Launched in January 1990, AMSAT-OSCAR 16 (AO-16) -- a digital satellite -- has been operating as a voice repeater since January 2008, using FM voice on the uplink and transmitting DSB voice on the downlink (best received on SSB). But according to the satellite's command team, the satellite's orbit might force this to end sometime before the end of the year.

According to Mark Hammond, N8MH, a member of the AO-16 command team, AO-16 has a hardware/watchdog timer that resets the satellite and shuts the transmitter down. This timer in AO-16 will fire -- and cannot be reset -- when the satellite's temperature is 15 degrees Celsius or cooler. When the timer "fires," it shuts down the transmitter. "When the bird's temperature is more than 15 degrees Celsius," Hammond said, "the hardware timer behaves and continuous operations are sustained."

The satellite's temperature depends upon solar illumination. Hammond said that the "magic number" is around 85 percent of the orbit in sunlight: If the orbit puts AO-16 with less than 85 percent illumination, the spacecraft's temperature falls below 15 degrees and the hardware timer fires. "Illumination projections, as well as subsequent temperature predictions, suggest that we might be able to sustain operations until sometime in the window of November 22 until December 4, 2008," Hammond predicted. "So if you want to make some AO-16 contacts, you had better get them as soon as possible!"

Hammond said that long term-orbital projections suggest that if the satellite hardware remains fundamentally unchanged -- such as no deterioration of on-board components -- "it will be nearly 10 years before AO-16 receives sufficient illumination to warm up the spacecraft enough to again support sustained operations."

It is possible that the transmitter on AO-16 will turn off sometime in the next few days or weeks, Hammond said. "This requires some commanding to get it running again, meaning a pass over the eastern coast of the United States is required for a change in operational status. We expect that as the spacecraft cools down, transmitter shutdowns will become more frequent. You can be sure that we'll continue to probe the craft with commands, in hopes that we something will change in a good way that will allow us to use the bird for operations of some sort."

AMSAT Vice President of Operations Drew Glasbrenner, KO4MA, said the satellite hears very well; the reduced bandwidth by using either USB or LSB on the ground station receiver "allows for a very robust downlink. Tuning the downlink is just like on a linear transponder, meaning it is tight and with fast Doppler. Uplink tuning is not required, just as with the FM mode V/U satellites. My personal observations include being able to access and hear the satellite within one degree of the horizon, much lower than any other current bird for my location [in Florida]. This should be an easy satellite with omni antennas and a 70 cm preamp."

AO-16's uplink is 145.9200 MHz FM; the downlink is 437.0260 MHz SSB. Users are asked to restrict their uplink power to a reasonable power level, and not to transmit without being able to hear the downlink; all general single-channel guidelines apply. "Enjoy this grand old bird while you can!" said Hammond.