No insulation on rocket

[totalitor]

What if there is no insulation on cryogenic rocket? I know liquid oxygen would boil off but how fast? 

What if that rocket would be kept on container below boiling point? When fuelled and ready to launch container roof would go away and rocket would be  launched. No time to boil off until the rocket is flying.

A rocket small enough and fuel lets say to one minute burning - how much weight saving is possible? Or does liquids boil off too much?

Think small, not big. Is this idea doomed? Are there rockets using liquid oxygen without insulation (Copenhagen Suborbital Nexo I has no insulation when flying)?

[cubinator]

I think it's easier to put insulation around a particular fuel tank that needs it than to make a giant fridge to store an entire rocket at <90 K and still have it be able to work properly.

[Kerbart]

It stands to reason that an an industry that is is obsessed with weight savings that if they're willing to pack on the pounds needed for insulation, it is really needed.

[Kryten]

I can't think of any rocket using 'soft' cryogens like liquid oxygen that has external insulation, the boiloff during flight isn't worth the extra weight. Conversely, rockets using liquid hydrogen always have insulation, both because it boils off much more rapidly and because it creates much higher volumes of gas as it does. There have been cases of hydrolox stages rupturing after insulation issues, despite having pressure relief valves; the boil-off is so rapid it overwhelms the valve.

[Starman4308]

The external insulation thing isn't a huge deal; it's much cheaper and easier just to top the rocket off just before launch and retract the fuel pumps at the last possible moment.

During flight, well, some cryogenics can last through a flight with trivial boiloff without much insulation, but as others have mentioned: try to fly with liquid hydrogen and no insulation, and your rocket will swiftly have neither insulation nor liquid hydrogen.

[Phineas Freak]

For liquid Oxygen you do not need insulation, the ice formed on the surface of the tank is adequate. For Liquid Hydrogen on the other hand, insulating the tanks is a must: you will loose 300 - 500 Kg per minute without it. As @Kryten mentioned, It is also very dangerous since the ullage will have enough back pressure to blow the tanks (see Atlas Centaur AC-01).

Insulation is relatively light these days so it makes sense to pack a little more propellant than you need (to account for the inflight boiloff). From the fiberglass panels (early - mid Centaurs) to the honeycomb insulation (Saturn V S-II) and, currently, sprayed foam (Centaur 5, Shuttle ET & SLS, Delta IV CBC & DCSS) the mass efficiency of cryo insulation has improved a lot!

[p1t1o]

Some excellent reading here:

https://history.msfc.nasa.gov/saturn_apollo/documents/Second_Stage.pdf

 

On another note, I recall hearing an anecdote about this, but I cant remember which rocket it referred to - whether it was the space shuttle main tank, or a Saturn V stage or something else I dont recall, but it went something like: The insulation between the hydrogen and oxygen tanks was tuned in such a way that enough heat flowed from the warmer O2 tank into the H2 tank that O2 boiloff was essentially zero, meaning only the hydrogen tank had to be equipped to handle significant boiloff, ie: the H2 tank actively cooled the O2 and only one boiloff system was required ~(saving mass yadd-yadda...).

 

**edit**

More:

http://history.nasa.gov/afj/s-ii/s-ii-insulation.html

 

Edited October 31, 2016 by p1t1o

[totalitor]

Thank you for your answers.

I was thinking small, something like this: If I build a rocket 1 meter height (3 feet) and I use liquid oxygen and kerosine.

Just thinking if there is enough benefit not to insulate. Weight saving would be...1 kg? Max? Is it worth? I guess not. 

Is it possible to use liquid oxygen boiloff instead of pressure feeding system using nitrogen or helium? Weight saving you know...

[Phineas Freak]

1 hour ago, totalitor said:

Is it possible to use liquid oxygen boiloff instead of pressure feeding system using nitrogen or helium?

No because the relative LOX ullage is too small to support indigenous pressurization (and would only work for the LOX tank). Now, if you had something like a Vulcan CBC (CH4/LOX) then it is possible.

Speaking about insulation, the common bulkhead of the Centaur upper stage is a really wonderful piece of art: there is a small gap between the two parts of the bulkhead and it is filled with Nitrogen. Upon loading the tanks with LH2 and LOX the Nitrogen solidifies, creating a near perfect vacuum. And you cannot get a more perfect insulator than the vacuum itself!