Returning to Hydrogen Gas : a Strategic Decision to Continue Achievement of Stratospheric Balloons Flights

The Balloons Sub-directorate of the French Space Agency (CNES) has developed and operated a wide range of balloon vehicles which include Zero-pressure Stratospheric Balloons (BSO) since the early 1960’s, for the national and international scientific community. Until winter 1999/2000, the BSO main envelope was inflated with hydrogen gas. The use of this gas for balloon inflation also included transport and storage issues, and was then part of the operational team expertise. By 2000, helium gas had been chosen to replace hydrogen gas for the main envelop inflation for safety reasons. Indeed helium has some advantages (inert gas, safety handling), but also presents some drawbacks:  Nonrenewable resource.  Expensive to extract.  Supply difficulties (few storage sites).  Increasing cost, due to constant growth of industrial and scientific applications combined with the decrease of the supply of the world market, are now becoming alarming for CNES Balloons program sustainability. Compared to helium, hydrogen gas is produced from primary sources (natural gas, hydrocarbons or biomass), which ensures the energy source sustainability and consequently, there are many storage places, closer to our various launching sites, lowering the transport cost to an acceptable level. In addition, taken into account balloon performances, hydrogen as gas inflation allows a 7% decrease in the required gas volume to raise a load and the balloon rises faster and higher. The only “dark” side of hydrogen gas is related to its high flammability properties. A working group has been mandated by the Director of the Toulouse Space Center, in order to gather information to make a decision about the replacement. The group has raised questions, particularly related to safety. A hazard study was carried out by experts of the National Industrial Environment and Risks Institute (INERIS). Potential accidental events (ERC) have been highlighted in the implementation and the operability of a BSO for each of the phases of a flight (negative countdown during ground operations, ascending to ceiling, flight, flight ending and recovery). This paper presents the results of the hazard study with its impacts on the modification of the hardware (ground and flight segments), as well as the impact on the operations for the preparation and the release of the balloon.