After seeing all the Starship failures, having something with a membrane keep things in place seems like an obvious solution. Has it been considered or tested - or do we simply lack a material that is elastic at the (cryogenic) temperatures required? What would it theoretically take? What subjects would you need to study to develop such a material?

  • 1
    $\begingroup$ A similar idea is using moving diaphragms for the tank ends. No image link but this Youtube video shows an example (link is to point in video where diagram is shown). $\endgroup$ Commented Apr 21, 2021 at 8:44
  • 1
    $\begingroup$ @BenCrowell I presume that's a reference to the various Starship prototypes. SN1, SN2, ... $\endgroup$ Commented Apr 21, 2021 at 18:46
  • 1
    $\begingroup$ @BenCrowell ...with SN standing for Serial Number. $\endgroup$ Commented Apr 21, 2021 at 18:54

1 Answer 1


They do!

Many propellant tank, especially those required to work in zero-g environments, do use just such a bladder-inside-a-tank for the fuel. Typically monopropellants for thrusters. enter image description here

It completely removes the requirement for Ullage of the propellants, but adds complexity, cost, mass and failure modes.

Additionally, flexible bags are a bit hard to make at deep cryogenic temperatures.
Additionally, flexible bags that can contain 200 tons of cryogenic liquid sloshing around under 5 g of acceleration are.... simply impossible to manufacture.
I don't think we will ever have the technology to make a soft bag that can hold 1000tonnes (200 tonnes under 5g) of cryogenic liquid that is sloshing around.

For interest: take a peek at this. Work on developing a bladder that is cryogenic compatible. But max size very much small.

  • $\begingroup$ It's worth noting that the ones that operate long term aren't cryogenic fuels, so... $\endgroup$
    – PearsonArtPhoto
    Commented Apr 20, 2021 at 20:32
  • 2
    $\begingroup$ Do any boosters use these? $\endgroup$ Commented Apr 20, 2021 at 21:08
  • $\begingroup$ @OrganicMarble From the first link: "Our bladder tanks are used on the 400 N Attitude and Orbital Control System (AOCS) of all versions of Ariane 5 and in the VEGA 200 N Roll and Attitude Control System (RACS)." $\endgroup$
    – Dan Mašek
    Commented Apr 21, 2021 at 8:05
  • 2
    $\begingroup$ Those are RCS systems. Not the booster tankage. $\endgroup$ Commented Apr 21, 2021 at 11:09
  • $\begingroup$ Aahh... it's the math again :-D $\endgroup$
    – Dagelf
    Commented Apr 23, 2021 at 20:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.