1. G. Leopold, Russian hacker group taps satellite links for attacks, Defense Systems, September 10, 2015, 〈https://defensesystems.com/articles/2015/09/10/turla-apt-group-satellite-link-hacks.aspx〉.
2. C. Baraniuk, “GPS errors caused ‘12 hours of problems' for companies”, BBC News, 4 February 2016. North Korea has also threatened to disrupt South Korean GPS signals since 2010, on various occasions (“S. Korea preparing for NK GPS disruption”, Yonhap News Agency, February 19, 2016).
3. See also “Hacking Satellites: Look Up to the Sky”, InfoSec, September 18, 2013.
4. See Union of Concerned Scientists Satellite Database, updated through December 31, 2015, 〈http://www.ucsusa.org/nuclear-weapons/space-weapons/satellite-database.html#.VgQDWcub7IU〉.
5. The procedures for satellite filings with the International Telecommunications Union’s Radiocommunication Bureau in ITU-R, Performance Report for 2013, Geneva, 2014. In this context, satellite orbits include geosynchronous orbit, 35,786 km above sea level, as well as several other orbital levels.