GPS
1978-present
The satellite navigation constellation your phone uses every day. 31 operational satellites, each broadcasting an atomic-clock timestamp.
Specs
First satellite 22 Feb 1978; 24-satellite constellation operational 1993; ~20,200 km altitude; 11 h 58 min orbit; clocks corrected +38 microseconds/day (relativity).
Why it matters
Your phone's position - accurate to a few metres - is computed from signals of 4+ satellites 20,000 km up. It works for billions of people daily and needs no 'drones' anywhere.