UPDATED 8.41am: The launch of NASA's giant balloon from Wanaka's airfield has been postponed again.

Radio Wanaka's Mike Regal says the wind hasn't come around to the right direction.

"Ideal conditions, perfect day in Wanaka, but the wind has not come around into the North, into the direction they wanted it to for the launch.

"So postponed, evaluation tomorrow."

The NASA crew has to pick its moment perfectly - they only have enough helium to do one launch, and if it's botched - they all go home.