I've personally flown on private IFR flights where the flight plan was filed something like 10 minutes (or even less) before departure (or amended several times

I've personally flown on private IFR flights where the flight plan was filed something like 10 minutes (or even less) before departure (or amended several times, etc). It doesn't seem like a good way to go about knowing where someone is. Everything regarding elonjet only applies to the aircraft and it's likely he loans out his aircraft to other execs/employees at his companies, miscellaneous friends and family, etc. So even if you somehow developed some methodical and resource-intensive master plan to attack the aircraft or movement associated with it you wouldn't have any guarantee you'd get your intended target. A missile defense system was announced for Gulfstream aircraft at a cost of about $3.5m[0], which for a ~$65m aircraft isn't really that expensive... [0] - https://www.aerospaceonline.com/doc/farnborough-gulfstream-offers-missile-defense-0001 https://www.aerospaceonline.com/doc/farnborough-gulfstream-o...