from the three-letter-agencies-rejoice dept.
gyrogeerloose writes "During its last mission, astronauts from the Space Shuttle Atlantisinstalled an Automatic Identification System antenna on the outside of the International Space Station that will allow astronauts aboard the ISS to monitor signals from the AIS transmitters mandated to be installed on most large ocean-going craft. Although these VHF signals can be monitored from the Earth's surface, their horizontal range is generally limited to about 75 km (46 mi), leaving large areas of the ocean unwatched. However, the signals easily reach the 400 km (250 mi) orbit of the ISS. The European Space Agency sees this experiment as a test platform for a future AIS-monitoring fleet of satellites that will eventually provide worldwide coverage of sea traffic."
We warn the reader in advance that the proof presented here depends on a
clever but highly unmotivated trick.
-- Howard Anton, "Elementary Linear Algebra"