$ Try this - NK-33s on the original Antares booster: nasaspaceflight.com/2016/01/orbital-atk-antares-second-life $\endgroup$
    – Puffin
    Commented Mar 11, 2016 at 21:25
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    $\begingroup$ @Puffin that article is hard for me to understand - there is discussion of a LOX sub-cooler at the pad as an alternative to better insulation for LOX transfer lines, and I see here something about turbo pump bearings needing sub-cooled LOX, but does this mean a rocket using NK-33 engines must have a tank full of sub-cooled LOX? $\endgroup$
    – uhoh
    Commented Mar 12, 2016 at 3:05
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    $\begingroup$ @uhoh Its not my field so I didn't want to intervene on the sub/super discussion. However, I took a stronger interpretation on the NSF link, to me sub cooling is mentioned in context sufficiently to conclude that they at least meant that the NK-33 carries LOX deliberately below boiling point, i.e. it supports your question. Given that, the wiki article you linked is at least consistent with that. Neither says how much below boiling, so we don't get any insight to compare with the F9FT though from the wiki the motivation seems to be metallurgy rather than tank capacity. $\endgroup$
    – Puffin
    Commented Mar 12, 2016 at 12:08
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    $\begingroup$ @uhoh I've just seen Lord Bubbacub's answer. Perhaps the point about equal densities between LOX and RP1 would offer a clue as to the LOX working temperature. Ideally one would need to know the RP1 temperature too but perhaps its own density is varies more slowly with the degree of chilling. $\endgroup$
    – Puffin
    Commented Mar 12, 2016 at 12:14

3 Answers 3

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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 in this way more fuel available for first stage landings. Since Falcon 9 FT is a rocket that could be used to transport astronauts in space and also using the supercooled LOX is not an easy process which could be risky and needs a very secure technology to complete this process, it gives attention and fame to Falcon 9 FT for this part. But the Falcon 9 FT is not the first using supercooled LOX. Other rockets have used it before the SpaceX’s rocket and according the information of some websites even in lower temperatures than Falcon 9 FT rocket uses. So the supercooled is not used only in laboratories for studying it, but also in real rockets putting in to practice and being operational for years.

The rocket for which I am referring is the two stage R-9A intercontinental ballistic missile (ICBM) also known as SS-8 Sasin. We know that most of the missiles use very toxic hypergolic propellant or solid propellant. But the R-9A was a launcher that used cryogenic propellants, kerosene and liquid oxygen, for its first stage.

R-9A launch pad

Transportation and installation of the missile R - 9A / 8K75 on the launch pad . The launch complex " Desna -N" at Baikonur Cosmodrome 1961-1963

The R-9 represented Korolev's last attempt to develop a practical military rocket and to prove the military worth of the non-toxic LOX/kerosene propellant combination. (1)

It was projected and being operational at the beginning of the space rockets developments when a lot of experiments and test were done for new and unknown technologies at that time. So was even for R-9A rocket in which new technology was applied for the supercooled LOX.

Designed in 1959 and first Flight tests of rocket R-9A started on April 9, 1961 and the first successful launch took place on April 21, 1961. It entered in service on July 21, 1965 and remained in service for more than 10 years. A total of only 27 operational launchers and 70 missiles were built.

Previous Soviet designs, fuelled with cryogenic LOX and kerosene, commonly took hours to fuel and launch, around 2 hours. The R-9A, on the other hand, could be launched after 20 minutes from the time a launch order was given. So for R-9A new achievements were the capability of using the supercooled oxygen and also the process of fueling and launching quickly a production missile using cryogenic LOX.

In order to achieve this, new technologies had to be mastered.

