Indian scientists to send weather balloon carrying 90kg instruments into coldest parts of atmosphere
Troposphere is the lowest layer of the atmosphere, stretching up to 16 to 17 km above the Earth’s surface over India and stratosphere lies above the troposphere, up to 50km widemumbai Updated: Mar 20, 2018 16:58 IST
India’s scientific balloon facility has scored several firsts, with scientists developing a hybrid weather balloon that can carry a record 10 instruments into the coldest region of the atmosphere to study a subset of air pollution – aerosols - which could become important for future climate projections.
The Tata Institute of Fundamental Research Balloon Facility (TIFR-BF), Hyderabad, in a joint collaboration, will send the indigenously designed and manufactured zero-pressure hybrid plastic balloon in July-August, with ten payloads weighing 90kg to measure the properties of aerosols, clouds, and trace gases in the boundary layer of the upper-troposphere lower-stratosphere (UTLS) region over Asia – also called the Asian Tropopause Aerosol Layer (ATAL).
The test flight last month was successful. Troposphere is the lowest layer of the atmosphere, stretching to 16to 17 kilometres above the Earth’s surface over India, and stratosphere lies above the troposphere, up to 50km wide. Aerosols are fine particles released from man-made and natural processes such as vehicle exhaust, waste-burning, wind-blown dust and volcanic eruptions.
“ATAL is like a blanket of aerosols extending above Asia in summer near the stratosphere. Aerosols can reflect and absorb sunlight, and can be important for atmospheric chemistry and cloud formation,” said Jean-Paul Vernier, NASA Langley Research Centre, who is part of the experiment, in an email interview. “Aerosols also represent the highest source of uncertainties for future climate projections. That’s why it’s important to study them.”
ATAL stretches from the east Mediterranean Sea to West China during the Asian summer-monsoon months of June, July and August.
So far, all studies and experiments that record local atmosphere use ground-based instruments equipped with a pump and filter, and operate at temperatures between 15 degrees Celsius and 40 degrees Celsius. The challenge for TIFR-BF therefore was to get these instruments ready for space environment with regard to both temperature and pressure. Scientists conducted several space tests in a thermo-vacuum chamber in the laboratory by creating an atmosphere that is present from 16km to 18km from the Earth’s surface with temperatures as low as minus 80 degrees Celsius. To adapt to the atmospheric pressure that decrease at that altitude, the team created thermal insulations for the ten instruments and batteries that would pump air using small vacuum motors.
“After successful tests in the laboratory, we created a module to launch balloon flights,” said B Suneel Kumar, scientist in-charge, TIFR-BF. “No atmospheric science experiments have been conducted floating the balloon at that altitude.”
Since 2014, TIFR-BF, the National Atmospheric Research Laboratory-Indian Space Research Organisation (NARL-ISRO), Physical Research Laboratory, Ahmedabad, National Aeronautics and Space Administration (NASA), Centre National de la Recherche Scientifique (CNRS-Orleans, France) and other national research institutes have sent different types of weather balloons with payloads of various weights to study the nature, formation and impacts on the tropopause.
“Generally zero-pressure plastic balloons are used to carry payloads weighing between 400kgs to 2000kgs at 32kms-43kms altitudes for astronomical study experiments” said professor Devendra K Ojha, chairperson, Balloon Facility Centre, TIFR-BF.
The challenge for the August 2018 flight, said scientists was to fabricate a balloon that would not only stay afloat at minus temperatures between 16km and 18km altitude, but also to get 10 instruments weighing around 90kg ready to operate in the space environment.
Unlike most experimentalists in India or abroad that use latex balloons, the TIFR balloon team decided to develop hybrid zero-pressure plastic balloon with a volume of 1200 cubic metres that would provide a positive lift inside the balloon.
Latex balloons carry instruments that can ascend to a maximum altitude of 22kms to 29kms. Since latex expands and bursts, experimenter’s can collect data on aerosols only at some points as the balloon crosses the 16kms to18kms altitude.
“Atmospheric pressure at ground level is much higher than it is high up in the thinner atmosphere. As pressure outside the balloon drops, the latex balloon attempts to expand to equalize the pressure. At some point when the skin thickness reaches a critical value, the balloon will burst because the pressure of the gas inside will exceed the strength of the elastic balloon material,” said Kumar.
The hybrid zero-pressure plastic balloon on the other hand has been developed to ascend and float at the 16km-18km altitude, while simultaneously getting the aerosol data.
“These plastic balloons are attached to two open ducts at the bottom called side-escape tubes to vent out the excess gas if the expansion is above the volume capacity of the balloon, and maintains the same pressure at balloon bottom as atmospheric pressure and floats at the same altitude,” said Kumar.
In addition to the balloon, the team had to ensure the instruments function in the coldest region of the earth’s atmosphere. “Most science instruments are designed for ground-based observations, and have been used for the first time in ballooning to assess their capability for in situ measurements and future airborne measurements,” said Venkat Ratnam, scientist, NARL, Gadanki, Andhra Pradesh.