NASA and industry partners have been successfully launching a series of super-pressure balloons over Antarctica for long-endurance scientific missions in the upper atmosphere. These could get even longer as balloon technology advances.
The most recent mission launched from the Ross Ice Shelf near from McMurdo Station in Antarctica in January and touched down after spending more than three weeks at a consistent altitude of 111,000ft (33,550m) with a deviation of less than 500ft, says balloon manufacturer Raven Aerostar. The 396,000m3 (14 million ft3) envelope is capable of carrying a gross payload of 1,815kg (4,000lb).
"Super pressure" means there is a higher pressure inside the balloon than outside, with positive pressure on the order of around 0.002bar (0.0363lb/in2) under the highest pressure loading, although it is usually much lower, NASA says.
A super-pressure aerostatic balloon is constructed of a non-elastic material that keeps the volume of the balloon relatively constant in the face of changes in the temperature of the lifting gas, allowing the balloon to maintain altitude for long periods - as opposed to a variable-volume balloon, which is partially filled and relies on gas venting and ballast to maintain altitude as the gas volume changes with temperature.
Since ballast and gas are finite, the endurance of a variable-volume balloon is less than of a super-pressure balloon, which is thus better suited for the high-altitude, long-endurance atmospheric and Earth science experiments.
In addition to being the perfect vantage point for studying the ozone layer, other parts of the atmosphere and the Earth below, the extremely high altitudes of such balloons - anything higher than 100,000ft - allows for a clear view of space without atmospheric distortion at a much lower cost than a rocket-launched satellite mission, NASA says.
The trade off is that a super-pressure balloon must be constructed of much stronger materials than a non-pressurised balloon. Raven Aerostar says the material used in construction is a multilayer co-extruded polyethylene film made to NASA specifications, uniform in thickness and with exceptional heat-sealing ability.
Though the most recent test mission lasted 23 days, Raven says the balloon was showing no signs of stress and future flights could last up to 100 days. NASA's longest balloon flight was 41 days 21h 36min, in December 2004, over Antarctica.
Source: Flight International