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Near the boundaries of Space: stratospheric balloons

Near the boundaries of Space: stratospheric balloons

Although stratospheric balloons remain within the boundaries of Space, their scientific missions are complementary to those of satellites: something to discover at a Special Evening starting at 5pm on 6 April at Cité de l’Espace.

We have all seen children releasing a helium balloon only to realise they cannot retrieve it as it rises beyond reach into the sky…

Scientific stratospheric balloons can rise up some 50km on the same principle, using helium, too. Since helium is seven times lighter than air, a balloon filled with this gas rises as long as its container is not too heavy, as explained by Archimedes’ principle (see the CNES site).
The higher the altitude, the lower the density of air: this explains why stratospheric balloons — which reach the part of the atmosphere known as stratosphere, as the name implies — culminate some 50km above sea level. The largest balloons can lift up to 3 metric tons of equipment! Although they don’t actually reach Space — which begins officially at 100km — they can conduct experiments in conditions similar to those that exist in orbit, minus certain difficulties.

Preparation of the launch of a stratospheric balloon carrying PILOT (foreground, left) to an altitude of some 40km. Designed to map weak polarised light emitted by interstellar dust grains, PILOT cannot operate efficiently from the ground. This launch was made from Canada in September 2015. Credit: CNES / Emmanuel Grimault

Preparation of the launch of a stratospheric balloon carrying PILOT (foreground, left) to an altitude of some 40km. Designed to map weak polarised light emitted by interstellar dust grains, PILOT cannot operate efficiently from the ground. This launch was made from Canada in September 2015. Credit: CNES / Emmanuel Grimault

In fact, complementarity is the rule between satellites and stratospheric balloons and the French Space Agency CNES is recognised worldwide for its capability in this field! Balloons make it possible in particular to test the principle of instruments subsequently intended for satellites, calibrate instruments for certain satellites thanks to additional measurements and even undertake specific scientific campaigns to obtain further data to complete those from satellites or observatories in orbit.

In the latter case, Enjoy Space presented a recent concrete example: the PILOT (Polarized Instrument for Long-wavelength Observations of the Tenuous interstellar matter) programme. Lifted under a balloon to an altitude of some 40km, PILOT mapped the polarised light emitted by dust between the stars. This “signal” interferes with data collected by the ESA (European Space Agency) Planck satellite, which observed cosmic background radiation: light emitted 380,000 years after the Big Bang. Thanks to PILOT, astrophysicists will be able to delete these “parasite” signals from Planck’s data with greater precision to improve our knowledge of the first moments in the life of the Universe. This is what Muriel Saccocccio, PILOT Project Manager at CNES, explains in this video.

In this case, recourse to a stratospheric balloon was necessary to lift the instrument to an altitude where there is virtually no humidity and the density of the air is considerably less than on the ground, to have the best conditions for detecting polarised light.

In the context of the Astronautics meetings organised in partnership with CNES and the Association Aéronautique & Astronautique de France, Cité de l’Espace in Toulouse offers a very interactive and user-friendly way of discovering the fascinating world of stratospheric balloons through a choice of 9 themes.

This event is free of charge and will take place on Wednesday 6 April from 5pm to 11pm.

Des ballons pour la Science à la frontière de l’espace

We can also note that small stratospheric balloons are often used to help young people learn about Space Science and Techniques (obviously under the supervision of appropriated trained adults). The video below shows the launch of a balloon with ESA astronaut Léopold Eyharts at the Astronomy Festival of Fleurance in 2014 (video by Espace & Exploration).