Imagine a balloon the size of the Melbourne Cricket Ground floating through our skies. UNSW Canberra academic Dr Ravi Sood uses these monstrous scientific balloons for his research and we asked him all about it.
Imagine a balloon the size of the Melbourne Cricket Ground floating through our skies. UNSW Canberra academic Dr Ravi Sood uses these monstrous scientific balloons for his research and we asked him all about it.
What is a scientific balloon and why is it used?
Scientific balloons are often confused with meteorological balloons. The latter type of balloons are small, and carry very light instruments to measure the wind speed and direction, and the temperature of the atmosphere to assist aircraft navigation.
A scientific balloon flight is conducted for other very specific reasons. These include:
These studies help to study the physics of black holes, very rapidly spinning dense stars, and the formation of stars and galaxies. Certain types of radiation from stars and galaxies get absorbed in the earth’s atmosphere, and the only way to make these observations is either to send the instrument into space in a satellite, or to fly it suspended from a stratospheric balloon floating at the edge of space. The latter is several orders of magnitude cheaper, and it takes less time to develop and complete a balloon-borne experiment.
How do scientific balloons ‘fly’?
Virtually all commercial aircraft fly below 60,000 ft (18.2 km) altitude. Useful astrophysical observations can only be made at altitudes above about 30 km, a region of the atmosphere known as the stratosphere. The air density in the stratosphere is very low, and for a balloon to be able to float there carrying a typical scientific instrument presents enormous challenges. To lift a present day instrument weighing 1 tonne to an altitude of 40 km will require a balloon that is 1 million cubic metres in volume, about the size of about the Melbourne Cricket Ground. The balloon has to be made from very thin plastic material, typically the thickness of gladwrap, in order to keep the balloon weight down. The balloon material is specially developed to be able to have high tensile strength and to be able to withstand extremely low temperatures encountered in the stratosphere. The balloon is filled with helium gas, and because it is so large and thin, it can be used only once.
How high can a scientific balloon go?
The float height that a stratospheric balloon needs to attain is entirely determined by the aims of the experiment. An infra-red detector telescope can operate satisfactorily at 25-30 km altitude, while an X-ray or gamma-ray telescope would work best at about 40 km. The highest altitude attained by a stratospheric balloon is 53 km, which is above 99.95% of the atmosphere.
Do scientific balloons ever get lost and how would you retrieve it?
Stratospheric balloon flights have to comply with strict regulations imposed by the Civil Aviation Safety Authority, and by Airservices Australia. Each balloon flight is treated like an aircraft movement, and approval is given by Air Traffic Control for all phases of the flight.
Approval is sought from Air Traffic Control before a flight is terminated. The scientific payload descends to ground on a parachute. At flight termination, the balloon material is automatically ripped and the balloon material descends to ground separately. Recovery operations are carried out using all-terrain vehicles, helicopters and aircraft, depending on where the payload lands. The balloon carcass is collected and disposed of separately. Flights launched from Balloon Launching Station in Alice Springs have been terminated over eastern Queensland, South Australia, and close to the coast in Western Australia.
If you could ride in a scientific balloon for a day, what do you think the experience would be like?
The atmospheric environment encountered in a stratospheric balloon flight is extremely harsh and dangerous. Temperatures can plummet down to -80°C during ascent, while there is virtually no air to breath at high altitudes. A ride on such a flight would require either a pressurised gondola which is temperature controlled, or a fully fitted space suit.