India joins an elite club, one of 5 countries to use Rubidium Atomic Clock in their GPS satellite
India's ISRO joins an elite club of space agencies which use a very complex and technical device, a Rubidium atomic clock in their GPS satellites. Only 4 other national space agencies use this atomic clock - USA's NASA, EU's ESA, China's CNSA and Russia's ROSCOSMOS.
Source: firstpost.com