Tracking EPIRBs and Wildlife: Houston – we’ve got a problem here.

I just returned from Washington D. C. to garner support for a satellite launch necessary to maintain the Argos satellite-based wildlife tracking system that is critical for much of our research on Alaska’s marine wildlife. The launch schedule for a new Argos receiver keeps getting pushed back, potentially to the year 2022. This satellite launch will also host a receiver for another very similar tracking system: SARSAT (Search and Rescue Satellite Aided Tracking). NOAA, the U.S. agency that operates SARSAT, aptly states that “SARSAT takes the search out of search and rescue”. SARSAT is critical for locating and rescuing mariners, aviators and outdoor enthusiasts in distress, worldwide and at any time. SARSAT picks up transmissions from emergency beacons, including EPIRBs, ELTs and PLBs.

So what’s the problem? In a nutshell, Argos and SARSAT are in jeopardy! At some point in the near future, we may no longer be able to track wildlife via Argos. More importantly, in a worst case scenario, an emergency beacon activated in distress will not provide a location to send search teams to.


Tracking wildlife via Argos is similar to tracking emergency beacons. Argos transmitters are really ultra-miniaturized PLBs (let’s call them ALBs – Animal Locator Beacons). The smallest tags have a mass of a few grams! Many can do much more than transmit beacon signals. They have a microprocessor and many sensors to tell how deep an animal dives, how fast it swims, when it eats something or when its host gets eaten (check out These data also get transmitted back to our labs via Argos.


Argos and SARSAT share the Low Earth Orbit (LEO) satellites the receivers ride on. Due to their extremely small size, Argos tags only work with the closer LEO satellites, they cannot reach a distant geostationary satellite. There are six LEO satellites that carry Argos receivers, five of these also carry SARSAT receivers. Why so many? As the earth rotates during each 100-minute LEO orbit, a satellite returns over a previous location every 12 hrs. It also takes 2-6 hours to downlink a received message. So, there is a delay of up to 18 hours for a distress message reaching Mission Control with only one satellite. Furthermore, transmissions from difficult settings (very choppy sea, in a tight fjord or shadow of a steep mountain) may not reach a satellite on the first pass. More satellites means quicker Search and Rescue response and greater likelihood of good locations. For Argos, it means that we get more data from our ALBs. In fact, ALBs very often miss multiple satellite passes because our animals happen to be underwater when the satellite passes.

Here now is our problem: 


Four of five SARSAT LEO satellites are on their last leg, many years past their projected life. Modern satellites have a life of 3-5 years. The oldest Argos / SARSAT satellite was launched in 1998 and is now more than 15 years past the projected life! In satellite terms, this machine has a biblical age. Kudos to the builders to make it work so long, but talk about asking for trouble! There is only one healthy SARSAT satellite (Metop-B) with a design life into early 2018. What will happen to SARSAT and Argos after that? That may depend entirely on these geriatric LEO satellites.

There is a single new combined Argos – SARSAT launch planned with NOAA’s Cooperative Data and Rescue Services (CDARS) Program. This launch has already been postponed from the original schedule of 2019, to 2020 or 2021. Even that launch date is in jeopardy unless funds in support of this launch are included in this coming U.S. federal budget.

There are currently about 22,000 active Argos transmitters out there. We estimate that about 50% of the 1.5 to 2 million emergency beacons out there are not GPS enabled, and only provide locations via the SARSAT LEO satellites.

If the ancient ones die, no one will listen….

This web page shows all recent SARSAT rescues in the U.S.: Without SARSAT, they would likely not have made it.

Written by: Dr. Markus Horning

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