To retain the gas in a balloon and achieve the desired shape, a material was chosen, latex, which was flexible but, at the same time, capable of trapping the molecules inside and withstanding the pressure.
The choice of the gas that should be inside the balloon was not trivial. It is necessary for the balloon to be inflated with a gas that is less dense than air so that it floats and does not fall under its own weight, so that the balloon-gas pairing has a lower weight than the same volume of air. For this reason, helium was chosen, which has a much lower density than air.
Helium is an odorless, colorless, tasteless, inert, monatomic gas, that is, all its particles are made up of a single atom, and it lacks toxicity. In the periodic table it occupies the first place in the group of noble gases and its boiling point is the lowest of all the elements.
Archimedes’ principle
The molecules that make up helium are lighter than the main components of air –nitrogen and oxygen-. Applying Archimedes’ principle, which says that any body totally or partially submerged in a fluid at rest experiences an upward force called thrust, which is equivalent to the weight of the fluid displaced by the body.
As the balloon rises, the pressure of the air around it decreases, while the helium inside it expands. applying the Archimedes’ principlethe helium balloons will stop rising as soon as the density of the helium matches that of the surrounding air.
On the other hand, the false belief is widespread that the greater the amount of gas, the longer the balloon will float. This is not true since the greater the pressure inside the balloon, the greater the tension exerted on the surface.
It could be said that there are several factors that allow the elevation of the balloon and limit the durability of the balloon in the air: its quality, the pressure inside it and the low density of helium.
Karman’s line
Once all these characteristics are known, we have to specify where space begins and if a helium balloon can reach it. Space could be defined as the limit where the aeronautical flight ends and the astronautic begins.
There is an imaginary line -defined by the Hungarian engineer and physicist Theodore von Karmán (1881-1963)- located 100 kilometers above sea level. The Karmán line corresponds to the altitude from which the atmosphere becomes ‘too thin’ to guarantee aeronautical safety. An airplane stays in flight thanks to the surrounding air and its airfoil, both of which allow adequate lift, such that the higher it flies, the less lift the air provides and will, in principle, require more airspeed to compensate.
So is it possible for a helium balloon to pass the Karman line? An experimental study showed that a balloon of these characteristics, under optimal conditions, can amount to more than 10 kilometers highstay in the air more than 24 hours and travel a distance of up to 3,000 kilometers horizontally. In other words, a helium balloon can’t reach space, it explodes sooner.