The balloon looks like a pumpkin

He said that Nasa had decided to proceed with the test flight on Saturday despite bad weather conditions because it would still have provided information needed for research.

A first attempt to circle the globe by high-altitude balloon took place on 25 February after long delays due to bad weather. But that balloon was destroyed when controllers brought it down by remote control after it sprang a leak a few hours into its flight.

This second flight was intended to find clues to why the first balloon failed. Initial observations suggest it may have met with a similar fate.

Little atmosphere

Nasa hopes the balloons could be a cheap alternative to rocket-borne satellites, with flights lasting up to 100 days.

The pumpkin-shaped Ultra-Long-Duration Balloon (ULDB) is designed to inflate gradually to the size of a football field as it approaches the outer reaches of the Earth's atmosphere.

It is the largest single-cell, fully sealed balloon ever flown, with a fully inflated diameter of 58.5 metres (193 feet) and height of 35 metres (115 feet).

It is intended to travel at an altitude of 35 km (20 miles), three to four times higher than passenger aircraft fly. The balloon would ride above all but 1% of the Earth's atmosphere.