[tankenmate]

LNG tanks are far from lightweight; to keep LNG at room temperature is about 320 atmospheres of pressure. Liquid propane on the other hand is about 8 atmospheres. Mind you at altitude it's around -50 ~ -60 C, but that will only reduce the pressure requirements to approx 100 atm. Also, LNG has about 60% of the energy density of kerosene. SO to use LNG you'd be taking a double whammy, lower density and heavier tanks.

[srssays]

Sounds like propane is a winner. Would it help to use a composite tank a la SpaceX?