text: only four satellites are capable of providing navigation services which is the minimum number required for service to remain operational.
  Indian Atomic clock
  In order to reduce the dependency on imported frequency standards  ISRO's Space Applications Centre (SAC), Ahmedabad had been working on domestically designed and developed Rubidium based atomic clocks. To overcome the clock failures on first generation navigation satellites and its subsequent impact on NavIC's position, navigation, and timing services, these new clocks would supplement the imported atomic clocks in next generation of navigation satellites.
  On 5 July 2017, ISRO and Israel Space Agency (ISA) signed an Memorandum of Understanding to collaborate on space qualifying a Rubidium Standard based on AccuBeat model AR133A and to test it on an ISRO satellite.
  Future developments
  India's Department of Space in their 12th Five Year Plan (FYP) (2012–17) stated increasing the number of satellites in the constellation from 7 to 11 to extend coverage. These additional four satellites will be made during 12th FYP and will be launched in the beginning of 13th FYP in geosynchronous orbit of 42° inclination. Also, the development of space-qualified Indian made atomic clocks was initiated, along with a study and development initiative for an all optical atomic clock (ultra stable for IRNSS and deep space communication).