2010-09-03

Below are successful digipeats via ISS from Redwood City, CA, USA.

It appears to be feasible to submit position reports via ISS, and it should be easier while at sea outside a coastal environment, where there is practically no competition for the digipeater while the radio footprint isn't over land.

I will attempt an experiment on Monday, Sept. 6th while taking a day cruise from Santa Cruz, CA, USA, using coastal (144.390 MHz) stations between ISS passes.

2010-09-02 07:51:06 UTC: N8QH-3>SW3PPY,RS0ISS-4*,qAR,N6VUD-2:'2)Al <0x1c>Y/]Maritime callsign WDF2783, MMSI 367431840=

2010-09-02 07:52:18 UTC: N8QH-3>SW3PPY,RS0ISS-4*,qAR,N8QH-10:'2)Al <0x1c>Y/]Maritime callsign WDF2783, MMSI 367431840=

2010-09-02 07:53:07 UTC: N8QH-3>SW3PPY,RS0ISS-4*,qAR,W6MSU-7:'2)Al <0x1c>Y/]Maritime callsign WDF2783, MMSI 367431840=

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Update: 2010-09-15

The experiment successfully sent position reports via ISS. ISS was 799 miles away at the closest point of passage, at an elevation above the horizon of only 23.6 degrees. I was able to send two packets within that 5 minute window. The position reports were sent from a sailing vessel afloat in the San Francisco (California) Bay.

(YYYYMMDDHHMMSS UTC : APRS SSID, Equip Type, ISS Callsign, "q" code, Terrestrial SatGate Callsign, Symbol, Lat, Lon, course/speed)

20100916012932 : N8QH-8]APT3A2, RS0ISS-4* ,qAR,N6VUD- 2:!3731.68N/ 12211.83WY219/ 005

20100916012802 : N8QH-8]APT3A2, RS0ISS-4* ,qAR,N6VUD- 2:!3731.80N/ 12211.71WY205/ 006

The reports were transmitted using a 10 watt MT-AIO transmitter and a simple 1/4 wave non-directional antenna. The transmitter was attached with a velcro strap to the stern pulpit railing, which functioned as an antenna counterpoise.

The experiment demonstrates the feasibility of submitting real-time vessel position reports on a VHF band beyond the usual line-of-sight VHF limitations (from anywhere on Earth), while using a simple, self-contained, and inexpensive portable transmitter. This is a capability that is otherwise beyond the reach of most sailors aboard small and rented vessels.

The only other VHF alternative is AIS. However, AIS wasn't designed to accommodate reception from space. Experiments are underway to receive AIS data from space, but the implementation is very problematic due to frequency congestion (contentioning) that occurs when the receiver is elevated above the surface by even a few thousand feet. From hundreds of miles above the surface, the challenge is practically insurmountable. Too many AIS stations are transmitting simultaneously within the satellite's reception footprint. This problem can be overcome in APRS with the addition of very simple and inexpensive technology.

In the meantime, sailors should be able to transmit multiple position reports per day since so few stations are transmitting during ISS transits over large bodies of water -- the frequency is practically unoccupied at exactly the times that cruising sailors would use it for position reports. Provided at least one terrestrial SatGate is within the footprint, the position reports will be posted on the Internet.

73

N8QH
Global Maritime Distress and Safety System Operator/Maintainer