"Dr Shailesh Nayak, Secretary Earth Sciences is given additional charge of Secretary DOS (Department of Space)," a top ranking ISRO official told PTI.
This appointment comes in the wake of superannuation of Radhakrishnan who led ISRO through many milestones in the last five years being at the helm of affairs.
The tenure of Radhakrishnan as ISRO chief, Secretary, Department of Space and Chairman, Space Commission was extended by four months in August this year till December 31, 2014 on "functional grounds and in public interest.
He has also served at Indian National Centre for Ocean Information Services from May 2006 to August 2008.
Shailesh Nayak assumed charge as Secretary, Ministry of Earth Sciences on August 27, 2008.