As a follow up to Are there liquid fueled rocket boosters having coaxial fuel/oxidizer tanks? and thinking about JCRM's answer pointing the issue of having a huge contact surface between inner and outer tank, requiring efficient insulation between the two (which means relatively thick low density material)
Why did Orbex choose to use propane in combination with liquid oxygen, instead of for example methane, which boiling point is very close to oxygen's boiling point, allowing use of very thin insulation or even only structural skin?
- How are the two coaxial tanks structurally linked together so that the entire system saves weight compared to classic stacked one above the other tanks? (maybe another question, even if it's all about coaxial tanks architecture, in this case.)