Österreichisches Weltraum Forum Austrian Space Forum
Next Passepartout launch:Earth’s atmosphere seems immense and taken for granted – but if we look at our planet from outer space, we realise it is actually only a thin layer. As it is not only a thin layer, but also a very sensitive system, the study of our atmosphere is important to understand the environment we live in. There are several ways to do this, and one increasingly popular method is to employ balloons.
13. Aug 2011 (morning) in Graz
In this new, 6 part series about „Passepartout“, the stratospheric balloon of the Austrian Space Forum, we will introduce you to the physics involved and offer an insight into the PolAres project.
But first, a short introduction into the layout of the atmosphere: between 0 and 15km is what is called the Troposphere, which is the most important layer for every day human life. In it all weather phenomena take place. Next (from 15 to about 50km) is the Stratosphere, followed (50 to 80km) by the Mesophere and Thermosphere (80 to about 400km). Finally, the Exosphere is the outermost layer.
The temperature gradient within the different layers differes due to the individual properties of each layer. It can therefore be used to distinguish between the layers. In the Troposphere, temperatures fall with hight (down to -50 degrees Celsius), while it rises again up to 0 degrees Celsius in the Stratosphere (also called Inversionlayer). Once we reach the Thermosphere, temperature rises first only slightly, but the higher we get the steeper the gradient gets too. The temperatue is influenced by geographical properties, time of day and also the space weather.
Since gravity binds air to the earth and is decreasing with hight, density and therefore pressure decrease with hight. Aside from this, pressure also depends on air temperature and can be influenced by the same phenomena as temperature.
Shuttle Endavour during sunset, photographed from ISS (c) NASA
Die Stratosphäre selbst hat keinen Einfluss auf unser tägliches Leben, doch sie absorbiert die für uns gefährliche UV-Strahlung. Dieser Effekt kommt von der bekannten Ozonschicht, welche in 20km Höhe ihre höchste (Ozon-)Dichte hat. Durch die Bindung und den Abbau von Ozon, welche unterschiedliche Wellenlängen absorbieren, bildet die Ozonschicht die Inversionsschicht.
The Stratosphere does not have a direct influence on our daily life on earth, but it absorbes the dangerous UV radiation. This is mostly done by the famous ozone layer, which has its highest density at a hight of about 20km. With different creation and destruction of ozone which in turn absorbs different wavelengths, the ozon layer is also the cause of the inversion layer.
Not only electromagnetic waves hit the earth. 1912 Viktor Franz Hess discovered particle radiation during balloon flight experiments (he received the Nobel price for this discovery 1937). This particle radiation is made up from protons and alpha particles, and a very small part from heavier atoms. They originate from our sun, the galaxy and in some rare cases even from extra galactic sources. Since the energies of the particles differ according to the source, they can be distinguished. Particles with low energies come from our sun, high energies from the galaxy and extremely high charged particles from extragalactic sources. The longer a particles journey has been, the less likely is its detection here on earth. Because of the high velocities with which they hit the atmosphere, they destroy oxygen and nitrogen atoms and create secondary particle radiaton. This secondary radiation consists of Myons which in term decay into other particles.
View from the edge of space (at 34km hight) taken from Passepartout in october 2008.
Thanks to the ability of balloons and satellite to enter less dense layers, they can measure the particles directly and offer perfect tools to study low energy particles.
Thanks to these properties the stratosphere can be seen as an interesting lab to study weather phenomena, astronomy, perform low density experiments, it is a place for spy satellites or just to break records (as has been done by the Red Bull balloon “Stratos”).
To enable „Passepartout“ to reach the Stratosphere, the ascending force is generated by so called lifting gas. Such a gas has to be lighter than the surrounding air, which means that even hot air can be employed in some cases (like hot air balloons). However, this is not effective enough to reach the Stratosphere. Therefore, either Helium or Hydrogen is used. Both have different conserns relating safety, costs and effectiveness.
Dieser Artikel ist auch verfügbar auf: German