ARISS APRS operating again

Michael Callaham

After a long outage. the APRS (Automatic Position Reporting System)
aboard the International Space Station (ISS) is again operating, as may
be seen at <>.

On the Arlington County Net yesterday, I announced an imminent pass of
the ISS over Arlington starting 23:51:5 UTC (7:51:59 pm EDT) and lasting
10 minutes 49 seconds. This prediction was generated by my Debian
(debian dot org) package gpredict using Keplerian elements ("keps")
updated yesterday. However, two stations reported that they tried to
hear, but did not hear, the ISS APRS downlink.

This often happens when the ISS maneuvers (firing its engines) or docks
or undocks a supply or crew spacecraft (these actions change the mass
and the area, hence the drag, of the ISS, and hence the data on which
orbital predictions are based.) The lesson here is to be skeptical of
predictions and the data on which the predictions are based: are they

Here are some links that may help:

<>: a NASA-recommended Java application for predicting sighting opportunities for the space station, which are passes of the ISS when the ISS may be seen, if skies are clear. This does not predict all passes of the ISS when the ISS may be heard or contacted by Amateur Radio.

NASA's predictions of passes of the ISS over Arlington, at times when it
may be seen (if clouds do not intervene).

<>: Documentation for the GNOME
Predict (gpredict) application I use on Debian (debian dot org). This
predicts all passes, visible or not.

Enuf for now.


Science matters. Matter matters.
Energy matters, including dark energy.

Paul Wilson KI4PW

Thanks, Mike. I use and get alerts on my phone and via email regarding upcoming ISS passes.

A couple of other items if using an HT: note the azimuth indications for the pass and make sure your body is not shielding the radio. Last night's pass had a zenith of 58 degrees above the horizon, so if you're pointed the wrong way your body may block the signals. Also, holding the antenna in a horizontal position helps. I prefer the Yaesu FT60 with its manual squelch knob, rather than the Baofeng, which buries the squelch setting in a menu. Generally you want the squelch wide open. You'll hear the data packets interrupting the noise. If you want to know what APRS sounds like, tune your HT to 144.390 and you can hear terrestrial APRS digipeaters.

I'll keep a lookout for the next [good] pass and give it a try.

Paul / KI4PW