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ALTEN and pressurised stratospheric balloons

The stratosphere is a place where only balloons can fly. Too low for satellites, too high for planes and traversed too quickly by rockets, only stratospheric balloons can stay there sustainably, making them essential tools for scientific research.

The French National Centre for Space Studies (CNES), an ALTEN customer for more than 20 years, is aware of this and maintains one of the largest “balloon” activities in the world.

These stratospheric balloons, which have been deployed in the air for more than 50 years, have never carried passengers but measuring instruments instead. Several long-haul flight missions have been successfully completed since the STRATEOLE -VORCORE campaign in Antarctica (2005).

In autumn 2019, the STRATEOLE-2 programme made its first releases as part of an approval campaign.

This observation mission is carried out by stratospheric pressurised balloons launched from Mahé airport in the Seychelles and aims to study the dynamics of the atmosphere in the intertropical zone.

The aims are to better understand the climate and climate phenomena and improve weather forecasting.

The STRATEOLE-2 mission is part of the World Meteorological Organization’s SPARC programme and has also confirmed the observations made by the European Space Agency’s AEOLUS satellite (2018).

The project STRATEOLE-2 between 2019 and 2024:


long-life balloons


meters in diameter


of altitude

Balloons are a unique tool in the space field that have successfully carved out a space for themselves in the scientific community since the Montgolfier brothers.

The STRATEOLE-2 project consists of launching nearly 50 long-life balloons between 2019 and 2024. These balloons, made of a transparent barrier material that measures between 11 and 13 meters in diameter, are closed and filled with helium. They fly at an altitude of between 18 and 20 km, maintaining themselves above civil aviation’s flight altitude.

© CNES/DE PRADA Thierry, 2020

More recently on the STRATEOLE-2 project, ALTEN engineers contributed to the approval of the mechanical flight train of the on-board system as well as the Assembly-Integration-Tests (AIT) of the service gondolas.

These gondolas are the balloon’s brains: they carry on-board computers, solar panels and energy management systems, transponders and communication antennas as well as some of the instrumental measurements.

ALTEN has been a partner of CNES balloon projects since the 2000s and has participated in the development of all types of balloons.

© CNES/Prodigima Films/GABORIAUD Romain, 2019

During this four-year AIT phase, all the systems/equipment were qualified in near-operational conditions. Six test engineers brought their expertise to bear in tests in fields such as in electronics, mechanics, thermals, radio frequency, and software.

The quality of their work was displayed when the STRATEOLE-2 system successfully passed its trial campaign, which began in late 2019. This campaign saw eight pressurised balloons take off, travelling the globe for several weeks and accumulating 680 flight days, or 85 days on average per balloon.

The scientific data collected is invaluable for CNES and the research laboratories associated with the experiments to refine their knowledge of the atmosphere in the intertropical zone and improve weather models in this region. A new STRATEOLE -2 campaign should begin in mid-October with 20 to 25 balloons.

Watch the launch videos of the STRATEOLE-2 programme: