ISS on 121.750 MHz: Orlan spacesuits and Soyuz on AM

What you hear

On most days nothing at all. On the day of a Russian spacewalk, voices in AM: the two cosmonauts in their Orlan suits talking to each other and to the station, short commands, confirmations, counted steps, breathing between words, the sound of people working with their hands in a vacuum. When a Soyuz with a crew or a Progress cargo ship is on its way to the station, the ship's voice channel can be heard here too during the passes over Russian ground stations, in the same clipped style. Each pass gives at most ten minutes, with the Doppler shift on this band small enough to ignore.

Honesty requires a caveat. Listeners have reported the Russian suit and ship radios in the range from 121.1 to 121.75 MHz over the years; which frequency is in use during a given spacewalk is not announced, and the sessions are rare. This entry is a long shot by design, and an empty pass is the normal outcome.

Who transmits and why

The cosmonauts of the Russian segment and the crews of Soyuz ships. The Orlan suit carries its own radio, and the Soyuz has a VHF voice channel for the launch, the approach and the return, a design that goes back decades and has kept the same simple amplitude modulation. These are working channels of a space programme, sent openly; a receiver only listens, and in most countries receiving an open transmission is legal, while passing its content on may be restricted. Know the rules where you live.

When and where to listen

Russian spacewalks happen a few times a year, are announced days in advance by the space agencies and last six or seven hours, so they span several passes; the voices come only on the passes that cross Russia and eastern Europe, where the ground stations are. Soyuz crews rotate a couple of times a year and Progress ships arrive several times a year, with the approach and docking lasting a few hours. The frequency sits inside the aviation band, next to the emergency frequency on 121.5 MHz, so a receiver with an airband profile covers it in AM, and aircraft may be heard around it. The receiver must be inside the station's footprint, roughly 2000 kilometres around the point beneath it.

In ShackDeck

Station catalogue → ISS → ISS: spacesuits and Soyuz. When you click, the program asks where the station is at that moment, looks for a public receiver with the frequency inside its footprint, takes the nearest one, tunes it to 121.750 MHz in AM and tells you which receiver the station is over; no receiver, antenna or account of your own is needed. When the station is out of reach of every receiver, it says where the station is and when the next pass over your own location begins, from the locator in the settings. Use the Satellites tab to plan: it shows the track and footprint on the map, the passes of the next 24 hours, and a bell that reminds you ten minutes before one. On any ordinary day the everyday entry is the service channel on 143.625 MHz, where the crew can be heard most working days.