Long duration balloon flights: A probe for deep hard X-ray astronomy investigation

In this note the state of the art of our knowledge of the high energy sky will be reviewed, with particular regard to the hard X-ray range.The use of more complex and sophisticated payloads that is necessary to obtain up-to-date results mandatory to achieve a better understanding of the actual scenario in the range 15–300 keV, causes new continuous requirements for long duration balloon flights.The needs for astronomy oriented scientific ballooning will be considered and discussed.