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High altitude scientific balloons offer unique opportunities to carry scientific payloads to stratospheric altitudes at a cost several orders of magnitude lower than corresponding satellite missions. Balloon-borne payloads are easy to implement allowing quick experiment turn-around times and inexpensive reflights can be conducted as payload is most of the times recovered. In addition, in-situ and high resolution spatial and temporal measurements of the earth's atmosphere can be made that might not be feasible with satellites. It is also used as a testbed to prove technologies for future satellite missions. Scientific ballooning was initiated at the Tata Institute of Fundamental Research (TIFR) in the year 1945 when scientific instruments were flown to stratospheric altitudes using a cluster of weather balloons for cosmic ray research. The need to have balloons float at constant stratospheric altitudes for astronomy studies led to the initiation of work on design and fabrication of Zero-Pressure polyethylene (ZP) balloons at TIFR in 1956. Since then several ZP balloon flights were conducted for studies in astronomy, atmospheric science, astrobiology, balloon technology and space technology development, leading to several important scientific results. In the year 2018, TIFR balloon program crossed an important milestone of conducting more than 500 ZP balloon flights. This paper presents recent advancements made in some areas of scientific ballooning and the details of balloon experiments conducted in the past two decades., Comment: 22 pages, 5 figures, Accepted in Current Science on March 22, 2021

Balloon experiments are an economically feasible method of conducting observations in astronomy that are not possible from the ground. The astronomical payload may include a telescope, a detector, and a pointing/stabilization system. Determining the attitude of the payload is of primary importance in such applications, to accurately point the detector/telescope to the desired direction. This is especially important in generally unstable lightweight balloon flights. However, the conditions at float altitudes, which can be reached by zero pressure balloons, could be more stable, enabling accurate pointings. We have used the Inertial Measurement Unit (IMU), placed on a stratospheric zero pressure balloon, to observe 3-axis motion of a balloon payload over a fight time of 4.5 hours, from launch to the float altitude of 31.2 km. The balloon was launched under nominal atmospheric conditions on May 8th 2016, from a Tata Institute of Fundamental Research Balloon Facility, Hyderabad., Comment: 9 pages, 11 figures, available at URL: http://hdl.handle.net/2248/6993, IIA Technical Report Series No. 16, pp. 1-9, 2016

Ever since its inception four decades back, Balloon Facility of Tata Institute of Fundamental Research (TIFR), Hyderabad has been functioning with the needs of its user scientists at its focus. During the early nineties, when the X-ray astronomy group at TIFR expressed the need for balloons capable of carrying the X-ray telescopes to altitudes up to 42 km, the balloon group initiated research and development work on indigenous balloon grade films in various thickness not only for the main experiment but also in parallel, took up the development of thin films in thickness range 5 to 6 microns for fabrication of sounding balloons required for probing the stratosphere up to 42 km as the regular 2000 grams rubber balloon ascents could not reach altitudes higher than 38 km. By the year 1999, total indigenisation of sounding balloon manufacture was accomplished. The work on balloon grade ultra-thin polyethylene film in thickness range 2.8 to 3.8 microns for fabrication of balloons capable of penetrating mesosphere to meet the needs of user scientists working in the area of atmospheric dynamics commenced in 2011. Pursuant to the successful trials with 61,000 cu.m balloon made of 3.8 microns Antrix film reaching stratopause (48 km) for the first time in the history of balloon facility in the year 2012, fine tuning of launch parameters like percentage free lift was carried out to take the same volume balloons to higher mesospheric altitudes. Three successful flights with a total suspended load of 10 kg using 61,000 cu.m balloons were carried out in the month of January 2014 and all the three balloons crossed in to the mesosphere reaching altitudes of over 51 km. All the balloons flown so far are closed system with no escape ducts. Balloon fabrication, development of launch hardware, flight control instruments and launch technique for these mesospheric balloon flights are discussed in this paper., Comment: 19 pages, 15 figures, 4 tables. Accepted for publication in Journal of Astronomical Instrumentation