A suspected leak means Nasa's stadium-sized super pressure balloon will be brought back down to earth well short of its planned 100 day journey.
Three days after a successful launch from the Wanaka Airport the 532,000cu m balloon lost altitude after travelling through a cold storm.
Since then, the balloon has continued to lose altitude at night, and then repressurise and return to an altitude of 33.2km during the day.
The balloon is designed to maintain a stable altitude during the heating and cooling of the day-night cycle.
Nasa's balloon programme office chief Debbie Fairbrother said it was clear the balloon was no longer operating as designed and the data pointed to a leak in the balloon.
The balloon is currently floating above the Pacific Ocean close to the Pitcairn Islands.
"This is an unfortunate development in out test flight, but we're gaining some important data from this mission that will apply to future flights."
Once the balloon crosses the Pacific Ocean, Nasa will seek a safe area to terminate flight and recover the balloon and payload.
