Radhakrishnan, who was on his visit to Sree Krishna Temple Guruvayoor in Thrissur on Saturday evening, Oct 24, was informed about his appointment over phone from New Delhi.
He then gave the number of the temple board office in Thrissur where his appointment copy was faxed, he said.
Radhakrishnan succeeds G Madhavan Nair and will take over as chairman on Oct 31.
Speaking to reporters, Radhakrishnan said, "A huge responsibility has been placed on me and at this moment I would like to thank all my gurus (teachers) and among them are Nair and other former ISRO chairmen like Kasturi Rangan and UR Rao."
He also said that his first priority would be to see that the first indigenously developed cryogenic engine be made ready for the launch of the GSLV.
Radhakrishnan did his electrical engineering degree from Kerala University in 1970. He also holds an MBA from Indian Institute of Management-Bangalore and a doctorate from Indian Institute of Technology-Kharagpur.
For 5 years (2001-2005), Radhakrishnan was on deputation to the ocean development as founder-director of the Indian national centre and project director of the early warning system for tsunami and storm surges.
He was also vice-chairman of the inter-governmental oceanographic commission (IOC) of Unesco 2001-05.
Radhakrishnan was a member of the Indian delegation to the UN committee on peaceful use of outer space since Jun 2006.