The rise of giant balloons at the edge of space
The NASA mission that brought the giant balloon down on a remote cattle station, in south-west Queensland, in April was to test the feasibility for using stratospheric balloons for scientific research.
Although this mission was a misadventure, it has a number of advantages over satellites orbiting the Earth.
They can stay afloat for up to six months above 99 percent of Earth’s atmospheric pressure. So, they can be used to transport instruments in astronomy and astrophysicists. They can do all this for a fraction of the price of putting such instruments on satellites.
Such experiments can be carried out much faster than satellite-borne experiments. A super-pressure balloon can also be used as a platform for monitoring the atmosphere and environment of Earth over a long period.
Space Age Balloons
NASA and the French, Japanese and other space agencies have been developing super-pressure balloons for almost two decades. The ultimate goal of the project is to carry instruments up to 2 tonnes at stratospheric heights up to about 40 km, and keep them afloat.
You can find out the size balloon required to lift a certain weight to stratospheric heights by consulting Archimedes Principle.
At ground level, the density of air is 1.3kg/m 3. A balloon with a volume of 1m 3 can lift only 1.3kg. The air density at 40km is 330 times lower, so a balloon with a volume of 330m 3 will be needed to lift 1.3kg.
The typical balloon flight train just before lift-off. As the balloon rises, it will expand into less dense air. Ravi Sood is the Author.
The NASA super-pressure ball had to lift both its own mass (2.268kg) and the payload (1.588), so it needed a volume about the same as the Melbourne Cricket Ground.
The majority of stratospheric balloons are “zero pressure” balloons, which have the envelope open at the bottom. The balloons gradually lose helium, which limits the flight time.
Our group, then at Melbourne University, had managed to fly a similar balloon for 22 consecutive days in January 1983. It was launched from Alice Springs.
NASA’s super-pressure balloons are sealed and made from thicker materials. They can stay aloft for up to several months.
Although the environment is harsh, it’s still a good thing. The ultraviolet radiation and temperature are intense. This is because the tensions within the envelope of the balloon can cause deformations or leaks.
When this occurs on a balloon in Australia’s Airspace, Airservices Australia requires that we at UNSW Canberra terminate the flight so there is no risk to aircraft during flight descent. In order to land safely, we must also avoid restricted or inhabited areas. This is exactly what we did on the last flight.
The NASA Balloon flight: The Rise and Fall
The drift of a balloon cannot be controlled. Therefore, the best time to fly is when wind direction and speed are predictable.
Approximately six months of each year, the stratospheric wind blows strongly eastward. Then, they switch and blow strongly westward.
The NASA super-pressure ball launch coincided with a change in the direction of the wind that occurred in April. The balloon was expected to travel around the globe at the same latitude as the launch site in Wanaka on New Zealand’s South Island.
The balloon performed well after the launch on March 27 this year. It drifted as predicted over South America, then South Africa.
A change in direction
The stratospheric wind over the Indian Ocean had an unexpected north-south component (see the image below), and this led to it drifting towards Queensland.
The flight path of the super-pressure balloon from launch to end. NASA/Google Earth
As soon as this balloon entered Australian airspace, it was our responsibility to ensure that its safety, in accordance with Australian aviation and security regulations, was maintained.
I obtained approval from Airservices Australia and the Civil Aviation Safety Authority to ensure that the flight would comply with our regulations.
NASA informed me on the morning of the 28th that the balloon was leaking. The projected flight path was towards Adelaide, so it was decided to end the flight when it was above sparsely populated areas.
The emergency services of Queensland were alerted after Air Traffic Control in Melbourne approved the termination time and place.
The was terminated by 1:03pm (AEST) and the payload, with parachute, hit the ground at 1.44pm (AEST), 107 km north-east of Tibooburra.
The balloon descended independently and landed at a distance of 10km from its payload.
The super-pressure ball payload recovered. NASA Columbia Scientific Balloon Facility Author provided
Loading the recovered super-pressure ballon. NASA Columbia Scientific Balloon Facility Author provided
The super-pressure balloon flight was a simple engineering test to evaluate the performance of the balloon. NASA plans to fly a super-pressure balloon again in 2016, but this time from Wanaka, New Zealand.