Long-Term Cryogenic Storage

NASA's Glenn Research Center is about to start a conceptual design study on the storage of cryogenic propellants for Exploration missions (i.e. Moon and Mars). Basically they need to figure out how to store liquid oxygen, liquid methane and liquid hydrogen for long periods. You can't just let it "boil off" as we do now.

"These concepts will require the cryogenic propellant inventory in the vehicle to be maintained during ground hold, the launch transient, during a long term, quiescent in-space storage at the ISS, for lunar injection, and during lunar operations. The cryogenic propellants must also be delivered in a vapor free condition to the Reaction Control Systems (RCS) thrusters and the Orbital Maneuvering Systems (OMS) engines of the vehicle."

It will be interesting to see how they approach this problem. Some kind of on-board cryogenic cooler? Ultra-insulated tanks? Extremely pressurized tanks? All of the above?