APRS through the ISS

Everything on this page except the VIA ISS mark in the packet log needs APRS Connect Pro.

The International Space Station carries an amateur radio packet digipeater, run by ARISS (Amateur Radio on the International Space Station). It listens and transmits on 145.825 MHz, 1200 baud AFSK, worldwide, and repeats any packet whose path asks for it. A station on the ground can hear it, and be heard by it, only while the station is above the horizon: a pass lasts about ten minutes, and there are several a day.

The ISS screen is in the drawer.

Where it is

The screen says whether the station is above your horizon right now, how high it stands and in which direction, and where it is over the earth. The numbers are computed on the phone from the station's published orbit — a two-line element set from CelesTrak — which is fetched when there is a connection and refreshed about twice a day. A fetched orbit is kept and used for days, so the screen works with no signal once it has one. The line under the position says how old the orbit is.

Whether the station is above you needs your own position, which the screen asks for the same way the map does. A line under the position says how old the orbit is, and Update orbit data fetches a fresh one on demand; for an hour after a fetch the button is absent and the line says when it returns, as a courtesy to CelesTrak's free service.

Show on the map turns on the Space station map layer and centres the map on the station. The layer draws three things: the station itself as the APRS satellite symbol, updated every couple of seconds; the dashed circle of ground from which it is currently above the horizon, which is the area it can hear a packet from; and its ground track for the next orbit. Tap the symbol to open the ISS screen. The layer is also in the map's LAYERS panel, and off by default.

Next passes

The screen lists the next three passes over your position: when each starts, how long it lasts, how high it gets and in which direction. A pass under way is listed first with the time it ends. Passes that peak under 10° above the horizon are not listed; a handheld does not hear them. Next 5 days of passes opens the rest, grouped by day.

Every pass has a Notify button. Tapping it asks for a notification five minutes before that one pass, whatever the settings below say; tapping again withdraws it.

Notifications

Every pass posts a notification before each pass that fits two limits: Only above sets the peak elevation a pass has to reach (10°, 20°, 30° or 45°), and Between sets the local times of day you are willing to be notified in. The same time in both boxes means any time of day; a window that ends before it starts runs through midnight. Tap a time to open a picker — twelve hours and AM or PM on a 12-hour clock, twenty-four hours on a 24-hour one, then five-minute steps — with a box at the top for typing a time instead. Times follow the app's clock setting. Minutes before a pass sets how far ahead the notification comes: 2, 5, 10, 15 or 30 minutes, with 5 the default.

The notification carries the duration, the peak, the frequency and the path. Notifications are off by default, ask for permission when first switched on, and have their own Android notification channel, ISS passes, so they can be silenced on their own. They are scheduled from the orbit and your position when a setting changes, when the app returns to the foreground, and when a fresh orbit arrives, and they fire whether or not the app is running.

Beaconing through it

A packet asks the station to repeat it with the path ARISS, and nothing after it. When the station repeats a packet it writes its own callsign into the path as the used hop, RS0ISS*, the way a terrestrial digipeater does with WIDE1-1.

Add ISS beacon creates a beacon profile with that path, a fixed rate of once a minute, and only your radio channels selected, then opens it in the editor. It is an ordinary beacon otherwise, and it is created switched off. Once a profile with the ISS path exists, the screen shows that profile in place of the button.

Send during passes is the switch that sends it. With it on, the ISS beacon goes out once a minute while the station's orbit puts it above your horizon, and whenever anything it repeated is heard on your radio — its own beacon, or anyone's packet with RS0ISS* in the path. Nothing is sent between passes, and the profile itself stays switched off. The channel is shared by every station under the footprint, so once a minute is the accepted rate. The radio has to be on 145.825 MHz; the app does not tune it.

Sending a message through it

Long-press any outbound message that has not been answered and choose Send via the ISS. The app stops sending it on the ground and holds it; when the station is next heard on your radio the message goes out with the ARISS path, over the radio only, on the usual retry schedule. If that pass does not deliver it, the next pass gets another try, three in all over two weeks, the same schedule as retry when heard. The Waiting to be heard screen lists the message with a VIA ISS mark, and Stop waiting lets it go.

Heard via ISS

The bottom of the screen lists every station whose packets the ISS has repeated, from the packet log, newest first, with a count and when it was last heard. Your own station is highlighted. Tap a row to open the station, or Show in packet log to see the packets themselves under the log's Via ISS filter.

The same fact appears in three other places: a VIA ISS tag in the packet log's left-hand gutter on each packet the station repeated, a Via ISS row on a station's page once it has been heard that way, and a VIA ISS chip in the view filter's Show only row that narrows the map, the Stations list and the packet log to stations the space station has repeated. All three are free.

Only a packet that came back down counts. A packet that asked for the station and was not repeated — ARISS still unmarked in its path — is the usual outcome of transmitting at a satellite, and is not listed. The list reaches back as far as the packet log is kept; see how long the log is kept.

Links

The screen links to ariss.org and to ARISS's page on the current status of the station's radios. The digipeater is switched off during some crew activities; the app only knows what it has heard, and the status page is where ARISS says so. The links tell ARISS's website that the visit came from APRS Connect, and nothing else about you.

Beaconing — everything else about a beacon profile.
Messaging — retry when heard, and Waiting to be heard.
Map — the Space station layer beside the other layers.
Packet log — where the repeated packets are.
Stations — the station page and its Via ISS row.

Last updated 8 September 2026