India's Swadeshi GPS Develops A Problem, But Remains Functional

[abhinaba]

India's home-made navigational system, named NAVIC by Prime Minister Narendra Modi, has developed a technical problem. One of the seven satellites in the Indian version of the American Global Positioning System or GPS is malfunctioning, as a result of which it's not visible. The seven satellites together provide strategic services, the last of them was launched in April last year. Despite the flaw, the Indian Regional Navigation Satellite System is still functional. "The on-board atomic clock has developed a problem and we are trying to revive it," said Dr Kiran Kumar, Chairman of ISRO or the Indian Space Research Organization, to NDTV.
Atomic clocks are used for precision time- keeping; India had imported these for the constellation of seven satellites in its GPS. In a similar fashion, atomic clocks on Europe's satellite navigation system Galileo have also been failing, leaving half of its 18 satellites in orbit without clocks. When the time signal is missing, getting true positional accuracy is eroded. India has spent close to 1,700 crores on this navigation system, named NAVIC or Navigation with Indian Constellation. The NAVIC system is akin to the American Global Positioning System (GPS) but it is regional in nature covering the Indian region and ISRO claims it gives a much higher accuracy for military users than other systems like it.

Source: Indias Swadeshi GPS Develops A Problem, But Remains Functional - NDTV.com

 

[abhinaba]

Additional input:

Three Atomic Clocks Have Failed Onboard India’s ‘Regional GPS’ Constellation
BY VASUDEVAN MUKUNTH ON 30/01/2017

Three atomic clocks onboard one of the satellites of the Indian Regional Navigation Satellite System (IRNSS) have failed, as ISRO chairman A.S. Kiran Kumar told The Hindu. The IRNSS is India’s version of the US’s globally used GPS system, and covers a wide swath of Asia and the Indian Ocean. It is a constellation of seven satellites in a geosynchronous orbit around Earth, and they coordinate to provide centimetre-level tracking precision to the Indian armed forces. The three atomic clocks used onboard each satellite of the IRNSS are used for precise coordination and to well- account for the effects of general relativity. With the failure of all three clocks – one primary and two backups – onboard IRNSS 1A, Kumar has said a replacement satellite, 1H, will be launched in the second half of 2017. It is unclear what caused the failure, although the issue is neither new nor likely to be unique. Earlier this month, the European Space Agency (ESA) reported that three rubidium atomic clocks and six hydrogen maser clocks onboard its counterpart of the IRNSS, called Galileo, had failed. Neither ESA nor ISRO have declared their respective constellations ineffective as a result. The IRNSS should be back to normal with the launch of 1H while the Galileo is still not at full strength: only 18 of 30 satellites are currently online. Moreover, a seventh hydrogen maser clock that failed has managed to restart itself. In the same vein, ISRO is also attempting to restart its clocks. Until such time, Kumar said the constellation will continue to work normally while the 1A provides fuzzy, imprecise measurements. All the rubidium atomic clocks onboard IRNSS and Galileo – as well as China’s Compass navigational constellation – were manufactured by the Swiss company Spectracom, purported to be a market leader. While China’s space programme has been typically closed off to foreign media, ESA and ISRO have yet to clarify whether the fault lies with Spectracom’s design or with something about current conditions in space. It is pertinent at this point to note that two atomic clocks on two Galileo satellites had already begun to fail in March and July, 2016. Rubidium atomic clocks, though less accurate at measuring the passage of time than are hydrogen maser clocks, are still quite accurate, relatively cheap and widely used. They neither gain nor lose a second in tens of millions of years. They measure time according to the frequency of microwave emissions by electrons in a cooled rubidium atom, called the rubidium standard. When the atoms are of the element caesium instead, the resulting clock is also referred to as a primary frequency standard given its use in defining the standard times of many countries. Our own Indian Standard Time is ‘kept’ by caesium atomic clocks in Delhi’s National Physical Laboratory.

Source: 3 Atomic Clocks Fail Onboard India's 'Regional GPS' Constellation

 

[Sarkar]

Isro should take steps to produce them locally instead of importing  :dodgy