From the article: Most of the maser failures (5) have occurred on the satellites that were originally sent into orbit to validate the system, whereas all three

From the article: Most of the maser failures (5) have occurred on the satellites that were originally sent into orbit to validate the system, whereas all three rubidium stoppages are on the spacecraft that were subsequently launched to fill out the network. Rubidium clock failures are being seen in "operational" Galileo satellites. First operational Galileo was launched in 2011. And, first operational Indian navigational satellite was launched in 2013. So, there's not much difference in the timeline or aging of Rubidium atomic clocks between ESA and ISRO satellites. Anyway, ISRO will be switching to indigenous atomic clocks for next generation navigation satellites[1]. [1] http://www.thehindu.com/news/national/tamil-nadu/india-developing-atomic-clocks-for-use-on-satellites/article7229191.ece http://www.thehindu.com/news/national/tamil-nadu/india-devel...