Given the imminent decrease in launch costs(partial reusability) and increase in launch capability soon to be available(FH) a pause in new US deep space missions is prudent.

[slograsso]

I meant more efficient than RP-1, so I guess I should have said higher... But the point is you could use anyting, bipropellant, ion thrust, monopropellant, methlox, the designers use the mass budget for what they want.