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From my related question, it turns out cryo tanks are not double-walled for insulation purposes. So now I will continue along a similar line and ask, aren't cryo tanks heavier than normal tanks on a per surface area basis?

A normal tank would be one for kerosene or hypergolics---room temperature normal pressure things.

My thinking is that the extremely cold conditions of the tank would make them more brittle or structurally weaker somehow, so they'd hafta be thicker to be stronger. OR they could have some other insulation besides double-walls that weighs them down.

You can pick either LOX or LH2 tanks. If there's some major structural difference between them, well then I'm actually looking forward to learn about it.

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  • $\begingroup$ If there is no insulation at all, the weight of the ice formation on the tank walls may be more than the weight of the tank walls. The vibrations after launch may remove a lot of ice. $\endgroup$
    – Uwe
    Oct 10, 2017 at 19:07

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Not necessarily. For a counterexample, we can look at one of IMHO the coolest boosters ever, the Atlas 1. This is as close as the US has ever come to an operational SSTO vehicle and one of the reasons is its amazing construction.

This vehicle utilized the famous balloon tank design in which the tank walls were so thin that they could not even support their own weight without being pressurized. The propellants were RP-1 (room temperature hydrocarbon) and LOX. Tankage for the entire vehicle was built from "a special cold-rolled austenitic steel (A1S1 grade 301) which was produced by the Washington Steel Corporation." (All quotes are from "Spacecraft and Boosters" by Gatland - basically a collection of articles from Flight International magazine in the Space Age, and a superb book). Pages 219-225 give a detailed description of the construction and state that "several of the 27 (ring) sections are thinner than the walls of a milk carton. The heaviest skin gauge is less than 40 mil."

So, for this missile at least, there was no significant difference in the tank construction for the RP-1 and LOX tanks.

Here's a poor-quality scan of one of the great schematics from this book. It shows how the tankage is the vehicle.

enter image description here

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  • $\begingroup$ Wow thanks for that example! Does it mention if those tanks were a lot more expensive to construct? Otherwise I would wonder why this wasn't done on, say, Saturn vehicles. Finally, please can you find the dry LOX tank weight and its dimensions (diameter and height)? Assuming its a domed cylinder, we can then estimate the weight per surface area of tank and use it as a comparison for other tanks. If the RP-1 tank was built the same way, please get its weight and dimensions too. Thanks again! $\endgroup$
    – DrZ214
    Jul 23, 2015 at 20:24
  • $\begingroup$ I'll leave that as an exercise for the student. $\endgroup$
    – Organic Marble
    Jul 23, 2015 at 23:48
  • $\begingroup$ I don't have that book and I'm not in a position to purchase it any time soon. Can you help me out? $\endgroup$
    – DrZ214
    Jul 24, 2015 at 5:19
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Generally speaking, yes. This is because the tank must act as an insulator to prevent these cryogenic propellants from reaching their boiling point. Additionally, they must be thicker due to the thermal stress from the temperature differential between the inside and outside of the tanks.

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    $\begingroup$ shattertheearth, welcome to Space Exploration! While what you say makes perfect sense, and I appreciate your expert knowledge on the matter, we also like to include some citations / links for further reference. Would you please be so kind and edit to include some? I'm sure you'd know of just the right ones to do the job... Cheers! $\endgroup$
    – TildalWave
    Jul 22, 2015 at 7:35
  • $\begingroup$ The (equally unreferenced) counter-argument is that insulation is extremely light by its very nature. Also cyrogenic hydrogen is very light, at 81kg/m^2, compared with at least 900kg/m^2 for RP-1. The significantly lower weight could reduce the required strength of the tank. $\endgroup$
    – Blake Walsh
    Jul 23, 2015 at 20:53
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    $\begingroup$ When you put a cryogenic fluid in a room temperature environment, it will boil at some point, no matter the insulation. The question is how much will boil off. What LV do you know of, that uses insulation on an oxygen tank? (Other than the Space Shuttle, where the insulation is mainly for the hydrogen) $\endgroup$
    – Rikki-Tikki-Tavi
    Jul 23, 2015 at 22:11
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    $\begingroup$ Shuttle ET insulation was only to prevent ice formation in order to protect the tiles. $\endgroup$
    – Organic Marble
    Jul 25, 2015 at 16:51

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