Debris Search in Space
The new space radar GESTRA will take action against space debris in the future. The radar system was developed and built by the Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR on behalf of the space management at the German Aerospace Center (DLR). GESTRA can monitor space objects in near-Earth orbit around the clock.
In the last few decades, humanity has not only managed to pollute the earth, but also the near-Earth space. This is the name given to the area up to orbital altitudes of 36,000 kilometers above our heads. It is estimated that billions of pieces of space debris with a total mass of around 7,600 tons orbit the earth every day – and the trend is rising. The size of the particles varies between a few micrometers and several meters. Due to the high speeds of typically eight kilometers per second, even the approximately 700,000 to 900,000 particles larger than one centimeter are high-energy projectiles with energies of 50 kilojoules. That corresponds to an explosive force of around twelve grams of TNT. This vagrant junk has the potential to cause major damage to space-based infrastructure. Whether navigation, telecommunications or weather information, today's society is dependent on functioning satellites. A failure would have serious and far-reaching consequences for both civilian and military concerns. It is therefore important to protect this infrastructure. But how?
Artificial satellites orbit the Earth in different orbits. Navigation satellites such as GPS or Galileo, for example, are on orbits at medium altitudes. Space experts call this the Medium Earth Orbit (MEO) with orbital altitudes of around 2,000 to 35,000 kilometers. However, most manned and unmanned spaceflights take place in Low Earth Orbit (LEO) between about 200 and 2000 kilometers altitude. The International Space Station ISS and astronomical instruments such as the Hubble Space Telescope are also stationed in LEO.
Communications and TV broadcasting satellites, such as ASTRA, as well as satellites for meteorological purposes are mainly located in geostationary orbit (GEO). Satellites located here move in a circular orbit at an altitude of 35786 kilometers above the equator. The orbital period around the earth corresponds exactly to its rotation period: 23 hours, 56 minutes and 4 seconds. So for an observer on Earth, the satellite is always "at the same point in the sky".
Another trend has recently emerged: the use of huge satellite constellations such as OneWeb or Starlink. These aim to provide the world with fast and inexpensive broadband internet. These mega-constellations should consist of several tens of thousands of small satellites in near-Earth space and thus increase the population of existing satellites in Earth orbit more than tenfold. This increases the risk potential and unfortunately also has serious consequences for astronomical research.
Space junk is also distributed in the different orbits around the earth. However, the main part, about 75 percent, is in LEO, since most space activities take place here and the corresponding orbital heights can be reached comparatively energy- and cost-effectively.
The composition of space debris is diverse: discarded upper stages of rockets, cover plates, lost astronaut tools and decommissioned satellites. However, the largest contribution comes from satellite collisions and explosions caused, for example, by the ignition of residual propellants.