A system for overcooling, durable storage, and high-speed filling of the rocket with supercooled LOX has been developed and the problem of durable storage of oxygen without losses has been solved. (3)

Vasily Mishin developed new materials and machinery to precool the liquid oxygen to around -210 Celsius (°C), then devised vacuum isolation storage systems that reduced boil-off losses during storage, transport, and fueling operations by 500 times. All the processes followed before launching are described here (audio is in Russian language). Using the supercooled LOX was very important for this project. Studies have shown that there are additional opportunities to improve the efficiency of the supercooled LOX. Using it gave a lot of advantages to R-9A. First it takes a smaller volume, secondly sharply decrease evaporation losses and thirdly can be implement high-speed refueling in this way the oxygen getting into a warm tank will not boil rapidly, as it usually happens. In this case supercooled LOX at a temperature of -210 Celsius (°C), strongly increases its fluidity and allowed them to drastically reduce refueling time which was very important for the missile to be fueled and launched quickly as fast as possible for emergency or tactical launches in case that will be needed. We know how the tension was at its peak in the beginning of 1960s. The R-9A despite that it had nuclear weapon as payload was a launcher, which probably after some modifications done to it and with a 3rd stage mounted to reach orbital speed, could have the capability to launch small payloads in orbit according to its specifications. Information of websites confirms that the LOX used in R-9A was supercooled. But some websites say -186 °C, but I doubt this because at some of them the temperature is shown with (?) mark. According to tonnel-ufo.ru and astronautix.com, the temperature of liquid oxygen was -210 Celsius (°C) = 346 Fahrenheit (°F) = 64 Kelvin (K), which means lower than Falcon 9 FT 66 K (-340 F). So by this information it means that the R-9A could be the launcher that uses the LOX in the lowest temperatures ever. Anyway the most important thing that has to do also with your question, is to be sure that the Falcon 9 FT is not the first real launch carrying a payload that uses supercooled LOX, because at least one another launcher has been using it long before than Falcon 9 FT.

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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 to weight ratio of the NK-15 and NK-33 engines. The subcooled liquid oxygen was also required to lubricate the turbopump. It never made it to orbit unfortunately, but it had four real launches with payloads as per the question.

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    $\begingroup$ OK this is interesting. The density of boiling LOX is about 1.14 g/cm^3, and RP-1 varies a lot with temperature, and is roughly 0.9 g/cm^3 at 0C Wikipedia mentions 0.8-1.02 g/cm^3, so we need to look further to see how sub-cooling the LOX brings their densities closer together. I have a feeling that upon further cooling, RP-1 will turn to wax before it would reach a density of even 1.14 g/cm^3. $\endgroup$
    – uhoh
    Commented Mar 12, 2016 at 13:09
  • $\begingroup$ I may have misunderstood something - both this answer and the comment above make sense in isolation but seem inconsistent with one another. @Uhoh is that what you meant? On a possibly separate topic, the wiki RP-1 article has a curious sentence: "For a short period, the Soviets achieved even higher densities by super-chilling the kerosene in a rocket’s fuel tanks, but this partially defeated the purpose of using kerosene over other super-chilled fuels." Does anyone understand the last bit? $\endgroup$
    – Puffin
    Commented Mar 12, 2016 at 21:41
  • $\begingroup$ @Puffin on the surface they seem inconsistent to me also, thus the "OK this is interesting." But there is probably just a little more information we are missing at the moment. I'm reading about cold RP-1 now, will update if I find anything. $\endgroup$
    – uhoh
    Commented Mar 13, 2016 at 8:33
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    $\begingroup$ @Puffin I've done what searching I can on-line, and raised this as a question now. Curiouser and curiouser! $\endgroup$
    – uhoh
    Commented Mar 15, 2016 at 8:28
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    $\begingroup$ @puffin: the reason to use kerosene is that you can use it at room temperature so you don't need complicated cooling arrangements for the fuel. This in contrast to hydrogen or methane, which do need cooling. Cooled kerosene defeats that purpose. $\endgroup$
    – Hobbes
    Commented Mar 19, 2016 at 17:59
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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.

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  • $\begingroup$ For those of us (like myself) that can't do the Kelvin to Fahrenheit conversions in our head: 78 K ~= -320 F. 90 K ~=-297 F $\endgroup$
    – AWinkle
    Commented Dec 22, 2015 at 20:06
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    $\begingroup$ If "boiling liquid oxygen" is 90K and "sub-cooled liquid oxygen" is 66K (per the question), then the technical name for 78K is"lukewarm liquid oxygen" or "tepid liquid oxygen" or "not-boiling liquid oxygen." $\endgroup$
    – uhoh
    Commented Mar 12, 2016 at 3:11
  • $\begingroup$ @AWinkle I've started plotting with four different temperature scales because I can't do it in my head either! $\endgroup$
    – uhoh
    Commented Mar 15, 2016 at 15:03

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