Unexplored frequency bands for data traffic between earth and satellites are in great demand. For the first time in the world, Styrian researchers received signals in the “W frequency band” from a handy satellite box that they sent into space at the end of June. It could be used to connect large high-performance satellites to the Internet, said Michael Schmidt from Joanneum Research in Graz to the APA. Before doing this, however, you have to get to know the frequency street in all weathers.
On June 30, a Falcon 9 rocket with research satellites was launched from the spaceport in Cape Canaveral (USA). One of them belongs to the Graz researchers and their international project partners: It is a “triple cubesat”, that is, a box ten by ten centimeters in footprint and thirty centimeters high. “All around are solar cells that can generate a total of 16 watts of electrical power, and a battery is on board because it flies repeatedly in the shadow of the earth,” explained Schmidt. Its “polar orbit” at an altitude of 540 kilometers leads it almost at right angles to the equator just above the poles.
“It flies at seven kilometers per second, which is seven times faster than a bullet,” said the researcher. He usually comes over and near Graz three times a day and three times at night. He can be radioed for five to 15 minutes at a time, to save energy he sleeps the rest of the time. Using the precalculated path data or with the help of a “mono path tracking” device developed in-house, which practically doesn’t let you out of your sight once it has spotted him, the Graz researchers align their antenna with him. “It’s not that easy at all because the beam width to reach it is very small at 0.2 degrees,” said Schmidt: “In comparison with the moon, it is two and a half times as wide”.
Before the satellite was delivered into space, the researchers sought to use the desired frequency. The frequencies are assigned by the International Telecommunication Union (ITU). “The spectrum is finite, you can’t expand it,” said Schmidt: “There is a quasi-battle between zero Hertz and the wavelength of light for each section to see who gets it”. “Because we only want to test a single tone with 75 gigahertz with very little power, this is initially very harmless for possible competitors and we do not disturb anyone.” Even so, it took two years for the permit to arrive.
The researchers now have two to five years to demonstrate that they can do something useful with this frequency, such as establishing an Internet connection via feeder links for high-throughput satellites (HTS). Then they could be used commercially with additional permits from the local authorities. “That will also be necessary in the future, because otherwise we will not achieve the necessary capacity for the Internet connection with the high-performance satellites,” he says.
The researchers received a 75 GHz signal from the satellite. “That was a pioneering achievement, nothing like it existed anywhere in the world before,” said Schmidt. “Each frequency here has its own propagation characteristics”, he explained: “At 60 gigahertz, for example, it is very bad because the oxygen in the air dampens these vibrations almost entirely”.
Until now, the only known thing about the 75 gigahertz frequency is its attenuation in the earth’s atmosphere by measuring relatively short terrestrial connections. The researchers are therefore investigating how the most varied of droplet sizes, from drizzle to strong thunderstorms, influence the waves. In the case of a rain front, the attenuation can change many times over within a second, and you have to know how to lay out the ground stations in order to still be able to communicate reliably with the satellites, says Schmidt. The researchers get the weather data for their model calculations from the Austrian Central Institute for Meteorology and Geodynamics (ZAMG). In addition, they measure, for example, the droplet size distribution with a self-developed “distrometer”.
The project was funded by the Ministry of the Environment with around 1 million euros, the funding is provided by the Research Promotion Agency (FFG) as part of an ESA project, says Schmidt.