British aerospace company Orbex is developing a small orbital rocket called Prime, which uses propane and liquid oxygen in two coaxial tanks.
One key aspect of propane is that it remains liquid at cryogenic temperatures. That enabled a “coaxial tank” design for Prime where a central tube of propane is surrounded by an outer tank of liquid oxygen, creating structural mass savings in the rocket.
How are inner and outer tank structurally linked together, and where come weight savings from?
To add food of thought, I came across these pieces of text found here
"Prime launchers are up to 30% lighter and 20% more efficient than any other vehicle in the small launcher category, packing more power per cubic litre than many heavy launchers."
"If only the outer LOX tank needed to bear structural loads and the inner propane tank just needed nothing more than to physically separate that fuel from the LOX with no thought to insulation, might that account for the 30% mass savings?"
"If the inner tank was even inflatable like a bladder or balloon within the LOX, might a single pressurization system suffice for both propellants?"
"Flexible cryogen bag tanks are apparently a thing, so tension anchoring the thing in the LOx tank is certainly doable."