The International Space Station is flying hundreds of miles above our heads, but keeping in contact with the astronauts on the space station isn't as difficult as it sounds. In fact, ham radio operators can listen, and even speak, to the astronauts every once in a while.
Indeed, anyone with a radio licence and the right equipment can transmit to the crew and talk to them. A licence is not required to listen in, however.
In order to make contact with the space station, the ISS has to be flying overhead, because radio operators need line of sight with the station. Once they connect, it's possible the operators could hear comments from the astronauts aboard the station or even talk to them. And occasionally, radio operators can even pick up actual images sent from ISS.
Last weekend, Russian astronauts aboard ISS used the slow-scan television transmissions to send some images to earth, and student Radoslaw Karwacki was lucky enough to pick them up.
To pick up the photos, he had to use an RTL-SDR dongle, an antenna, the SDRSharp program and MMSTV software to translate the information. It was Karwacki's first time using the equipment, but somehow he still managed to pick up the signal. The dongle only costs about $15, and the software is free.
‘Before the picture transmission started, I could hear an astronaut voice - "This is Romeo Sierra Zero India Sierra Sierra" - which is RS0ISS in the Nato phonetic alphabet.
This is one of the images that Karwacki received from the ISS.
RS0ISS is the call sign Russian astronauts us, while American astronauts use the sign NA1SS. The Russians sent 12 total images, including several commemorating Yuri Gagarin, who was the first person to ever go to space.