I'd heard this was a relatively newer discovery -- that a blunt-body object travelling through a gas experiences a reduction in drag if that same gas is turned into plasma. I'm haven't read exactly why this occurs, but I'd presume that a gaseous fluid medium becomes easier to pass through if its usual constituent diatomic molecules are broken down into lower-mass monoatomic ions. I dunno -- that's just my guess. Anyway, I have read skeptics point out that the energy required to ionize the atmosphere in front of your aerobody could instead be applied for greater thrust, with the same net resultant speed increase. But clearly for hypersonic vehicles, which encounter tremendous heating issues, then perhaps it might then be worth it to channel some energy into the plasma drag reduction rather than purely into thrust, in order to alleviate the frictional heating problems. Additionally, the gas in the upper atmosphere through which the hypersonic vehicle would travel might be a little more readily ionizable, which helps. What would then be the best, most efficient/effective method to ionize a gas in front of a hypersonic vehicle, in order to mitigate drag and heating effects? A long electrode spike protruding out in front of the vehicle? Femtosecond laser pulses? Microwaves? Which way is best?