A poppy is flying on the payload of NASA's super-pressure balloon, which has launched from Wanaka Airport on its eighth attempt.
The balloon, which will inflate to the size of a football stadium, left the ground at 10.50am on Anzac Day.
The previous attempts, the last of which was on Saturday, were called off because of unfavourable winds.
The balloon is designed to run for 100 or more days, floating more than 33km above the Southern Hemisphere's mid-latitude band.
NASA balloon programme office chief Debbie Fairbrother says validating the super pressure balloon technology is the flight's main objective.
She says key lessons have been learnt from the 2015 and 2016 flights that launched from Wanaka.
It is also a mission of opportunity for the International Extreme Universe Space Observatory on a Super Pressure Balloon (EUSO-SPB) payload.
EUSO-SPB's objective from a high-altitude vantage point is to detect ultra-high energy cosmic rays from beyond the galaxy as they penetrate the Earth's atmosphere.
As the high-energy particles enter the atmosphere, they interact with nitrogen molecules in the air and create a UV fluorescence light.
The project's principal investigator, Chicago University professor Angela Olinto, says EUSO-SPB is searching for the most energetic cosmic particles ever observed.
"The origin of these particles is a great mystery that our pioneering mission will help to solve," she said.
"Do they come from massive black holes at the centre of galaxies? Tiny, fast-spinning pulsars? Or somewhere else?"
The balloon's progress can be tracked from their website.