ISRO will launch three satellites to enhance the Indian Regional Navigation Satellite System (IRNSS), said Union MoS for Space Dr Jitendra Singh in Parliament. NVS-03 will lift off by year-end, while NVS-04 and NVS-05 will follow every six months. Presently, only four satellites out of the 7-satellite constellation which provides navigation over India and 1,500 km beyond are operational.