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A year's planning went into Monday's launch of a balloon from the shores of Lake Wakatipu - to 30km into space - and its successful landing in a Ranfurly paddock.
The scenic launch site was determined by a computer program which took into account the size of the balloon, payload and weather conditions, to also fix its Ranfurly landing.
''It blew us away that we got it so incredibly close,'' project co-ordinator Amadeo Enriquez-Ballestero said.
A group of school-aged astronomy enthusiasts took part in the planning, launch and recovery of the former Niwa weather balloon, which was filled with 4cu m of helium courtesy of Boc NZ.
''Every kid had a role ... When I was a kid I would have loved to have done this,'' he said.
The balloon was carrying a box loaded with three cameras, one of which was trained on two marshmallows dangling on a rope as part of a space experiment.
''As the pressure decreases, the marshmallows expand as it goes into space.''
Another aim of the expedition was to record the curvature of the earth, he said.
A big part in the successful recovery was the ingenuity of an 8-year-old member of the group, who supplied a back-up GPS, which was called into action when a computer failed.
''He saved the mission.''
That back-up plan helped the group locate the balloon with barely minutes of daylight left.
Footage of the expedition, dubbed Operation ECO, would be viewed for the first time by the group at Kavanagh College on Sunday.