How to Track and Decode APRS Packets from the ISS Digipeater

Thousands of hams and makers have already had their callsign appear on aprs.fi with the path “RS0ISS” or “ARISS” – meaning their packet was literally bounced off the ISS. Here’s exactly how you can join them.

Every 93 minutes, a 2-meter radio station traveling at 28,000 km/h passes overhead and will happily relay your tiny data packet back to Earth. That station is the International Space Station (ISS), and its ARISS APRS digipeater is one of the most exciting targets in amateur radio.

What Is the ISS APRS Digipeater?

The ISS carries a Kenwood TM-D710G (or its successor) in the Columbus module with the callsign RS0ISS (Russia) and NA1SS/OR4ISS for voice. When the APRS digipeater is enabled, anyone on Earth can send a standard 1200-baud AFSK packet on 144.390 MHz, and if the timing is right, the ISS will retransmit it for the world to hear.

Your position, a short 60-character message, or telemetry can then be seen globally on sites like aprs.fi – with the ultimate QSL card: digipeated via space.

When Is It On?

The digipeater is usually active 24/7 except:

• During school contacts
• Crew sleep periods
• Docking or EVA operations
• Occasional maintenance

Real-time status:
https://www.ariss.net/
https://amsat.org/status/
https://nasa.gov/iss (look for “ARISS” mentions)

Step-by-Step: How to Work the ISS APRS Digipeater

1. Find the Next Good Pass

Use one of these trackers (all free):

• https://www.n2yo.com/pass/?s=25544
• https://heavens-above.com
• https://amsat.org/track/
• Apps: Look Up, ISS Detector, or GoSatWatch

Look for passes with maximum elevation >30° for best results.

2. Gear You Need

You don’t need much:

• Any 2 m FM transceiver (handheld or mobile)
• A decent antenna: Arrow II, Elk, or even a simple vertical/turnstile
• Sound card interface or SignaLink / Mobilinkd TNC
• Computer or Raspberry Pi (or a phone with Robot36/Repeater app + VOX setup)

Minimum power: 5–25 W into a good antenna is plenty. Many succeed with an HT and a rubber duck from a second-story window!

3. Software That Works in 2025

• Dire Wolf (Linux/Windows/macOS) – the gold standard
• UZ7HO SoundModem (fast and reliable)
• APRSDroid (Android) + Mobilinkd
• AGWPE + UI-View32 (classic Windows setup)
• YAAC (Java, cross-platform)

4. Critical Settings

• Frequency: 144.390 MHz (Region 2 & 3 standard)
• Path: APRS or ARISS or RS0ISS (all work)
• Some use APRS,WIDE1-1 – it still gets digipeated as long as the ISS hears you
• Beacon text example:
  73 from [YourCall] via ISS! EL29
  or add /ISS for fun

5. Handle Doppler Shift

At AOS (acquisition of signal), the ISS is ~3.5 kHz high. At TCA (closest approach) it’s on frequency, then goes ~3.5 kHz low.

Solutions:

• Manually tune ±3–4 kHz during the pass
• Use Dire Wolf with “-d doppler” or SoundModem’s built-in ISS tracking
• Many just pre-correct to 144.393–144.395 MHz and leave it

6. Fire When Ready!

When the pass starts:

1. Wait until the ISS is above 15–20° (stronger signal)
2. Send 2–3 unproto beacons 10–15 seconds apart
3. Watch aprs.fi/?call=RS0ISS or the live packet list

If you see something like:
YOURCALL>APRS,RS0ISS*,qAR,gate:: message
→ Congratulations! You just worked the International Space Station.

Pro Tips from People Who Do This Weekly

• Best success rate: 40–70° elevation passes
• Use an omnidirectional antenna if you’re mobile or lazy – turnstile or eggbeater works great
• The digipeater alias is sometimes ARISS instead of RS0ISS – Both are correct
• Your packet may be heard worldwide – people in Europe often get your packet when the ISS is over North America

Bonus: See Yourself on the Map

Go to https://aprs.fi and search for your callsign-11 or just watch the RS0ISS page during your pass. When your packet appears with RS0ISS* Take a screenshot – it’s the ultimate space QSL.

Final Thought

There are only a handful of satellites you can work with a $35 Baofeng and a homemade antenna. The ISS APRS digipeater is the most reliable and most rewarding of them all.

Next good pass over your QTH? Grab your radio, point it skyward, and add “via ISS” to your ham radio resume – permanently.

Clear skies and 73 de the ARISS APRS community! 🚀